UL873

UL 873
ISBN 1-55989-682-5
Temperature-Indicating and
-Regulating Equipment
MAY 4, 2001 UL 873 tr1
Underwriters Laboratories Inc. (UL)

333 Pfingsten Road
Northbrook, IL 60062-2096
UL Standard for Safety for Temperature-Indicating and -Regulating Equipment, UL 873
Eleventh Edition, Dated December 22, 1994
Revisions: This Standard contains revisions through and including May 4, 2001.
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tr2 MAY 4, 2001 UL 873
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Copyright 2001 Underwriters Laboratories Inc.

MAY 4, 2001 UL 873 tr3
This Standard consists of pages dated as shown in the following checklist:
Page Date
1-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . May 4, 2001

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19-20 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . December 22, 1994
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24-29 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . December 22, 1994
30-33 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . October 24, 1995
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60-70 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . December 22, 1994
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101-109 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . December 22, 1994
110 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . October 24, 1995
111-112B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . May 4, 2001
113 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . December 22, 1994
114-114B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . March 4, 1999
115-116 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . December 22, 1994
117-119 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . May 4, 2001
120 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . June 2, 1998
121-122B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . May 4, 2001
123-153 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . December 22, 1994
154-154B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . May 4, 2001
155-162 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . December 22, 1994
163 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . June 2, 1998
164-165 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . December 22, 1994
166-166B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . May 4, 2001
167 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . June 2, 1998
168-170 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . December 22, 1994
171-172B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . March 4, 1999
tr4 MAY 4, 2001 UL 873
173 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . December 22, 1994

174-178 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . May 4, 2001
A1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . June 2, 1998
A2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . December 22, 1994
CRG1-CRG6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . June 2, 1998
CRG7-CRG8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . May 4, 2001
DECEMBER 22, 1994
(Title Page Reprinted: May 4, 2001)
UL 873
Standard for Temperature-Indicating and -Regulating Equipment
First Edition August, 1942

Second Edition March, 1945
Third Edition January, 1947
Fourth Edition June, 1953
Fifth Edition December, 1956
Sixth Edition December, 1958
Seventh Edition May, 1970
Eighth Edition September, 1972
Ninth Edition May, 1979
Tenth Edition September, 1988
Eleventh Edition
December 22, 1994
An effective date included as a note immediately following certain requirements

is one established by Underwriters Laboratories Inc.
The Department of Defense (DoD) has adopted UL 873 on January 17, 1992.
The publication of revised pages or a new edition of this Standard will not
invalidate the DoD adoption.
Revisions of this Standard will be made by issuing revised or additional pages

bearing their date of issue. A UL Standard is current only if it incorporates the
most recently adopted revisions, all of which are itemized on the transmittal notice
that accompanies the latest set of revised requirements.
ISBN 1-55989-682-5
COPYRIGHT 1979, 2001 UNDERWRITERS LABORATORIES INC.

2 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 MAY 4, 2001
No Text on This Page

MAY 4, 2001 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 3
CONTENTS
FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
INTRODUCTION
1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
2 Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
3 Units of Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
4 Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
CONSTRUCTION
6 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
7 Frame and Enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10A
7.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10A
7.2 Accessibility of live parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
7.3 Covers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
7.4 Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
7.5 Cast metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
7.6 Sheet metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
7.7 Polymeric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
7.8 Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
7.9 Room thermostats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
7.10 Openings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
7.11 Screens and expanded metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
7.12 Wiring openings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22A
7.13 Raintight and rainproof enclosures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
8 Mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
9 Parts Containing Liquid Metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
10 Adjustment Stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
11 Operating Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
12 Reset Mechanism Limiting Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
13 Means for Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
14 Protection Against Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
15 Insulating Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
16 Supply Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
16.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
16.2 Equipment permanently connected electrically . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
16.3 Cord and plug connected portable equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
16.4 Stationary equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
17 Current-Carrying Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
18 Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
19 Internal Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
20 Low-Voltage External Wiring Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
21 Grounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
21.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
21.2 Grounding means . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
21.3 Equipment permanently connected electrically . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
21.4 Terminals and leads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
22 Bonding of Internal Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
22.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

22.2 Construction and connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
23 Protection of Users and Service Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
23.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
23.2 Mechanical servicing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47
23.3 Electrical servicing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48
24 Protection Against Injury to Persons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
24.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
24.2 Sharp corners and edges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
24.3 Moving parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
24.4 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
24.5 Mounting devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50
24.6 Strength of parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50
25 Capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
26 Fuseholders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
27 Receptacles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
28 Protection of Control-Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52
28.1 Conductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52
28.2 Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54
29 Short-Circuit, Ground-Fault, Overload, and Thermal Protection . . . . . . . . . . . . . . . . . . . . . . . . . . .55
30 Mercury-Tube Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
31 Coil Windings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
32 Spacings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
32.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
32.2 Line-voltage circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56
32.3 Magnet coil windings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60
32.4 Low-voltage circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60
32.5 Isolated limited secondary circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
33 Alternate Spacings Clearances and Creepage Distances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62
34 Wiring Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63
35 Separation of Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64
36 Class 2 Power Sources and Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
36.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
36.2 Interconnections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
36.3 Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
36.4 Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66
36.5 Power limiting components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66
36.6 Overcurrent protection components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66
37 Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67
PERFORMANCE
38 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67
38.1 Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67
38.2 Electric heat thermostat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68
38.3 Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
38.4 Baseboard heater controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
38.5 Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
38.6 Electric range controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70
38.7 Auxiliary electric range controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75
38.8 Conditioning at elevated temperature household range control switch body . . . . . . . .75
38.9 Temperature-limiting controls for electric ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76
39 Power Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76
MAY 4, 2001 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 4A
40 Temperature Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76A

41 Leakage Current Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80
42 Leakage Current Following Humidity Conditioning Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
43 Operation Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
44 Calibration-Verification Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84
45 Overload Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85
46 Endurance Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90
47 Dielectric Voltage-Withstand Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93
47.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93
47.2 Induced potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94
47.3 Induced potential repeated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94
48 Volt-Ampere Capacity Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94
49 Burnout Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95
50 Short Circuit Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96
50.1 Mercury-tube switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96
50.2 Conductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96
50.3 Equipment for motor control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97
51 Parts Containing Liquid Metal Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97
52 Two-Step Operation Surface-Unit Controls Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
52.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
52.2 Push- and pull-and-turn controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
52.3 Other types of controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99
53 Strain-Relief Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99
54 Accelerated Aging Tests on Gaskets, Sealing Compounds, and Adhesives . . . . . . . . . . . . . . . .99
55 Metallic Coating Thickness Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101
56 Rain Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103
57 Time-Calibration Verification Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106
57.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106
57.2 Bimetal-heater design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106
57.3 Initial time-calibration-verification Test I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106
57.4 Initial time-calibration-verification Test II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107
57.5 Endurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107
57.6 Time-verification and dielectric voltage-withstand tests after endurance . . . . . . . . . . . .107
57.7 Other designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
58 Snap-On Covers Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107
59 Bonding Conductor Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108
59.1 Overcurrent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108
59.2 Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109
60 Permanence of Marking Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109
60.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109
60.2 Oven-aging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109
60.3 Immersion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110
60.4 Standard-atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110
60.5 Unusual condition exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110
60.6 Humidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110
61 Strength of Adjustment Stop Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110
62 Polymeric Materials Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112
62.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112
62.2 Flammability of enclosure 5 inch (127 mm) flame . . . . . . . . . . . . . . . . . . . . . . . . . . . . .113
62.3 Thermal aging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .115
62.4 Exposure to ultraviolet light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .116
62.5 Water exposure and immersion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117
62.6 Volume resistivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117
4B TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 MAY 4, 2001
62.7 Resistance to hot-wire ignition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .118

62.8 Heat deflection temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .118
62.9 Resistance to impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .118
62.10 Crush resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .119
62.11 Mold-stress evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .120
62.12 Dielectric strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .120
62.13 Conduit connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .120
62.14 Knockouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122
62.15 Abnormal operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122
62.16 Resistance to ignition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122
62.17 Creep and overcurrent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122A
63 Class 2 Power Sources and Circuit Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122A
63.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122A
63.2 Ambient air temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127
63.3 Open-circuit secondary voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127
63.4 Maximum current of inherently limited power source . . . . . . . . . . . . . . . . . . . . . . . . . . . . .130
63.5 Maximum current of not inherently limited power source . . . . . . . . . . . . . . . . . . . . . . . . .136
63.6 Maximum power of not inherently limited power source . . . . . . . . . . . . . . . . . . . . . . . . . .136
63.7 Calibration of overcurrent-protective devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .137
63.8 Rated secondary output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .137
63.9 Rated output heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .138
63.10 Dielectric voltage withstand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .138
63.11 Component breakdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .138
63.12 Overload heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .138
63.13 Repeat dielectric voltage withstand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .140
63.14 Overload of overcurrent- or overtemperature-protective devices . . . . . . . . . . . . . . . . . .140
63.15 Endurance of automatic-reset overtemperature-protective devices . . . . . . . . . . . . . . .140
64 Isolated-Limited Secondary and Non-Class 2 Circuits Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . .141
MANUFACTURING AND PRODUCTION TESTS
65 Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .141
65.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .141
65.2 Marked-off position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .142
66 Grounding Continuity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .142
RATING
67 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .142
68 Class 2 Power Sources and Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .143
MARKING
69 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .144
70 Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .146
71 Calibration Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .147
72 Elevated Air Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .148
73 Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .149
74 Cautionary Markings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .149
75 Class 2 Power Sources and Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .150
76 Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .151
MAY 4, 2001 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 4C
SPECIAL-PURPOSE DEVICES
77 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .151
78 Fan/Heat Sequencers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .151
78.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .151
78.2 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .152
78.3 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .153
78.4 Mechanical and production tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155
78.5 Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155
78.6 Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155
79 Fluorescent-Lamp-Ballast Protectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155
79.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155
79.2 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155
79.3 Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155
79.4 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .156
79.5 Manufacturing and production tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157
79.6 Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157
80 Control-Circuit Temperature-Limiting Devices for Temperature Protection of Enclosures of
Motors and Generators for Use in Hazardous Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157
80.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157
80.2 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .158
80.3 Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .158
80.4 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .158
80.5 Manufacturing and production tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159
80.6 Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159
80.7 Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159
81 Single-Operation Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160
81.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160
81.2 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160
81.3 Operation mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160
81.4 Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160
81.5 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .161
81.6 Manufacturers inspection and test program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162
81.7 Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162
81.8 Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162
82 Thermal Protective Devices for Lighting Fixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162
82.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162
82.2 Enclosures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163
82.3 Accessibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163
82.4 Open hole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .164
82.5 Insulating materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .164
82.6 Wiring connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .164
82.7 Mounting hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .165
82.8 Spacings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .165
82.9 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .165
82.10 Manufacturing and production-line tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .172A
82.11 Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173
82.12 Markings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173
83 Controllers for Solar-Energy Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173
83.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173
83.2 Supply connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173
83.3 Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174
83.4 Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174
4D TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 MAY 4, 2001
84 Temperature-Regulating Thermostats for Household Drip-Type Coffee Makers . . . . . . . . . . . .175

84.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .175
84.1A Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .175
84.2 Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .176
84.3 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .176
84.4 Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178
84.5 Markings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178
APPENDIX A
Standards for Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1
CANADIAN REQUIREMENTS COMPARISON GUIDE CRG 873
UL AND CANADIAN STANDARDS FOR TEMPERATURE-INDICATING AND -REGULATING

EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .CRG1

6 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 MARCH 4, 1999
FOREWORD
A. This Standard contains basic requirements for products covered by Underwriters Laboratories Inc. (UL)
under its Follow-Up Service for this category within the limitations given below and in the Scope section
of this Standard. These requirements are based upon sound engineering principles, research, records of
tests and field experience, and an appreciation of the problems of manufacture, installation, and use
derived from consultation with and information obtained from manufacturers, users, inspection authorities,
and others having specialized experience. They are subject to revision as further experience and
investigation may show is necessary or desirable.
B. The observance of the requirements of this Standard by a manufacturer is one of the conditions of the
continued coverage of the manufacturers product.
C. A product which complies with the text of this Standard will not necessarily be judged to comply with
the Standard if, when examined and tested, it is found to have other features which impair the level of
safety contemplated by these requirements.
D. A product employing materials or having forms of construction which conflict with specific requirements
of the Standard cannot be judged to comply with the Standard. A product employing materials or having
forms of construction not addressed by this Standard may be examined and tested according to the intent
of the requirements and, if found to meet the intent of this Standard, may be judged to comply with the
Standard.
E. UL, in performing its functions in accordance with its objectives, does not assume or undertake to
discharge any responsibility of the manufacturer or any other party. The opinions and findings of UL
represent its professional judgment given with due consideration to the necessary limitations of practical
operation and state of the art at the time the Standard is processed. UL shall not be responsible to anyone
for the use of or reliance upon this Standard by anyone. UL shall not incur any obligation or liability for
damages, including consequential damages, arising out of or in connection with the use, interpretation of,
or reliance upon this Standard.
F. Many tests required by the Standards of UL are inherently hazardous and adequate safeguards for
personnel and property shall be employed in conducting such tests.
DECEMBER 22, 1994 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 7
INTRODUCTION
1 Scope
1.1 These requirements cover electrical equipment for control of air-conditioning, heating, cooking,
refrigeration, and humidity, rated 600 volts or less, to be used in ordinary locations in accordance with the
National Electrical Code, NFPA 70.
1.2 These requirements cover general-use equipment for field-installation and controls intended to be
factory installed on or in certain appliances as safety, limiting, or operating controls. These controls
respond directly or indirectly to changes in temperature, humidity, or pressure to effect control of
equipment or appliance operation. Devices covered by these requirements include:
a) Refrigeration Controllers Humidistats for factory installation on or in refrigeration equipment;

pressure, temperature, pneumatic pressure, motor, timer, bimetallic-heater, magnetically-
operated controls, and the like, and combinations thereof in control panels with or without
transformers. See 1.4.
b) Industrial Operating Controls Temperature controllers for industrial, farm, and boiler room
applications; snow melting controls; return-duct humidistats; humidity controllers; pneumatic
pressure regulators; transformer (low-voltage secondary) relays; pneumatic pressure,
bimetallic-heater, motor, timer, and magnetically operated sequence switches; stoker controls;
indicating and recording controls; and motor operators for actuating air dampers. These
requirements do not cover output connected apparatus such as dampers, linkages, or valves.
c) Residential Operating Controls Room thermostats, room humidistats, and other operating
controls for residential heating and cooling appliances.
d) Controls for Factory Installation on or in Appliances
1) Controls as mentioned in (a) (c) but specifically intended for use on, in, or as a part
of the end-use equipment.
2) Electric water-heater controls intended to regulate or limit water temperature.
3) Other controls including door-interlock thermostats for self-cleaning ovens; baseboard

heater temperature-limiting controls; humidifier controls; fan thermostats; and
temperature-regulating and -limiting thermostats for electric heating equipment such as
clothes dryers, air heaters, household and commercial cooking appliances, beauty-parlor
equipment, steam and dry bath heaters, and ranges (controlling oven or surface
elements).
1.3 Certain safety controls, and safety control circuits on operating controls, are investigated under the
requirements in this standard, insofar as they apply, and also under the applicable requirements for limit
controls.
1.4 The following devices are among those considered to be refrigeration controllers:
a) A control that either directly or indirectly controls the starting and stopping of a compressor
motor of refrigeration or air-conditioning equipment because of variations in temperature,
pressure, refrigerant level, or the like.
b) A pressure limiting device and a defrost temperature-limiting device for refrigeration or air-
conditioning equipment.
c) An auxiliary device, such as a defrost timing control, a defrost temperature regulating control,
a start winding relay for a compressor motor, a control or defrost or heat pump change-over,
fan or pump motor, vane or load capacity regulator, or a similar device that primarily serves
refrigeration or air-conditioning equipment.
d) A control panel that, incorporates one or more of the functions described in (a) (c) for
programming refrigeration or air-conditioning equipment.
1.5 A wall-mounted room thermostat not intended for mounting in or on refrigeration or air-conditioning
equipment is investigated as a thermostat and not as a refrigeration controller.
1.6 Industrial temperature-indicating and -regulating controls include controls that are intended, among
other applications, for installation in or on industrial apparatus, or for boiler or furnace room, farm, outdoor,
and comparable locations that may not always be clean and dry.
1.7 A residential control is one intended for indoor comfort control use in clean, dry, nonindustrial
environments, such as dwellings, offices, and stores.
1.8 A humidistat is investigated in the same manner as a thermostat.
1.9 Requirements for controls intended to be factory installed on or in appliances may include
requirements appropriate for the end-use appliance. The spacing requirements for several such controls
are specified in Table 32.1.
1.10 These requirements do not cover primary safety or limit controls for gas, oil, or electric-fired
central-heating furnaces or boilers; duct heaters; oil or gas burners; or stokers; nor do they cover controls
for oil pumps and oil level regulators; boiler-feed or low-water cut-offs; or furnace fan or boiler circulators.
1.11 These requirements do not cover low-voltage thermostats, damper controls or similar devices
intended for connection only to a low-voltage circuit of limited power supplied by a primary battery or by
a Class 2 transformer. An assembly consisting of a line-voltage transformer with a low-voltage secondary
incorporated as an integral part of a control, such as a thermostat or a damper control, is considered to
be within the scope of these requirements. See 6.1.
1.12 A product that contains features, characteristics, components, materials, or systems new or different
from those covered by the requirements in this standard, and that involves a risk of fire or of electric shock
or injury to persons shall be evaluated using appropriate additional component and end-product
requirements to maintain the level of safety as originally anticipated by the intent of this standard. A
product whose features, characteristics, components, materials, or systems conflict with specific
requirements or provisions of this standard does not comply with this standard. Revision of requirements
shall be proposed and adopted in conformance with the methods employed for development, revision, and
implementation of this standard.
1.12 revised May 4, 2001
2 Glossary
2.1 For the purpose of this standard the following definitions apply.
2.2 CLASS 2 TRANSFORMER A stepdown transformer of the low-secondary-voltage type (30 volts
or less) rated for use with Class 2 remote-control circuits, low-energy power circuits, and signal circuits
(including bell or buzzer circuits and the like) in accordance with the National Electrical Code, ANSI/
NFPA 70-1993. Unless such a transformer is of the energy-limiting type having sufficient winding
impedance to limit the current output to a specified maximum value, it is required to be provided with a
fuse or other overcurrent-protective device rated for the application.
2.3 EQUIVALENT SELF-HEATING THERMAL PROTECTOR A SHTP that is identified as being

equivalent with another SHTP and is intended to be used in a lighting fixture interchangeably with the
other SHTP without adversely affecting the compliance of the lighting fixture with the requirements for
the fixture.
2.4 ISOLATED-LIMITED-ENERGY CIRCUIT A circuit derived from an isolated secondary winding of

a transformer having a maximum capacity of 100 volt-amperes and an open-circuit secondary voltage
rating not exceeding 1000 volts.
2.5 LINE-VOLTAGE CIRCUIT A circuit involving a potential of not more than 600 volts and having
circuit characteristics in excess of a low-voltage or isolated-limited-energy circuit.
2.6 LOW-VOLTAGE CIRCUIT A circuit involving a potential of not more than 30 volts and supplied by
a primary battery, by a standard Class 2 transformer, or by a combination of a transformer and a fixed
impedance that, as a unit, complies with all the performance requirements for a Class 2 transformer. A
circuit derived from a line-voltage circuit by connecting resistance in series with the supply circuit as a
means of limiting the voltage and current is not considered to be a low-voltage circuit.
2.7 PORTABLE EQUIPMENT Cord and plug connected equipment that is capable of being carried or
moved about.
2.8 SELF-HEATING THERMAL PROTECTOR (SHTP) A thermal protective device consisting of a

temperature sensitive switching element and a load voltage heater within a common housing. When
mounted on a non-Type IC recessed fixture, the SHTP is intended to cycle under field related abnormal
heating conditions.
2.9 STATIONARY EQUIPMENT Cord and plug connected equipment that is intended to be fastened
in place, or located in a dedicated space.
2.10 THERMAL PROTECTOR A thermal protective device consisting of a temperature sensitive

switching element with or without a series heater within a common housing.
3 Units of Measurement
3.1 Values stated without parentheses are the requirement. Values in parentheses are explanatory or
approximate information.
4 Components
4.1 Except as indicated in 4.2, a component of a product covered by this standard shall comply with the
requirements for that component. See Appendix A for a list of standards covering components generally
used in the products covered by this standard.
4.2 A component is not required to comply with a specific requirement that:
a) Involves a feature or characteristic not required in the application of the component in the
product covered by this standard, or
b) Is superseded by a requirement in this standard.

4.3 A component shall be used in accordance with its rating established for the intended conditions of
use.
4.4 Specific components are incomplete in construction features or restricted in performance capabilities.
Such components are intended for use only under limited conditions, such as certain temperatures not
exceeding specified limits, and shall be used only under those specific conditions.
5 References
5.1 Any undated reference to a code or standard appearing in the requirements of this standard shall be
interpreted as referring to the latest edition of that code or standard.
CONSTRUCTION
6 General
6.1 A temperature-indicating or -regulating device or system that falls within the scope of 1.11, but has a
maximum secondary potential of more than 30 volts or a maximum secondary output more than that
specified for a standard Class 2 transformer under any service condition or load shall be investigated
under conditions of intended service to determine whether it is acceptable for the intended application.
6.1 revised June 2, 1998
6.2 An electronic or solid-state circuit used in a back-up, limiting, or other safety control, including controls
that require a calibration test, shall acceptably complete a component evaluation of electronic devices and
is investigated on the basis of its compliance with the requirements in this standard, in addition to
complying with the specific requirements for the control.
7 Frame and Enclosure
7.1 General
7.1.1 Temperature-indicating and -regulating equipment shall be formed and assembled so that it will
have the strength and rigidity necessary to resist the abuses to which it may be subjected, without
increasing the risk of fire, electric shock, or injury to persons due to total or partial collapse with resulting
reduction of spacings, loosening or displacement of parts, or other serious defects.

7.2 Accessibility of live parts
7.2.1 Electrical parts of a device, other than a supply cord or low-voltage terminals, shall be located or
enclosed to reduce the risk of unintentional contact with an uninsulated live part. Additionally, electrical
parts shall be located or enclosed so that protection against unintentional contact or shorting of live parts
that could result in a malfunction of the controlled equipment is provided. For the purpose of these
requirements, film-coated wire is considered to be an uninsulated live part.
Exception: An enclosure is not required for a device intended for assembly as part of another device.
7.2.1 effective August 28, 1995
7.2.2 An opening in an enclosure of a control is acceptable if an accessibility probe as illustrated in Figure

7.1, when inserted into the opening, cannot be made to touch any part that involves a risk of electric shock
to the end-user or service personnel. However, in no case shall the opening be large enough to permit
the entrance of a 1 inch (25.4 mm) diameter rod.
7.2.2 effective February 28, 1997
12 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 DECEMBER 22, 1994
This is generated text for figtxt.
Figure 7.1
Accessibility probe
Note: All length dimensions in millimeters

7.2.3 The accessibility probe shall be articulated into any configuration and shall be rotated or angled to
any position before, during, or after insertion into the opening, and the penetration shall be to any depth
allowed by the opening size, including minimal depth combined with maximum articulation.
7.2.4 If any part of the enclosure must be opened or removed as part of normal operation, regular
adjustment, or regular or required maintenance (set point adjustment, timer or time of day clock
adjustment, battery replacement, and the like) with or without the use of tools, or can be opened or
removed without the use of tools, the accessibility probe is to be applied without the part in place.
7.2.5 Deleted effective August 28, 1995

7.3 Covers
7.3.1 An enclosure and a part of an enclosure such as a door, cover, or tank, shall be provided with
means for firmly securing it in place.
7.3.2 Sheet-metal screws threading directly into metal shall not be used to attach a cover, door, or other
part removed to install field wiring or for operation of the equipment. Sheet-metal screws may thread into
sheet-metal nuts that are permanently mounted and protected against corrosion, and machine screws and
self-tapping machine screws may thread directly into sheet-metal walls. See 19.12.
7.3.3 Sheet-metal screws mounting internal components that are not removed for installation or operation
may thread directly into metal.
7.3.4 An enclosure cover shall be hinged if it gives access to fuses, thermal cutouts, or any other
overload-protective device, the functioning of which requires renewal, or if it is necessary to open the
cover in connection with intended operation of the device.
7.3.5 A door or cover giving access to a fuse or thermal cutout in other than a low-voltage circuit shall
shut closely against a 1/4-inch rabbet or the equivalent, have turned flanges for the full length of four
edges, or have angle strips fastened to it. Flanges or angle strips shall fit closely with the outside of the
walls of the box proper and shall overlap the edges of the box not less than 1/2 inch (12.7 mm). A
construction that affords equivalent protection or a combination of flange and rabbet is acceptable.
7.3.6 A strip used to provide a rabbet and an angle strip fastened to the edges of a door shall be secured
at not less than two points, not more than 1-1/2 inches (38.1 mm) from each end of each strip and at
points between these end fastenings not more than 6 inches (152 mm) apart.
7.3.7 A hinged cover shall not depend solely upon screws or other similar means requiring the use of a
tool to hold it closed, but shall be provided with a spring latch or catch.
Exception: A cover that is hinged but is not required to be hinged for holding the cover may be held
closed by a clasp, a sliding latch, or other means.
7.3.8 A snap-on cover that gives access to bare live parts and that does not require a tool for removal
shall withstand the tests described in Snap-On Covers Test, Section 58.
7.3.9 The continuity of a bonding means for a snap-on or fastener-attached cover shall comply with the
requirements in Bonding of Internal Parts, Section 22.
7.4 Transformers
7.4.1 A transformer shall be housed within its own enclosure, within the main enclosure of
temperature-indicating and -regulating equipment, or within a combination of the two.
7.4.2 A sheet-steel transformer enclosure shall have a thickness of not less than 0.026 inch (0.66 mm) if
uncoated and not less than 0.029 inch (0.74 mm) if galvanized.
Exception: Sheet steel having a thickness of not less than 0.020 inch (0.51 mm) if uncoated and not less
than 0.023 inch (0.58 mm) if galvanized may be used for a drawn end bell having maximum dimensions
of 2-1/4 inches (57.2 mm) on the flat portion and 1-1/2 inches (38.1 mm) at the base of the drawn portion.
7.4.3 A cast-metal transformer enclosure shall comply with the requirements in 7.5.1. A transformer
enclosure of other material shall have strength and rigidity, and otherwise be rated for the purpose.
7.5 Cast metal
7.5.1 A cast-metal enclosure shall be at least 1/8 inch (3.2 mm) thick at every point, more than 1/8 inch
thick at reinforcing ribs and door edges, and not less than 1/4 inch (6.4 mm) thick at tapped holes for
conduit.
Exception: Other than at plain or threaded conduit holes, die-cast metal may be:
a) Not less than 3/32 inch (2.4 mm) thick for an area greater than 24 square inches (154.8 cm 2
) or having dimensions more than 6 inches (152 mm).
b) Not less than 1/16 inch (1.6 mm) thick for an area of 24 square inches or less and having no
dimensions more than 6 inches. The area limitation may be obtained by the provision of
reinforcing ribs subdividing a larger area.
c) Not less than 0.035 inch (0.89 mm) thick if the enclosure will not be used as a splice box and
if the voltage rating of the complete device is such that the voltage between any two conductors
is 250 volts or less, and is limited to direct current or single-phase alternating current.
d) Not less than 0.028 inch (0.71 mm) thick if the enclosure houses only low-voltage circuits.
7.6 Sheet metal
7.6.1 Other than at points where a wiring system is to be connected, the thickness of a sheet-metal
enclosure shall not be less than that specified in Tables 7.1 and 7.2.
Exception: A room thermostat shall be as specified in 7.9.3.
7.6.2 At points at which a wiring system is to be connected, uncoated steel shall not be less than 0.032
inch (0.81 mm) thick, zinc-coated steel shall not be less than 0.034 inch (0.86 mm) thick, and nonferrous
metal shall not be less than 0.045 inch (1.14 mm) thick.
7.6.3 Tables 7.1 and 7.2 are based on a uniform deflection of the enclosure surface for a given load
concentrated at the center of the surface regardless of metal thickness.
7.6.4 With reference to Tables 7.1 and 7.2, a supporting frame is a structure of angle or channel or a
folded rigid section of sheet metal that is rigidly attached to and has essentially the same outside
dimensions as the enclosure surface, and that has sufficient torsional rigidity to resist the bending
moments that may be applied via the enclosure surface when it is deflected. Construction that is
considered to have equivalent reinforcing may be accomplished by designs that will produce a structure
that is as rigid as one built with a frame of angles or channels. Construction considered to be without
supporting frame includes:
a) Single sheet with single formed flanges formed edges,
b) A single sheet that is corrugated or ribbed,
c) An enclosure surface loosely attached to a frame, for example, with spring clips.
7.7 Polymeric
7.7.1 A polymeric enclosure or enclosure part shall have mechanical strength and durability and be
formed so that operating parts will be protected against damage, and shall resist the abuses likely to be
encountered during installation and intended use and service.
7.7.2 An enclosure or enclosure part shall protect persons against a risk of electric shock. The enclosure
material shall not create or contribute to a risk of fire, electric shock, or injury to persons.
Table 7.1
Minimum thickness of sheet metal for enclosures carbon steel or stainless steel
With supporting frame or equivalent

Without supporting framea reinforcinga
Maximum widthb, Maximum lengthc, Maximum widthb, Maximum length, Minimum thickness, inch (mm)
Inches (cm) Inches (cm) Inches (cm) Inches (cm) Uncoated Metal coated
4.0 (10.2) Not limited 6.25 (15.9) Not limited 0.020d (0.51) 0.023d (0.58)
4.75 (12.1) 5.75 (14.6) 6.75 (17.1) 8.25 (21.0)
6.0 (15.2) Not limited 9.5 (24.1) Not limited 0.026d (0.66) 0.029d (0.74)
7.0 (17.8) 8.75 (22.2) 10.0 (25.4) 12.5 (31.8)
8.0 (20.3) Not limited 12.0 (30.5) Not limited 0.032 (0.81) 0.034 (0.86)
9.0 (22.9) 11.5 (29.2) 13.0 (33.0) 16.0 (40.6)
14.0 (35.6) 18.0 (45.7) 21.0 (53.3) 25.0 (63.5)
20.0 (50.8) 25.0 (63.5) 29.0 (73.7) 36.0 (91.4)
25.0 (63.5) 31.0 (78.7) 35.0 (88.9) 43.0 (109.2)
29.0 (73.7) 36.0 (91.4) 41.0 (104.1) 51.0 (129.5)
38.0 (96.5) 47.0 (119.4) 54.0 (137.2) 66.0 (167.6)
47.0 (119.4) 59.0 (149.9) 68.0 (172.7) 84.0 (213.4)
60.0 (152.4) 74.0 (188.0) 84.0 (213.4) 103.0 (261.6)
73.0 (185.4) 90.0 (228.6) 103.0 (261.6) 127.0 (322.6)
a See 7.6.4.
b The width is the smaller dimension of a rectangular sheet metal piece that is part of an enclosure. Adjacent surfaces of an
enclosure may have supports in common and be made of a single sheet.
c Not limited applies only if the edge of the surface is flanged at least 1/2 inch (12.7 mm) and fastened to adjacent surfaces not
normally removed in use.
d Sheet steel for an enclosure intended for outdoor use raintight or rainproof shall not be less than 0.034 inch (0.86 mm)
thick if zinc coated, and not less than 0.032 inch (0.81 mm) thick if uncoated.
OCTOBER 24, 1995 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 17
Table 7.2
Minimum acceptable thickness of sheet metal for enclosures aluminum, copper, or brass
Table 7.2 revised October 24, 1995
Without supporting framea With supporting frame or equivalent reinforcinga

Minimum
Maximum widthb, Maximum lengthc, Maximum widthb, Maximum length, thickness
Inches (cm) Inches (cm) Inches (cm) Inches (cm) inch (mm)
3.0 (7.6) Not limited 7.0 (17.8) Not limited 0.023d
3.5 (8.9) 4.0 (10.2) 8.5 (21.6) 9.5 (24.1) (0.58)
4.0 (10.2) Not limited 10.0 (25.4) Not limited 0.029
5.0 (12.7) 6.0 (15.2) 10.5 (26.7) 13.5 (34.3) (0.74)
6.5 (16.5) 8.0 (20.3) 15.0 (38.1) 18.0 (45.7) (0.91)
9.5 (24.1) 11.5 (29.2) 21.0 (53.3) 25.0 (63.5) (1.14)
14.0 (35.6) 16.0 (40.6) 30.0 (76.2) 37.0 (94.0) (1.47)
20.0 (50.8) 25.0 (63.5) 45.0 (114.3) 55.0 (139.7) (1.91)
29.0 (73.7) 36.0 (91.4) 64.0 (162.6) 78.0 (198.1) (2.41)
42.0 (106.7) 53.0 (134.6) 93.0 (236.2) 114.0 (289.6) (3.10)
60.0 (152.4) 74.0 (188.0) 130.0 (330.2) 160.0 (406.4) (3.89)
a See 7.6.4.
b The width is the smaller dimension of a rectangular piece of sheet metal that is part of an enclosure. Adjacent surfaces of an
enclosure may have supports in common and be made of a single sheet.
c Not limited applies only if the edge of the surface is flanged at least 1/2 inch (12.7 mm) and fastened to adjacent surfaces not
normally removed in use.
d Sheet copper, brass, or aluminum for an enclosure intended for outdoor use raintight or rainproof shall not be less than
0.029 inch (0.74 mm) thick.
7.7.3 Among the factors that are to be taken into consideration when investigating the acceptability of a
polymeric enclosure are:
a) Mechanical strength;
b) Resistance to impact;
c) Moisture absorption;
18 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 JUNE 2, 1998
d) Resistance to combustion and to ignition from electrical sources;
e) Dielectric properties, insulation resistance, and resistance to arc tracking; and
f) Resistance to distortion and creeping at temperatures to which the material may be subjected
under conditions of normal or abnormal use.
7.7.4 A material shall not display a loss of the properties specified in 7.7.3 beyond the minimum
acceptable level as a result of aging.
7.7.5 The tests for determining compliance of a polymeric enclosure used with equipment covered by this
standard are described in Polymeric Materials Tests, Section 62.
Exception: The cover of a wall-mounted room thermostat need not comply with the requirements in
Polymeric Materials Tests, Section 62, but will be subjected to an appropriate investigation.
7.7.6 The polymeric enclosure material shall be rated for the normal operating temperature encountered
in service and have a temperature rating at least equal to the normal operating temperature as determined
by the temperature test described in Temperature Test, Section 40.
7.7.7 If continuity of a grounding system relies on dimensional integrity of a nonmetallic material, the
dimensional stability of the material shall be considered in addition to the factors mentioned in 7.7.3.
7.7.8 A part, such as a dial or nameplate, that is a part of an enclosure shall be metal or other material
as specified for the enclosure in 7.5.1 7.7.6.
7.7.9 A nonmetallic part such as a reset knob, lever, or button that protrudes through a hole in the
enclosure that is not larger than the area of a 7/8-inch (22.2-mm) diameter circle shall be made of a
material classified as V-0, V-1, or V-2 in the Tests for Flammability of Plastic Materials for Parts in Devices
and Appliances, UL 94.
7.7.9 revised June 2, 1998
7.7.10 A nonmetallic part that protrudes through a hole larger than the area of a 7/8-inch (22.2-mm)
diameter circle shall be made of a material that complies with the requirements in 7.7.1, 7.7.2, and 7.7.8.
See 7.10.6.
7.7.11 A nonmetallic cover that gives access to bare live parts shall comply with the requirements in 7.3.8
and Snap-On Covers Test, Section 58 and there shall be no exposure of live parts.
7.7.12 A cover attached by screws shall comply with the requirements in 7.3.8 with the screws tightened,
and with the screws loosened one full turn.
7.8 Windows
7.8.1 Glass covering an observation opening shall be reliably secured in place so that it cannot be readily
displaced in service, and shall provide mechanical protection for the enclosed parts.
7.8.2 Glass for an opening not more than 4 inches (102 mm) in any dimension shall not be less than 1/16
inch (1.6 mm) thick, and glass for a larger opening, but not more than 144 square inches (929 cm 2 ) in
area and having no dimension greater than 12 inches (305 mm), shall not be less than 1/8 inch (3.2 mm)
thick. Glass that covers a larger area shall not be less than 1/8 inch thick and shall conform to one of the
following:
a) The glass shall be of a nonshattering or tempered type that, when broken, shall conform to the
performance specifications in the Safety Performance Specifications and Methods of Test for
Safety Glazing Material Used in Buildings, ANSI Z97.1-1984; or
b) Shall withstand a 2-1/2 foot-pound (2.41 J) impact from a 2-inch (50.8-mm) diameter, 1.18
pound (535 g) steel sphere without cracking or breaking to the extent that a piece is released or
dropped from its intended position.
7.8.3 A transparent material other than glass employed as a covering over an opening in an enclosure
shall be investigated to determine if it has adequate mechanical strength and is otherwise acceptable for
the purpose.
7.9 Room thermostats
7.9.1 A room thermostat intended for assembly on a flush-mounted box shall be provided with a box of
sheet steel not less than 0.053 inch (1.35 mm) thick 0.056 inch (1.42 mm) if zinc coated; or with a
cast-metal box not less than 1/8 inch (3.2 mm) thick.
Exception: A room thermostat need not be furnished with a box if means for mounting on a standard
outlet box minimum inside width 1-13/16 inches (56.0 mm), minimum inside length 2-27/32 inches (72.2
mm) is provided and if, when so mounted on the intended box and when the full displacements and
tolerances permitted by the mounting means are considered, at least the minimum required spacings are
provided.
7.9.2 Zinc-base die-cast metal shall not be used for a flush box.
7.9.3 A residential room-thermostat cover having no dimension greater than 6 inches (152 mm) and
having no surface greater than 18 square inches (116.1 cm 2 ) may be not less than 0.020 inch (0.51 mm)
thick uncoated steel, 0.023 inch (0.58 mm) zinc-coated steel, 0.023 inch nonferrous metal, or 0.035 inch
(0.89 mm) die-cast metal.
Exception No. 1: A 0.016-inch (0.41-mm) thick uncoated steel, 0.019-inch (0.48-mm) zinc-coated steel,
0.018-inch (0.46-mm) nonferrous metal, or 0.032-inch (0.81-mm) die-cast metal may be employed if there
are no live parts exposed when the thermostat cover is removed.
Exception No. 2: The thickness of a cover that is decorative only is not specified; the mounting plate and
mechanism shall comply with the enclosure requirements with the cover removed.
7.9.4 The enclosure of a room thermostat is to be formed so that its shape and means of support provide
adequate mechanical strength.
7.10 Openings
7.10.1 An opening shall not be provided in an enclosure that houses a fuse or any portion of a circuit
breaker other than the operating handle, unless the construction affords containment of electrical fault
disturbances equivalent to that provided by an enclosure complying with the requirements in 7.3.5 7.3.7.
7.10.2 The following requirements apply to openings other than those provided in the enclosure of a room
thermostat:
a) An opening shall not be provided in a compartment or part of an enclosure that contains

field-wiring splices in a line-voltage circuit.
b) No openings shall be located in the mounting surface of an enclosure.
Exception: The following openings may be located in the mounting surface of an enclosure:
1) A mounting opening;
2) A maximum of four openings provided for the escape of air or paint during a painting
process. The maximum dimension of such an opening shall not exceed 1/8 inch (3.2 mm);
or
3) A maximum of four unused holes provided for mounting of internal components. The
maximum dimension of such an opening shall not exceed 3/16 inch (4.8 mm).
c) If the bottom surface is not the mounting surface, an opening may be provided in the bottom
surface of an enclosure if the opening does not permit materials to fall directly out from the interior
of the unit. See Figure 7.2 for an example of a construction that may be used.
d) The shortest distance between an opening and the bottom of an enclosure or a wall-mounting
surface shall be at least one-quarter of the enclosure height or depth, respectively, or 1 inch (25.4
mm), whichever is less.
e) There shall be no emission of flame or molten material, or manifestation of risk of fire, during
normal or abnormal tests on the control, such as transformer burnout and burnout of a relay or
solenoid with blocked armature.
f) Unless the construction of a device provided with forced ventilation is such that there is no
direct path between live parts and the outlet opening, burnout tests in addition to those mentioned
in (e) shall be conducted to determine that there is no emission of flame or molten material
through that opening.
g) Air from an opening, either forced or otherwise, shall not be directed into a duct or into a
concealed space in a building, against the mounting surface, and so that a disturbance would be
propagated to other equipment.
h) No more than four holes for mounting an enclosure having a maximum dimension of 18 inches
(457 mm); six holes for an enclosure with a maximum dimension of more than 18 inches, but less
than 48 inches (1.2 m); eight holes for an enclosure with a maximum dimension of 48 inches or
more. Four of the holes for mounting an enclosure with a maximum dimension of 12 inches (305
mm) may be keyhole slots having the configuration illustrated in Figure 7.3. The dimensions
shown in Figure 7.3 may vary if the area is equivalent. Four of the holes for mounting a larger
enclosure may be keyhole slots, the dimensions of which are not specified, and which shall be
investigated with regard to the enclosure dimensions and configuration.
JUNE 2, 1998 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 21
Figure 7.2
Bottom surface openings of enclosures
Figure 7.3
Keyhole slot
Figure 7.3 effective February 28, 1997
7.10.3 Deleted effective February 28, 1997

7.10.4 A room thermostat rated more than 300 volts, with the outer cover on or removed, shall comply
with the requirements in 7.2.2.
7.10.5 An opening, such as a perforated hole, a louver, or an opening protected by wire screening,
expanded metal, or a perforated cover, in the enclosure of a room thermostat the rating of which includes
a value of 300 volts or less shall not permit passage of a 17/64-inch (6.7-mm) diameter rod.
Exception No. 1: If the distance between an uninsulated live part and the edge of an opening is 2-1/2
inches (63.5 mm) or more, the opening may permit passage of a 17/64-inch diameter rod but shall not
permit passage of a 33/64-inch (13.1-mm) diameter rod.
Exception No. 2: If other means, such as an internal barrier or arrangement of parts provides equivalent
protection, the maximum size of an individual opening in an enclosure is not specified.
7.10.6 The smaller dimension width of an opening in an enclosure around a dial, adjusting knob, lever,
handle, pointer, or the like shall not be more than 1/8 inch (3.2 mm) for any setting or position of the dial,
knob, or other members.
7.10.7 Deleted effective February 28, 1997

7.10.8 A plate or plug for an unused conduit opening or other hole in an enclosure shall have a thickness
not less than 0.014 inch (0.36 mm) for steel or 0.019 inch (0.48 mm) for nonferrous metal for a hole having
a 1/4-inch (6.4-mm) maximum dimension and 0.027-inch (0.69-mm) steel or 0.032-inch (0.81-mm)
nonferrous metal for a hole having a 1-3/8-inch (34.9-mm) maximum dimension. A closure for a larger
hole shall have a thickness equal to that required for the enclosure of the device or a standard knockout
seal shall be used. Such a plate or plug shall be securely mounted.
7.11 Screens and expanded metal
7.11.1 The wires of a screen shall not be less than No. 16 AWG for screen openings 1/2 square inch (3.2
cm2) or less in area, and shall not be less than No. 12 AWG for larger screen openings.
7.11.2 Perforated sheet steel, and sheet steel employed for expanded metal mesh, shall not be less than
0.042 inch (106.7 mm) thick 0.045 inch (114.3 mm) if zinc coated for mesh openings or perforations
1/2 square inch (3.2 cm2) or less in area and shall not be less than 0.080 inch (203.2 mm) thick 0.084
inch (213.3 mm) if zinc coated for larger openings.
Exception: Expanded metal mesh that complies with the requirements in 7.11.3 may be used.
7.11.3 In a small device where the indentation of a guard or enclosure will not alter the clearance
between uninsulated, movable, current-carrying parts and grounded metal, so as to adversely affect
performance or reduce spacings below the minimum acceptable values specified in Table 33.1,
0.020-inch (0.51-mm) expanded metal mesh 0.023-inch (0.58-mm) if zinc coated may be employed,
provided the exposed mesh on any one side or surface of the device so protected has an area of not more
than 72 square inches (464.5 cm2) and has no dimension greater than 12 inches (305 mm) or the width
of an opening so protected is not greater than 3-1/2 inches (88.9 mm).
7.12 Wiring openings
7.12.1 If threads for the connection of conduit are tapped all the way through a hole in an enclosure wall,
or if an equivalent construction is used, there shall be no less than three threads in the metal, and the
construction of the control shall be such that a conduit bushing can be attached as intended.

7.12.2 If threads for the connection of conduit are not tapped all the way through a hole in an enclosure
wall, conduit hub, or the like, there shall not be less than 3-1/2 threads in the metal and there shall be a
smooth, rounded inlet hole for the conductors that affords protection to the conductors equivalent to that
provided by a standard conduit bushing and that has an internal diameter approximately the same as that
of the corresponding trade size of rigid conduit.
7.12.3 In an enclosure threaded for support by rigid conduit at least five full threads shall be provided for
engaging the conduit.
7.12.4 A conduit hub or nipple attached to the enclosure of a pressure switch or similar equipment by
swaging, staking, or similar means shall withstand, without pulling apart, a direct pull of 200 pounds (890
N), a bending moment of 600 pound-inches (67.8 Nm), and a torque of 600 pound-inches, each applied
in turn for 5 minutes.
7.12.5 For the pullout test, the equipment is to be supported by a rigid conduit in the intended manner
and is to support a weight of 200 pounds (90.8 kg).
7.12.6 For the bending and torsion tests, the equipment is to be rigidly supported by means other than
the conduit fittings.
7.12.7 In the bending test, the force is to be applied to the conduit at right angles to its axis, and the lever
arm is to be measured from the wall of the enclosure in which the hub or stud is located to the point of
application of the bending force.
7.12.8 In the torsion test, the force is to be applied to the conduit in a direction tending to tighten the
connection, and the lever arm is to be measured from the center of the conduit.
7.12.9 With reference to 7.12.5 7.12.8, some distortion of the enclosure under test may result. The test
may be discontinued when noticeable distortion occurs.
7.12.10 Clamps and fasteners for the attachment of conduit, electrical metallic tubing, armored cable,
nonmetallic flexible tubing, nonmetallic-sheathed cable, service cable, and the like that are supplied as a
part of an enclosure shall comply with the requirements in the Standard for Fittings for Cable and Conduit,
UL 514B.
7.12.10 revised June 2, 1998
7.12.11 A knockout in a sheet-metal enclosure shall be reliably secured but shall be capable of being
removed without undue deformation of the enclosure.
7.12.12 A knockout shall be provided with a flat surrounding surface adequate for proper seating of a
conduit bushing, and shall be located so that installation of a bushing at any knockout likely to be used
during installation will not result in a spacing between uninsulated live parts and the bushing less than that
required by this standard.
7.12.13 For an enclosure not provided with conduit openings or knockouts, spacings not less than the
minimum required in this standard shall be provided between uninsulated live parts and a conduit bushing
installed at any location likely to be used during installation. Permanent marking on the enclosure, a
template, or a full-scale drawing provided with the device may be used to limit such a location.
7.12.14 In measuring a spacing between an uninsulated live part and a bushing installed in the knockout
referred to in 7.12.12 and 7.12.13, it is to be assumed that a bushing having the dimensions in Table 7.3
is in place, and that a single locknut is installed on the outside of the enclosure.
Table 7.3
Dimensions of bushings
Overall diameter, Height,

Trade size of conduit,
inches inches (mm) inches (mm)
1/2 1 (25.4) 3/8 (9.5)

3/4 1-15/64 (31.4) 27/64 (10.7)
1 1-19/32 (40.5) 33/64 (13.1)
1-1/4 1-15/16 (49.2) 9/16 (14.3)
1-1/2 2-13/64 (56.0) 19/32 (15.1)
2 2-45/64 (68.7) 5/8 (15.9)
2-1/2 3-7/32 (81.8) 3/4 (19.1)
3 3-7/8 (98.4) 13/16 (20.6)
3-1/2 4-7/16 (112.7) 15/16 (23.8)
4 4-31/32 (126.2) 1 (25.4)
4-1/2 5-35/64 (140.9) 1-1/16 (27.0)
5 6-7/32 (158.0) 1-3/16 (30.2)
6 7-7/32 (183.4) 1-1/4 (31.8)
7.12.15 No wire other than wires leading to a part mounted on a door or cover shall be brought out
through the door or cover.
7.13 Raintight and rainproof enclosures
7.13.1 When subjected to the Rain Test, Section 56, an enclosure designated as:
a) Raintight shall restrict rain from entering the enclosure.
b) Rainproof shall restrict rain from interfering with the successful operation of the apparatus used
within the enclosure.
7.13.2 A raintight or rainproof enclosure shall be marked as specified in 69.7.
7.13.3 A gasket employed to make an enclosure raintight or rainproof shall be tested as specified in
Accelerated Aging Tests on Gaskets, Sealing Compounds, and Adhesives, Section 54.
7.13.4 A raintight or rainproof enclosure shall be provided with external means for mounting.
Exception: A rainproof enclosure may be provided with internal means for mounting if the mounting
means is intended to restrict water from entering the enclosure.
7.13.5 An opening for conduit in a raintight enclosure, other than in the bottom of the enclosure shall be
threaded.
7.13.6 An opening for conduit in a rainproof enclosure shall be threaded unless located wholly below the
lowest terminal lug or other live part within the enclosure. There shall be provision for drainage of the
enclosure if a knockout or unthreaded hole is provided other than in the bottom.
8 Mounting
8.1 Provision shall be made for mounting a device securely in position. Bolts, screws, or other parts used
for mounting a device shall be independent of those used to secure components of the device to the
frame, base, or panel.
8.2 A control switch, a lampholder, an attachment-plug receptacle, or a plug connector provided as a part
of a device shall be mounted securely and shall be prevented from turning by means other than friction
between surfaces.
8.3 A properly applied lock washer may be used as a means to restrict a control switch from turning.
9 Parts Containing Liquid Metal
9.1 A part of a control intended for use with cooking or other food-handling appliances that contains
mercury and the parts of any control that contain sodium-potassium shall be constructed of metal that:
a) Has a tensile yield strength at a temperature of 120 percent of the maximum normal use
Fahrenheit temperature equal to at least four times the hoop stress or other stress on the part at
that temperature.
b) Is known not to be susceptible to corrosion-stress-cracking when exposed to the contained

liquid metals and external agents, or is subjected to appropriate tests.
10 Adjustment Stop
10.1 A part of a control that is user operated and that limits the degree of rotation or length of movement
of an adjustment hereinafter referred to as the adjustment stop shall be constructed so that it
withstands the usage encountered in its intended operation as determined by the applicable tests in
Strength of Adjustment Stop Test, Section 61.
10.2 If it is intended that the end-product incorporate the means to limit the movement of the adjustment
stop as described in 10.1, the requirements are to be applied to the end-product and not to the control,
however:
a) If an extended handle or the like is intended to be added on the appliance, the adjustment stop
for the control shall have the strength necessary to prevent both damage and a change in
calibration during shipping and handling.
b) If a control has no adjustment stop and is intended to be assembled into an appliance plug or
other mechanism, the adjusting means shall be provided with a temporary seal to reduce the
likelihood of damage or a change in calibration prior to final assembly.
c) The adjustment stop is to be tested as specified in Strength of Adjustment Stop Test, Section
61, except that the torque or force applied to the adjusting means need not be greater than 1
pound-inch (0.1 Nm) or 1 pound (4.5 N).
11 Operating Mechanism
11.1 A temperature-indicating or -regulating device shall be assembled so that it will not be adversely
affected by the vibration of normal operation.
11.2 Screws and nuts that attach operating parts to movable members shall be upset or otherwise locked
to reduce the likelihood of loosening under the conditions of actual use.
11.3 An operating mechanism shall not subject manually operated switch parts to undue stress.
11.4 The position of an operating handle shall be marked if necessary as a guide for proper operation.
11.5 A control that is intended for factory installation on an appliance and that has or is intended to have
a marked off position or an implied off position see 11.7 11.9 shall:
a) Open all ungrounded conductors of the circuit when the adjusting means is in the off position;
and
b) Be restricted from functioning automatically when in the off position either by a positive
mechanical means or as specified in 11.10.
Exception No. 1: If unintentional energization of the appliance in which the control is intended to be used
will not result in a risk of fire or electric shock for example, a range oven having no live parts exposed
to the user the control need not comply with this requirement.
Exception No. 2: For a control intended for use in conjunction with another control, the requirement can
be met by the combination of the two controls.
Exception No. 3: If energization of the appliance in which the control is intended to be used will not result
in a risk of electric shock during operation or cleaning, or the like, but may result in a risk of fire or injury
to persons if unintentionally energized for example, a hot plate the control need only open a sufficient
number of conductors to de-energize the circuit.
11.6 A capillary-type control if specified for use in the end-product for example, certain
temperature-regulating controls for commercial cooking appliances is to comply with the requirements
specified in 11.5 with the capillary tube normal and cut, in separate tests.
11.7 A thermostat or a thermostatically controlled switching device intended for direct control of indoor
electric space-heating equipment that is to be permanently connected electrically shall disconnect all
ungrounded conductors of the supply circuit when:
a) The actuating member is placed in a marked off position, or
b) The actuating member is placed in an unmarked off position that is implied by the fact that
there is a marked on position.
11.8 A device that is marked with a phrase such as no heat or cold that conveys the same meaning
as the word off shall also comply with the requirement in 11.7.
11.9 A single-pole thermostat marked Lo Normal High or having a temperature scale such as 40
80 or a numerical scale such as 1 5 (not including the numeral 0) is not considered to have an off
position as defined in 11.7.
11.10 A thermostat or thermostatically controlled switching device intended for direct control of indoor,
electric-space-heating equipment that is to be permanently connected electrically that has a marked off
position, or an unmarked off position that is implied by the fact that there is a marked on position shall not
function as a thermostat (shall not respond to temperature changes) while the actuating member is in the
off position.
11.11 A thermostat that does not reclose (remains open) when cooled to a temperature of minus 35C
(minus 31F) is acceptable with respect to the requirement in 11.10.
11.12 A combined manual switch and thermostat intended for direct control of indoor electric
space-heating equipment that is to be permanently connected electrically shall disconnect all ungrounded
conductors of the supply circuit regardless of temperature, and shall be constructed so that the circuit
cannot be energized automatically after the device has been manually placed in the off position.
11.13 A device involving electronic control circuits shall be investigated under conditions of actual service
to determine if it complies with all applicable requirements and is otherwise acceptable for its intended
application.
11.14 A marked off position shall have an air-gap construction.
Exception: A solid-state device may be employed but shall be subjected to an appropriate investigation
to determine equivalent protection.
11.15 A component, such as a resistor, capacitor, diode, and the like, shall not be connected across the
contacts of a safety control or a protective or limiting device.
Exception: A component may be connected across the contacts if investigated and found to be
acceptable in the end product.
11.16 A water-heater temperature-limiting control shall be a manually reset control.
Exception: A temperature-limiting control for a marine-type storage-tank water heater may be a

single-operation device. See Single-Operation Devices, Section 81.
11.17 A water-heater temperature-limiting control shall have no operating part in common with a
water-heater temperature-regulating control, but a common mounting bracket or a common enclosure
may be employed for both controls.
11.18 A temperature-regulating thermostat or control for a household electric storage tank water heater
shall be set before leaving the factory to a control position corresponding to a temperature no higher than
60C (140F). This setting may be approximate, for a marking on the control that reads
Low-Medium-High or the equivalent.
12 Reset Mechanism Limiting Control
12.1 A control shall not reset or be resettable manually or otherwise so that operation of the controlled
appliance can be resumed until after a safe operating condition is restored. For example, pressure or
temperature returned to a value at or below the control set point.
12.2 A control that is intended to be reset manually shall not reset automatically as a result of changes
in environmental temperature at temperatures above minus 35C (minus 31F) for a regular limiting
control or a marine-type storage-tank water heater temperature-limiting control, and above 0C (32F) for
a non-marine storage-tank water heater temperature-limiting control.
Exception: This requirement does not apply if it is not required for the end-use product.
12.3 A manually reset device shall be trip-free; that is, the automatic tripping shall be independent of the
manipulation or position of the reset button, handle, lever, or the like.
12.4 A manually reset device of a control may provide one or another of the following kinds of reset
function:
a) For a control designated Manually Reset 1 or M1, the control shall automatically reset to
the closed position after normal operating conditions have been restored, if the reset means is
held in the reset position. The operating tolerances specified in Calibration-Verification Test,
Section 44, shall not be exceeded if the reset means is held in the reset or on position.
b) For a control designated Manually Reset 2 or M2, the control shall not function as an
automatically reset device if the reset means is held in the reset or on position.
12.5 The means for resetting a control with a manual reset shall be external to the control enclosure.
Exception: If the control enclosure complies with the requirements for protection as specified in
Protection of Users and Service Personnel, Section 23, and Protection Against Injury to Persons, Section
24, the means for resetting need not be external.
12.6 A manually reset mechanism shall not subject the operating mechanism or means of support to
stress.
13 Means for Calibration
13.1 The following controls shall comply with the requirements in 13.2 13.8:
a) A water-heater control;
b) A refrigeration pressure-limiting device;
c) An appliance temperature-limiting control including some regulating controls if limiting-control

features are specified in the end-product standard;
d) A time-delay or thermal relay that responds to a limiting control;
e) A range oven-door-lock control;
f) A clean-temperature control for a self-cleaning range oven; and
g) A hot tub/spa water temperature control.
13.2 A means provided for factory calibration shall be factory-secured to restrict unintentional shifting
after calibration.
13.3 A means for calibration that is accessible or apparent shall be modified, guarded, or sealed by a
means such as soldering to effectively restrict manipulation by hand or an ordinary tool subsequent to
factory calibration.
13.4 With reference to 13.3, a calibration means that is not considered to be accessible or apparent is a
means that does not show, is not exposed to manipulation by a conventional tool, or is not readily
displaced. Complete concealment of a conventional tool-engaging means in a screw, such as a slot,
recessed head, or the like, by the use of solder, brazing material, or cement rated for the purpose is
adequate to restrict manipulation if the calibration means cannot be changed readily by gripping with a
conventional tool and engagement or manipulation is restricted at all other locations.
13.5 Enamel and other polymeric materials used to secure or seal the means of calibration at the factory
are rated only for exposure to temperatures of 121C (250F) or less, unless they have been subjected to
thermal aging tests and have been found acceptable for use at higher temperatures.
13.6 An adjustable control shall comply with the requirements in 13.2 and 13.3 with respect to the
maximum temperature, pressure, or similar setting.
13.7 A temperature or pressure adjustment means, including a trim screw or the equivalent, shall be
provided with a stop to restrict manipulation beyond a setting, or concealed or sealed, and in either case,
factory-secured as required by 13.2.
13.8 Performance tests such as the calibration-verification tests, are to be conducted on samples having
the highest setting permitted by the adjustment means, including a trim screw or the equivalent.
14 Protection Against Corrosion
14.1 Iron and steel parts shall be protected against corrosion by enameling, galvanizing, sherardizing,
plating, or other equivalent means.
Exception No. 1: Bearings, thermal elements, or the like need not be protected if such protection is
impracticable.
Exception No. 2: Small minor parts of iron or steel such as washers, screws, bolts, and the like that do
not carry current need not be protected if corrosion of such unprotected parts would not be likely to result
in a risk of fire, electric shock, or injury to persons.
Exception No. 3: Parts made of stainless steel, properly polished or treated if necessary need not be
protected.
14.2 The requirement in 14.1 applies to all enclosing cases whether of sheet steel or cast iron, and to all
springs and other parts upon which proper mechanical operation may depend.
14.3 An enclosure designated either raintight or rainproof shall be protected against corrosion in
accordance with the requirements in 14.4 14.18.
14.4 Metal shall be used in combinations that are galvanically compatible.
14.5 A hinge or other attachment shall be resistant to corrosion.
14.6 These requirements do not contemplate corrosion that might be caused by exposure to the earth or
other corrosive agents.
14.7 The requirements specified in 14.8 14.18 do not apply to a part, such as a decorative grille, that
is not a required part of an enclosure.
14.8 A nonmetallic enclosure is to be investigated on the basis of the effect of exposure to ultraviolet light
and water.
14.9 A metallic enclosure shall be protected against corrosion as specified in 14.10 14.18. See 7.5.1
7.6.4 for the required enclosure thickness.
30 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 OCTOBER 24, 1995
14.10 Copper, bronze, brass containing not less than 80 percent copper, or stainless steel may be used
without additional protection against corrosion. Aluminum sheet, extrusion, or casting die-cast zinc, or
other metal shall be of a grade or alloy having resistance to atmospheric corrosion, equivalent to that
specified for sheet steel of the required thickness or shall be subjected to appropriate tests, or shall be
additionally protected against corrosion.
14.11 An enclosure of cast iron or malleable iron at least 1/8 inch (3.2 mm) thick shall be protected
against corrosion by a 0.00015-inch (0.0130-mm) thick coating of zinc, cadmium, or the equivalent on the
outside surface and a visible coating of such metal on the inside surface, or one coat of an organic finish
of the epoxy or alkyd-resin type or other outdoor paint on each surface.
14.12 Unless acceptability of the paint can be determined by consideration of its composition, corrosion
tests are required.
14.13 An enclosure of sheet steel having a thickness less than 0.126 inch (3.20 mm) if zinc-coated or
0.123 inch (3.12 mm) thick if uncoated shall be protected against corrosion by one of the following means
or by other metallic or nonmetallic coatings that have been found to give equivalent protection as
described in 14.16.
a) Hot-dipped mill-galvanized sheet steel conforming with the coating Designation G90 in the
Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed)
by the Hot-Dip Process, ASTM A653/A653M-94, with not less than 40 percent of the zinc on any
side, based on the minimum single-spot test requirement in this ASTM designation. The weight of
zinc coating may be determined by any suitable method; however, in case of question, the weight
of coating shall be established in accordance with the Test Method for Weight of Coating on
Zinc-Coated (Galvanized) Iron or Steel Articles, ASTM A90-81(1991).
b) A zinc coating, other than that provided on hot-dipped mill-galvanized sheet steel, uniformly
applied to an average thickness of not less than 0.00061 inch (0.0155 mm) on each surface with
a minimum thickness of 0.00054 inch (0.0137 mm). The thickness of the coating shall be
established by the Metallic Coating Thickness Test, Section 55. An annealed coating shall also
comply with 14.18.
c) A zinc coating conforming with 14.14 (a) or (b) with one coat of an organic finish of the epoxy
or alkyd-resin type or other outdoor paint applied after forming on each surface. The acceptability
of the paint is to be determined by consideration of its composition or by corrosion tests.
d) A cadmium coating not less than 0.001 inch (0.03 mm) thick on both surfaces. The thickness
of coating shall be established in accordance with the Metallic Coating Thickness Test, Section
55.
e) A cadmium coating not less than 0.00075 inch (0.0191 mm) thick on both surfaces with one
coat of outdoor paint on both surfaces, or not less than 0.00051 inch (0.013 mm) thick on both
surfaces with two coats of outdoor paint on both surfaces. The thickness of the cadmium coating
shall be established in accordance with the Metallic Coating Thickness Test, Section 55, and the
paint shall be as specified in (c).
14.13 revised October 24, 1995
14.14 An enclosure of sheet steel 0.126 inch (3.20 mm) thick if zinc-coated or 0.123 inch (3.12 mm) thick
if uncoated or heavier shall be protected against corrosion by one of the following means or by other
metallic or nonmetallic coatings that have been shown to give equivalent protection as described in 14.16.
a) Hot-dipped mill-galvanized sheet steel conforming with the coating Designation G60 or A60in
the Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated
(Galvannealed) by the Hot-Dip Process, ASTM A653/A653M-94, with not less than 40 percent of
the zinc on any side, based on the minimum single-spot test requirement in this ASTM
designation. The weight of zinc coating may be determined by any suitable method; however, in
case of question, the weight of coating shall be established in accordance with the Test Method
for Weight of Coating on Zinc-Coated (Galvanized) Iron or Steel Articles, ASTM A90-81(1991).
b) A zinc coating, other than that provided on hot-dipped mill-galvanized sheet steel, uniformly
applied to an average thickness of not less than 0.00041 inch (0.0104 mm) on each surface with
a minimum thickness of 0.00034 inch (0.0076 mm). The thickness of the coating shall be
established by the Metallic Coating Thickness Test, Section 55.
c) Two coats of an organic finish of the epoxy or alkyd-resin or other outdoor paint on each
surface. The acceptability of the paint is to be determined by consideration of its composition or
by corrosion tests.
d) Any one of the means specified in 14.13.

14.14 revised October 24, 1995
14.15 The requirements specified in 14.14 also apply to sheet steel 0.056 inch (1.42 mm) thick if
zinc-coated or 0.053 inch (1.35 mm) thick if uncoated or heavier for an enclosure to be mounted within
and protected from direct exposure to weather by the enclosure of other equipment, such as an air
conditioner. Such an enclosure is not to be marked rainproof or raintight.
14.16 With reference to 14.13 14.15, other finishes, including paints, metallic finishes and combinations
of the two may be accepted when comparative tests with galvanized sheet steel without annealing,
wiping or other surface treatment conforming with 14.13(a) or 14.14(a), as applicable, indicate they
provide equivalent protection. Among the factors that are to be taken into consideration when judging the
acceptability of such coating systems are exposure to salt spray, moist carbon dioxide-sulfur dioxide-air
mixtures, moist hydrogen sulfide-air mixtures, and ultraviolet light and water.
14.17 Test specimens of a finish as described in 14.14 or 14.16, 14.13(c), or 14.14(c), if the paint is
tested, are to be consistent with the finish that is to be used in production with respect to the base metal,
cleaning or pretreatment method, application method, number of coats, curing method, thickness, and the
like.
14.18 A hot-dipped mill-galvanized A60 (alloyed) coating or an annealed zinc coating that is bent or
similarly formed after annealing and that is not otherwise required to be painted shall be painted in the
bent or formed area if the bending or forming process damages the zinc coating, except that such areas
on the inside surface of an enclosure that water does not enter during the Rain Test, Section 56, need not
be painted. The zinc coating is considered to be damaged if flaking or cracking of the zinc coating at the
outside radius of the bent or formed section is visible at 25 power magnification. Simple sheared or cut
edges and punched holes are not considered to be formed.
15 Insulating Material
15.1 A base for the support of a live part shall be of strong, noncombustible, moisture-resistant, insulating
material.
15.2 A material other than slate, porcelain, phenolic or cold-molded composition, or one that is rated for
the support of live parts shall be investigated under conditions of intended service to determine if it has
the necessary electrical and mechanical properties and is otherwise rated for the application.
15.3 A base shall be constructed so that, considering the material used, it will withstand the most severe
condition likely to be met in service.
15.4 Insulating material, including a barrier between parts of opposite polarity and material that may be
subjected to the influence of an arc formed by opening a switch, shall be rated for the application.
15.5 Vulcanized fiber may be used for an insulating bushing, a washer, a separator, or a barrier, but not
for the sole support of an uninsulated live part of other than a low-voltage circuit.
16 Supply Connections
16.1 General
16.1.1 Connections to wiring terminals of equipment that is to be permanently connected electrically and
supply connections are connections that are made in the field when the equipment is installed.
16.1.2 Wires within an enclosure, compartment, raceway, or the like shall be routed or protected so that
damage to conductor insulation cannot result from contact with a rough, sharp, or moving part.
16.2 Equipment permanently connected electrically
16.2.1 General
16.2.1.1 Wiring terminals or leads shall be provided and shall be rated for the connection of conductors
having an ampacity not less than the largest of the following ratings that are applicable:
a) One hundred twenty-five percent of the ampere rating of electric heating equipment for pools,
hot tubs/spas, and space-heating equipment;
b) One hundred twenty-five percent of the full-load motor-current rating in accordance with 67.4
and 67.5. See Table 45.2 or 45.3 for the ampere rating corresponding to the horsepower rating;
c) For a combination load, 125 percent of the full-load motor current of the largest motor, plus 125
percent of the ampere rating of electric heating equipment for pools, hot tubs/spas, and
space-heating equipment, plus 100 percent of the sum of the current ratings of all other loads;
d) For direct-current-motors intended to be operated from a rectified single-phase power supply

unless marked in accordance with 70.10;
1) One hundred ninety percent if a half-wave rectifier is used, or
2) One hundred fifty percent if a full-wave rectifier is used; or

e) The ampere rating of the equipment, for a load not specified in (a), (b), (c), and (d).
16.2.1.2 With reference to 16.2.1.1, it is assumed that 75C (167F) conductors will be employed for
currents of more than 100 amperes.
16.2.1.3 A field-wiring terminal marked to indicate that it is rated for use with a copper, a copper-clad
aluminum, or an aluminum power supply conductor shall comply with the requirement in 16.2.1.1 for a
wire of each metal for which it is marked.
16.2.1.4 A terminal box or compartment on equipment that is to be permanently connected electrically

shall be located so that the wire connections therein will be accessible for inspection, without disturbing
the line-voltage or safety-circuit wiring after the equipment is installed in the intended manner.
Exception: Wire connections to equipment intended to be mounted on an outlet box may be accessible
upon removal of the equipment from the box.
16.2.1.5 The free lead length of a field-wiring lead shall not be less than 6 inches (152 mm); insulation on
the conductor shall comply with the requirements in 19.1 19.5.
16.2.1.6 A field-wiring lead, other than a lead for connection of a Class 2 circuit, shall not be more than
two standard wire sizes smaller than the copper conductor to which it will be connected, and shall not be
smaller than No. 18 AWG (0.82 mm 2 ) for example, a No. 10 AWG (5.3 mm 2 ) or larger field-wiring
lead is required for connection to a No. 6 AWG (13.3 mm 2 ) field-provided conductor. See Table 16.1.
Exception No. 1: A lead may be more than two wire sizes smaller than the field-provided copper conductor
to which it will be connected, but not smaller than No. 18 AWG, if more than one factory-provided copper
lead is intended for connection to the same field-provided lead, and the construction complies with the
following conditions:
a) A wire connector for connection of the field-provided wire is provided as part of the unit or
remote-control assembly, and the wire connector is rated for the combination of wires that will be
spliced;
b) The factory-provided leads are bunched or otherwise arranged to restrict stress on an

individual lead; and
c) The equipment is marked in accordance with 70.9.
Exception No. 2: A single No. 18 AWG field-wiring lead may be connected to a No. 12 AWG field-provided
conductor.
Table 16.1
Field-wiring lead size
Field-wiring lead wire size determination by 16.2.1.1, AWG Required size of internal lead for field-wiring, AWG
14 or 12 18
12 16
10 14
8 12
6 10
4 8
3 6
2 4
1 3
1/0 2
2/0 1
3/0 1/0
4/0 2/0
250 kcmil 3/0
16.2.1.7 A lead provided for connection to an external line-voltage circuit shall not be connected to a
wire-binding screw or pressure terminal connector located in the same compartment as the splice unless
the screw or connector is rendered unusable for field-wiring connection or the lead is insulated at the
unconnected end, and a marking on the equipment clearly indicates the intended use of the lead.
16.2.1.8 The free end of a field-wiring lead that will not be used in every installation such as a tap for
a multivoltage transformer or one free lead for a single-pole, double-throw switch shall be insulated. For
a grounding lead, see 21.4.10.
16.2.1.9 For power-circuit connections, equipment that is to be permanently connected electrically shall
have provision for the connection of a wiring system.
16.2.1.10 A device that is rated for use with a fitting for only one type of wiring system shall be supplied
with such a fitting.
16.2.1.11 An opening for the entry of a conductor or conductors of a circuit of limited power and voltage
shall be provided with an insulating bushing. The bushing may be mounted in place in the opening or may
be within the enclosure so that it may be properly mounted when the device is installed.
16.2.1.12 The opening mentioned in 16.2.1.11 may be used for accommodating armored cable or
conduit.
16.2.1.13 A bushing of rubber or rubber-like material provided in accordance with 16.2.1.11 shall be 1/8
inch (3.2 mm) or more thick, except that it may be not less than 3/64 inch (1.2 mm) thick if the metal
around the hole is eyeletted or similarly treated to provide smooth edges. A bushing shall be located so
that it will not be exposed to oil, grease, oily vapors, or other substances having a deleterious effect on
the material of the bushing. A hole in which such a bushing is mounted shall be free from sharp edges,
burrs, projections, or the like that might damage the bushing.
16.2.2 Terminals
16.2.2.1 Terminal parts by which supply connections are made shall be such as to provide reliable
connections even under hard usage.
16.2.2.2 Soldering lugs or solderless (pressure) wire connectors shall be used. A solderless (pressure)
connector intended for connection of a No. 14 AWG or smaller copper conductor shall comply with the
torque test specified in the Standard for Wire Connectors and Soldering Lugs for Use With Copper
Conductors, UL 486A or the Standard for Equipment Wiring Terminals for Use With Aluminum and/or
Copper Conductors, UL 486E, with a tightening torque of not less than 7 pound-inches (0.8 Nm).
Exception: For a No. 10 AWG or smaller wire, the parts to which wiring connections are made may
consist of clamps or binding screws with terminal plates having upturned lugs or the equivalent to hold
the wires in position.
16.2.2.3 A wire-binding screw employed at a wiring terminal shall not be smaller than No. 8.
Exception: A No. 6 screw may be used for the connection of one No. 14, 16, or 18 AWG conductor.
16.2.2.4 Other than as noted in 16.2.2.5, a terminal plate tapped for a wire-binding screw shall be of
metal not less than 0.030 inch (0.76 mm) thick for a No. 14 AWG or smaller wire, and not less than 0.050
inch (1.27 mm) thick for a wire larger than No. 14 AWG. There shall not be less than two full threads in
the metal.
16.2.2.5 A low-voltage transformer may have terminal plates 0.030 inch (0.76 mm) thick for either primary
or secondary connections.
16.2.2.6 A terminal plate formed from stock having the minimum required thickness specified in 16.2.2.1
16.2.2.4 may have the metal extruded at a tapped hole for a binding screw so as to provide two full
threads.
Exception: Two full threads are not required if fewer threads make a connection in which the threads do
not strip when it is subjected to a 20 inch-pound (2.3 N) tightening torque.
16.2.2.7 A wire-binding screw shall not thread into material other than metal.
16.2.2.8 In order to polarize the wiring of equipment that is to be permanently connected electrically and
is intended to be connected to more than one wire of a supply circuit rated at 125 volts or 125/250 volts
or less and employing an Edison screw-shell lampholder or a single-pole switch or overcurrent-protective
device other than an automatic control, one terminal or lead shall be identified for connection to the
grounded conductor of the supply circuit. A terminal or lead identified for connection to the grounded
supply conductor shall be electrically connected to screw shells of lampholders, and shall not be
connected to a single-pole switch or a single-pole overcurrent-protective device.
16.2.3 Outlet-box-mounted devices
16.2.3.1 Wiring terminals and other live parts and sharp-edged grounded or dead metal parts of a device
intended for mounting on an outlet box or similar enclosure shall be located or protected so that they will
not be forced against wiring in the box during installation.
16.2.3.2 With reference to the requirements in 16.2.3.1, back wiring terminals may be employed if they
are recessed or are protected by close-fitting barriers of insulating material or the equivalent that will
restrict contact with wiring installed in the box.
16.2.3.3 Terminals that do not project into a box beyond the plane of the front edge of the box may be
used.
16.2.3.4 With reference to 16.2.3.2, guards provided alongside terminals and extending at least 1/4 inch
(6.4 mm) beyond the terminals before wiring, with a corresponding guard between double-pole switching
mechanisms, may be used.
16.2.3.5 To determine whether a construction other than that described in 16.2.3.4 restricts wiring in the
box from being forced against live parts or sharp edges, a trial installation using only ordinary care is to
be made on an appropriately sized outlet box, employing both copper and aluminum Type TW wire having
ampacities in accordance with the rating of the device. The wire is to extend 6 inches (152 mm) inside the
box from its point of entrance into the box.
16.3 Cord and plug connected portable equipment
16.3.1 Portable equipment shall be provided with a length of flexible cord and an attachment plug for
connection to the supply circuit. The type of cord shall be rated for the application, and the rating of the
plug and the ampacity of the cord shall be as specified in 16.2.1.1.
16.4 Stationary equipment
16.4.1 General
16.4.1.1 In determining the acceptability of a cord and plug connection for equipment that is intended to
be fastened in place or located in a dedicated space, the decision is to include consideration of:
a) Whether:
1) The cord connection of the equipment facilitates frequent interchange,
2) Reduction of the transmission of noise or vibration is accomplished, or
3) The fastening means or mechanical connections are intended to permit removal for
maintenance and repair, and
b) Whether the equipment is to be connected at the end of the run.
16.4.1.2 The cord on stationary equipment shall be Type SJ or equivalent hard-service cord, not more
than 3 feet (914 mm) long, directly connected to the equipment and terminated in an attachment plug. The
rating of the plug and the ampacity of the cord shall be as specified in 16.2.1.1.
16.4.2 Strain relief
16.4.2.1 Strain relief shall be provided so that mechanical stress on a flexible supply cord will not be
transmitted to terminals, splices, or interior wiring.
16.4.2.2 A strain-relief device shall be subjected to the test described in Strain-Relief Test, Section 53.
16.4.2.3 Surfaces against which a knot in a flexible cord that serves as strain relief may bear or which it
may contact shall be free from projections, sharp edges, burrs, fins, and the like, that may abrade the
insulation on conductors.
16.4.3 Bushings
16.4.3.1 Where a flexible cord passes or is intended to pass through an opening in a wall, barrier, or
enclosing case, there shall be a bushing rated for the application or the equivalent that is reliably secured
in place, and has a smooth surface against which the cord may bear. An insulating bushing shall be
provided for a cord lighter than Type SJ that passes through a wall or barrier of metal if the construction
is such that the cord may be subjected to stress or motion.
16.4.3.2 A cord hole with a smooth surface through wood, porcelain, phenolic composition, or other
nonconductive material rated for the application is considered to be the equivalent of a bushing.
16.4.3.3 Ceramic materials and some molded compositions may be used for insulating bushings; but a
separate bushing of wood or so-called hot-molded shellac and tar composition may not be used.
16.4.3.4 A fiber bushing shall not be less than 3/64 inch (1.2 mm) thick, shall be formed and secured in
place so that it will not be adversely affected by conditions of ordinary moisture, and shall not be employed
where it will be subjected to a temperature higher than 90C (194F) under normal operating conditions.
16.4.3.5 A soft-rubber bushing shall not be less than 3/64 inch (1.2 mm) thick and shall be located so that
it will not be exposed to oil, grease, oily vapor, or other substances having a deleterious effect on rubber.
Such a bushing may be used only in the frame of a motor or for a cord connected to a supply circuit of
limited voltage and power. A hole in metal in which a soft-rubber bushing is employed shall be free from
sharp edges, burrs, projections, and the like, that would be likely to cut into the rubber.
16.4.3.6 Insulating material in an insulated metal grommet employed in lieu of an insulating bushing shall
not be less than 1/32 inch (0.8 mm) thick and shall completely fill the space between the grommet and
the metal in which it is mounted.
16.4.4 Polarity
16.4.4.1 The attachment plug of a cord-connected product shall be of the polarized type if the product is
not provided with a grounding type attachment plug see 21.1.1.
16.4.4.2 The blade of the attachment plug identified for connection to the grounded supply conductor
shall not be electrically connected to a single-pole switching device, intended for product on-off operation,
but shall be connected electrically to the screw-shell of an Edison-base lampholder and to the identified
terminal of a receptacle.
17 Current-Carrying Parts
17.1 A current-carrying part shall have the necessary mechanical strength and ampacity for the service,
and shall be of metal that is rated for the application.
17.2 An uninsulated live part, including a terminal, shall be secured to its supporting surface by a means
other than friction between surfaces so that it will be restricted from turning or shifting in position if such
motion may result in reduction of spacings to less than those required by this standard. The security of
contact assemblies shall provide continued alignment of contacts.
17.3 A lock washer properly applied may be used at a terminal or connection stud.
18 Switches
18.1 A switch provided as part of a product intended to be connected to a power-supply circuit having a
potential to ground of more than 150 volts shall be rated for the maximum potential to ground of the circuit.
18.2 A nominal 208-volt, single or 3-phase or a 120/240 volt, single-phase product is considered to
involve a potential to ground of less than 150 volts. A 2-wire, single-phase or a 3-wire, 3-phase product
with a rating in the range from 220 250 volts is considered to involve a potential to ground in excess of
150 volts.
Exception: A product marked in accordance with 74.10 or 74.11 need not comply with this requirement.
19 Internal Wiring
19.1 Internal wiring shall consist of insulated conductors, including conductors covered with insulating
tubing or with noncarbonizable beads, having adequate ampacity for the service.
19.2 A No. 18 or 16 AWG (0.82 or 1.3 mm2) rubber-covered wire in other than a low-voltage circuit as
described in 2.6 shall be at least Type RFH-1 with impregnated braid, for a potential of 300 volts or less;
and shall be at least Type RFH-2 with impregnated braid and shall be rated for the application for a
potential of 301 600 volts.
19.3 A No. 14 AWG (2.1 mm2) or larger conductor shall be Type TW, RH, or RHW wire.
19.4 Other types of conductors that have been found to be acceptable may also be employed; Type TF
wire may be used wherever Type RFH-1 or RFH-2 wire may be used.
19.5 If necessitated by temperatures, Type SF-1 fixture wire may be used for a potential of 300 volts or
less; and Type V, AVA, or AVB wire or Type SF-2 fixture wire may be used for a potential of 600 volts or
less.
19.6 If the use of a short length of insulated conductor is not feasible for example, a short coil lead or
the like electrical insulating tubing may be employed.
19.7 Tubing shall not be subjected to sharp bends, tension, compression, or repeated flexing, and shall
not contact sharp edges, projections, or corners. Tubing may be used in dry or damp locations but may
not be used in wet locations.
19.8 The wall thickness of electrical insulating tubing shall comply with the requirements for such tubing,
except that the thickness at any point for the smaller sizes of polyvinyl chloride tubing shall not be less
than 0.017 inch (0.43 mm). Insulating tubing of other types shall have a wall thickness not less than that
providing mechanical strength, dielectric properties, heat- and moisture-resistant characteristics, and the
like, at least equal to those of 0.017-inch-thick polyvinyl chloride tubing.
19.9 Internal wiring and connections between parts shall be protected or enclosed.
19.10 Rubber-insulated conductors shall not be exposed to oil, grease, oily vapor, or other substance
having a deleterious effect on rubber.
19.11 A wireway shall be smooth and free from sharp edges, burrs, fins, moving parts, and the like, which
may abrade insulation on conductors.

19.12 Mounting screws and nuts shall be made or located so that sharp edges will not damage wiring. A
screw shall have a flat or blunt end. The end of a screw shall have no burrs, fins or sharp edges that might
abrade wire insulation, and shall not project more than 3/16 inch (4.8 mm) into a wireway.
19.13 A hole in a sheet-metal wall through which insulated wires pass and on which they may bear shall
be provided with a smooth bushing or shall have smooth surfaces upon which the wires may bear, to
reduce the likelihood of abrasion of insulation.
19.14 A bushing used over other than smooth, rounded surfaces of a hole through which wires pass shall
be of material that has mechanical and heat-resistant properties rated for the application such as
porcelain, phenolic, fiber at least 3/64 inch (1.2 mm) thick, or smooth, rounded metal. A soft-rubber
bushing or the like shall not be used for other than low-voltage wiring see 16.2.1.13 unless the material
has been evaluated and found to be acceptable.
19.15 Insulated wires that are entirely enclosed within metal walls may be bunched and passed through
a single opening.
19.16 A bare conductor or a conductor insulated with noncarbonizable beads shall be enclosed. A bare
conductor within an enclosure shall be supported so that the required spacings will be maintained.
19.17 A short length of rubber-insulated flexible cord may be exposed to a temperature in excess of the
normal maximum allowable temperature for the compound involved in a location such as at a terminal if
supplementary heat-resistant insulation of acceptable dielectric properties is employed on individual
conductors of the cord to prevent deterioration of the rubber. In any case, rubber insulation shall be of a
type normally available that has a temperature limit as close as possible to or higher than the temperature
involved.
19.18 A joint or connection shall be mechanically secure and shall provide reliable electrical contact
without stress on a connection or a terminal.
19.19 A soldered connection shall be made mechanically secure before being soldered.
Exception: A connection for which:
a) A soldering or brazing material having a softening or melting point greater than 454C (849F)
is used;
b) A hand-soldered lead passed through a hole in a printed wiring board and bent 90 degrees to
the board to make contact with the conductor before soldering;
c) Soldering on a printed wiring board is done by a machine process in which the soldering time
and solder temperature are automatically controlled bending over of leads is not required; or
d) The lead wire is strapped in place, or the equivalent, adjacent to the soldered connection so
as to hold the lead end in place.
19.20 A joint shall be provided with insulation equivalent to that on the wires involved if permanence of
spacing between the joint and uninsulated live parts of opposite polarity or grounded dead metal parts
may not be maintained.
19.21 A nominal 0.110-, 0.125-, 0.187-, 0.205-, or 0.250-inch quick-connect terminal shall comply with the
Standard for Electrical Quick-Connect Terminals, UL 310. Other sizes of quick-connect terminals shall be
investigated with respect to crimp pullout, engagement-disengagement forces of the connector and tab,
and temperature rise; all tests shall be conducted in accordance with UL 310.
19.21 effective November 15, 1996
20 Low-Voltage External Wiring Requirements
20.1 A cable external to the equipment and supplied by the manufacturer for connection in a low-voltage
Class 2 circuit shall be rated for the intended application as specified in Article 725 of the National
Electrical Code, ANSI/NFPA 70-1993.
21 Grounding
21.1 General
21.1.1 There shall be provision for grounding all dead metal parts of the following controls that are
exposed or that are likely to be touched by a person during normal operation or adjustment and that are
likely to become energized through electrical fault.
a) A stationary control or a control that is to be permanently connected electrically.
b) A cord-connected control for a room air conditioner or dehumidifier, for outdoor or industrial
equipment, or for equipment that is required to be grounded.
c) A portable control for use on a circuit involving a potential of more than 150 volts to ground.
d) A control provided with a grounding means, whether required or not.
21.1.2 A motor or motor operator shall be provided with means for the attachment of an
equipment-grounding conductor termination for wire-to-wire or fixed-terminal connections. The means for
such connections may be located either inside or outside the motor terminal housing.
Exception No. 1: The grounding means need not be provided if grounding is not required by 21.1.1.
Exception No. 2: The grounding means need not be provided on a motor that is to be installed as part of
factory-wired equipment and that has its dead metal parts bonded to the grounding terminal of the overall
equipment. See Bonding of Internal Parts, Section 22.
21.1.3 To determine whether a part is likely to become energized, such factors as construction, the
proximity of wiring, a dielectric voltage-withstand test after the overload and endurance tests, and burnout
tests are to be evaluated.
21.1.4 All dead metal parts of a room thermostat rated more than 300 volts that are exposed to contact,
with or without the outer cover in place, shall be in electrical connection with the point of connection of the
grounding means.
21.2 Grounding means
21.2.1 An equipment-grounding terminal or lead grounding point shall be connected to the frame or
enclosure by a positive means, such as by a bolted or screwed connection.
21.2.2 A grounding connection shall reliably penetrate a nonconductive coating, such as paint or vitreous
enamel.
21.2.3 A grounding point shall be located so that it is unlikely that the grounding means will be removed
during normal servicing.
21.2.4 The following are acceptable means for grounding equipment that is to be permanently connected
electrically:
a) An equipment-grounding terminal or lead in:
1) A room thermostat,
2) A control intended for use in a residence,
3) A device intended to be connected to a nonmetallic-enclosed wiring system, for

example, a nonmetallic-sheathed cable, or
4) A device intended to be grounded by an isolated ground and intended to be connected

to a metal-enclosed wiring system.
b) A knockout or equivalent opening in a metal enclosure of a nonresidential control intended to

be connected to a metal-enclosed wiring system.
c) An equipment-grounding terminal or lead installed on a device that is intended to be mounted

on an outlet box.
Exception: If the device is marked in accordance with 70.11(a), the equipment-grounding

terminal or lead need not be provided on the device as shipped. If marked in accordance with
70.11(b), the grounding means may be in the form of a kit.
21.3 Equipment permanently connected electrically
21.3.1 A device employing field-wiring leads in flexible metal conduit, where flexing of the conduit is
required for adjustment or movement after installation, shall have an equipment-grounding conductor of
the size specified in 22.2.8 installed in the flexible conduit.
21.4 Terminals and leads
21.4.1 A wire-binding screw intended to connect an equipment-grounding conductor shall have a

green-colored head that is hexagonal, slotted, or both.
21.4.2 A pressure wire connector intended to connect an equipment-grounding conductor shall be plainly
identified, such as by being marked G, GR, GND, Ground, and Grounding; or by an acceptable
marking on a wiring diagram on the control.
21.4.3 A wire-binding screw or pressure wire connector intended to connect an equipment-grounding

conductor shall be located so that it is unlikely to be removed during normal servicing.
21.4.4 A terminal for connection of an equipment-grounding conductor shall be capable of securing a

conductor of the necessary size and shall be constructed as specified in 16.2.1.3 16.2.2.4.
21.4.5 A grounding terminal for a No. 10 AWG (5.3 mm 2 ) or smaller wire may be a threaded stud
welded to the enclosure or equivalent. Such a terminal shall be of suitable material, for example, it shall
be plated if of steel; and shall also comply with 21.4.1 21.4.4 and 16.1.1 16.2.2.4.
21.4.6 A soldering lug, a push-in (screwless) connector, or a quick-connect or similar friction-fit connector,
shall not be used for a grounding terminal.
21.4.7 A lead intended for connection to an equipment-grounding conductor shall be of the size specified
in 22.2.8, and shall have a free length of 6 inches (152 mm) or more.
21.4.8 The surface of an insulated lead intended solely to connect an equipment-grounding conductor
shall be green with or without one or more yellow stripes, and no other lead visible in a field wiring
compartment to the installer shall be so identified.
21.4.9 The color coding requirement specified in 21.4.8 does not apply to a low-voltage nonsafety circuit
under the following conditions:
a) Leads or wiring to low-voltage terminals are remote from the location where the line-voltage
connections are made, and connectors and live parts are segregated in accordance with 35.5 and
35.6, or
b) Leads or low-voltage terminals are specifically marked with the intended use, such as
Thermostat, so that reference to a wiring diagram is not necessary.
21.4.10 The free end of an equipment-grounding conductor shall be insulated for example, shall have
the end folded back and taped to the lead unless the conductor is located so that it cannot contact live
parts in the event that the conductor is not used in the field.
21.4.11 The following are acceptable means for grounding stationary, pendant, and portable equipment:
a) For pendant, cord-connected equipment a terminal for bonding the grounding conductor of
a multiple-conductor cord to the enclosure, and
b) For portable or stationary equipment a multiple-conductor cord with a grounding conductor

to the frame or enclosure of the equipment. The line fitting of such a cord, shall have a fixed
contacting member for the grounding conductor.
21.4.12 The surface of an insulated grounding conductor of a flexible cord shall be green with or without
one or more yellow stripes and no other lead shall be so identified.
21.4.13 The grounding conductor of a power-supply cord shall be attached to the grounding blade of an
attachment plug and shall be connected within the frame or enclosure by means of a screw not likely to
be removed during servicing not involving the power-supply cord. A grounding conductor shall be
arranged so that an external pull on a power-supply cord will not transmit stress to the grounding
connection on a frame or enclosure before line-voltage connections are broken.
21.4.14 Circuitry shall be arranged so that an equipment-grounding connection or conductor, an

enclosure, a frame, a component mounting panel, and earth ground do not carry current except in the
event of an electrical fault.
Exception: A single-point reference ground may be employed in a low-voltage or isolated-limited-energy-

secondary circuit. An enclosure, frame, or panel, including bolted joints, may carry the current of a
low-voltage circuit. Such current shall not be carried by a field-equipment grounding means, a metallic
raceway or other power-supply grounding means, or earth ground in either case.
21.4.15 The grounded-circuit conductor shall not be grounded at or in conjunction with

temperature-indicating and -regulating equipment.
22 Bonding of Internal Parts
22.1 General
22.1.1 Equipment required to be grounded or grounded if not required as specified in 21.1.1 and 21.1.4,
and an exposed noncurrent-carrying metal part that is likely to become energized through electrical fault
see 21.1.3 shall be reliably bonded to the point of connection of the field-equipment grounding means.
22.1.2 A guard, baffle, or cover that can be removed without a tool is to be removed when determining
whether a part is exposed to contact by the user. A part that can be contacted by a 3/8-inch (9.5-mm)
diameter rod having a hemispherical end inserted through an opening in a permanently attached guard or
baffle for a distance of 4 inches (102 mm) is considered exposed for the purposes of grounding.
22.1.3 Uninsulated metal parts such as cabinets, electrical enclosures and covers, motor frames and
mounting brackets, controller mounting frames and brackets, capacitors, other electrical components,
interconnecting tubing and piping, valves, and plumbing accessories, shall be electrically bonded together
if they may be contacted by a user or serviceperson. See 22.1.5 22.1.7 and 22.1.9 for parts to which
this requirement does not apply.
22.1.4 Operations and adjustments that subject parts to contact by a user include actions taken at the
time of installation and during normal use, such as seasonal adjustments, relamping, replacing fuses,
resetting overload devices, and oiling motors. These procedures and those specified in Protection of
Users and Service Personnel, Section 23 subject parts to contact by a serviceperson.
22.1.5 A part on the back side of a component mounting panel and a part located so as to require major
disassembly by using tools are not considered to be exposed to the user; such parts are not considered
to be exposed to a serviceperson unless it is likely that servicing will be performed while the equipment
is energized after disassembly.
22.1.6 A metal part, such as an adhesive-attached metal-foil marking, a screw, or a handle that is located
on the outside of an enclosure or cabinet and isolated from electrical components and wiring by grounded
metal parts so that it is not likely to become energized, or separated from wiring and spaced from
uninsulated live parts as if it were a grounded part, need not comply with the requirement in 22.1.1.
22.1.7 The requirement in 22.1.1 does not apply to a small internal assembly screw, or other small
fastener, such as a rivet, a handle for a pull-out disconnect switch, or a magnet or armature of a relay or
contactor.
22.1.8 Uninsulated live parts and wiring shall be held away from moving parts, such as relay and
contactor magnets and armatures, by clamping, routing, or equivalent means that will provide permanent
separation.
22.1.9 A metal panel or cover need not comply with the requirement in 22.1.1 if:
a) The panel or cover is insulated from electrical components and wiring by an insulating barrier
of vulcanized fiber, varnished cloth, phenolic composition, or other moisture-resistant material not
less than 1/32 inch (0.8 mm) thick and reliably secured in place;
b) The panel or cover does not enclose uninsulated live parts, and wiring is positively separated
from the panel or cover so that it is not likely to become energized; or
c) The panel or cover is isolated from live parts and wiring by grounded or bonded interposing
metal so that the interposing metal would be subject to an electrical fault before the isolated metal
part in question.
22.1.10 If a component such as a compartment temperature-control thermostat or a defrost timer is likely

to be separated from its normal grounding means after installation in an end-use appliance for purposes
of testing or adjustment while the equipment is energized, it shall be provided with a bonding terminal or
with a bonding conductor so that it is not necessary to remove it from the component for such service.
22.2 Construction and connection
22.2.1 Parts shall be bonded by metal-to-metal contact or by a separate bonding jumper in accordance
with 22.2.2 22.2.9.
22.2.2 A separate bonding conductor shall be copper, a copper alloy, or other material acceptable for use
as an electrical conductor.
22.2.3 A ferrous metal part in a grounding path shall be protected against corrosion by enameling,
galvanizing, plating, or other equivalent means.
22.2.4 A separate bonding conductor or strap shall be protected from mechanical damage or shall be
located within an outer enclosure or frame, and shall not be secured by a removable fastener used for
any purpose other than bonding unless the bonding conductor is unlikely to be omitted after removal and
replacement of the fastener.
22.2.5 The ends of a bonding conductor shall be in metal-to-metal contact with the parts to be bonded.
22.2.6 A splice shall not be employed in a wire used for bonding purposes.
22.2.7 An internal connection for bonding internal parts to an enclosure for grounding, but not for a
field-installed grounding conductor or for the grounding wire in a supply cord, may employ a quick-connect
terminal if:
a) The connector is not likely to be displaced,
b) The terminal has the dimensions specified in Table 22.1, and
c) The component is limited to use on a circuit having a branch-circuit protective device as

specified in Table 22.1.
Table 22.1
Quick-connect terminals for grounding internal parts
Nominal size of terminal, inch

Rating of branch-circuit
Width Thickness Length protective device, amperes
0.187 0.020 1/4 20 or less
0.187 0.032 1/4 20 or less
0.205 0.032 1/4 20 or less
0.250 0.032 5/16 60 or less
22.2.8 A separate component-bonding conductor shall not be smaller than:
a) That specified in Table 22.2,
b) The conductor supplying the motor or component, whichever is the smaller, or
c) The bonding conductor shall comply with the performance requirements in Bonding Conductor
Tests, Section 59.
Table 22.2
Bonding conductor size
Rating or setting of
automatic overcurrent Size of bonding conductora
device in circuit ahead
of equipment, conduit,
and the like, not Rigid conduit or pipe, Electrical metallic
exceeding, amperes Copper wire, AWG Aluminum wire, AWG inches tubing, inches
20b 12 10 1/2 1/2
30 10 8 1/2 1/2
40 10 8 1/2 1/2
60 10 8 1/2 1/2
100 8 6 1/2 1/2
200 6 4 1/2 1
400 3 1 3/4 1-1/4
600 1 2/0 3/4 1-1/4
800 1/0 3/0 1 2
1000 2/0 4/0 1 2
1200 3/0 250 kcmil 1 2
a Or equivalent cross-sectional area.
b For a cord-connected device, the grounding wire in the cord may be the same size as the current-carrying conductors.
22.2.9 If more than one size of branch-circuit overcurrent protective device is involved, the size of the
bonding conductor is to be based on the rating of the overcurrent device intended to provide ground-fault
protection for the component bonded by the conductor. For example, if a motor is individually protected
by a branch-circuit overcurrent device smaller than other overcurrent devices used with the equipment, a
bonding conductor for that motor is to be sized on the basis of the overcurrent device intended for
ground-fault protection of the motor.
23 Protection of Users and Service Personnel
23.1 General
23.1.1 The requirements in this section do not apply to live parts in low-voltage circuits.
23.1.2 Live parts shall be arranged and covers located so that persons are not likely to be exposed to a
risk of electric shock while removing and replacing a cover.
23.1.3 Live parts shall be:
a) Recessed at least 1/8 inch (3.2 mm) from the plane of the front of the fixed portion of an
enclosure;
b) Recessed at least 1/8 inch from the front edge of a wiring compartment, in the case of a device
mounted to the face of a wiring compartment; or
c) Provided with equivalent protection by projections or guards.
23.1.4 To determine whether live parts recessed or protected in accordance with 23.1.3 comply with the
requirement in 23.1.2, the cover is to be removed and replaced; contact of either a person or a conductive
cover with a live part is unacceptable.
23.1.5 Unless a cover complies with the requirements for hinged covers in 7.3.4 and 7.3.7, and unless all
live parts are protected as specified in 23.1.7, a handle, a knob, or other manual operating means shall
be arranged so that it can be operated from outside the control enclosure. The position of such an
operating means shall be marked, if necessary, as a guide for proper operation.
23.1.6 A device that involves manual operations that may be performed by a user only at the time of
installation, during a servicing procedure, or seasonally, need not comply with 23.1.5 if it complies with
the requirements in 23.1.7, 23.2.2, 23.2.5, 23.3.2, and 23.3.3. The requirements in Bonding of Internal
Parts, Section 22 apply in any case.
23.1.7 An uninsulated live part or moving part capable of causing injury to persons shall be located,
guarded, or enclosed so as to reduce the likelihood of contact of such part by a person while changing a
lamp or fuse, lubricating a motor, adjusting a control, or during other normal operations, including those
performed only at the time of installation, during a servicing procedure, or seasonally.
23.1.8 A live heat sink for a solid-state component, a live relay frame, and the like shall comply with
23.1.7, 23.2.2, and 23.3.2, and unless the equipment is marked in accordance with 74.4, shall also be
guarded to reduce the risk of contact by persons, regardless of the location of the parts.
Exception: If the part is considered exposed to contact by a user as provided in 23.1.10 and 23.1.11, it
need not comply.
23.1.9 With reference to 23.1.7, the size, shape, material, and color give a heat sink or relay-frame the
appearance of a dead metal part. Other live parts that can be mistaken for dead metal parts are to be
investigated similarly.
23.1.10 A guard, baffle, or cover that can be removed without a tool is to be removed when determining
whether a part is exposed to contact by a user. A part that can be contacted by a 3/8-inch (9.5-mm)
diameter rod having a hemispherical end inserted through an opening in a permanently attached guard or
baffle for a distance of 4 inches (102 mm) is considered to be exposed for the purpose of protecting
persons.
23.1.11 A part on the back side of a component mounting panel or located so that major disassembly by
using a tool is necessary to expose it is not considered to be exposed to a user; such a part is not
considered to be exposed to a service person unless it is likely that servicing will be performed while the
part is energized after disassembly.
23.1.12 If a marking or an operating instruction refers a user to a hole or opening in an enclosure through
which a tool is to be inserted for adjustment or a similar purpose, it shall not be possible to contact an
uninsulated live part through a hole or opening with a 1/16-inch (1.6-mm) diameter rod.
23.1.13 A live adjustment means shall not be accessible for user operation.
23.1.14 A live service adjustment shall be insulated from contact by persons or metal tools, or shall be
provided with a fixed cover that cannot be removed with an ordinary tool.
Exception: A factory only adjustment that is obviously a live part need not be so guarded.
23.2 Mechanical servicing
23.2.1 The requirements specified in 23.2.2 are intended to provide a reasonable degree of protection to
a serviceperson performing a mechanical function on energized equipment. Such a service function does
not in itself cause exposure to live parts or moving parts capable of causing injury to persons but it is
commonly necessary to perform the function with the equipment energized.
23.2.2 An uninsulated live part or a moving part capable of causing injury to persons shall be located,
guarded, or enclosed so as to reduce the risk of unintentional contact by a serviceperson adjusting or
resetting a control, or performing a mechanical service function that may have to be performed with
equipment energized.
23.2.3 Mechanical service functions that may have to be performed with equipment energized include
operating a valve or connecting a fitting that may be necessary during charging or adjusting a pneumatic
system; adjusting a water control, or expansion valve; adjusting the setting of a temperature or pressure
control with or without marked dial settings; resetting a control trip mechanism; operating a manual switch;
adjusting an air-flow damper or lubricating a motor. A control that has the set point sealed at the factory
as described in 13.1 13.4 and that does not have marking or instructions for adjustment, is not
considered to be adjustable.
23.2.4 The requirements in 23.2.2 do not apply to a mechanical service function that is not normally
performed with equipment energized, such as opening a drain plug, adjusting or replacing a drive belt or
replacing a refrigerant-containing component.
23.2.5 An adjustable or resettable electrical control or manual-switching device may be located or

oriented with respect to uninsulated live parts so that manipulation of the mechanism for adjustment,
resetting, or operation can be accomplished in the normal direction of access if uninsulated live parts are
not located in front in the direction of access of the mechanism, and are not located near any side or
behind the mechanism, unless guarded.
23.2.6 The requirements in 23.2.2 23.2.5 do not apply to bare live parts in a 30-volt or less
limited-energy circuit.
23.3 Electrical servicing
23.3.1 The requirements in 23.3.2 specify the location of certain electrical components within an overall
assembly so that the necessary space is provided for working on the components while the equipment is
energized.
23.3.2 An electrical component that may need to be examined, adjusted, serviced, or maintained while
the equipment is energized shall be located and mounted with respect to other components and with
respect to grounded metal parts so that it is accessible for electrical servicing without subjecting a
serviceperson to a risk of electric shock or to a risk of injury by adjacent moving parts. Access to a
component shall not be impeded by other components or by wiring.
23.3.3 Compliance with the requirement in 23.3.2 may be obtained by mounting control components in
an assembly so that unimpeded access to each component is provided through an access cover or panel
in the outer cabinet, if provided, and the cover of the control assembly enclosure.
23.3.4 Electrical components to which 23.3.2 and 23.3.3 apply include fuses; adjustable or resettable
overload relays; manual or magnetic motor controllers; magnetically operated relays; adjustable or
resettable pressure or temperature controllers; manual switching devices; clock timers;
incremental-voltage tap, and motor-speed tap terminals for variable-speed motors. Such components in a
limited-energy circuit of 30 volts or less shall comply with the requirements in 23.3.2 in their relation to
bare live parts in a circuit of greater energy level and to moving parts capable of causing injury to persons.
23.3.5 A totally enclosed current or potential-type start relay for a single-phase motor is not required to
be accessible in accordance with 23.3.2 and 23.3.3.
23.3.6 The following are not considered to be uninsulated live parts: coils of controllers, relays and
solenoids, and transformer windings, if the coils and windings are provided with acceptable insulating
overwraps at least 1/32 inch (0.8 mm) thick, or the equivalent, in accordance with 32.2.13; enclosed motor
windings; terminals and splices with acceptable insulation; and insulated wire.
23.3.7 A device having exposed Class 2 outputs that:
a) May be contacted during normal operation or servicing, and
b) Have clearances between the Class 2 circuit and an overvoltage protected line-voltage circuit
that have been evaluated in accordance with Clearance B requirements in the Standard for
Insulation Coordination Including Clearances and Creepage Distances for Electrical Equipment,
UL 840, shall be provided with a mechanism to indicate the failure of the overvoltage protective
device or system. For example, the provision of a detection circuit that would indicate a transient
voltage surge suppressor is no longer functional due to the absorption of an excessive amount of
energy.
24 Protection Against Injury to Persons
24.1 Scope
24.1.1 The requirements in 24.2.1 24.6.8 apply to equipment the normal operation of which may involve
a risk of injury to persons.
24.1.2 There are risks of injury to persons inherent in some equipment that, if completely eliminated,
would defeat the utility of the equipment. The requirements in this section are intended to minimize such
risks, while retaining the normal function of the equipment.
24.2 Sharp corners and edges
24.2.1 A part subject to contact during normal operation and user servicing shall be free of sharp corners
and edges.
24.3 Moving parts
24.3.1 A hinged or pivoted panel or cover shall be positioned or arranged so that it is not subject to falling
or swinging due to gravity or normal vibration in such manner as to cause injury to persons by the panel
or cover, by other moving parts capable of causing injury or by uninsulated live parts. See 23.2.2 23.3.4.
24.3.2 The rotor of a motor, a pulley, a belt, gears, a chain, a fan, or other moving part that could cause
injury to persons shall be enclosed or guarded to reduce the risk of unintentional contact with the moving
part.
24.3.3 Among the factors to be considered in investigating the acceptability of an exposed moving part
are:
a) The degree of exposure,
b) The sharpness of the moving part,
c) The likelihood of unintentional contact with it,
d) The speed of the moving part, and
e) The likelihood that fingers, arms, or clothing would be endangered by the moving part.
24.3.4 Unless it complies with the requirement in 58.1, a guard or enclosure for a moving part capable of
causing injury to persons shall be secured to the equipment so that it cannot be removed without using a
tool.
24.4 Temperature
24.4.1 During the Temperature Test, Section 40, the maximum temperature of a handle, a lever, a button,
or a knob that is contacted by a user during normal operation shall not exceed 60C (140F) for a metal
surface or 85C (185F) for a nonmetallic surface.
24.4.2 With reference to the requirement in 24.4.1, a nonmetallic handle, lever, button, knob, or the like
that is plated or clad with metal 0.005 inch (0.13 mm) thick or less is to be investigated as a nonmetallic
part.
24.4.3 The maximum temperatures specified in 24.4.1 do not apply to equipment intended specifically for
use in an ambient temperature exceeding 85C (185F).
24.5 Mounting devices
24.5.1 A device weighing more than 5 pounds (2.3 kg) and relying on a mounting means other than its
own enclosure, if malfunction of the mounting means will result in a risk of injury to persons, shall
withstand for 1 minute, without dislocation of the mounting means or evidence of damage, a force equal
to three times the weight of the device but not less than 20 pounds (9.1 kg) applied as described in 24.5.2.
24.5.2 With the device mounted in accordance with the manufacturers instructions, force is to be applied
through the approximate center of gravity of the device. The force is to be increased gradually to reach
the required value in 5 10 seconds and is to be maintained at that value for 1 minute.
24.6 Strength of parts
24.6.1 A device that is actuated by an external source of pressure and that employs a bourdon tube, a
flexible metal bellows, a diaphragm, or the like rated 300 psig (2069 kPa) or more and not contained within
an enclosure, shall withstand for 1 minute without bursting a hydraulic pressure equal to four times the
maximum rated operating pressure of the device.
24.6.2 To determine whether a part complies with the requirement in 24.6.1, a sample is to be subjected
to a hydrostatic pressure test. The sample is to be filled with water to exclude air and is to be connected
to a hydraulic pump. The pressure is to be raised gradually to the required test pressure. Except as
indicated in 24.6.3 24.6.7, the sample is to withstand the test pressure for 1 minute without leakage or
rupture.
24.6.3 Leakage at a gasket or fitting during the hydrostatic pressure test is acceptable unless it occurs at
a pressure 50 percent or less of the required test pressure.
24.6.4 If leakage occurs during the test, the test is to be continued to four times the maximum rated
operating pressure of the device, test equipment permitting. If the leakage is due to external fittings,
modifications may be made to permit completion of the test.
24.6.5 A bourdon tube, a flexible-metal bellows, a diaphragm, or the like that is contained within an
enclosure shall comply with the requirement in 24.6.1 or shall:
a) Withstand for 1 minute without visible leakage a hydraulic pressure in accordance with the
second column of Table 24.1; and
b) Except as indicated in 24.6.7, withstand a hydraulic pressure for 1 minute equal to four times
the maximum rated operating pressure of the device without rupture that may present a risk of
injury to persons.
Table 24.1
Test pressures for devices with enclosures
Marked maximum operating-pressure Test pressure for (a) of

rating 24.6.5 24.6.7
300 2000 psig (2069 137,900 kPa) Two times maximum rated operating Three times maximum rated operating
pressure pressure
24.6.6 With reference to 24.6.5(b), a bourdon tube, diaphragm, or bellows may split if no part is released
outside the enclosure; a joint or a gasket may leak with acceptable results if the required pressure value
is reached and maintained for 1 minute; a leaking gasket or flexible member may be replaced by a heavier
disc to permit the required pressure value to be reached.
24.6.7 With reference to 24.6.6, if leakage becomes excessive so that the four times pressure cannot
reasonably be reached that is, if the part functions as if it has a ruptured disc the part is acceptable
if:
a) A pressure in accordance with the third column in Table 24.1 is reached;
b) No part capable of causing injury to persons is released outside the enclosure; and
c) It can be demonstrated by test which may be at a low pressure or otherwise, that the outer
enclosure can either relieve a pressure equal to the maximum rated operating pressure of the
device without rupture that presents a risk of injury to persons, or can withstand a pressure equal
to the maximum rated operating pressure.
24.6.8 A pressure vessel, an air filter, a piston operator, or similar device shall withstand
hydrostatic-strength tests consistent with the intended use unless it is certified by the National Board of
Boiler and Pressure Vessel Inspectors and bears an ASME Code inspection symbol other than the UM
symbol.
25 Capacitors
25.1 A capacitor shall employ such materials and shall be constructed so that it will not constitute a risk
of fire. It shall not be adversely affected by the temperatures it reaches under the most severe conditions
of normal use. A paper capacitor shall be impregnated or enclosed to exclude moisture. An electrolytic
capacitor and a capacitor intended for connection directly across the line shall be rated for the application.
26 Fuseholders
26.1 A fuseholder shall be of either the cartridge-enclosed or plug-fuse type. Plug fuses are limited to use
with equipment rated not more than 125 or 125/250 volts.
27 Receptacles
27.1 A receptacle provided on equipment that is grounded as required by 21.1.1 shall be of the grounding
type. Receptacles on other equipment shall be of the polarized type.
28 Protection of Control-Circuits
28.1 Conductors
28.1.1 A conductor of a control circuit that is connected to the load side of a branch-circuit short-circuit
protective device common control shall be provided with overcurrent protection in accordance with
Table 28.1 by a protective device located within the controller. See 28.1.2.
Exception No. 1: If the rating of the intended branch-circuit short-circuit protective device is not more than
the applicable value specified in Table 28.2, additional protection is not required provided the controller is
marked in accordance with 69.14.
Exception No. 2: The protection and marking required do not apply to:
a) A control circuit conductor that is not smaller than the main circuit conductors;
b) A limited-energy control circuit, such as a Class 2 circuit;
c) A short, direct lead, generally 12 inches (305 mm) long or less, such as transformer leads or
a printed-wiring assembly having no connection external to the controller; and
d) Short, direct leads from contacts of a thermostat, pressure-operated switch, or the like for
connection within the enclosure to field wiring that will be protected by a remote protective
device. See 16.2.1.6.
Exception No. 3: The protection requirements do not apply to a lead, a strap, or a bus that withstands the
applicable short-circuit test in accordance with the requirements in Short Circuit Test, Section 50. The
controller shall be marked as specified in 69.15.
Exception No. 4: A control-circuit conductor, supplied from the secondary of a single-phase transformer
that is connected so that only a 2-wire (single voltage) secondary is used, may be protected by an
overcurrent device(s) located on the primary side of the transformer if the rating of the device does not
exceed the applicable value specified in Table 28.2 multiplied by the ratio of secondary-to-primary rated
transformer voltage.
28.1.1 revised May 4, 2001
Table 28.1
Overcurrent protection
Control-circuit wire size, Maximum rating of protective device,

AWG (mm2) amperes
22 (0.32) 3
20 (0.52) 5
18 (0.82) 7
16 (1.3) 10
14 (2.1) 20
12 (3.3) 25

Table 28.2
Control circuit short-circuit protection
Control-circuit wire size, Maximum rating of protective device, amperes
Circuit does not leave

AWG (mm2) enclosure Circuit leaves enclosure
22 (0.32) 12 3
20 (0.52) 20 5
18 (0.82) 25 7
16 (1.3) 40 10
14 (2.1) 100 45
12 (3.3) 120 60
28.1.2 The protective device required by 28.1.1 shall be either a supplementary or a branch-circuit
overcurrent-protective device. A fuse shall be factory installed in a supplementary fuseholder, but may be
omitted if a branch-circuit-type fuseholder is provided. The controller shall be marked in accordance with
69.16. If the controller has a rating of more than 50 horsepower (37 kW output), only a branch-circuit
overcurrent-protective device rated for the available fault current involved shall be used. If a fuse is used,
it shall be Class CC, G, J, K, R, or T, and the fuseholder shall be appropriate for the fuse used. See also
50.3.1.
28.1.3 Internal conductors of a control circuit that are connected to a remote source of supply not a
common control shall be provided with overcurrent protection in accordance with Table 28.1 or the
controller shall be marked in accordance with 69.17. The internal conductors shall not be smaller than No.
20 AWG (0.52 mm2).
Exception No. 1: These requirements do not apply to a limited-energy control circuit, such as a Class 2
circuit.
Exception No. 2: These requirements do not apply to a short, direct lead, generally 12 inches (305 mm)
long or less, such as transformer leads or a printed-wiring board assembly.
Exception No. 3: These requirements do not apply to short, direct leads from contacts of a thermostat,
pressure-operated switch, or the like for connection within the enclosure to field wiring that will be
protected by a remote protective device.
Exception No. 4: These requirements do not apply to a lead, a strap, or a bus that withstands the
applicable short-circuit test in accordance with the requirements in Short Circuit Test, Section 50. The
controller shall be marked as specified in 69.15.
Exception No. 5: A control-circuit conductor, supplied from the secondary of a single-phase transformer
that is connected so that only a 2-wire (single voltage) secondary is used, may be protected by an
overcurrent device located on the primary side of the transformer if the rating of the device does not
exceed the applicable value specified in Table 28.2 multiplied by the ratio of secondary-to-primary rated
transformer voltage.
28.2 Transformers
28.2.1 Protection of a transformer is considered to be protection of the coil windings, and is distinct from
protection of inherent or connected conductors in the primary or secondary.
28.2.2 A control circuit transformer shall be provided with one or more of the following types of
overcurrent protection:
a) An overcurrent device located in the primary circuit that is rated or set as indicated in Table
28.3;
b) Secondary circuit protection rated or set at not more than 125 percent of the rated secondary
current of the transformer if the primary feeder circuit has protection rated or set at not more than
250 percent of the rated primary current of the transformer;
Exception: If the rated secondary current of the transformer is 2 amperes or more, the current
rating of the secondary overcurrent device may be as indicated in line 2 or 3 of Table 28.3, as
applicable.
c) Coordinated thermal overload protection arranged to interrupt the primary circuit if the primary
circuit overcurrent device is rated or set to open at a current of not more than:
1) For a transformer having not more than 6 percent impedance, six times the rated
current of the transformer; or
2) For a transformer having more than 6 but not more than 10 percent impedance, four
times the rated current of the transformer.
Exception No. 1: Overcurrent protection need not be provided if the primary feeder circuit
overcurrent device provides the required protection of primary and secondary circuit
conductors and windings.
Exception No. 2: Overcurrent protection of the windings or secondary circuit wiring need
not be provided if the transformer is rated less than 50 volt-amperes and is an integral
part of the controller of a Class 2 or Class 3 type that complies with the requirements for
such devices. See 28.1.1 or 28.1.3 for primary circuit conductor protection.
Exception No. 3: Overcurrent protection of the primary winding need not be provided for
a Class 1 power-limited transformer that complies with the National Electrical Code,
ANSI/NFPA 70-1993. See 28.1.1 or 28.1.3 for primary and secondary circuit conductor
protection.
Table 28.3
Maximum rating of overcurrent device
Maximum rating, percent of transformer primary current

Current, amperes rating
Less than 2 500
More than 2 and less than 9 167
9 or more 125a
a If 125 percent of the rated primary current does not correspond to a standard rating of fuse or nonadjustable circuit breaker,
the next higher standard rating of protective device may be used. For the purpose of this requirement, the standard ampere
ratings for fuses and inverse time circuit breakers are considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125,
and 150.
29 Short-Circuit, Ground-Fault, Overload, and Thermal Protection
29.1 Motor overload relays, thermal protectors for motors, and impedance-protected motors are to be
examined and tested in accordance with the requirements for such devices.
29.2 Equipment having a rating of more than 50 horsepower (37 kW output) shall be tested in accordance
with 50.3.1. See 69.21.
30 Mercury-Tube Switches
30.1 A mercury-tube switch shall be rated for the application. It shall be firmly supported, reliably
mounted, and housed in an acceptable enclosure. Wire leads shall be as short as possible and shall
terminate in eyelets or the equivalent, or in soldered connections at terminal plates on the supporting
base, or shall be fastened so that no stress will result. See also 47.1.9 and 47.1.10.
31 Coil Windings
31.1 Coil windings of a motor, relay, or transformer, shall resist the absorption of moisture.
32 Spacings
32.1 General
32.1.1 A live screwhead or nut on the underside of a base shall be countersunk not less than 1/8 inch
(3.2 mm) in the clear, and covered with a waterproof, insulating, sealing compound that will not melt at a
temperature 15C (27F) higher than the normal operating temperature of the device, but not less than
65C (149F).
Exception: If such a part is staked, upset, or otherwise reliably restricted from loosening, it need not be
recessed, and may be insulated from the mounting surface by material other than sealing compound or
by the provision of spacings through air and over surface as required in this standard.
32.1.2 A spacing at a wiring terminal is to be measured with appropriate wires connected to the terminals
as in intended service.
32.1.3 For the purpose of these requirements, the voltage and volt-ampere ratings are those recorded
with the equipment connected to a supply circuit as specified in Table 38.1.
32.1.4 Uninsulated live parts connected to different circuits shall be spaced from each other as if they
were parts of opposite polarity, in accordance with the requirement in 32.2.1, and shall be investigated on
the basis of the highest voltage involved.
32.2 Line-voltage circuits
32.2.1 Other than as indicated in 32.2.2, 32.2.8, 32.2.11, 32.2.12, 32.3.1, 32.3.2, and as provided in
Alternate Spacings Clearances and Creepage Distances, Section 33, spacings shall not be less than
those specified in Table 32.1. Greater spacings shall be provided in an enclosure that because of its size,
shape, or the material used, is not sufficiently rigid to maintain the minimum spacings.
32.2.2 The spacings specified for a 0 300 volt potential in columns B, C, and D of Table 32.1 are
applicable to equipment or circuits rated not more than 15 amperes at 51 150 volts, and 10 amperes at
151 300 volts. The spacings specified for a 301 600 volts potential in column B of Table 32.1 are
applicable to equipment or circuits rated not more than 5 amperes at 301 600 volts.
32.2.3 With reference to the requirement in 32.2.2, the spacings applicable to a device of the type
described also apply to that device when controlling more than one load if the total load connected to the
line at one time does not exceed 2 horsepower (1492 W output), or have a current rating greater than 30
amperes at 51 150 volts, 20 amperes at 151 300 volts, or 10 amperes at 301 600 volts.
32.2.4 To determine the rating of a device as referenced in columns B, C, and D of Table 32.1 and 32.2.2,
the input rating of the device is to be added to the rating of the equipment that the device is intended to
control. The sum of the inputs to and the switch ratings of the device is the rating. This applies to a device
that does not contain a number of individual components as mentioned in 32.2.6 and also to individual
components investigated in accordance with 32.2.6.
32.2.5 The volt-ampere equivalent of a horsepower rating is the product of the voltage and the full-load
current as specified in Tables 45.2 and 45.3 and for a polyphase device, the appropriate numerical
multiplier.
32.2.6 In multicomponent equipment, spacings from one component to another, and from a component
to the enclosure and to other uninsulated dead metal parts, excluding the component mounting surface,
are based on the maximum voltage and total volt-ampere rating of the complete equipment; not on the
individual component ratings. Spacings inherent in an individual component such as a relay or a
temperature controller, including spacings from a live part to a mounting surface other than the enclosure,
are to be investigated on the basis of the volt-amperes used and controlled by the individual component.
32.2.7 For a multipole, a double-throw, or a sequencing device or the like, the volt-ampere rating is the
maximum sum of the power consumption of the device and the simultaneously controlled load.
32.2.8 Other than as noted in 32.2.9, spacings inherent in a component such as a snap switch, a
lampholder, a motor, or a clock motor are investigated under the requirements for the component.
Spacings from such a component to another component and to the enclosure, and spacings at wiring
terminals shall comply with the requirements in 32.2.1 and Table 32.1.
32.2.9 Spacings in a wiring device, such as a snap switch that is a part of a safety-control circuit, a
water-heater temperature-limiting control, a baseboard-heater temperature-limiting control, or the like,
shall comply with the requirements in 32.2.1 and Table 32.1.
32.2.10 Spacings at a fuse and fuseholder are to be measured with a fuse that has maximum standard
dimensions for the rating in place and shall not be less than those specified in column A of Table 32.1.
32.2.11 An insulating barrier or liner that is used to provide spacings, including spacings in conjunction
with the required over surface spacings, shall not be less than 0.028 inch (0.71 mm) thick. A barrier or
liner that is used in conjunction with a spacing through air or oil not less than one-half the required spacing
may be less than 0.028 inch but not less than 0.013 inch (0.33 mm) thick, if the barrier or liner is an
acceptable insulating material resistant to moisture and has the necessary mechanical strength if exposed
or otherwise likely to be subject to mechanical damage, reliably held in place, and located so that it will
not be adversely affected by operation of the equipment in service particularly arcing.
Exception: An insulating barrier may be thinner than specified, as specified in 32.2.13.

Table 32.1
Minimum spacings, inch (mm)
Table 32.1 revised March 4, 1999
Maximum rating of 600 volts,

unlimited volt-amperes
Maximum rating of 600 Maximum rating of Maximum rating of
volts, unlimited volt- 600 volts, 2000 300 volts, 2000 Controls for installation on or in
amperes volt-amperes volt-amperes appliances
A B C D E F
Refrig-
Residen- eration
tial and
operating safety Water heater
Industrial operating controls controls and hot tub/
Generala,l controlsm,n m,o l,m,p spa controlsq Other controlsr,s
Potential 0- 151 - 301 - 0 - 300 301 - 0 - 300 0 - 300 0- 301 - 0 - 300 301 -
involved, 150 300 600b 600 300 600 600
volts
Between Through 1/8d,e 1/4e 3/8e 1/16d,e 3/16d,e 1/16d 1/8d,e 1/8d,e,f 1/4e 1/16 1/4 e,g
any air or oil (3.2) (6.4) (9.5) (1.6) (4.8) d,e,f,g
unisulated
live part
and an
uninsulated
live part of
opposite
polarity,
an
uninsulated
grounded
dead
metal part
other than
the
enclosure,
or an
exposed
dead
metal part
that is
insulatedc
Over 1/4e 3/8e 1/2e 1,8d,e 3/8e 1/16d,e 1/4e 1/4e,f 1/4e 1/16 1/4 e,g
surface (12.7) c,d,e,f,g,h
Between Shortest 1/2k 1/2k 1/2 1/4 1/2 1/4 1/4 1/4 1/4 1/4 1/4
any distance
uninsulated
live part
and the
walls of a
metal
enclosure,
including
fittings for
conduit or
armored
cable i,j
Table 32.1 Continued on Next Page

MARCH 4, 1999 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 59
Table 32.1 Continued
a A control rated 50 volts or less that is not a safety control may have the spacings in column C, 0 300 volts. A production
control dielectric voltage-withstand test is not required.
b For refrigeration and safety controls that are self-actuated, alternating-current, pilot-duty contact devices which may have a
manually reset means and which have an external adjusting knob or handle, but not an operating one for such as on, off,
constant, start, and the like rated not more than 125 volt-amperes, 301 600 volts, and responding to changes in
temperature, pressure, humidity, liquid level, and the like, the spacings may be those specified under column A, 151 300
volts, in which case a representative sample of the device selected annually is to show acceptable results when subjected to
the applicable overload and dielectric voltage-withstand tests. Operating controls of this rating are covered by column B.
c In a safety control, a water-heater or hot tub/spa temperature-limiting control, and the like, the spacing between wiring
terminals, regardless of polarity, and the spacing between a wiring terminal and a grounded dead metal part including the
enclosure shall not be less than 1/4 inch.
d The spacing between wiring terminals of opposite polarity and between a wiring terminal and a grounded or an exposed dead
metal part shall not be less than 1/4 inch if short-circuiting or grounding of such terminals may result from projecting strands of
wire.
e In a water-heater or hot tub/spa temperature-limiting control, a baseboard-heater temperature-limiting control, and a safety
control, the spacing between same polarity live parts on opposite sides of a switching mechanism, except at contact point, shall
not be less than 1/32 inch (0.8 mm) through air and 1/16 inch over surface.
f At closed-in points only, such as the screw-and-washer construction of an insulated terminal in metal, the spacing may be not
less than 3/64 inch (1.2 mm).
g In a control, other than a water-heater or hot tub/spa temperature-limiting control and a baseboard-heater temperature-limiting
control, intended for installation on or in an appliance, the spacings between same polarity live parts on opposite sides of a
switching mechanism, except at contacted points, shall not be less than 1/32 inch through air and 3/64 inch over surface.
h For a device with a 1/16 inch over-surface spacing, all electrical parts of the device are to be subjected to regular production
control dielectric voltage-withstand tests. The applied test potential shall be as specified in 47.1.1 47.1.6, with an additional
20-percent voltage applied if the test time is 1 second instead of 1 minute.
i A metal piece attached to the enclosure is considered to be a part of the enclosure if deformation of the enclosure is likely to
reduce the spacing between the metal piece and uninsulated live parts.
j Spacing to a metal enclosure does not apply to the housing or frame of a device intended for installation within an end-product
enclosure.
k For a household room thermostat rated 300 volts or less and intended for outlet box mounting, through air spacings between
an uninsulated live part and the top, bottom, and side walls of the box may be not less than 1/4 inch. Over-surface spacings
between those parts may be 1/4 inch in such a thermostat rated 0 150 volts and 3/8 inch in one rated 151 300 volts.
l
1) Other than as noted in item (3), an auxiliary control for refrigeration or air-conditioning equipment that complies with
the rating requirements in columns B and D of Table 32.1 and 32.2.2 at a rating of 600 volts or less may have the
spacings specified in column B:
2) Controls that may be judged under column B include those for a fan, pump, or vane motor, resistance heater; timer;
valve; solenoid; compressor-motor-start winding, and the like [see 1.4(c)];
3) Controls that are not to be judged under column B include compressor-motor control [see 1.4(a)]; a temperature,
pressure, or other limiting control [1.4(b)]; or a control that is subject to condensation or defrost water as may occur
within a refrigerated compartment of a refrigerator or freezer or on the outside of an air-conditioning plenum or duct.
m See 32.2.2.
n Includes controls for boiler and furnace rooms, farms, outdoor use, and the like.
o Includes room thermostats.
p Includes interlock thermostats for self-cleaning oven doors.
q Includes water-heater temperature-limiting controls.
r Includes controls for clothes dryers, ranges, air heaters, household and commercial cooking appliances, steam and dry bath
heaters, fans, beauty-parlor equipment, office appliances, temperature limiting controls for baseboard heaters, and the like.
s Excluding limiting controls for boilers, central furnaces, duct heaters, refrigeration equipment, heat pump duct heaters, and the
like.
32.2.12 An insulating barrier or liner used as the sole separation between live parts and grounded parts
or between live parts of opposite polarity shall be material that is rated for mounting uninsulated live parts
and is not less than 0.028 inch (0.71 mm) thick. Otherwise, a barrier shall be used in conjunction with at
least a 1/32-inch (0.8-mm) air spacing.
Exception: An insulating barrier may be thinner than specified as provided in 32.2.13.
32.2.13 Insulating material having a thickness less than that specified in 32.2.11 and 32.2.12 may be
used if, upon investigation, it is found to be acceptable for the application, and is equivalent in all respects
to materials of the thicknesses specified in 32.2.11.
32.2.14 Mica used in lieu of the through-air spacing required in Table 32.1, may be less than 1/32 inch
(0.8 mm) thick but not less than 1/64 inch (0.4 mm) thick if the mica is tightly held in place by the parts
involved.
32.2.15 Film-coated wire is considered to be an uninsulated live part in determining the spacing
requirements in this standard.
32.3 Magnet coil windings
32.3.1 Insulation required in place of spacings between a magnet-coil winding and other uninsulated live
parts or grounded dead metal parts may differ in type and thickness from that required by 32.2.11. The
type and thickness of crossover-lead insulation and insulation under coil terminals secured to the coil
winding may be less than that specified in 32.2.12 if:
a) The insulation is at least 0.013 inch (0.33 mm) thick; or
b) The coil withstands the dielectric voltage-withstand test specified in either (1) or (2):
1) Application of the test potential in accordance with 47.1.1 47.1.6 between coil-end
leads after breaking the inner coil lead where it enters the layer, or an equivalent opposite
polarity test; or
2) Application of the induced potential tests described in 47.2.1 47.3.2.
32.3.2 A slot in a molded bobbin for guiding the crossover- or start-lead unspliced at the windings of
a magnet-coil is to be filled with an insulating material unless the slot provides a graduated spacing to the
winding, increasing to the end turns, and the magnet-coil winding withstands the induced potential tests
in 47.2.1 47.3.2.
32.4 Low-voltage circuits
32.4.1 Safety controls
32.4.1.1 If a short circuit between the parts in a safety control may result in operation of the controlled
device likely to result in a risk of fire, electric shock, or injury to persons spacings shall be as specified in
32.4.1.2 32.4.1.4, or as described in Alternate Spacings Clearances and Creepage Distances, Section
33.
32.4.1.2 Spacing between an uninsulated live part and the wall of a metal enclosure, including fittings for
connection of conduit or armored cable, shall not be less than 1/8 inch (3.2 mm). A greater spacing may
be required if an enclosure is not sufficiently rigid to maintain the required spacing because of its size,
shape, or the material used.
32.4.1.3 Spacing between wiring terminals, regardless of polarity, and between a wiring terminal and a
dead metal part including an enclosure that may be grounded when the device is installed shall not
be less than 1/4 inch (6.4 mm).
32.4.1.4 Spacing between uninsulated live parts, regardless of polarity, and between an uninsulated live
part and a dead metal part, other than the enclosure, that may be grounded when the device is installed
shall not be less than 1/32 inch (0.8 mm), if the construction of the parts is such that spacings will be
permanently maintained.
32.4.2 Other than safety controls
32.4.2.1 Other than as noted in 32.4.1.1 32.4.1.4, spacing between uninsulated live parts of opposite
polarity and between such parts and dead metal that may be grounded in service is not specified for a
low-voltage circuit.
32.5 Isolated limited secondary circuits
32.5.1 Safety controls
32.5.1.1 If short-circuiting of parts in a safety control circuit of an isolated-limited-secondary circuit will not
result in unsafe operation of the controlled device, the spacings shall not be less than that specified in
Table 32.2 or as provided in Alternate Spacings Clearances and Creepage Distances, Section 33.
Table 32.2
Minimum spacing in safety circuits in isolated-limited-secondary circuits
Potential involved (volts)
Spacing between uninsulated live 0 600 601 1000

parts and Inch mm Inch mm
A. Exposed isolated Through air 1/8 3.2 1/4 6.4
(insulated) dead
metal part
Over surface 1/4 6.4 3/8 9.5
B. Grounded dead Through air 1/16 1.6 3/16 4.8
metal part other
than the enclosure
Over surface 1/16 1.6 3/16 4.8
C. Uninsulated live Through air 1/16 1.6 3/16 4.8
part of opposite
polarity
Over surface 1/16 1.6 3/16 4.8
D. Wall of metallic Through air 1/4 6.4 1/2 12.7
enclosure
Over surface 1/4 6.4 1/2 12.7
32.5.2 Other than safety controls
32.5.2.1 Spacing between uninsulated live parts of opposite polarity and between such parts and dead
metal that may be grounded in service is not specified for an isolated-limited-secondary circuit. The
spacing is based on acceptable performance of applicable dielectric voltage-withstand and abnormal
operation tests.
33 Alternate Spacings Clearances and Creepage Distances
33.1 As an alternative to the specified spacing requirements of Spacings, Section 32, the spacing
requirements in the Standard for Insulation Coordination Including Clearances and Creepage Distances
for Electrical Equipment, UL 840, may be used. The spacing requirements in UL 840 shall not be used for
field wiring terminals and spacings to a dead metal enclosure. In determining the pollution degree and
overvoltage category, the end-use application is to be considered and may modify those characteristics
specified in 33.2 33.5.
33.2 When applying specific requirements in UL 840, it is anticipated that the degree of pollution expected
or controlled will be as indicated in Table 33.1.
Table 33.1
Degrees of pollution
Equipment Pollution degree

Hermetically sealed or encapsulated equipment or printed 1
wiring boards with a protective coatinga.
Equipment for ordinary locations and indoor use, such as 2
residential controls, commercial controls for use in a clean
environment, nonsafety controls for insulation on or in
appliances.
All safety or limit controls, equipment for indoor use, and 3
equipment influenced by surrounding environment, such as
industrial controls, refrigeration controls, and water heater
controls.
a Tested in accordance with the protective coating test in the Standard for Insulation Coordination Including Clearances and
Creepage Distances for Electrical Equipment, UL 840.
33.3 When applying specific requirements in UL 840, it is anticipated that the equipment will be identified
by overvoltage categories as indicated in Table 33.2.
Table 33.2
Overvoltage categories
Equipment Overvoltage category

Intended for fixed wiring connection III
Portable and stationary cord-connected II
Power-limited and safety a low voltage I
a Applicable to low-voltage circuits if a short circuit between the parts involved may result in operation of the controlled
equipment that would increase the likelihood of a risk of fire or electric shock.
33.4 In order to evaluate clearances where the levels of overvoltage are controlled, control of overvoltage
shall be achieved by providing an overvoltage device or system as an integral part of the product. The
equipment shall be evaluated for the rated impulse withstand voltage specified in UL 840.
33.5 Printed wiring boards constructed of Types XXXP, XXXPC, G-10, FR-2, FR-3, FR-4, FR-5, CEM-1,
CEM-3, GPO-2, or GPO-3 industrial laminates in accordance with the Standard for Polymeric Materials
Industrial Laminates, Filament Wound Tubing, Vulcanized Fibre, and Materials Used in Printed Wiring
Boards, UL 746E, are considered to have a minimum comparative tracking index of 100 without further
investigation.
34 Wiring Space
34.1 Ample space shall be provided within an enclosure for the distribution of wires and cables required
for the proper wiring of the product.
34.2 The wire-bending space within the enclosure of a controller shall be in accordance with Table 34.1.
Bending space is to be measured in a straight line from the end of the lug, connector, or terminal to the
wall or barrier, in the direction the wire leaves the terminal.
Table 34.1
Minimum wire-bending space at terminals of enclosed controllers
Bending space, inches (mm)

Wires per terminal
Conductor size, AWG or kcmil (mm2) 1 2
14 10 (2.1 5.3) Not Specified
86 (8.4 13.3) 1-1/2 (38.1)
43 (21.2 26.7) 2 (50.8)
2 (33.6) 2-1/2 (63.5)
1 (42.4) 3 (76.2)
1/0 (53.5) 5 (127) 5 (127)
2/0 (67.4) 6 (152) 6 (152)
3/0 4/0 (85.0 107.2) 7 (178) 7 (178)
250 (127) 8 (203) 8 (203)
300 (152) 10 (254) 10 (254)
350 500 (177 253) 12 (305) 12 (305)
600 700 (304 355) 14 (356) 16 (406)
750 900 (380 456) 18 (457) 19 (483)
Note If provision for three or more wires per terminal exists, the minimum wire-bending space shall be in accordance with the
National Electrical Code, ANSI/NFPA 70-1993.
34.3 Any supplementary terminal supplied with the controller shall be of a type identified by the
manufacturer for use with the product, and shall not reduce the minimum wire-bending space.
35 Separation of Circuits
35.1 Insulated conductors shall be segregated or separated by barriers from:
a) Each other if used in different internal wiring circuits, and
Exception: Conductors provided with insulation rated for the highest voltage involved need not
comply.
b) Uninsulated live parts connected to different circuits.
35.2 With reference to 35.1, segregation of internal insulated conductors may be accomplished by
clamping, routing, or equivalent means that will provide a minimum permanent 1/4 inch (6.4 mm)
separation from an insulated conductor or an uninsulated live part of a different circuit.
35.3 The equipment shall be constructed so that field-installed conductors of any circuit shall be
segregated see 35.5 or separated by barriers from:
a) Field-installed conductors connected to any other circuit unless:
1) Both circuits are Class 2 or Class 3 or both circuits are other than Class 2 or Class 3,
and
2) Both circuits will be insulated for the maximum voltage of either circuit;
b) Uninsulated live parts of any other circuit of the device, and from any uninsulated live parts the
short-circuiting of which may result in operation of the controlled device so as to present a risk of
fire or electric shock;
Exception No. 1: Field-installed conductors may make contact with wiring terminals if Type RH,
RFH-2, or equivalent conductors are used.
Exception No. 2: Field-installed conductors that have insulation less than those types of wire
mentioned in Exception No. 1 may contact low-voltage wiring terminals if the short-circuiting of
such terminals would not result in operation of the controlled device so as to present a risk of fire
or electric shock.
c) Factory-installed conductors connected to any other circuit, unless the conductors of both
circuits will be insulated for the maximum voltage of either circuit.
35.4 With respect to 35.3, if the intended uses of the device are such that in some applications a barrier
is required while in some other applications no barrier is required, a removable barrier or one having
openings for the passage of conductors may be employed. Instructions for the use of such a barrier are
to be a permanent part of the device. Complete instructions in conjunction with a wiring diagram may be
used in lieu of a barrier if, upon investigation, the combination is found to be acceptable.
35.5 Field-installed conductors may be segregated from each other and from uninsulated live parts or
factory-installed conductors of the product connected to different circuits by locating openings in an
enclosure for the various conductors with respect to the terminals or other uninsulated live parts so
that a minimum permanent 1/4 inch (6.4 mm) separation is provided.
35.6 With reference to 35.5, if the number of openings in the enclosure does not exceed the minimum
required for the proper wiring of the device, and if each opening is located opposite a set of terminals, it
is to be assumed that a conductor entering an opening will be connected to the terminal opposite that
opening. If more than the minimum number of openings are provided, the possibility of a conductor
entering an opening other than the one opposite the terminal to which it is intended to be connected and
the likelihood of it contacting insulated conductors or uninsulated current-carrying parts connected to a
different circuit is to be investigated.
35.7 To determine if a device complies with the requirement of 35.3, it is to be wired as intended for
service with a reasonable amount of slack left in each conductor within the enclosure and not more than
average care is to be exercised in stowing the slack into the wiring compartment.
36 Class 2 Power Sources and Circuits
36.1 General
36.1.1 The term power source denotes a primary battery, a Class 2 transformer, or a combination of a
transformer and power limiting components. See 36.5.1.
36.1.2 The voltage, current, and power limitations specified in 63.3.1 and 63.4.2 normally apply to Class
2 circuits that extend beyond the equipment. These values, however, may be used to limit the energy level
of a circuit within the equipment.
36.1.3 These requirements, including those relating to installations where wet contact is likely to occur,
do not cover immersion.
36.2 Interconnections
36.2.1 Other than as noted in 36.2.2 and in the Exceptions to 36.4.2, the output of a transformer or power
source supplying a Class 2 circuit and provided as a part of the equipment shall not be interconnected
with the output of another power source. See 75.6.
36.2.2 With reference to 36.2.1, the output of two or more such transformers or power sources may be
interconnected if the voltage and current measurements at the output terminals are within the values for
a single Class 2 power source.
36.2.3 The outputs of two or more transformers or power sources, all of which are investigated as Class
2 in accordance with the requirement in 2.6 and that are not interconnected, are to be considered as
separate circuits. If the wiring terminals or leads for two or more Class 2 circuits are located in the same
wiring compartment, the compartment shall be such that room is provided for intended wiring without
crowding, and such that stowed wiring of one circuit will not be forced against terminals or live parts of
another circuit. See 75.7.
36.3 Circuits
36.3.1 There shall be no electrical connection between the primary and secondary windings of a
transformer, or between a primary or secondary circuit and any exposed or grounded part including the
enclosure.
Exception: A single-point reference ground may be employed in a secondary circuit. An enclosure,

frame, or panel, including bolted joints, may carry the current of a circuit. Such current shall not be carried
by a field-equipment grounding means, a metallic raceway or other power-supply grounding means, or
earth ground.
36.4 Transformers
36.4.1 A transformer coil shall be provided with insulation between the various windings, and between the
windings and the core and the enclosure.
36.4.2 A Class 2 transformer shall have only one secondary winding, that shall be insulated from the
primary winding. A winding having intermediate taps is considered to be a single winding.
Exception No. 1: Two or more secondary windings may be considered as a single winding. Interposing
insulation between the secondary windings is not required if, when interconnected, the windings are in
compliance with the performance requirements for a single-winding transformer.
Exception No. 2: A transformer of the inherently limiting type marked in accordance with 74.9 may have
two secondary windings that, when interconnected, are not in compliance with the performance
requirements for a single-secondary winding construction.
Exception No. 3: A transformer intended only for use in other equipment may have more than one
secondary winding if isolation of all circuits can be maintained.
36.5 Power limiting components
36.5.1 A power limiting component resistor, positive temperature coefficient resistor, diode, or the like
employed to limit the output of a power source to within the required current or power levels, or
otherwise relied upon to comply with the performance requirements in Class 2 Power Sources and Circuit
Tests, Section 63, shall have permanence and stability so as not to decrease its limiting capabilities.
Among the factors considered when investigating the acceptability of a power limiting component are:
a) Effect of operating temperature,
b) Electrical stress level,
c) Effect of transient surges,
d) Resistance to moisture,
e) Endurance,
f) Temperature change shock, and
g) If appropriate, thermal runaway.
36.6 Overcurrent protection components
36.6.1 Overcurrent protection components include fuses, overtemperature and overcurrent protectors,
thermal protectors, components employing eutectic materials, and similar components intended to
interrupt the flow of current as a result of overload.
36.6.2 Overcurrent protection provided with a not-inherently limited power source shall be a one-time or
manual-reset protector. An automatic reset device may be employed in addition to the required one-time
or manual-reset protector.
36.6.3 If a replaceable overcurrent protection component, such as a fuse, is provided in a not-inherently

limited power source, it shall not be interchangeable with a component having a higher current rating.
36.6.4 Spacings between parts of the same polarity specified in notes e and g to Table 32.1, 32.4.1.4,
and 32.5.1.1 do not apply to the protective component(s) of a Class 2 power source.
37 Barriers
37.1 A barrier used to provide separation between the wiring of different circuits shall be of metal or of
acceptable insulating material having the necessary mechanical strength if exposed or otherwise likely to
be subjected to mechanical damage, and shall be reliably held in place. Unclosed openings in a barrier
for the passage of conductors shall not be larger than 1/4 inch (6.4 mm) in diameter and shall not exceed
in number, on the basis of one opening per conductor, the number of wires that will need to pass through
the barrier. The closure for any other opening shall have a smooth surface wherever an insulated wire
may contact it and the area of any such opening, with the closure removed, shall not be larger than
required for the passage of the necessary wires. See 19.13.
37.2 A barrier used to provide separation between the field wiring of one circuit and the wiring or
uninsulated live parts of another shall be spaced not more than 1/16 inch (1.6 mm) from the enclosure
walls and from interior mechanisms and component-mounting panels, or the like that serve to provide
segregated compartments.
37.3 A metal barrier used to provide segregation shall have the necessary strength and rigidity, and shall
be at least the thickness specified under the column in Table 7.1 titled With supporting frame or
equivalent reinforcing, for the dimensions of the barrier. A barrier of insulating material shall be of such
thickness and be supported so that its deformation cannot be readily accomplished so as to defeat its
purpose, but in any case, the thickness shall not be less than 0.028 inch (0.71 mm). A barrier between
uninsulated live parts connected to different circuits, and a barrier between uninsulated live parts of one
circuit and the wiring of another circuit shall also comply with the requirements in 32.2.11 and 32.2.12.
PERFORMANCE
38 General
38.1 Samples
38.1.1 Unless otherwise indicated, a representative commercial sample is to be subjected to the tests
described in the performance section. The order of tests, as far as applicable, is to be as specified in
Table 38.1 and, unless otherwise specified, the various tests are to be conducted at rated frequency and
at the voltage specified in the Table 38.1.
Table 38.1
Values of voltage for tests
Voltage rating of product and corresponding test potential, voltsa Number of

section that
Test 110 120 220 240 254 277 440 480 550 600 applies
Input 120 240 277 480 600 35

Temperature 120 240 277 480 600 36
Operation 39
Overvoltage, a-c or 132 264 305 528 660
d-c
Undervoltage, a-c 102 204 235 408 510
Undervoltage, d-c 96 192 222 384 480
Calibration verification b b b b b 40
Overload 120 240 277 480 600 41
Endurance 120 240 277 480 600 42
Dielectric voltage withstand c c c c c 42
Volt-ampere capacity 120 240 277 480 600 44
Burnout 120 240 277 480 600 45
Short circuit 120 240 277 480 600 46
a If the rating of the device does not fall within any of the indicated voltage ranges, it is to be tested at its rated voltage, except
that for the operation test, the test voltages are to be as specified in Operation Test, Section 43.
b Any convenient test voltage.
c As described in text.
38.1.2 An alternating-current product that does not have a frequency rating is to be tested on a circuit
having a frequency of 60 hertz, except that a circuit having a lower frequency may be employed with the
concurrence of those concerned.
38.1.3 A multiple-pole, a sequencing, a double-throw, or a double-pole, single-throw (normally open,

normally closed sometimes called double-pole, opposite-throw) control and the like shall be tested with
a load on each pole. The loads on a double-pole or multiple-pole control shall be connected so that
opposite polarity on the poles results unless a same polarity rating is assigned to the control.
38.1.4 A product that must be mounted in a definite position in order to function properly is to be tested
in that position and shall be marked in accordance with 69.5.
38.2 Electric heat thermostat
38.2.1 A wall-mounted room thermostat intended for direct control of electric space-heating equipment
that is to be permanently connected electrically shall be subjected to the applicable tests described in the
performance section, except that two samples shall be subjected to the tests specified in Table 38.2 in
the order specified.
Table 38.2
Sequence of tests for wall-mounted room thermostats intended for direct control of electric
space-heating equipment that is to be permanently connected electrically
Paragraph number that applies
Tests Sample 1 Sample 2
Overload 45.1 45.1

Endurance 46.1 46.2a
Added endurance 46.3
Dielectric voltage withstand 47.1.1 47.1.1
Added dielectric voltage withstand 47.1.2
a No examination of contacts for burning or pitting.
38.2.2 A room thermostat intended for permanent installation that includes an ampere rating other than
one associated with a pilot duty or with a motor rating is to be tested in accordance with the requirements
that apply to a wall-mounted room thermostat intended for direct control of electric space-heating
equipment that is to be permanently connected electrically.
38.3 Controller
38.3.1 For a motor controller tested with the motor or motors with which it is to be used, the values of
stalled-rotor current and full-load running current employed in the overload and endurance tests need not
be the values specified in Tables 45.1 45.3.
38.3.2 For a combustion control intended to control a transformer as well as a motor, the test load is to
include as large a transformer as is likely to be used in the field, unless the control has a transformer
rating.
38.4 Baseboard heater controls
38.4.1 If intended for use with a baseboard heater, the contacts of a safety control or of a
temperature-limiting control that is actuated by a change in pressure of a fluid confined in a self-contained
bulb or capillary tube shall assume the open position upon loss of the fluid charge.
38.5 Relays
38.5.1 A time-delay relay or thermal relay a contact device, generally normally open, operated by a
bimetal-heater or hot wire, and the like that responds to a temperature- or pressure-limiting control or
other calibrated control is to be tested as specified in (a) (f). A magnetic relay is to be subjected to these
tests, except the calibration verification test is to be waived. See Table 38.3 for specific test conditions for
electric range controls.
a) Heating test at rated ambient air temperature Temperature Test, Section 40.
b) Initial calibration Time-Calibration Verification Test, Section 57 allowable tolerance time,

10 percent or 5 seconds, whichever is greater.
c) Overload and endurance at rated ambient air temperature Overload Test, Section 45 and
Endurance Test, Section 46. Number of cycles in accordance with Table 38.3 or Table 46.1.
d) Dielectric voltage withstand Dielectric voltage-Withstand Test, Section 47.
e) Recalibration Time-Calibration Verification Test, Section 57. Allowable drift time, 10 percent
or 5 seconds.
f) Also see Means for Calibration, Section 13, Details, Section 65, and Calibration Setting,
Section 71.
Exception: Wider tolerances than specified in (b) and (e) may be used for a control investigated in the
end-use application and found to be acceptable.
38.6 Electric range controls
38.6.1 A control for an electric range, including a separate surface cooking unit or a wall-mounted oven,
intended for mounting where exposed to elevated temperatures shall be subjected to the temperature,
overload and endurance tests while mounted in an oven maintained at the assigned ambient air
temperature, with the temperature sensor operated at maximum rated set-point temperature of the control,
and under other temperature conditions that represent rated service conditions, such as mounted on a
heated surface, with a heated pressure connection, bimetal heater, or the like. For specific test conditions
see 38.6.5 38.6.9.
Exception No. 1: Temperature tests are usually waived for a control intended to be entirely located in the
air to be controlled as it is assumed that the entire control will be at the temperature of the surrounding
air. The overload and endurance tests are to be conducted with the control entirely within the test oven in
air at the maximum set-point temperature.
Exception No. 2: For a control with a long capillary tube or similar semiremote sensor where heat transfer
to the switch head will not be significant, the temperature test may be conducted with the sensor at room
temperature.
38.6.2 A pressure- or mechanically-operated control or one that is intended for a mechanical load shall
be subjected to maximum rated stress during the test.
38.6.3 Tests are to be conducted with maximum rated temperatures, pressures, mechanical loads,
electrical loads, and the like, that are consistent with maximum normal service conditions imposed
simultaneously on the device. For a device that has different sets of ratings, such as different ampere
ratings at different ambient-air-temperature ratings, separate tests are to be conducted. For a line of
devices of the same construction that have different temperature or pressure settings, tests at the highest
rated settings are usually considered representative. Separate tests are to be conducted on devices
having different constructions.
Table 38.3
Electric range-control test conditions
Revised Table 38.3 effective June 2, 2000
Test temperatureb
Test No. Control functiona Test sequence Test description Switch head Bulb
Sample 1
1c,d,e All Elevated-temperature Temperature Test, Cook 25F (14C) below
heating Section 40, cutout
temperature rise;
Table 40.1 and its
note c and 40.3
2e,f All Heating Temperature Test, Room Room
Section 40,
temperature rise;
Table 40.1 and its
note c
Sample 2-1 and 2-2

3 C,D,L Calibration 44.3 44.7 or 38.5.1 Room Cutout
verification and Time-Calibration
Verification Test,
Section 57
Sample 2-1
4e,g B,D Aging 250 hours in test Clean 25F (14C) below
oven; rated electrical cutout
load
5d,g B,D Overload 50 cycles; Overload Clean Cutout
Test, Section 45
6-1n 6-2n Bo,D Endurance B: 100,000 cycles, Cook Cutout
Endurance Test,
Section 46
D: 100,000 cyclesp Actuation or cook Cutout
Endurance Test,
Section 46
Sample 2-2
7e,g,h C,Lm Aging 250 hours in test Clean 25F (14C) below
oven; rated electrical cutout
load
8g C,Lm Overload 50 cycles; Overload Clean Cutout
Test, Section 45
9g,n C,Lm Endurance I 2000 cycles, except Clean Cutout
manually reset to be
1000 with load, and
1000 no load;
Endurance Test,
Section 46
10-1n Co Endurance II C: 98,000 cycles; Cook Cutout
Endurance Test,
Section 46
10-2 Lm L: 98,000 cycles with Cook Cutout
load Endurance Test,
Section 46; except
manually reset to be
run 4000 no load

Test temperatureb
Samples 2-1 and 2-2

11 All Dielectric Dielectric voltage- Warm from endurance
Withstand Test,
Section 47
12 C,D,L Recalibration 44.3 44.7 or 38.5.1 Room Cutout
verification and 44.3
Sample 3 Bulb Excursion

13i,j B,D,L Calibration 44.3 44.7 Room Cutout
verification
14i,j,k B,D,L Bulb excursion 250 cycles 1/2 Room Cycling 104
hour at 1000F 1000F (40 538C)
(538C), 1/2 hour at
104F (40C)
nominal; no load
15i,j B,D,L Recalibration 44.3 44.7 Room Cutout
verification
Sample 4 S,SN
16e,g S,SN Aging 250 hours in test Clean 25F (14C) below
oven; not energized cutout
17d,g S,SN Overload 50 cycles; Overload Clean Cutout
Test, Section 45
18-1n SNo Endurance 100,000 cycles; Cook Cutout
Endurance Test,
Section 46
18-2n S Endurance 100,000 cycles; Cook
automatic at highest
cycling temperature
setting; Endurance
Test, Section 46
19 S,SN Dielectric withstand Dielectric voltage- Warm from endurance
Withstand Test,
Section 47
Sample 5 S (automatic contacts tested manually)
20 S Aging 250 hours in test Clean
oven, not energized
21g S Overload 50 cycles; Overload Clean
Test, Section 45
22g,n S Endurance 10,000 cycles; Cook
Endurance Test,
Section 46, manual,
off to mid-
temperature setting
to off
23 S Dielectric withstand Dielectric Voltage- Warm from endurance
Withstand Test,
Section 47
Sample 6 Manual contactsi
24i l Aging 250 hours in test Clean

oven; rated electrical
load

Test temperatureb
25g S,SN Aging 250 hours in test Clean

oven; not energized
26g All Overload 50 cycles; Overload Clean
Test, Section 45
27g,i,n B,C,L Endurance I M 2000 cycles; Clean
Endurance Test,
Section 46, manual
28i,n B,C,L Endurance II M 4000 cycles; Cook
Endurance Test,
Section 46, manual
29-1i,n Dp, S,SN Endurance 6000 cycles; Cook
Endurance Test,
Section 46, manual
29-2i,n Dp Endurance 6,000 cycles; Section Actuation or cook
46, manual
30 All Dielectric withstand Dielectric voltage- Warm from endurance
Withstand Test,
Section 47


Test temperatureb
a A thermal or magnetic relay see 38.5.1 or a thermal cycling switch or other control not specifically mentioned is to be
tested for the conditions of the control or control function with which it is employed.
Control Function Code:
B Bake/broil or other oven cooking or temperature-regulating control.
C Cleaning temperature oven control.
D Door interlock for oven.
L Limiting temperature control. Test conditions may vary if the setting is for Type B, C, S or SN usage.
S Surface element control, bimetal heater or hot-wire type, or the like.
SN Surface element control other than Type S.
b For devices used on electric ranges, see 38.6.6. For other applications, test temperatures are to be in accordance with the
ratings.
c See 38.8.1 and 38.8.2 for a range control switch body other than Type L. These paragraphs are not applicable to a limiting
control or to other than a range control.
d For an interlock that is mechanically operated only, materials are assumed to operate at ambient temperature. The overload
test is not applicable.
e A surface-element control is to be tested as specified. The elevated-temperature heating test for an oven control is to be
conducted with the bulb heated to the maximum rated normal-use oven temperature, such as bake/broil or 25F (14C) below
cutout, if the control is calibrated to open at the maximum normal-use oven temperature. See Exception No. 2 to 38.6.1.
f Test 2 may be waived if results of Test 1 indicate that the results of Test 2 will be acceptable.
g For a control not intended for use with a self-cleaning oven, the clean test temperature specified is to be the cook
temperature. Aging test is to be omitted.
h Aging may be conducted after Endurance I or I M for 250 hours minus the time elapsed during Endurance I or I M, or, if
the assigned clean and cook switch head temperatures are the same, aging may be omitted if the total time elapsed during
Endurance I and Endurance II is at least 250 hours.
i See 44.3 44.4 for tolerances for a control used as an oven-door interlock or for a temperature-limiting function. For bake/
broil, other cooking control, or where calibration change will not cause unsafe operation of the appliance, calibration verification
may be waived or tolerances are not specified. After the bulb excursion test, the control is to be operable without damage to the
switch or mechanism.
j The test for nonself-cleaning oven controls is to be waived.
k Test cycle may vary provided the bulb is stabilized at each temperature if agreeable to those concerned. Heat shock greater
than normal use is not contemplated.
l Manual contacts on a Type B, C, D, or L oven control that operate during the self-cleaning cycle, or that terminate the cycle,
are to be subjected to Tests 24, 26 28, and 30 in sequence except as noted in note h. Manual contacts on controls that are
not switched during the self-cleaning cycle are to be subjected either to Test 24 if the contacts carry current during the self-
cleaning cycle or to Test 25 if the contacts do not carry current during the self-cleaning cycle, and then to Test 26, 29, and 30
in sequence.
m A temperature-limiting control shall not function during normal appliance operation.

Test temperatureb
n The endurance test is to be conducted as follows:
Maximum cycle rates, cycles per minute
Number of endurance cycles First portion of test Last portion of test
Number of Cycles per Number of Cycles per

With load Without load cycles minute cycles minute
1000 5000 1000 1 5000 6

6000 6000 1
(automatic)
6000 6000 6
(manual)
10,000 10,000 6
30,000 24,000 6 6000 1
100,000 75,000 6 25,000 1
Magnetic, manual, motor-operated switches, and the like and switches that snap with lost motion and do not creep may be
tested at a rate of 6 cycles per minute for all controls, the test is to be conducted with 50 20 percent on time. A temperature-
or pressure-operated control is to be tested using a slow rate of change.
For endurance tests consisting of two parts [such as tests 9 and 10 (Endurance Tests I and II)], the number of endurance
cycles is to be the sum of the cycles required for each part. For example, the number of endurance cycles for tests 9 and 10 is
to be 100,000 cycles (the sum of 2000 and 98,000 cycles). When no current is used, the switch may be operated at any
convenient speed.
o If the control is intended to be used in conjunction with a temperature-limiting control, the endurance test need only be 30,000
cycles of operation.
p See 38.6.6.1 and 38.6.6.2.
38.6.4 Tests on a control for combination use shall be conducted to cover conditions of each use;
separate samples may be used for each set of tests. See 38.9.2. More samples than specified are to be
tested if needed for additional ratings, or the like.
38.6.5 A control intended for mounting in an electric range, including a separate wall-mounted oven and
a surface cooking unit, shall be tested under the conditions specified in Table 38.3. Wherever
calibration-verification tests are specified, except for bulb excursion alone, see Details, Section 65
(manufacturing calibration-verification and dielectric voltage-withstand tests), Calibration Setting, Section
71 (temperature marking), and Means for Calibration, Section 13 (fixing of setting). Refer to 11.13 and 6.2
for electronic components or circuits.
38.6.6 In Table 38.3, cook corresponds to the control compartment ambient temperature during
cooking, clean corresponds to the control compartment temperature during self-cleaning, and
actuation corresponds to the maximum compartment temperature when the device is actuated to lock,
latch, unlock or unlatch the door of a self-cleaning oven (the actuation temperature is typically lower than
the self-clean temperature and may or may not be higher than the cook temperature.) These temperatures
are as specified by the manufacturer. The 1000F temperature corresponds to the typical oven
temperature during self-cleaning; higher or lower temperatures may be used at the manufacturers
request. Either cook or actuation temperatures, or both may be specified at the manufacturers option.
Revised 38.6.6 effective June 2, 2000
JUNE 2, 1998 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 74A
38.6.6.1 Mechanical parts and electro-mechanical parts of an oven door latch or lock mechanism that do
not switch current, such as linkages, springs, levers, solenoids, motors and the like, and that operate only
during self-cleaning operation shall withstand 6,000 cycles of operation at normal load at the temperature
specified in Table 38.3. Parts that operate during cooking or other appliance operating modes, such as
bi-metal devices, shall withstand 100,000 cycles of operation at normal load at the temperature specified
in Table 38.3.
Added 38.6.6.1 effective June 2, 2000
38.6.6.2 Oven door lock thermostats and switching components of an oven door latch or lock system that
cycle electrically (make or break current) during self-cleaning operation and that carry current or cycle
without electrical load during cooking or other operating modes shall withstand 6,000 cycles of operation
at normal electrical load, plus an additional 94,000 cycles at no load. Oven door lock thermostats and
switching components that may cycle electrically one or more times during cooking or other appliance
operating modes, shall withstand 100,000 cycles of operation at normal electrical load.
Added 38.6.6.2 effective June 2, 2000
38.6.7 An automatic cycling control is to be tested as specified in Table 38.3. See 65.1.4. An automatic
cycling control is a contact device, usually normally closed, that cycles automatically due to a bimetal
heater, hot-wire mechanism, or the like, being controlled by the contacts that also control the load; the
cycling rate is fixed, or variable on a manually adjustable or infinite switch.
38.6.8 A time-delay relay or a thermal relay that responds to another control is to be tested as specified
in Table 38.3. This type relay is a contact device, usually normally open, operated by a bimetal heater,
hot-wire mechanism, or the like. A magnetic relay is to be subjected to these tests, except the
calibration-verification test is to be omitted.
38.6.9 These requirements do not necessarily apply to controls for commercial ranges.
74B TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 JUNE 2, 1998

38.7 Auxiliary electric range controls
38.7.1 For the controls in (a) (d), the function of which will be bypassed during certain tests of the
end-use appliance, the endurance test described in Endurance Test, Section 46 is to consist of 6000
cycles of operation:
a) A thermostat that detects a hot surface of a glass/ceramic cooking surface to control an

indicating lamp;
b) A thermostat that limits the temperature of a glass/ceramic cooking surface, but does not
function during the normal cooking operation;
c) A thermostat that controls a cooling fan for a control compartment; and
d) An auxiliary control that does not control cooking or cleaning temperatures, and that is not
depended upon to reduce the risk of unsafe temperatures.
38.7.2 A calibration-verification test is not required for the controls described in 38.7.1 (a) (d).
38.8 Conditioning at elevated temperature household range control switch body
38.8.1 If, when tested at the cook temperature ambient see 38.6.6 the insulating switch body of a
range control, including a separate surface cooking unit or a wall-mounted oven control, and other than a
temperature-limiting control, exceeds the allowable temperature rise in Table 40.1 as adjusted in
accordance with 40.3, the switch body shall be tested as follows:
a) Three complete samples of the control are to be conditioned for 1000 hours in an oven
without the control energized. The temperature of the oven is to be determined from the
formula:
in which:
t2 is the oven temperature in degrees C and
t1 is the measured temperature of the insulating body in degrees C; or
b) If the excess temperature is localized for example, due to a bimetal heater three samples
of the complete control are to be conditioned for 1000 hours in an oven maintained at the cook
temperature see 38.6.6 with the heater energized at 110 percent rated voltage or 110
percent rated current for a series type. Noncycling contacts are to be forced closed or bypassed
if necessary, to attain the most severe temperatures.
Exception: Insulating materials that have been investigated and found to be acceptable for the required
temperature.
38.8.2 Following the conditioning described in 38.8.1, the controls are to be examined and then subjected
to a 50-cycle overload test, a 1000-cycle endurance test, and a dielectric voltage-withstand test. These
tests may be conducted at room ambient air temperature. There shall be no undue deterioration of the
insulation or electrical or mechanical breakdown of the control.
38.9 Temperature-limiting controls for electric ranges
38.9.1 An automatically or manually reset control that is intended to limit temperatures of an electric
range, including a separate wall-mounted oven or a surface cooking unit, shall comply with the
requirements for a temperature-limiting control as specified in this standard. Wherever
calibration-verification tests are specified, except bulb excursion alone, see Details, Section 65
(production line calibration-verification and dielectric voltage-withstand tests), Calibration Setting, Section
71 (temperature marking), and Means for Calibration, Section 13 (fixing of setting). Tests are as specified
in Table 38.3. Refer to 11.13 and 6.2 for electronic components or circuits. For tests on an oven door
interlock used in lieu of a temperature-limiting control on a nonself-cleaning oven and for one used on a
self-cleaning oven, see Table 38.3.
38.9.2 An electric range temperature-limiting control, or combination limiting control and relay, shall have
no operating part in common with a temperature-regulating control. A common mounting bracket or a
common enclosure may be employed for both controls.
Exception No. 1: An oven-door interlock may use common parts with a temperature-limiting control.
Exception No. 2: An oven-door interlock, a temperature-limiting control or combination limiting control and
relay may have common parts with a control compartment cooling fan control if malfunction of the fan
control will not affect operation of the oven-door interlock or temperature-limiting feature. Tests on such a
combination control are to include 100,000 cycles thermal-mechanical endurance on all parts and
verification of operation with the fan contact not functioning.
Exception No. 3: For a self-cleaning oven, an oven cooking or cleaning temperature control may use
common parts with an oven door interlock but not with a temperature-limiting control. A single control may
combine all three functions. Tests on such a control are to include 100,000 cycles of thermal-mechanical
endurance on all parts.
39 Power Input
39.1 The power input to a temperature-indicating or -regulating device shall not exceed the marked rating
of the device by more than 10 percent when it is operated under the conditions of normal use and with
the device connected to a supply circuit as specified in Table 38.1.
40 Temperature Test
40.1 Temperature-indicating and -regulating equipment, when tested as described in this section, shall
not attain a temperature at any point sufficiently high to constitute a risk of fire, to damage any materials
employed in the equipment, or to exceed the temperature rises specified in Table 40.1.
40.2 All values for temperature rises specified in Table 40.1 apply to equipment intended for use at
ambient temperatures normally prevailing in occupiable spaces, which usually are not higher than 25C
(77F) but may occasionally be as high as 40C (104F) for brief periods. Tests of equipment for service
with such ambient temperatures may be conducted without correction at any ambient temperature in
the range of 10 40C (50 104F).

Table 40.1
Maximum temperature rises
Material and components C F
1. Knife-switch blades and contact jaws 30 54

2. Points on or within a terminal box or compartment including wiring on which conductors 35 63
to be connected to the control may resta
3. Laminated-contactsb 50 90
4. Terminalsa 50 90
5. Class 90 insulation systemc
Thermocouple method 50 90
Resistance method 60 108
6. Class 2 transformer enclosure see 2.2, 2.6, 7.4.1, and 7.4.2 60 108
7. Varnished cloth insulation 60 108
8. Solid contacts, busses, and connecting barsd 65 117
9. Fusese 65 117
10. Fiber employed as electrical insulation 65 117
11. Wood or other combustible material 65 117
12. Power transformer enclosure 65 117
13. Class A insulation systems on coil windingsf
A. In an open motor
B. In a totally enclosed motor
14. Class 105 insulation systems on coil windings other than in a motorc,f
15. Class 130 insulation systemsc,f
16. Phenolic composition employed as electrical insulation or as a part the deterioration of 125 225
which would result in a risk of fire or electric shockg
17. Rubber- or thermoplastic-installed wire and cord except those mentioned in item 18g 35 63
18. Types RFH, FFH, and RH wiresg 50 90
19. Other types of insulated wiresh
20. Sealing compoundsi
21. Capacitorsj

Material and components C F

a The temperature rise observed on the terminals and at points within a terminal box and a control for use with other than a
residential appliance that is rated for continuous use above 25C (77F) may exceed the values specified but may not attain a
temperature higher than 90C (194F). See 72.1 72.3.
b Multilayered, metallurgically bonded contacts are not considered to be laminated. See item 8.
c See 40.9.
d If contacts of any metal and their supporting blades, busses, and connecting bars attain a temperature greater than 90C
(194F) where a high ambient temperature or other external temperature prevails, or where affected by a bimetal-heater or
other heat source in the assembly, the control shall perform acceptably when subjected to overload and endurance tests
conducted at the high temperatures involved, except that contacts of silver or a silver alloy that do not attain a temperature
higher than 100C (212F) need not be subjected to overload and endurance tests conducted at the high temperature.
e A fuse that has been investigated and found acceptable for use at a higher temperature may be used at that temperature.
f Temperature rise measured by a thermocouple at a point on the surface of a coil, at which the temperature is affected by an
external source of heat, may be 15C (27F) higher than that specified, provided that the temperature rise by the resistance
method is not more than that specified.
g The limitation on phenolic composition and on rubber and thermoplastic insulation does not apply to compounds that have
been investigated and found to be acceptable for higher temperature.
h For standard insulated conductors other than those mentioned in items 16 and 17, reference to the National Electrical Code,
ANSI/NFPA 70-1993; and the maximum allowable temperature, corrected to a 25C (77F) assumed ambient temperature, is
not to exceed the marked temperature limit of the wire in question, except as noted in 40.3.
i The maximum acceptable temperature, corrected to a 25C (77F) assumed ambient temperature, of a sealing compound is
15C (27F) less than the melting-point temperature of the compound.
j For a capacitor, the maximum allowable temperature rise is the marked temperature limit of the capacitor minus an assumed
ambient temperature of 25C (77F).
40.3 Equipment intended specifically for use with a prevailing ambient temperature constantly more than
25C (77F) is to be tested at such higher ambient temperature, and the allowable temperature rises
specified in Table 40.1 are to be reduced by the amount of the difference between the higher ambient
temperature and 25C (77F).
40.4 A low-potential supply source may be used for conducting temperature tests on parts other than
coils or transformer windings. Unless otherwise noted, the tests on all parts are to be conducted
simultaneously, as the heating of one part may affect the heating of another part.
40.5 A control that is intended to be mounted in a chimney or vent connector, duct, plenum, or the like,
is to be so mounted above an operating appliance using the mounting bracket regularly supplied with the
control with the element inserted as far as permitted by any stop or flange so that service conditions will
be approximated. The ambient temperature surrounding the control outside the chimney or vent
connector, duct, or plenum is to be the highest temperature in which the control is intended to operate.
Typical required test conditions are illustrated in Figures 40.1 and 40.2.
Figure 40.1
Typical test setup for a chimney- or vent connector-mounted control
Boiler operation is to be adjusted so that the thermocouple senses a flue-gas temperature of 538C (1000F).
Figure 40.2
Typical test setup for a plenum-mounted control
Furnace operation is to be adjusted so that the thermocouple senses an air temperature equal to the maximum setting temperature
of the control.
40.6 If equipment is obviously not intended for continuous operation, such as some types of damper
controls, the heating test may be conducted so that the probable intermittent or short-time operation of the
equipment is considered.
40.7 If stalling of a motor on a timer, motor operator, damper control or the like is part of the normal
operation of a device while connected to a supply circuit as specified in Table 38.1, the temperature rise
shall not exceed the limits specified in Table 40.1 with the motor stalled.
40.8 If stalling of a motor as described in 40.7 is not part of the normal operation, the values specified in
Table 40.1 do not apply; but the motor shall have acceptable impedance, thermal, or overload protection.
40.9 Other than at coils, temperatures are to be measured by thermocouples consisting of wires not
larger than No. 24 AWG (0.21 mm2). See 40.13.
40.10 When thermocouples are used to determine temperatures in electrical equipment, it is common
practice to employ thermocouples consisting of No. 30 AWG (0.05 mm2) iron and constantan wires and
a potentiometer-type instrument. Such equipment is to be used whenever referee temperature
measurements by thermocouples are necessary.
40.11 The thermocouples and related instruments are to be accurate and calibrated in accordance with
standard laboratory practice. The thermocouple wire is to conform with the requirements for special
thermocouples as listed in the table of limits of error of thermocouples in Temperature Measurement
Thermocouples, ANSI MC96.1-1982.
40.12 A temperature is considered to be constant when three successive readings, taken at intervals of
10 percent of the previously elapsed duration of the test, but not less than 5-minute intervals, indicate no
change.
40.13 The preferred method of measuring temperatures on coils is the thermocouple method, but
temperature measurements by either the thermocouple or resistance method are acceptable, except that
the thermocouple method is not to be used for a temperature measurement at a point where
supplementary heat insulation is employed.
40.14 To determine if a device complies with the requirements in this section, it is to be operated under
normal conditions, except as otherwise noted. The potential of the supply circuit is to be as specified in
Table 38.1.
41 Leakage Current Test
41.1 The leakage current of a cord-connected product rated for a nominal 250-volt or less supply when
tested in accordance with 41.3 41.7 shall not be more than:
a) 0.5 milliampere for an ungrounded 2-wire portable, stationary, or fixed product;
b) 0.5 milliampere for a grounded 3-wire portable product; and
c) 0.075 milliampere for a grounded 3-wire stationary or fixed product employing a standard
attachment plug rated 20 amperes or less.
JUNE 2, 1998 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 80A
41.2 Leakage current refers to all currents, including capacitively coupled currents, that may be conveyed
between exposed conductive surfaces of a product and ground or other exposed surfaces of the product.
41.3 All exposed conductive surfaces are to be tested for leakage currents. The leakage currents from
these surfaces are to be measured to the grounded supply conductor individually as well as collectively,
if simultaneously accessible, and from one surface to another if simultaneously accessible. Parts are
considered to be exposed surfaces unless guarded by an enclosure considered acceptable for reducing
a risk of electric shock. Surfaces are considered to be simultaneously accessible if they can be readily
contacted by one or both hands of a person at the same time. These measurements do not apply to
terminals operating at voltages that are not considered to involve a risk of electric shock. If all accessible
surfaces are bonded together and connected to the grounding conductor of the power-supply cord, the
leakage current can be measured between the grounding conductor and the grounded supply conductor.
If exposed dead metal parts of the product are connected to the neutral supply conductor, this connection
is to be open during the test.
80B TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 JUNE 2, 1998

41.4 If a conductive surface other than metal is used for the enclosure or part of the enclosure, the
leakage current is to be measured using a metal foil with an area of 10 by 20 centimeters in contact with
the surface. If the surface is less than 10 by 20 centimeters, the metal foil is to be the same size as the
surface. The metal foil is not to remain in place long enough to affect the temperature of the product.
41.5 The measurement circuit for leakage current is to be as illustrated in Figure 41.1. The measurement
instrument is defined in (a) (c). The meter that is actually used for a measurement need only indicate
the same numerical value for a particular measurement as would the defined instrument. The meter used
need not have all the attributes of the defined instrument.
a) The meter is to have an input impedance of 1500 ohms resistive, shunted by a capacitance of
0.15 microfarad.
b) The meter is to indicate 1.11 times the average of the full-wave rectified composite waveform
of voltage across the resistor or current through the resistor.
c) Over a frequency range of 0 100 kilohertz, the measurement circuitry is to have a frequency
response ratio of indicated to actual value of current that is equal to the ratio of impedance of
a 1500-ohm resistor shunted by a 0.15-microfarad capacitor to 1500 ohms. At an indication of 0.5
or 0.75 milliampere, the measurement is to have an error of not more than 5 percent of 60 hertz.
41.6 Unless the meter is being used to measure leakage from one part of a product to another, it is to be
connected between the accessible parts and the grounded supply conductor.
41.7 A sample of the product is to be tested for leakage current starting with the as-received condition
the as-received condition being without prior energization, except as may occur as part of the
production-line testing. The supply voltage is to be adjusted to rated voltage. The test sequence, with
reference to the measurement circuit Figure 41.1 is to be as follows:
a) With switch S1 open, the product is to be connected to the measurement circuit. Leakage
current is to be measured using both positions of switch S2, and with the product switching
devices in all their normal operating positions.
b) Switch S1 is then to be closed energizing the product, and within 5 seconds, the leakage
current is to be measured using both positions of switch S2 and with the product switching
devices in all their normal operating positions.
c) The leakage current is to be monitored until thermal stabilization. Both positions of switch S2
are to be used in determining this measurement. Thermal stabilization is considered to be
obtained by operation as in the normal temperature test.
41.8 Normally the complete leakage current test, as specified in 41.7, is to be conducted without
interruption for other tests. With the concurrence of those concerned, the leakage current test may be
interrupted for the purpose of conducting other nondestructive tests.
Figure 41.1
Leakage current measurement circuit
NOTES
A Probe with shielded lead.
B Separated and used as clip when measuring currents from one part of product to another.
42 Leakage Current Following Humidity Conditioning Test
42.1 A product shall comply with the requirements for leakage current in Leakage Current Test, Section
41, following exposure for 48 hours to air having a relative humidity of 88 2 percent at a temperature of
32 2C (90 4F).
42.2 To determine whether a product complies with the requirement in 42.1, a sample of the product is
to be heated to a temperature just above 34C (93F) to reduce the likelihood of condensation of moisture
during conditioning. The heated sample is to be placed in the humidity chamber and conditioned for 48
hours under the conditions specified in 42.1. Following the conditioning, the sample is to be tested
unenergized as described in 41.5(a). The sample is then to be energized and tested as described in 41.5
(b) and (c). The test is to be discontinued when the leakage current stabilizes or decreases.
43 Operation Test
43.1 An electromagnet for use on direct current shall withstand a voltage 10 percent more than its rated
voltage continuously without damage to the operating coil and shall operate successfully at 20 percent
less than its rated voltage. If a device has a voltage rating within one of the ranges specified in Table 38.1,
that test voltage is to be used.
43.2 An electromagnet for use on alternating current shall withstand a voltage 10 percent more than its
rated voltage continuously without damage to the operating coil and shall operate successfully at 15
percent less than its rated voltage. If a device has a voltage rating within one of the ranges specified in
Table 38.1, the test voltage is to be used.
43.3 For operation at maximum voltage, the contactor coil is to be subjected to the overvoltage potential
until a constant temperature is reached and tested immediately for closing at the normal line voltage.
43.4 For operation at minimum voltage, the contactor coil is to be subjected to the normal line voltage
until a constant temperature is reached and tested immediately for closing at the minimum voltage.
43.5 If an electromagnet is energized through a transformer, rectifier, transformer and rectifier, or other
component, the voltage adjustments are to be made at the transformer primary or input terminals, using
the test values as specified for alternating current or direct current, as appropriate.
43.6 The test is to be conducted on samples, and using test conditions, that represent the most severe
application involved in the use of the device. Examples are:
a) Enclosed instead of open,
b) At elevated ambient temperature,
c) The impedance of upstream components, such as described in 43.5, and
d) Location near or with other heat producing components.

44 Calibration-Verification Test
44.1 For a water-heater control or a hot tub/spa water temperature control tested at the ambient-air
temperature or temperatures consistent with its intended use and for which it is to be rated, the cutout
temperature shall:
a) Be 5F (3C) of the set-point temperature for a water-heater temperature-limiting control,

and a hot tub/spa temperature-regulating and -limiting control;
b) Be 7F (4C) of the maximum temperature set point for a water heater temperature-
regulating control having a maximum temperature setting of more than 170F (77C). A water
heater temperature-regulating control with a maximum temperature set point of 170F or less is
not to be subjected to calibration-verification tests except as indicated in (c);
c) Be 5F of the temperature setting for a water heater temperature-regulating control having a

factory temperature setting no higher than 140F (60C). The test shall be performed on test
samples set at 140F or the maximum temperature setting; or
d) Not vary from the as-received temperature, following the endurance test, by more than 5
percent of the Fahrenheit set-point temperature, or by more than 10F (6C), whichever is the
greater, for either control mentioned in (a), (b), and (c).
44.2 For an electric-baseboard-heater temperature-limiting control tested at ambient-air temperature or

temperatures consistent with its intended use, the cutout temperature shall:
a) Be 15F (8C) of its marked set-point temperature; and
b) Not rise above the initial calibration temperature following the endurance test by more than 2
percent of the rated Fahrenheit temperature.
44.3 For a control other than those covered by 44.1 and 44.2, the cutout temperature of a
temperature-limiting control, when tested at ambient-air temperature or temperatures consistent with its
intended use shall:
a) Be 10F (6C) of its maximum marked set-point temperature up to a 300F (149C) rating,
4 percent of its maximum set-point Fahrenheit temperature up to 400F (204C), and 5 percent
above 400F; and
b) Not vary from the as-received cutout temperature following the endurance test by which ever
is greater:
1) More than 5 percent of the maximum set-point Fahrenheit temperature, or
2) More than 10F.
Exception: Downward drift in cutout temperature may exceed the value specified in
(b)(1) but not more than 20 percent of the maximum set-point Fahrenheit temperature
if such performance does not contribute to a risk of fire, electric shock, or injury to
persons. See 44.4.
44.4 Among the factors taken into consideration when investigating the downward-drift tolerance
mentioned in Exception to 44.3 are:
a) The possibility of user tampering,
b) Overlapping performance with a temperature-regulating control, and
c) Other similar conditions that might result in a risk of fire, electric shock, or injury to persons.
44.5 The calibration-verification tests on a temperature-responsive control are to be performed on

representative production samples that have been produced and calibrated within the same tolerances
permitted in factory production. The set-point temperature of the sample is to be the maximum for which
the device is intended. The tests are to be performed in a manner that will provide a true and measurable
sensing-element temperature.
44.6 Other than as noted in 44.8, a temperature-responsive control is to be mounted in an air oven having
forced circulation of at least 100 feet (30.5 m) per minute, and designed so as to nullify the effects of
radiation. Thermocouples are to be attached to the sensing element, on an adjacent identical element, or
located in air adjacent to the element. Indication of cutout is to be obtained by a low-energy circuit of such
value as to not provide a current assist, and the cutout temperature is to be determined as the average
of two trials.
44.7 Prior to calibration verification, uniform temperatures of all parts of a control are to be maintained by
holding the temperature approximately 20F (11C) below the set point until conditions of equilibrium have
been established. The temperature is then to be raised at a rate of not more than 1.0F (0.5C) per minute
until the control functions.
44.8 A temperature-responsive control of the immersion-element type shall be tested with the element
inserted in a circulating-water system. The conditions of test shall accomplish the performance
contemplated in 44.1 44.7.
44.9 A refrigeration-controller pressure-limiting device shall function as intended at a pressure not

exceeding 105 percent of its maximum marked setting see 71.2. After being subjected to the endurance
test, the cutout pressure shall not increase from the cutout pressure initially determined by more than 5
percent of the marked setting.
44.10 For the tests, a refrigeration-controller pressure-limiting device is to be connected to a source of

hydrostatic pressure that can be accurately controlled and measured. Pressures are to be increased or
decreased during the test at a maximum rate of 1/2 psi (3.5 kPa) per minute.
45 Overload Test
45.1 An ampere-rated switching device not intended for controlling a motor shall perform acceptably
when subjected to an overload test consisting of making and breaking for 50 cycles of operation, at a rate
of 6 cycles per minute, a current of 150 percent of the rated value, at the voltage specified in Table 38.1.
There shall be no electrical or mechanical breakdown or malfunction of the device, nor undue burning,
pitting, or welding of the contacts.
45.2 Other than as noted in 45.6 and 45.7, a switching device intended for full-voltage motor starting shall
perform acceptably when subjected to a locked-rotor test consisting of making and breaking for 50 cycles
of operation, at a rate of 6 cycles per minute, a current as described in 45.3 and Table 45.1, at the voltage
specified in Table 38.1. There shall be no electrical or mechanical breakdown or malfunction of the device,
nor undue burning, pitting, or welding of the contacts.
Table 45.1
Method of determining currents for overload tests
Current in amperes for overload test described in paragraph indicated

Device rated in Locked-rotor, 45.2, 45.6, and 45.7 150-percent-current, 45.6, and 45.7
Horsepower A-C: Six times the full-load current A-C: 1.5 times the full-load current
specified in Table 45.3 specified in Table 45.3
D-C: Ten times the full-load current D-C: 1.5 times the full-load current
specified in Table 45.2 specified in Table 45.2
Full-load and locked-rotor amperes Rated locked rotor amperes 1.5 times rated full-load amperes
45.3 The current of the overload tests mentioned in 45.2, 45.6, and 45.7 is to be as specified in Table
45.1.
45.4 A contact device designed for pilot duty shall perform acceptably when subjected to an overload test
consisting of 50 operations, making and breaking a circuit of rated frequency and 110 percent of the
voltage specified in Table 38.1, at intervals of 10 seconds, with the contacts closed for approximately 1
second each cycle. The load shall consist of an electromagnet representative of the magnet-coil load that
the device is intended to control the normal current is to be determined from the voltage and volt-ampere
rating of the device. The test coils shall be those described in 46.5. The test shall be conducted with the
contactor free to operate, for example, not blocked in either the open or closed position. There shall be no
electrical or mechanical breakdown or malfunction of the device nor undue burning, pitting, or welding of
the contacts.
45.5 A device that has been investigated and found to be acceptable for controlling an alternating-current
motor is acceptable for alternating-current pilot duty without additional overload or endurance tests if:
a) During the locked-rotor motor-controller test, the contacts were caused to make and break, for
50 cycles of operation at a rate of 6 cycles per minute, a current having a value as specified in
the second column of Table 45.1 at a power factor of 0.5 or less; and
b) The pilot-duty inrush current at the same voltage is not more than 67 percent of the rated
locked-rotor motor current of the device, or the locked-rotor current corresponding to the
horsepower rating, depending on the basis on which the device is rated.
45.6 A switch that is not intended primarily to make and break motor current under locked-rotor
conditions, but that has a manual adjusting or regulating means that may cause it to be so used, shall
comply with the requirements in 45.2 for locked-rotor test.
Exception: For a switch intended for operation on direct current, the number of operations shall be five,
conducted at intervals of 30 seconds, and the device shall also comply with the requirements in 45.7
pertaining to the 150-percent-overload test.
45.7 A switch that may make a motor circuit under locked-rotor conditions, but that will never be required
to break the circuit under such conditions, shall perform acceptably when subjected to an overload test
consisting of 50 cycles of making and breaking, at a rate of 6 cycles per minute, a current as specified in
the third column of Table 45.1. For an alternating-current device, the voltage of the test circuit shall have
the value specified in Table 38.1. For a direct-current device it shall be 50 percent of that value. The
switch shall also be subjected to the locked-rotor test described in 45.2, except that it is to make not
break the circuit only. There shall be no electrical or mechanical malfunction of the device, nor undue
burning, pitting, or welding of the contacts. A safety control that is subjected to the test of making but
not breaking locked-rotor current shall open the circuit under no-load conditions without more than a 20
percent change in its calibration.
45.8 The test cycle is to be 1 second on and 9 seconds off, if the design of the device permits the test
to be so conducted.
45.9 If an ampere-rated device has the same ampere rating at more than one voltage, a test at the
highest voltage is considered to be representative of tests at the lower voltages, but if the device has a
higher ampere rating at the lower voltage than at the higher ones, tests are to be conducted at the highest
and lowest voltages.
45.10 If a horsepower-rated device has more than one voltage rating, the overload test or tests are to
cover the conditions of maximum voltage, power, and current.
45.11 Other than as noted in 45.4 and 46.6, a current-interrupting device for use on direct current shall
be tested with a noninductive resistance load. A current-interrupting device for use on alternating current
shall be tested with an inductive load, except that a thermostat intended for controlling a noninductive
load, such as a range, water heater, clothes dryer, or the like, shall be tested with a noninductive
resistance load.
45.12 The power factor of an inductive load shall be 0.75 0.80, except that it shall be 0.40 0.50 for a
load simulating locked-rotor conditions in a motor, and shall not be more than 0.35 for a pilot-duty load.
45.13 Tables 45.2 and 45.3 give full-load currents corresponding to motor horsepower ratings, and are to
be used in determining loads for the various tests specified for horsepower-rated equipment.
Table 45.2
Full-load motor-running currents in amperes corresponding to various d-c horsepower ratings
110 120 220 240 550 600

Horsepower (W output) 90 volts volts 180 volts volts 500 volts volts
1/10 (75) 2.0 1.0

1/8 (93) 2.2 1.1
1/6 (124) 2.4 1.2
1/4a (187) 4.0 3.1 2.0 1.6
1/3 (249) 5.2 4.1 2.6 2.0
1/2 (373) 6.8 5.4 3.4 2.7
3/4 (560) 9.6 7.6 4.8 3.8 1.6
1 (746) 12.2 9.5 6.1 4.7 2.0
1-1/2 (1120) 13.2 8.3 6.6 2.7
2 (1490) 17.0 10.8 8.5 3.6
3 (2240) 25.0 16.0 12.2 5.2
5 (3730) 40.0 27.0 20.0 8.3
7-1/2 (5600) 58.0 29.0 13.6 12.2
10 (7460) 76.0 38.0 18.0 16.0
15 (11.2 kW) 110.0 55.0 27.0 24.0
20 (14.9 kW) 148.0 72.0 34.0 31.0
25 (18.7 kW) 184.0 89.0 43.0 38.0
30 (22.4 kW) 220.0 106.0 51.0 46.0
40 (29.8 kW) 292.0 140.0 67.0 61.0
50 (37.3 kW) 360.0 173.0 83.0 75.0
60 (44.8 kW) 206.0 99.0 90.0
75 (60.0 kW) 255.0 123.0 111.0
100 (74.6 kW) 341.0 164.0 148.0
125 (93.3 kW) 425.0 205.0 185.0
150 (112 kW) 506.0 246.0 222.0
200 (149 kW) 675.0 330.0 294.0
a The full-load current for a 1/4-horsepower, 32-volt direct current motor is 8.6 amperes.
Table 45.3
Full-load motor-running currents in amperes corresponding to various a-c horsepower ratings
110 120 volts 220 240 voltsa 440 480 volts 550 600 volts
Single- Single- Single- Single-

Horsepowera (W Output) phase 3-phase phase 3-phase phase 3-phase phase 3-phase
1/10 (75) 3.0 1.5
1/8 (93) 3.8 1.9
1/6 (124) 4.4 2.2
1/4 (187) 5.8 2.9
1/3 (249) 7.2 3.6
1/2 (373) 9.8 4.0 4.9 2.0 2.5 1.0 2.0 0.8
3/4 (560) 13.8 5.6 6.9 2.8 3.5 1.4 2.8 1.1
1 (746) 16.0 7.2 8.0 3.6 4.0 1.8 3.2 1.4
1-1/2 (1120) 20.0 10.4 10.0 5.2 5.0 2.6 4.0 2.1
2 (1490) 24.0 13.6 12.0 6.8 6.0 3.4 4.8 2.7
3 (2240) 34.0 19.2 17.0 9.6 8.5 4.8 6.8 3.9
5 (3730) 56.0 30.4 28.0 15.2 14.0 7.6 11.2 6.1
7-1/2 (5600) 80.0 44.0 40.0 22.0 21.0 11.0 16.0 9.0
10 (7460) 100.0 56.0 50.0 28.0 26.0 14.0 20.0 11.0
15 (11.2 kW) 135.0 84.0 68.0 42.0 34.0 21.0 27.0 17.0
20 (14.9 kW) 118.0 88.0 54.0 44.0 27.0 35.0 22.0
25 (18.7 kW) 136.0 110.0 68.0 55.0 34.0 44.0 27.0
30 (22.4 kW) 160.0 136.0 80.0 68.0 40.0 54.0 32.0
40 (29.8 kW) 208.0 176.0 104.0 88.0 52.0 70.0 41.0
50 (37.3 kW) 260.0 216.0 130.0 108.0 65.0 86.0 52.0
60 (44.8 kW) 154.0 77.0 62.0
75 (46.0 kW) 192.0 96.0 77.0
100 (74.6 kW) 248.0 124.0 99.0
125 (93.3 kW) 156.0 125.0
150 (111.9 kW) 180.0 144.0
200 (149.2 kW) 240.0 192.0
a To obtain full-load currents for 200 and 208 volt motors, increase the corresponding 220 240 volt currents by 15 and 10
percent, respectively, for single- and 3-phase motors. To obtain full-load currents for 265- and 277-volt motors, decrease the
corresponding 220 240-volt currents by 13 and 17 percent, respectively. The 265- and 277-volt ratings are applicable for
equipment rated 2 horsepower or less, single-phase only.
45.14 Current-interrupting tests shall be conducted at the voltage specified in Table 38.1.
Exception: For a direct-current device, current-interrupting tests shall be conducted at 50 percent of the
voltage specified in Table 38.1 in accordance with 45.7 and 46.1.
45.15 A circuit in which the closed-circuit voltage is 100 110 percent of the test potential specified in
Table 38.1 may be used for the tests mentioned in 45.14.
Exception: For a device rated more than 25 horsepower (18.7 kW) or more than 100 amperes, the
open-circuit voltage is to be 110 percent of the value specified in Table 38.1, or as much above that value
as the closed circuit voltage is below it, whichever is less.
45.16 Alternating-current interrupting tests are to be conducted on a circuit having a frequency of 60

hertz. Tests at 25 60 hertz may, however, be considered to be representative.
45.17 A 2-pole or 4-pole device is to be tested on a single-phase or direct-current circuit. In a 4-pole

device, adjacent poles are to be used, one pole being the nearest the enclosure. If the pole spacing
varies, an additional test is to be conducted between the poles with the smallest spacing, to cover use on
2-phase interconnected systems.
45.18 A 3-pole device for polyphase use shall be tested on a 3-phase circuit. A 3-pole device for use on
a direct-current or single-phase system with a grounded neutral shall be tested with rated voltage applied
to the outside poles and with the middle pole electrically connected to the line and to the midpoint of a
balanced load.
45.19 For a device that is intended for connection to a grounded-neutral system and is marked as
specified in 74.10 or 74.11, the enclosure shall be connected during the test through a 3-ampere cartridge
fuse to the grounded conductor of the circuit. For any other system, the enclosure is to be connected
through such a fuse to the live pole least likely to arc to ground.
46 Endurance Test
46.1 A switch shall perform acceptably when operated manually, by means of a machine, or by automatic
means for the number of cycles specified in Table 46.1, and at the rate specified unless the design of the
device requires a longer time to complete a cycle of operation. If an electrical load is involved, and except
as otherwise noted, a switch shall make and break its rated current at the voltage specified in Table 38.1.
Switch contacts for control of a motor are to be tested with full-load motor current; if the switch is rated in
horsepower instead of full-load motor current, the latter value is to be determined from Table 45.2 or 45.3,
whichever is applicable. If the switch contacts control a direct-current motor, and the switch normally will
make but not break the motor circuit under locked-rotor conditions, the potential of the test circuit is to be
50 percent of the value specified in Table 38.1. There shall be no electrical or mechanical breakdown of
the device, nor undue burning, pitting, or welding of the contacts.
46.2 Two samples of a wall-mounted room thermostat intended for direct control of electric space-heating
equipment that is to be permanently connected electrically (designated SAMPLE 1 and SAMPLE 2) are to
be subjected to an endurance test consisting of 6000 cycles of operation at the rate of not more than 1
cycle per minute and at 110 percent of both the rated current and the voltage specified in Table 38.1. The
on time is to be 50 20 percent, and operation is to be by thermal means. There shall be no electrical or
mechanical breakdown of either thermostat, and there shall be no undue burning or pitting of the contacts
of SAMPLE 1. See 46.3.
46.3 SAMPLE 2 is to be subjected to an additional 30,000 cycles of operation under the conditions
described in 46.2, except that the rated current and the test voltage specified in Table 38.1 is to be used.
The test may be discontinued if the thermostat becomes inoperative due to the contacts not opening or
closing. There shall be no indication of a risk of fire or electric shock.
46.4 The conditions for the endurance test are to be as described in 45.9 45.19.
46.5 A contact device designated for pilot duty is to perform acceptably when operated for the number of
cycles specified in Table 46.1, making and breaking a circuit of rated frequency and at the voltage
specified in Table 38.1. Unless the design of the device requires a longer time to complete a cycle of
operation, the rate of operation for the test is to be as follows:
a) For a manually operable device, the first 1000 cycles are to be at the rate of 1 cycle per
second except that the first ten or 12 operations are to be made as rapidly as possible and
the remaining cycles are to be at the rate of 6 cycles per minute, with the device closed for
approximately 1 second each cycle; and
b) For a self-actuated device the cycle rate is to be as specified in Table 46.1.
46.6 The load is to consist of an electromagnet representative of the magnet-coil load that the device is
intended to control. The normal current is to be determined from the voltage and volt-ampere rating of the
device. The test current is to be the normal current; and for an alternating-current device, the power factor
is to be 0.35 or less and the inrush current is to be ten times the normal current, unless marked in
accordance with 69.11. The test is to be conducted with the contactor free to operate, that is, not blocked
either open or closed. There shall be no electrical or mechanical breakdown of the device nor undue
pitting or burning of contacts.
46.7 If a device requiring an endurance test of 100,000 cycles has two or more electrical ratings for
example, different currents at different voltages it may be tested for not less than 25,000 cycles at each
rating, but the total number of cycles on any one sample is not to be more than 100,000. At least one
sample is to be tested for 100,000 operations.
46.8 If equipment requiring an endurance test of 30,000 cycles has two or more electrical ratings, it may
be tested for not less than 7,500 cycles at each rating, but the total number of cycles on any one sample
is not to be more than 30,000. At least one sample is to be tested for 30,000 operations.
Table 46.1
Number of cycles for endurance test
Item (e) of Table 46.1 revised May 4, 2001
Number of cycles of operationa

Maximum Maximum
Without cycles per cycles per
Types of devices With current current First minute Last minute
Safety controls including 100,000 75,000 6 25,000 1b
refrigeration pressure-
limiting controls, defrost
temperature-limiting
controls, and electric-
baseboard-heater
temperature-limiting
controls, and hot tub/spa
controls
Refrigeration controls 30,000 24,000 6 6,000 1b
Water-heater thermostats 30,000 30,000 1b
Range controls c c c c c

Number of cycles of operationa

Maximum Maximum
Without cycles per cycles per
Types of devices With current current First minute Last minute
Fan control for central 30,000 24,000 6 6,000 1b

electric air-heating
equipment
Manually operated switch 6,000 6,000 6
Protective switches not 1,000 5,000 1,000 1b 5,000 d
normally required to
make and break a circuit,
such as manually reset
safety controls, high-
pressure and high-
temperature cutouts used
in addition to the regular
operating control, and the
like, but not including
automatically-reset
controls
Disconnect switches, 1,000 5,000 1,000 6 5,000 d
such as a manual motor-

circuit switch that is
incorporated in a device
with a motor controller
Motor controllers and 6,000 6,000 1b

ampere-rated devices not
mentioned above, such
as thermostats,
humidistats, and timing
mechanismse
Appliance controls 6,000f 6,000 1b
30,000 24,000 6 6,000 1b
100,000 75,000 6 25,000 1b

a Magnetic, manual and motor-operated switches, or the like, and switches that snap with lost motion and do not creep, may be
tested at the rate of 6 cycles per minute.
b For all controls, the test is to be conducted with 50 20 percent on time. A temperature-or pressure-operated control is to be
so tested, using a slow rate of change.

c For range controls, refer to 38.6.1 38.9.2 and Table 38.3.
d When no current is used, the switch may be operated at any convenient speed.
e See 38.2 for wall-mounted room thermostats for direct control of fixed electric space heating.
f Number of operations are determined by requirements of an appliance.
47 Dielectric Voltage-Withstand Test
47.1 General
47.1.1 Equipment shall withstand for 1 minute, without breakdown, the application of an alternating
potential of 1000 volts plus twice maximum rated voltage:
a) Between line-voltage live parts and grounded or exposed metal parts or the enclosure with the
contacts open and closed;
b) Between line-voltage live parts of opposite polarity with contacts closed; and
c) Between live parts and line- and low-voltage circuits, line-voltage and isolated-limited-power
secondary circuits, and different line-voltage circuits.
47.1.2 A wall-mounted room thermostat intended for direct control of electric space-heating equipment
that is to be permanently connected electrically (designated SAMPLE 1) shall withstand for 1 minute,
without breakdown, the application of an alternating potential of 900 volts between the line and load
terminals. Supplementary insulation may be placed between the thermostat contacts during this test.
There shall be no breakdown either through or across the insulating material supporting the contact and
terminal assemblies.
47.1.3 A device employing a low-voltage circuit shall withstand for 1 minute, without breakdown, the
application of an alternating potential of 500 volts applied between low-voltage live parts of opposite
polarity with contacts closed, and between low-voltage live parts and the enclosure and grounded dead
metal parts.
47.1.4 The opposite polarity dielectric voltage-withstand test may be omitted for a portion of a
low-voltage, nonsafety circuit that is beyond any fixed impedance.
47.1.5 A transformer, shall withstand for 1 minute, without breakdown, the application of an alternating
potential of 1000 volts plus twice the maximum rated primary voltage, at rated frequency, between primary
and secondary windings and between the primary winding and the core or enclosure.
47.1.6 A power transformer shall withstand for 1 minute, without breakdown, the application of an
alternating potential of 1000 volts plus twice the maximum rated primary or secondary voltage, at rated
frequency, between primary and secondary windings, and shall withstand under the same conditions the
application of an alternating potential of 1000 volts plus twice the rated voltage of each winding, at rated
frequency, between each winding and the core or enclosure, except that the test between primary and
secondary windings is omitted for an autotransformer.
47.1.7 A device employing a barrier or liner to insulate an exposed dead metal part shall withstand a
dielectric voltage-withstand test as described in 47.1.1 between live parts and the exposed dead metal
part. See Table 32.1.
47.1.8 If a device involves a meter or meters, such instruments shall be disconnected from the circuit and
the complete device subjected to a dielectric voltage-withstand test as described in 47.1.1 47.1.7. The
meter or meters shall then be tested separately in accordance with the tests outlined in 47.1.1 47.1.3
whichever is applicable except that an ammeter in a line-voltage circuit shall be tested at 1000 volts.
47.1.9 After the conditioning specified in 47.1.11, the insulation on a flexible pigtail lead for a line-voltage
circuit or for a low-voltage safety-control circuit where breakdown will cause unsafe operation shall
withstand for 1 minute, without breakdown:
a) When dry, an alternating potential of 1000 volts plus twice maximum rated voltage, and
b) After exposure to moist air, an alternating potential of rated voltage plus 500 volts.
47.1.10 A flexible pigtail lead for low-voltage circuits other than specified in 47.1.9 shall comply with the
requirement in 47.1.3.
47.1.11 A lead that is to be tested dry is to be conditioned for 24 hours in a desiccator with dry calcium
chloride, and a lead that is to be tested after exposure to moist air is to be conditioned for 24 hours in air
having a relative humidity of 85 5 percent at a temperature of 32 2C (90 4F).
47.1.12 To determine if a lead complies with the requirement in 47.1.9, the straight conductor is to be
employed as one electrode and a 1-inch-wide metal-foil wrap, located away from the ends of the sample,
is to be the other electrode. The foil is to be located at three different positions or on three separate test
samples.
47.1.13 To determine whether a device complies with the requirements in 47.1.1 47.1.12, the device is
to be tested using a 500 volt-ampere or larger capacity transformer the output voltage of which is
essentially sinusoidal and can be varied. The applied potential is to be increased from zero until the
required test level is reached, and is to be held at that level for 1 minute. The increase in the applied
potential is to be at a substantially uniform rate and as rapidly as is consistent with its value being correctly
indicated by a voltmeter.
47.2 Induced potential
47.2.1 Each of three separate magnet-coil-winding samples shall withstand without breakdown the test
mentioned in 32.3.1(b)(2) after constant temperatures have been reached as the result of operation under
the conditions specified in Temperature Test, Section 40. While still heated, the coil winding shall be
subjected to an alternating potential of twice the rated voltage at any suitable frequency typically 120
hertz or higher for 7200 electrical cycles or for 60 seconds, whichever is less. The required test voltage
is to be attained by starting at one-quarter or less of the full value and increasing to the full value in not
more than 15 seconds. After being held for the time specified, the voltage is to be reduced within 5
seconds to one-quarter or less of the maximum value, and the circuit is to be opened.
47.3 Induced potential repeated
47.3.1 While heated following operation at 110 percent of rated voltage as specified in Operation Test,
Section 43, each of three samples shall withstand without breakdown a repeated induced potential test at
65 percent of the potential applied in accordance with 47.2.1.
47.3.2 If the temperature that a coil winding reaches in the tests described in 47.2.1 and 47.3.1 is known,
an oven may be set at the required temperature and used to condition the sample to that temperature
before conducting the test.
48 Volt-Ampere Capacity Test
48.1 An isolated limited-secondary circuit shall have a continuous-use capacity of 100 volt-amperes or
less when energized from a circuit of rated frequency at the voltage specified in Table 38.1.
48.2 A single-wound secondary transformer is to attain a temperature rise on the enclosure, core, or coil
of at least 50C (90F) when the secondary is loaded to the maximum output attainable or 100
volt-amperes, whichever is less.
48.3 Each secondary winding of a multisecondary transformer is to be loaded in turn with a variable
resistor. Starting with a cold transformer for each part of the test, the load resistance is to be decreased
from open-circuit to short-circuit in such a manner that the elapsed time is between 1-1/2 and 2-1/2
minutes. Depending upon the open-circuit voltage of the winding, the maximum outputs attained by this
method are to be as follows:
a) 350 volt-amperes for 0 15 volts;
b) 250 volt-amperes for 15.1 30 volts; and
c) 200 volt-amperes for 30.1 1000 volts.
49 Burnout Test
49.1 A continuous-duty resistor shall not burn out or be adversely affected by carrying the full normal
current on any step continuously. A resistor intended for intermittent use shall carry its rated current on
any step for as long a time as the apparatus that it controls will permit.
49.2 A power transformer, other than a transformer supplying a low-voltage, electronic, or

isolated-limited-secondary circuit is to be operated as described in 49.3. There shall be no damage to the
enclosure or emission of flame or molten metal.
49.3 The device is to be operated continuously at the voltage and frequency specified in Table 38.1 and
38.1.2, with the enclosure grounded. The load connected to the output terminals is to be a resistance of
such value that three times full rated current will be drawn from the secondary winding of the device, and
operation is to be continued until constant temperatures are indicated on the enclosure or until burnout
occurs.
49.4 A circuit on which a transformer is tested is to be protected by fuses rated at least ten times the
primary current rating of the transformer, and opening of the fuses is acceptable. The test is to be
conducted with the output terminals short-circuited, if such a condition results in less than three times
full-rated current being drawn from the secondary. If other means of limiting the load to less than three
times normal is inherent in or provided as part of the product, these features are to be given consideration
and the burnout test conducted at the maximum load permitted by the limiting features.
49.5 A transformer supplying an isolated-limited-secondary circuit or an electronic circuit that is not Class
2 is to be tested in accordance with 49.2 49.4, except all secondary windings are to be short-circuited.
See 63.1.4.
49.6 A transformer or power source supplying a Class 2 circuit is to be tested as specified in 63.12.1
63.12.7.
50 Short Circuit Test
50.1 Mercury-tube switch
50.1.1 Equipment employing a mercury-tube switch intended for connection to a line-voltage circuit shall
perform acceptably when tested in series with a standard, nonrenewable cartridge fuse on a direct-current
circuit of the voltage specified in Table 38.1, except that alternating current with a noninductive load may
be employed if the product is intended for use on alternating current only. The fuse rating and capacity of
the test circuit is to be as specified in Table 50.1.
Table 50.1
Mercury switch short-circuit test conditions
Minimum fuse rating at least equal to switch amperes

rating, or the nearest standard fusea not exceeding four
times motor full-load ampere rating but not less than:
Circuit current,
Volts Maximum rating amperes 0 125 volts 126 250 volts 251 600 volts
0 250 2000 volt-ampere 1000 20 15
0 250 30 ampere 3500 30 30
0 250 60 ampere 3500 60 60
0 250 Over 60 ampere 5000 b b
251 600 Unlimited 5000 30
a For the purpose of this test, standard ampere ratings for fuses are 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110,
125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 601, 700, 800, 1000, and 1200.
b Fuse size as specified in heading.
50.1.2 There shall be no ignition of the cotton or insulation on circuit conductors, nor emission of flame
or molten metal mercury excepted from the enclosure housing the switch. Wiring attached to the
product, except tube leads, shall not be damaged.
50.1.3 The enclosure and any other exposed metal are to be grounded, and cotton is to be placed around
all openings in the enclosure. Successive operations are to be conducted by alternatively closing the short
circuit on the mercury-tube switch and closing the mercury-tube switch on the short circuit by means of a
switching device.
50.1.4 To determine if a mercury-tube switch complies with the requirements in 50.1.1 50.1.3, each of
three samples is to be operated three times with sufficient time between successive operations on any one
sample to permit cooling to room temperature, unless the switch is damaged so as to open the circuit
permanently before the specified number of operations is conducted. The switch need not be operative
after the tests.
50.2 Conductor
50.2.1 If required see Exception No. 3 to 28.1.1 there shall be no damage to any conductor, its
insulation, or termination as a result of the short-circuit test described in 50.2.2 50.2.5.
50.2.2 Three sets of samples are to be subjected to the test. Each set is to consist of a group of two
conductors; and one conductor a total of nine conductors. The conductors are to be of the type, size,
length, or the like used in the equipment with terminations as used in the equipment at each end. For each
sample the conductor or conductors are to be routed within a length of conduit, if so used in the
equipment, or they are to be placed on a metal plate.
50.2.3 The conduit or metal plate is to be connected to the unfused pole of the supply circuit. For the tests
on one set, the two conductors are to be connected to the power supply and the terminals at the load end
are to be connected together. For the tests on the other set, the conductor is to be connected across the
supply circuit.
50.2.4 The test circuit is to be a 2-wire circuit having a power factor of 0.9 1.0, and available current as
specified in Table 50.2, at the voltage specified in Table 38.1. The open-circuit voltage of the test circuit
is to be 100 105 percent of the specified voltage. A nonrenewable fuse that will not open in less than
12 seconds when carrying twice its rated current is to be connected to 1 pole of the supply circuit.
Table 50.2
Circuit capacity for conductor short-circuit test
Combined rating of device

Volt-amperes, Volt-amperes, Volt-amperes, Circuit capacity in
single-phase 3-phase direct-current Horsepower (W) Volts amperes
0 1176 0 832 0 648 1/2 maximum (373) 0 250 200
0 1176 0 832 0 648 1/2 maximum (373) 251 600 1000
1177 1920 833 1496 649 1140 over 1/2 (373) to 1 0 600 1000
maximum (746)
1921 4080 1497 3990 1141 3000 1 (746) to 3 (2200) 0 250 2000
4081 9600 3991 9145 3001 6960 3 (2200) to 7-1/2 0 250 3500
(5600)
9601 or more 9146 or more 6961 or more Over 7-1/2 (5600) 0 250 5000
1921 or more 1497 or more 1141 or more Above 1 (746) 251 600 5000
50.2.5 The fuse is to have a current rating equal to that of the branch-circuit overcurrent-protective device
to which the equipment will be connected, but not less than 20 amperes.
50.3 Equipment for motor control
50.3.1 Equipment having a rating of more than 50 horsepower (37 kW output) or one or more motor
overload relays shall comply with the applicable short-circuit test requirements in the Standard for
Industrial Control Equipment, UL 508.
51 Parts Containing Liquid Metal Test
51.1 Parts of a control intended for use with cooking or other food-handling appliances that contain
mercury, and parts of any control that contain sodium, potassium, or both shall withstand for 1 minute,
without leakage or rupture, a hydraulic pressure equal to five times the maximum operating pressure.
51.2 The hydraulic pressure is to be increased until rupture occurs. The rupture shall occur at the bellows
or diaphragm or other part that will be within the switch body or control enclosure; and for a control
intended for use with cooking or other food-handling appliances, outside of the food-containing space. See
51.4.
51.3 Parts of a control intended for use with cooking or other food-handling appliances that contain
mercury, and the parts of any control that contain sodium, potassium, or both shall:
a) Not leak or rupture when heated to 120 percent of the maximum load Fahrenheit temperature,
and
b) Comply with the requirements in 51.4 when the bellows or diaphragm is deliberately punctured
with a sharp pointed metal rod.
51.4 Mercury escaping due to the deliberate rupture by overpressure or deliberate puncture of a bellows
or diaphragm shall not enter an oven or food handling compartment, or contact food handling hardware,
or the like. It shall be contained in the switch body or control enclosure or be expelled outside the oven
or compartment. Sodium, potassium, or both shall be contained in the switch body or control enclosure.
There shall be no resulting risk of fire.
52 Two-Step Operation Surface-Unit Controls Test
52.1 General
52.1.1 A surface-unit control intended for use on a range or a counter-mounted cooking unit and required
to have a minimum of two operations or the equivalent shall comply with the requirements in this section.
Only one operation shall be required to turn such a control off. New samples are to be used for the tests
in this section.
52.2 Push- and pull-and-turn controls
52.2.1 A rotary switch having a push-and-turn or a pull-and-turn operating sequence shall comply with the
following:
a) The in-line force required to push or pull the shaft shall be at least 2 pounds (8.9 N), and the
travel from the normal rest position to the turn position shall be at least 1/32 inch (0.8 mm).
b) A 30-pound (134-N) in-line push or pull force on the adjusting shaft shall not damage the
switch.
c) For a control intended for use only with a knob having a grip diameter or length of 2 inches
(50.8 mm) or less:
1) A means provided to restrict rotation of the shaft and closing of the contacts without
prior push or pull operation shall not be defeated or damaged when a torque of 30
pound-inches (3.4 Nm) is applied to the shaft that is, the control shall remain a
two-operation type.
Exception: A stop that is defeated when a torque of at least 15 pound-inches (1.7 Nm)
is applied to the shaft may be used if:
i) The contacts remain open and cannot be closed in this or subsequent operations of the control; or
ii)The stop or detent is not broken but is overridden to close the contacts; and in subsequent
operation, requires both push-and-turn or the pull-and-turn to close the contacts.
2) There shall not be bridging or grounding of live parts or other risk of fire or electric
shock if the stop or detent of the control is broken or damaged when a torque of 30
pound-inches or more as specified in (c)(1) or 15 pound-inches or more as specified in
the Exception to (c)(1), whichever is appropriate, or a greater torque, is applied. A
torque greater than 50 pound-inches (5.7 Nm) is not used for this test.
3) The torque required to open the contacts shall not be more than 4 pound-inches (0.5
Nm).
d) A control intended for use with a knob having a grip diameter or length of more than 2 inches
(50.8 mm) shall comply with the requirements in (c)(1), (2), and (3) at a value of torque
increased proportionally to the grip diameter or length of the knob from those specified.
e) A control other than as mentioned in (f) shall comply with the requirements in (a), (b), and
(c) following an endurance test consisting of 6000 cycles of operation. A new sample is to be
pushed or pulled and turned in one direction to the high heat position then turned back to the
off position. If the construction is different in the other direction of rotation, a second endurance
test is to be conducted on a new sample operated in the other direction.
f) A control as described in the Exception (ii) to (c)(1) shall comply with the requirements in (e)
except that the actuator is to be turned for the first 1000 cycles of operation without first pushing
or pulling.
52.3 Other types of controls
52.3.1 A surface-unit control of other than a push- or pull-and-turn control shall be tested as appropriate
for its construction to demonstrate that it has strength and reliability at least equivalent to that required for
a push- or pull-and-turn control.
53 Strain-Relief Test
53.1 A strain-relief device shall comply with the requirement in 53.2.
53.2 A strain-relief device shall withstand without damage to the cord or conductors and without
displacement a direct pull of 35 pounds (156 N) applied to the cord for 1 minute. Supply connections within
the equipment are to be disconnected from terminals or splices during the test.
54 Accelerated Aging Tests on Gaskets, Sealing Compounds, and Adhesives
54.1 The requirements specified in 54.2 54.6 apply to gaskets and sealing compounds employed to
make an enclosure raintight or rainproof as determined in accordance with the requirements in Rain Test,
Section 56. The requirements specified in 54.7 apply to adhesives required to secure such gaskets to an
enclosure or cover.
54.2 Neoprene or rubber compounds, except foamed materials, used for gaskets to seal an enclosure,
shall have physical properties as specified in Table 54.1 before and after accelerated aging under the
conditions specified in Table 54.2.
100 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 APRIL 3, 1996
Table 54.1
Physical properties for gaskets
Polyvinyl chloride
Neoprene or rubber compound materials
Before test After test Before test After test
Recovery Maximum set when 1-inch 1/4 inch (6.4 mm) Not specified
(25.4-mm) gage marks are stretched to
2-1/2 inches (63.5 mm) held for 2 minutes
and measured 2 minutes after release
Elongation Minimum increase in distance 250 percent, 1 3-1/2 65 percent of original 250 75 percent
between 1-inch gage marks at break inches (25.4 88.9 mm) percent, 1 of original
3-1/2
inches
Tensile Strength Minimum force at 850 psi (5.9 MPa) 75 percent of original 1200 psi 90 percent
breaking point (8.3 MPa) of original
Table 54.2
Accelerated aging conditions
Table 54.2 revised April 3, 1996
Measured temperature rise

C F Material Test program
35 63 Rubber or neoprene Air oven aging for 70 hours at
100.0C 2.0C (212.0C
3.6F)
35 63 Thermoplastic Aged in full-draft, air-
circulating oven for 168 hours
at 87.0 1.0C (188.6
1.8F)
50 90 Rubber or neoprene Air oven aging for 168 hours
at 100.0C 2.0C (212.0F
3.6F)
at 100.0 1.0C (212.0
1.0F)
55 99 Rubber, neoprene or Aged in full-draft, air-
thermoplastic circulating oven for 168 hours
at 113.0 1.0C (235.4
1.8F)
65 117 Rubber or neoprene Aged in full-draft, air-
at 121.0 1.0C (249.8
1.8F)
at 121.0 1.0C (249.8
1.8F) for 1440 hours at 97.0
1.0C (206.6 1.8F)
80 144 Rubber, neoprene or Aged in full-draft, air-
thermoplastic circulating oven for 168 hours
at 136.0 1.0C (276.8
1.8F)
54.3 Foamed neoprene or rubber compounds used for gaskets to seal an enclosure are to be subjected
to accelerated aging under the conditions specified in Table 54.2. The compounds shall not harden or
otherwise deteriorate to a degree that will affect their sealing properties.
54.4 Thermoplastic materials used for gaskets to seal an enclosure shall be subjected to accelerated
aging under the conditions specified in Table 54.2. Thermoplastic material shall not deform or melt, or
otherwise deteriorate to a degree that will affect its sealing properties. Solid polyvinyl-chloride gasket
material shall have physical properties as specified in Table 54.1 before and after the accelerated aging.
54.6 A sealing compound shall be applied to the surface it is intended to seal. For a temperature rise not
exceeding 35C (63F), a representative sample of the surface with the sealing compound applied shall
be conditioned for 7 days in an air oven at 87C (189F). The sealing compound shall not melt, become
brittle or otherwise deteriorate to a degree that will affect its sealing properties as determined by
comparing the conditioned sample to an unconditioned sample.
54.7 If gaskets are secured by adhesives, samples of the gasket, adhesive and mounting surface shall
be exposed for 72 hours to each of the following conditions, for a temperature rise not exceeding 35C
(63F):
a) 100C (212F),
b) Immersion in distilled water, and
c) Minus 10C (14F).
54.8 The force required to peel the gasket from its mounting surface after exposure shall not be less than
75 percent of the value determined on as-received samples.
54.9 The temperature rises mentioned in this section correspond to the maximum temperature rise
measured on the gasket during the temperature test. Materials other than those mentioned in this section
shall be nonabsorptive and they, and any materials having higher temperature rises, shall provide
equivalent resistance to aging and temperatures.
55 Metallic Coating Thickness Test
55.1 The method of determining the thickness of a zinc or cadmium coating by the
metallic-coating-thickness test is described in 55.2 55.9.
55.2 The test solution is to be made from distilled water and is to contain 200 grams per liter of reagent
grade chromic acid (CrO3); and 50 grams per liter of reagent grade concentrated sulfuric acid (H2SO4).
The latter is equivalent to 27 milliliters per liter of reagent grade concentrated sulfuric acid, specific gravity
1.84, containing 96 percent of H2SO4.
55.3 The test solution is to be contained in a glass vessel such as a separatory funnel with the outlet
equipped with a stopcock and a capillary tube having an inside bore of 0.025 inch (0.64 mm) and a length
of 5.5 inches (140 mm). The lower end of the capillary tube is to be tapered to form a tip, the drops from
which are about 0.025 milliliters each. To preserve an effectively constant level, a small glass tube is to
be inserted in the top of the funnel through a rubber stopper and its position is to be adjusted so that, when
the stopcock is open, the rate of dropping is 100 5 drops per minute. If desired, an additional stopcock
may be used in place of the glass tube to control the rate of dropping.
55.4 The sample and the test solution are to be kept in the test room long enough to acquire the
temperature of the room, which is to be noted and recorded. The test is to be conducted at an ambient
temperature of 21.1 32.2C (70 90F).
55.5 Each sample is to be thoroughly cleaned before testing. All grease, lacquer, paint, and other
nonmetallic coatings are to be removed completely by means of solvents. Samples are then to be
thoroughly rinsed in water and dried. Care is to be exercised to avoid contact of the cleaned surface with
the hands or any foreign material.
55.6 The sample to be tested is to be supported from 0.7 1 inch (17.8 25.4 mm) below the orifice, so
that the drops of solution strike the point to be tested and run off quickly. The surface to be tested is to
be inclined about 45 degrees from horizontal material.
55.7 The stopcock is to be opened and the time in seconds until the dropping solution dissolves the
protective metallic coating, exposing the base metal, is to be measured. The end point is the first
appearance of the base metal recognizable by a change in color at that point.
55.8 Each sample of a test lot is to be subjected to test at three or more points, excluding cut, stenciled,
and threaded surfaces, on the inside surface and at an equal number of points on the outside surface, at
places where the metallic coating may be expected to be the thinnest. On enclosures made from
precoated sheets, the external corners that are subjected to the greatest deformation are likely to have
thin coatings.
55.9 To calculate the thickness of the coating being tested, select from Table 55.1 the thickness factor
appropriate from the temperature at which the test was conducted and multiply by the time in seconds
required to expose base metal as noted in 55.7.
Table 55.1
Thickness of coatings
Thickness factors 0.00001 inch (0.00025 mm) per second

Temperature, degrees F (C) Cadmium platings Zinc platings
70 (21.1) 1.331 0.980
71 (21.7) 1.340 0.990
72 (22.2) 1.352 1.000
73 (22.8) 1.362 1.010
74 (23.3) 1.372 1.015
75 (23.9) 1.383 1.025
76 (24.4) 1.395 1.033
77 (25.0) 1.405 1.042
78 (25.6) 1.416 1.050
79 (26.1) 1.427 1.060
80 (26.7) 1.438 1.070
81 (27.2) 1.450 1.080
82 (27.8) 1.460 1.085
83 (28.3) 1.470 1.095
84 (28.9) 1.480 1.100
85 (29.4) 1.490 1.110
86 (30.0) 1.501 1.120
87 (30.6) 1.513 1.130
88 (31.1) 1.524 1.141
89 (31.7) 1.534 1.150
90 (32.2) 1.546 1.160
56 Rain Test
56.1 Raintight or rainproof equipment shall be exposed to a water spray as described in 56.2 56.5. The
exposure shall not result in:
a) Entrance of water into a raintight enclosure, or
b) Entrance of water above the lowest live part or wetting of live parts in a rainproof enclosure.
Exception: Water may enter a rainproof enclosure above live parts if the design is such that no water is
visible on live parts, insulating materials, or mechanism parts and no water has entered any space above
live parts within the enclosure in which wiring may be present under any proper installation conditions.
56.2 A raintight or rainproof enclosure is to be attached to a vertical clapboard surface as in intended

service. Unspecified lengths of conduit are to be attached with normal torque and without a pipe thread
compound. At each unthreaded wiring opening, a locknut and bushing are to be used. The unattached
end of each conduit is to be covered to prevent entry of water during the test. Openings intended for the
entry of a conductor or conductors for Class 2 wiring in a low-voltage circuit are not to be sealed, and
openings in the enclosure bottom need not be closed.
56.3 The device is to be operated so that it is tested under the normal conditions judged most likely to
cause the entrance of water. It may be necessary to operate the unit under various modes of operation
and in different mounting or operating handle positions, if applicable, or to energize the unit if more
adverse conditions could result. Each exposure is to be for 1 hour. If more than one exposure is required,
the equipment is to be reconditioned, if necessary, prior to the second and each subsequent exposure so
that the results of the test will not be adversely affected by prior exposures.
56.4 At the conclusion of each test, the outside of the enclosure is to be wiped dry. The enclosure is then
to be opened for inspection.
56.5 The water spray apparatus is to consist of three spray heads mounted in a water supply pipe rack
as illustrated in Figure 56.1. Spray heads are to be constructed in accordance with Figure 56.2. The water
pressure for all tests is to be maintained at 5 psi (34.5 kPa) at each spray head. The distance between
the center nozzle and the unit is to be approximately 3 feet (0.9 m). The unit is to be brought into the focal
area of the three spray heads in such position and under such conditions that the greatest quantity of
water will enter the unit. The spray is to be directed at an angle of 45 degrees to the vertical toward the
device.
Figure 56.1
Spray-head pipe rack
Item inch mm
A 28 710
B 55 1400
C 2-1/4 55
D 9 230
E 3 75
Figure 56.2
Spray head
Item inch mm Item inch mm

A 1-7/32 31.0 N 1/32 0.80
B 7/16 11.0 P 0.575 14.61
C 9/16 14.0 0.576 14.63
D 0.578 14.68 Q 0.453 11.51
0.580 14.73 0.454 11.53
E 1/64 0.40 R 1/4 6.35
F c c S 1/32 0.80
G .06 1.52 T (No. 35)b 2.79
H (No. 9)b 5.0 U (No. 40)b 2.49
J 23/32 18.3 V 5/8 16.0
K 5/32 3.97 W 0.06 1.52
L 1/4 6.35
M 3/32 2.38
a Molded nylon Rain-Test Spray Heads are available from Underwriters Laboratories, Inc.
b ANSI B94.11 Drill Size Twist Drills, Straight Shank and Taper Shank Combined Drills, and Countersinks, ANSI 94.11M-
1979(R1987).
c Optional To serve as wrench grip.
57 Time-Calibration Verification Test
57.1 General
57.1.1 A time-delay or thermal relay that responds to a temperature-limiting control or other control
requiring a calibration-verification test see 38.5.1 or Table 38.3 is to be subjected to the following tests
in the order presented.
a) Initial time-calibration-verification Test I.
b) Initial time-calibration-verification Test II at different ambient air temperatures and voltages.
c) Endurance.
d) Time-calibration-verification after endurance.
57.2 Bimetal-heater design
57.2.1 A bimetal-heater, hot-wire, or similar device shall be time calibrated as specified in this section.
57.3 Initial time-calibration-verification Test I
57.3.1 The operating times determined in the initial time-calibration-verification tests shall be within the
tolerances allowed for the device function. See Table 38.3.
57.3.2 Initial time-calibration-verification tests shall be conducted on separate samples having the
shortest, average, and longest rated time settings, and on samples of different assigned production-time
tolerances, to represent the intended variations in a line of devices. One test is to be conducted on each
sample; or, at the manufacturers request, the time setting is to be recorded as the average of three tests.
57.3.3 For the time-to-close calibration-verification test, the device is to remain at room temperature with
the bimetal heater de-energized, until conditions have stabilized. The actuating heater is then to be
energized at rated voltage, and the time for each load circuit to close is to be determined and recorded.
The current through the load circuit is to be a value sufficient for detection purposes.
57.3.4 Room temperature is to be nominally 25C (77F), except that if the timing is severely affected by
ambient air temperature, the manufacturers specified ambient air temperature range is to be used.
57.3.5 For the time-to-open calibration-verification test, the device is to be at room temperature as noted
in 57.3.3 and 57.3.4 with the actuating heater energized at rated voltage and:
a) Maximum rated current through all load-circuit contacts, or
b) A detection current through the load contacts if current does not affect timing.
57.3.6 When thermal equilibrium is attained, the actuating heater is to be de-energized, and the time for
each load circuit to open is to be determined and recorded.
57.4 Initial time-calibration-verification Test II
57.4.1 Additional initial time-calibration-verification tests shall be conducted using the method described
in 57.3.3 57.3.6 except that the test conditions shall be:
a) Rated actuating heater voltage and an ambient air temperature of 0C (32F);
b) Rated actuating heater voltage and an ambient air temperature equal to the maximum rating,
but not less than 66C (151F);
c) Eighty-five percent of rated actuating heater voltage and room temperature; and
d) One hundred-ten percent of rated actuating heater voltage and room temperature.
57.4.2 The results are to be considered when investigating the control in the end-use equipment.
57.5 Endurance
57.5.1 An endurance test, preceded by an overload test as described in Overload Test, Section 45, shall
be conducted on one sample having the highest heating effect from the actuating heater, at maximum
current and at maximum rated ambient temperature.
57.5.2 The actuating heater is to be cycled using rated ambient temperature and rated voltage. The
number of cycles is to be as specified for the device function, see Table 38.3. The test is to be conducted
at a maximum rate of 1 cycle per minute or as specified in note a to Table 46.1. Only one pole of a
multistage device is to be loaded, unless loading of the other poles contributes to timing differences.
Additional overload and endurance tests are to be conducted on separate samples for additional ratings.
The samples need not be calibrated, unless such ratings contribute to timing differences.
57.6 Time-verification and dielectric voltage-withstand tests after endurance
57.6.1 The sample subjected to the endurance test shall be recalibrated using the method specified for
the Initial Time-Calibration-Verification Test I. The test results are to be judged by the requirements for the
device function, see Table 38.3. The dielectric voltage-withstand test is then to be conducted in
accordance with the Dielectric voltage-Withstand Test, Section 47.
57.7 Other designs
57.7.1 A limiting-type time-delay relay of a design not contemplated by these requirements shall be tested
in a manner appropriate for its design to obtain the results contemplated by 44.3 44.10 or 57.3.2
57.6.1.
58 Snap-On Covers Test
58.1 A snap-on cover that gives access to live parts or film-coated wire and that does not have a
tool-operated fastener shall have no apparent means of removal; such as an extending tab, and shall
withstand the following tests:
a) A cover that can be released from securement with one hand by a squeezing force shall, when
subjected to this test, either not be released, or when the cover is partially released, the opening
between cover and case shall not permit the probe illustrated in Figure 7.1 to touch live parts or
film-coated wire, require a subsequent operation to remove the cover, and comply with the tests
described in (b) and (c) in the partially-released position. A squeezing force of 14 pounds (62.3 N)
or less is to be applied at any two points, the distance between which shall not exceed 5 inches
(127.0 mm), as measured by a tape stretched tightly over that portion of the surface of the cover
that would be encompassed by the palm of the hand. The test shall be performed before and after
ten removal and replacement operations.
b) A cover shall, when subjected to this test, either not become disengaged, or when the cover
is partially released, the opening between cover and case shall not permit the probe illustrated in
Figure 7.1 to touch live parts or film-coated wire, require a subsequent operation to remove the
cover or enlarge the opening, and comply with the tests described in (a) and (c) in the partially
removed position. A direct pull of 14 pounds is to be applied. The cover is to be pried at any two
convenient points in one test and at any point in a separate test. The test is to be performed
before and after ten removal and replacement operations.
c) A cover shall withstand an impact force of 1 foot-pound (1.35 J) applied to accessible faces of
the cover one blow per face without being displaced, and there shall be no damage to internal
parts or malfunction of the control as a result of this test. A steel ball approximately 2 inches (50.8
mm) in diameter and weighing approximately 1.18 pounds (535 g) is to be used to apply the
impact.
59 Bonding Conductor Tests
59.1 Overcurrent
59.1.1 A bonding conductor that does not comply with the requirement in 22.2.8 is acceptable if:
a) The bonding conductor does not open when carrying for the time specified in Table 59.1, a
current that equals twice the branch-circuit overcurrent-device rating see 59.1.3 but not less
than 40 amperes; and
b) None of three samples of the bonding conductor, selected at random, opens during a limited
short-circuit test with a current as specified in Table 50.2 when in series with a fuse as described
in 59.1.2 and 59.1.3.
Table 59.1
Duration of current-flow, bonding-conductor test
Overcurrent-device rating, amperes Minimum duration of current flow, minutes

30 or less 2
31 60 4
61 100 6
59.1.2 The circuit for the test described in 59.1.1(b) is to have a power factor of 0.9 1.0 and is to be
limited to the current specified in Table 50.2, at the voltage specified in Table 38.1. The open-circuit
voltage of the test circuit is to be 100 105 percent of the specified voltage. The circuit is to be connected
through a nonrenewable fuse that does not open in less than 12 seconds when carrying twice its rated
current. One test is to be performed on each of three samples of the bonding conductor subject to the test.
59.1.3 The fuse mentioned in 59.1.1 is to have a current rating equal to that of the branch-circuit
overcurrent-device to which the equipment will be connected, but not less than 20 amperes.
59.2 Resistance
59.2.1 The resistance between two parts connected by a bonding conductor shall not be more than 0.1
ohm.
59.2.2 The resistance is to be kept as low as possible in the event that a control is subject to a 0.1 ohm
resistance requirement in end-use equipment.
59.2.3 Whether equipment complies with the requirements in 59.2.1 may be determined by any suitable
instrument. If the results are unacceptable, an alternating current of at least 20 amperes from a power
supply of not more than 12 volts is to be passed from the point of connection of the equipment grounding
means to the metal part in the grounding circuit, and the resulting drop in potential is to be measured
between the two points. The resistance in ohms is to be determined by dividing the drop in potential in
volts by the current in amperes passing between the two points. The grounding conductor of a
power-supply cord is not to be included in this measurement.
60 Permanence of Marking Test
60.1 General
60.1.1 Unless known to be acceptable for the application, a pressure sensitive label that is required to be
permanent shall be tested as described in 60.1.2.
60.1.2 After being subjected to the conditions described in 60.1.3 and 60.2 60.6, a pressure-sensitive
label or a label secured by cement or adhesive is considered to be permanent if immediately following
removal from each test medium and after being exposed to room temperature for 24 hours:
a) Each sample demonstrates good adhesion and the edges are not curled;
b) The label resists defacement or removal as demonstrated by scraping across the test panel
with a flat metal blade 1/16 inch (1.6 mm) thick, held at right angles to the test panel; and
c) The printing is legible and is not defaced by rubbing with thumb or finger pressure.
60.1.3 Labels intended for indoor residential equipment may be subjected to the humidity test specified
in 60.6.1 in place of the immersion test specified in 60.3.1.
60.2 Oven-aging
60.2.1 Three samples of the label applied to test surfaces as in the intended application are to be
conditioned for 240 hours in an air oven maintained at the temperature specified in Table 60.1.
Table 60.1
Oven-aging test temperature
Maximum temperature during normal temperature test of

surface to which applied Oven temperature
C F C F
60 or less 140 or less 87 189
80 or less 176 or less 105 221
100 or less 212 or less 121 250
125 or less 257 or less 150 302
150 or less 302 or less 180 356
Over 150 302 a
a A label that is applied to a surface attaining a temperature greater than 150C (302F), during the normal temperature test, is
to be oven-aged at a temperature representative of the temperatures attained by the appliance during normal and abnormal
operation.
60.3 Immersion
conditioned for 24 hours in a controlled atmosphere maintained at 23 2C (73 4F) with a relative
humidity of 50 5 percent. The samples are then to be immersed for 48 hours in water at a temperature
of 21 2C (70 4F).
60.4 Standard-atmosphere
conditioned for 72 hours in a controlled atmosphere maintained at 23 2C (73 4F) with a relative
humidity of 50 5 percent.
60.5 Unusual condition exposure
60.5.1 If a label is exposed to unusual conditions in service, three samples of the label applied to test
surfaces as in the intended application are to be conditioned for 24 hours in a controlled atmosphere
maintained at 23 2C (73 4F) with a relative humidity of 50 5 percent. The samples are then to be
immersed for 48 hours in a solution representative of service use maintained at the temperature the
solution would attain in service, but not less than 23 2C (73 4F).
60.5.1 revised October 24, 1995
60.6 Humidity
60.6.1 Three samples of the test panels are to be suspended in a humidity cabinet at 32 2C (90 4F)
with an 85 5 percent relative humidity for 72 hours.
61 Strength of Adjustment Stop Test
61.1 An adjustment stop of a control shall not be damaged so as to cause a reduction of spacings, too
high a temperature setting, or other condition that may result in a risk of fire, electric shock, or injury to
persons when subjected for 15 seconds to the tests described in 61.3 61.8.
61.2 As a result of the tests specified in this section:
a) If a change in setpoint is a factor, a calibration-verification test as specified in Calibration-

Verification Test, Section 44, is to be conducted before and after the strength test. The setpoint
after the test shall not differ from the as-received value more than the amount specified in
Section 44;
b) Spacings shall not be reduced to a value less than those specified in Spacings, Section 32;
and
c) The marked off position, if any, shall comply with the requirements in 11.5 11.12.
61.3 Breakage of the adjustment is acceptable if the requirements in 61.2 are met and the adjustment
stop withstands one-half the specified test value.
61.4 For a control that is operated by a push, pull, slide, toggle, or lever adjustment, a force is to be
applied to the free end of the adjustment in line with the intended movement in each direction of operation.
The force is to be 20 pounds (89 N) for a commercial or industrial control and 10 pounds (45 N) for a
household product control. A separate sample is to be used for each test.
61.5 A control adjustment operated as described in 61.4 and intended for use with an extended operator,
handle, or lever is to be tested with the in-line force applied to the free end of an extension representing
the intended end-use application.
61.6 For a control that is operated by a rotary adjustment intended for use with a knob having a grip
diameter or grip length of 1 inch (25.4 mm) or less, a torque is to be applied to the shaft in each direction
of intended operation. The torque is to be 9 pound-inches (1.0 Nm) for a commercial or industrial control
and 7 pound-inches (0.8 Nm) for a household product control. A separate sample is to be used for each
test.
61.7 A control that is operated by a rotary adjustment intended for use with a knob having a grip diameter
or grip length of more than 1 inch (25.4 mm) is to be subjected to a torque that is proportionally greater
than that specified in 61.6, based on the larger grip diameter or grip length of the knob used. The value
for the torque to be used is to be determined by the formula:
in which:
T is the test torque in pound-inches (Nm),
D1 is the grip diameter or grip length, as applicable, in inches (m),
D is 1 inch (0.025 m),
k is 9 pound-inches (1.0 Nm) for a commercial or industrial control, or 7 pound-inches (0.8

Nm) for a household control.
61.8 If a lever arm is intended to be attached to a rotary-control shaft, the assembly is to be tested as
described in 61.4 with the force applied to the free end of the lever.
61.9 If an adjustment means is not provided with a control, the manufacturer is to assign a maximum
dimension for the knob, lever, toggle, or the like to be used with the control, and this dimension is to be
used for determining the torque value.
62 Polymeric Materials Tests
62.1 General
62.1.1 An assumed ambient temperature of 40C (104F) is to be used in determining the required
temperature rating of the polymeric enclosure.
62.1.2 An enclosure of polymeric material, shall comply with the applicable requirements in Table 62.1
and the requirements in 62.3.1 62.3.3.
Table 62.1
Tests related to the use of polymeric materials for enclosures
Part 1 Conditions of use 1 2 3 4
Material is used as the indirect support of live parts. The No No Yes Yes
material is used to support electrical components that
contain live parts, for example, switches, relays, terminal
blocks, and the like
Part 2 Equipment description
Equipment is intended for indoor use Yes No Yes No

Equipment is intended for outdoor use No Yes No Yes
Part 3 Applicable requirements
Tests Paragraphs
1. Flammability 62.2.1 62.2.10 X X X X
2. UV resistance 62.4.1 62.4.7 X X
3. Water and moisture,
immersion and exposure:
Properties 62.5.1 62.5.2 X X
Dimensions X X X X
4. Volume resistivity 62.6.1, 62.6.2 X X X X
5. Resistance to hot wire ignition 62.7.1 62.7.3 X X X X
6. Heat deflection temperature 62.8.1 X X X X
7. Resistance to impact 62.9.1 62.9.3 X X X X
8. Crush resistance 62.10.1, 62.10.2 X X X X
9. Mold-stress relief 62.11.1, 62.11.2 X X X X
10. Dielectric strength 62.12.1 X X X X
11. Conduit connection 62.13.1.1 62.14. X X X X
12. Abnormal operation 62.15.1 62.15.3 X X X X
13. Resistance to ignition 62.16.1 X X
a Reference is to be made to Part 1 and Part 2 to find the column that matches the combination of conditions of use for the
polymeric material and the equipment under consideration. The X appearing in that column in Part 3 designates the
applicable requirements.

62.2 Flammability of enclosure 5 inch (127 mm) flame
62.2.1 Three samples of the equipment or three test specimens consisting of a part or section of the
polymeric enclosure are to be subjected to this test. Consideration may be given to leaving in place
components and other parts that may influence the performance.
62.2.2 The three test samples or specimens shall perform acceptably when subjected to the test. If one
of the three samples does not comply, the test is to be repeated on a new sample or specimen with the
flame applied under conditions the same as those under which unacceptable results were obtained. If the
new sample or specimen complies with the requirements, the material is acceptable.
62.2.3 Each sample is to be subjected to five 5-second applications of the test flame with an interval of
5 seconds between applications in accordance with 62.2.5 62.2.10:
a) The enclosure material shall not continue to burn for more than 1 minute after the fifth
application of the test flame;
b) Particles shall not drip from the test sample at any time during the test; and
c) The material shall not be destroyed in the area of the test flame to such an extent that the
integrity of the enclosure is affected.
62.2.4 The test samples are to be conditioned by placing them in an air-circulating oven maintained at a
uniform temperature not less than 10C (18F) higher than the maximum temperature of the material
measured under normal operating conditions but not less than 70C (158F) in any case. The samples
are to remain in the oven for 7 days. Prior to the test, the samples are to be returned to room temperature.
Exception: The test may be conducted on unconditioned test samples if it has been determined that the
material used as the enclosure does not exhibit a reduction in its flame resistant properties as a result of
long-term thermal aging, and the thermal-aging program used for such determination included specimens
having a thickness equal to or less than the wall thickness of the polymeric enclosure.
62.2.5 The test is to be conducted in a three-sided enclosure that is 12 inches (305 mm) wide, 14 inches
(356 mm) deep, and 24 inches (610 mm) high. The top and front of the enclosure are to be open. The
room or hood in which the enclosure is located for the test is to be adequately ventilated, but drafts are
to be prevented from affecting the test flame.
62.2.6 A 4-inch-square (102-mm-square) specimen of the molded composition in sheet form having a
thickness equal to the minimum thickness used for a part or the body of a box is to be secured with its
vertical axis in the center of the enclosure and with both axes parallel to the back of the enclosure. See
Figure 62.1.
Figure 62.1
Essential dimensions of apparatus and specimen
Figure 62.1 revised (date of publication)
SI values for the dimensions in this figure are:
Inches Millimeters
1-1/2 38
2 51
4 102
MARCH 4, 1999 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 114A
62.2.7 A Tirrill gas burner to which a gas pilot light is attached is to supply the test flame. The barrel of
the burner is to extend 4 inches (102 mm) above the air inlets and its inside diameter is to be 3/8 inch
(9.5 mm). While the barrel is vertical, the overall height of the flame is to be adjusted to 5 inches (127
mm). The blue inner cone is to be 1-1/2 inches (38 mm) high. Without disturbing the adjustments for the
height of the flame, the valves supplying gas to the burner and pilot flames are to be closed.
114B TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 MARCH 4, 1999

62.2.8 A wedge to which the base of the burner can be secured is to be provided for tilting the barrel 20
degrees from the vertical while the longitudinal axis of the barrel remains in a vertical plane. The burner
is to be secured to the wedge and the assembly is to be placed in an adjustable jig that is attached to the
floor of the enclosure. The jig is to be adjusted laterally see Figure 62.1 to place the longitudinal axis
of the barrel in the same vertical plane as the vertical axis of the specimen. The plane is to be parallel to
the sides of the enclosure.
62.2.9 The jig is also to be adjusted toward the rear or front of the enclosure see Figure 62.1 to
position point A, (which is the intersection of the longitudinal axis of the barrel with the plane of the tip of
the barrel), 1-1/2 inches (38 mm) from point B at which the extended longitudinal axis of the barrel meets
the front surface of the specimen. Point B is the point at which the tip of the inner blue cone will touch the
specimen. The specimen is to be adjusted vertically to place point B at the center of the specimen.
62.2.10 The valve supplying gas to the pilot is to be opened and the pilot flame lit. The valve supplying
gas to the burner is to be opened to apply the flame to the specimen automatically. This valve is to be
held open for 5 seconds and then closed for 5 seconds. This procedure is to be repeated four times for
a total of five applications of flame to the specimen.
62.3 Thermal aging
62.3.1 A material shall be resistant to thermal degradation at the maximum temperature to which it is
exposed during normal use of the equipment. The acceptability of the thermal aging characteristics of the
material are to be investigated by any one of the following procedures:
a) The material shall have a temperature index, based on historical data or a long-term thermal
aging program, that indicates its acceptability for use at the temperature involved;
b) The polymeric material is considered to be acceptable from a thermal aging standpoint if the
maximum temperature to which it is exposed during normal use of the equipment does not exceed
65C (149F); or
c) The polymeric material is considered to be acceptable from the thermal aging standpoint, if:
1) The maximum temperature to which the material is exposed during normal use is
between 65 80C (149 176F), and
2) The appliance complies with the requirements of 62.3.2 and 62.3.3.
62.3.2 With reference to 62.3.1(c)(2), three samples of the equipment are to be placed in an
air-circulating oven for 1000 hours. In some cases, parts of the equipment may be sufficient if such parts
are representative of the complete equipment with respect to the polymeric enclosure. The temperature of
the oven shall be maintained at 85C (185F) if the maximum temperature on the material during normal
use is higher than 65C (149F) but not higher than 75C (167F). The temperature of the oven shall be
maintained at 95C (203F) if the maximum temperature on the material during normal use is higher than
75C but not higher than 80C (176F).
62.3.3 After the equipment has cooled to room temperature following the oven test described in 62.3.2,
the enclosure shall be such that the equipment complies with the requirements for accessibility,
mechanical strength, flammability, and the like. Severe distortion that prevents replacement of
components associated with the equipment is not acceptable.
62.4 Exposure to ultraviolet light
62.4.1 A polymeric material used for the enclosure of equipment intended for outdoor installation shall be
resistant to degradation when exposed to ultraviolet light. The flammability classification of the material
shall not be reduced as a result of the ultraviolet conditioning. The physical property values after ultraviolet
conditioning shall be at least 70 percent of the values determined before ultraviolet conditioning. The
acceptability of the materials resistance to ultraviolet degradation shall be investigated by the procedure
described in 62.4.2 and 62.4.3.
62.4.2 Using standard test procedures, property values for the material are to be determined both before
and after exposure to ultraviolet light for 720 hours. Two sets of three samples each are to be used for
the tests.
62.4.3 The following properties are to be included in the evaluation:
a) Tensile strength Test Method for Tensile Properties of Plastics, ASTM D638-91;
b) Flexural strength Test Methods for Flexural Properties of Unreinforced and Reinforced
Plastics and Electrical Insulating Materials, ASTM D790-91;
c) Impact resistance Test Methods for Impact Resistance of Plastics and Electrical Insulating
Materials, ASTM D256-90b or Test Method for Tensile-Impact Energy to Break Plastics and
Electrical Insulating Materials, ASTM D1822-89;
d) Flammability Standard for Tests for Flammability of Plastic Materials for Parts in Devices and
Appliances, UL 94.
62.4.4 The samples are to be exposed to ultraviolet light from two enclosed carbon arcs formed between
vertical electrodes, 1/2 inch (12.7 mm) in diameter, located at the center of a revolvable vertical metal
cylinder 31 inches (787 mm) in diameter and 17-3/4 inches (451 mm) high. The arcs are to operate with
approximately 15 17 amperes, and the potential across the arcs is to be approximately 120 145 volts
alternating current. The arcs are to be enclosed by clear globes of No. 9200 PX Pyrex glass.
62.4.5 The cylinder is to be rotated about the arcs at one revolution per minute and a system of nozzles
is to be provided so that each sample is sprayed, in turn, with water as the cylinder revolves. The
temperature within the cylinder while the apparatus is in operation is to be approximately 60C (140F).
62.4.6 The samples are to be mounted vertically on the inside of the cylinder in the ultraviolet light
apparatus, with the width of the samples facing the arcs and not touching each other.
62.4.7 During each 20 minute operating cycle of the apparatus, two sets of samples are to be exposed
to light from the carbon arcs for 17 minutes, and to water spray with light for 3 minutes. The test is to be
continued until one set of samples has been exposed to ultraviolet light for a total of 306 hours and
ultraviolet light and water for a total of 54 hours and until the second set of samples has been exposed
for 612 hours and 108 hours, respectively, to the two different conditions of testing. After the specified test
exposure for each set, the samples are to be removed from the test apparatus, examined for signs of
deterioration such as crazing or cracking, and retained under conditions of ambient room temperature and
atmospheric pressure for not less than 16 nor more than 96 hours before being subjected to the tests
specified in 62.4.3.
62.5 Water exposure and immersion
62.5.1 A polymeric material used for an enclosure intended for outdoor installation shall not be degraded
as a result of exposure to water as described in 62.5.2 (a) or (b) to such extent that:
a) The flammability classification is reduced, or
b) Any other physical properties referenced in 62.4.3 are reduced to less than 50 percent of the
value obtained with the material in the as-received condition.
62.5.2 Using standard test procedures, property values for the material are to be determined both before
and after the conditioning described in (a) or (b):
a) For material classified as 5V, specimens are to be immersed in distilled water at 82C
(180F) for 7 and 14 days. A complete change of water is to be made on each of the first 5
days. Following the immersions, those specimens to be subjected to flammability tests are to be
conditioned in air at 23.0 2.0C (73.4 3.6F) with a 50 5 percent relative humidity for 2
weeks. Following the immersions, those specimens to be subjected to physical property tests
are to be immersed in distilled water at 23.0 2.0C for 1/2 hour.
b) For material classified as V-0, V-1, V-2, or HB, specimens are to be immersed in distilled
water at 70C (158F) for 7 and 14 days. A complete change of water is to be made on each of
the first 5 days. Following the immersions, the specimens to be subjected to flammability or
physical property tests are to be immersed in distilled water at 23.0 2.0C for 1/2 hour.
62.5.3 A material that exhibits any dimensional change greater than 0.1 percent after immersion for 24
hours in distilled water in accordance with the Test Method for Water Absorption of Plastics, ASTM
D570-81(1988) shall be the subject of an appropriate investigation, which may consist of immersion of the
entire enclosure to determine the extent of influence of the dimensional change.
62.5.3 revised May 4, 2001
62.6 Volume resistivity
62.6.1 The volume resistivity of a polymeric material shall not be:
a) Less than 50 megohm-centimeters in the as-received condition; or
b) Less than 10 megohm-centimeters after exposure for 96 hours to moist air having a relative
humidity of 85 5 percent at a temperature of 32.0 2.0C (89.6 3.6F).
62.6.2 The volume resistivity is to be determined in accordance with the Test Methods for D-C Resistance
or Conductance of Insulating Materials, ASTM D257-91.
62.7 Resistance to hot-wire ignition
62.7.1 A polymeric material shall:
a) Not ignite within 15 seconds when subjected to the test described in 62.7.2 and 62.7.3; or
b) Withstand without ignition of the enclosure 110, 135, and 200 percent of branch-circuit
protection current (20 ampere minimum) passed through current-carrying members in proximity
to the enclosure for 4 hours, 1 hour, and 2 minutes, respectively.
62.7.2 Each of three samples of the material, 5 inches (127 mm) long, 1/2 inch (12.7 mm) wide, and
having a thickness not more than the minimum thickness of the enclosure at any point, is to be wrapped
with five turns of resistance wire, with a spacing of 1/4 inch (6.4 mm) between turns.
62.7.3 The wire is to be No. 24 AWG (0.21 mm2), iron-free, 20 percent chromium and 80 percent nickel,
running 1.61 ohms per foot (5.28 ohms/m) and 865 feet per pound (40m/kg). The wire is to carry such
current as to dissipate 65 watts, and the measurement of the time is to begin when the current begins to
flow.
62.7.3 revised May 4, 2001
62.8 Heat deflection temperature
62.8.1 The heat deflection temperature measured at 66 pounds per square inch (455 kPa) shall be at
least 10C more than the maximum operating temperature of the material in the equipment when tested
as described in the Test Method for Deflection Temperature of Plastics Under Flexural Load, ASTM
D648-82(1988). Materials having a heat deflection temperature less than this may be investigated on the
basis of the results of the 7-hour oven test used to evaluate the effects of mold-stress relief.
62.9 Resistance to impact
62.9.1 Conditioning of the equipment as described in 62.9.2 and 62.9.3 shall not:
a) Reduce spacings below the minimum acceptable values;
b) Make any bare live parts or internal wiring accessible to contact;
c) Have an undue adverse effect on the insulation; or
d) Produce any other condition that might increase the risk of fire, electric shock, or damage of
the equipment.
62.9.2 Each of three samples of the equipment shall be subjected to an impact on any surface that is
exposed to a blow during normal use or during installation. For an enclosure having no surface area
exceeding 40 square inches (258 cm2), the impact is to be 5 foot-pounds (6.8 J) produced by dropping a
steel sphere 2 inches (51 mm) in diameter and weighing 1.18 pounds (0.535 kg) from a height of 51
inches (1.3 m). For an enclosure having any surface area of more than 40 square inches, the impact is
to be 10 foot-pounds (13.6 J) produced by dropping a steel sphere 2 inches in diameter and weighing 1.18
pounds from a height of 102 inches (2.6 m). Tests may be conducted at any ambient temperature within
the range of 10 40C (50 104F).
62.9.3 Each of three samples of the equipment shall be cooled to 0C (32F) for indoor applications and
minus 32C (minus 26F) for outdoor applications and maintained at that respective temperature for 3
hours. Immediately following removal from the cold chamber, the sample shall be subjected to the impact
described in 62.9.2.
62.10 Crush resistance
62.10.1 Conditioning of the equipment as described in 62.10.2 shall not cause any of the conditions
described in 62.9.1 (a) (d) to occur.
62.10.2 Three samples of the equipment shall be backed on the mounting side by a fixed, rigid supporting
surface. Crushing force shall be applied to the side opposite the mounting surface by applicators having
flat surfaces, each 4 by 10 inches (102 by 254 mm). Each applicator is to exert 100 pounds (445 N) on
the sample. As many applicators are to be used as the sample can accommodate on the surface opposite
the mounting surface, based on an arrangement of applicators illustrated in Figure 62.2. Tests are to be
conducted at any ambient temperature within the range of 10 40C (50 104F).
Figure 62.2
Arrangement of applicators
62.11 Mold-stress evaluation
62.11.1 Conditioning of the equipment as described in 62.11.2 shall not cause any of the conditions
described in 62.9.1 (a) (d) to occur.
62.11.2 Three samples of the complete equipment are to be conditioned in accordance with either (a) or
(b):
a) The samples are to be placed in an air-circulating oven maintained at a uniform temperature

at least 10C (18F) higher than the maximum temperature of the material measured under
normal operating conditions, but not less than 70C (158F) in any case. The samples are to
remain in the oven for 7 hours. After careful removal from the oven and return to room
temperature, each sample is to be investigated to determine whether it complies with the
requirements in 62.11.1.
b) The samples are to be placed in a test cell. The circulation of air within the cell is to simulate
normal room conditions. The air temperature within the cell, as measured at the surface
supporting the equipment, is to be maintained at 60C (140F). The equipment is to be operated
as in the normal temperature test for 7 hours. After careful removal from the test cell and return
to room temperature, each sample is to be investigated to determine whether it complies with the
requirements in 62.11.1.
62.12 Dielectric strength
62.12.1 Material of an enclosure depended upon as electrical insulation shall have a dielectric strength at
60 hertz of 175 volts per mil when tested in a 1/32 inch (0.8 mm) thickness.
62.13 Conduit connections
62.13.1 General
62.13.1.1 A polymeric enclosure intended for connection to a rigid conduit system shall withstand, without
pulling apart, or damage such as cracking and breaking, the pullout test, torque test, and bending test
described in 62.13.2.1 62.13.4.2.
Exception: The torque test does not apply to an enclosure that is not provided with a preassembled hub
and that has instructions stating that the hub is to be connected to the conduit before being connected to
the enclosure.
62.13.2 Pullout
62.13.2.1 The enclosure is to be suspended by a length of rigid conduit installed in one wall of the
enclosure and a direct pull of 200 pounds (90.8 kg) is to be applied for 5 minutes to a length of conduit
installed in the opposite wall.
62.13.3 Torque
62.13.3.1 The enclosure is to be securely mounted as intended in service. A torque is to be applied to a

length of installed conduit in a direction tending to tighten the connection. The tightening torque for rigid
conduit threaded into the opening in the enclosure is to be 800 pound-inches (90.4 Nm) for 3/4-inch and
smaller trade sizes, 1000 pound-inches (113 Nm) for 1-, 1-1/4-, and 1-1/2-inch trade sizes, and 1600
pound-inches (181 Nm) for 2-inch and larger trade sizes. The lever arm is to be measured from the center
of the conduit.
Exception: An end-of-line enclosure an enclosure that is intended to be connected at the end of a run
of conduit and has only one 3/4-inch maximum trade size opening for the connection of conduit need
only be subjected to a tightening torque of 200 pound-inches (22.6 Nm).
62.13.4 Bending
62.13.4.1 A length of conduit at least 1 foot (305 mm) long of the proper size is to be installed in the
center of the largest unreinforced surface, or in a hub or an opening if provided as part of the enclosure.
The enclosure is to be securely mounted as intended in service, but positioned so that the installed
conduit extends in a horizontal plane. The weight necessary to produce the desired bending moment
when suspended from the end of the conduit is to be determined from the formula:
in which:
W is the weight, in pounds, to be hung at the end of the conduit;
L is the length of the conduit, in inches, from the wall of the enclosure to the point at which the
weight is suspended;
C is the weight of the conduit, in pounds; and
M is the bending moment required in pound-inches.
62.13.4.2 The bending moment for the test described in 62.13.4.1 is to be as specified in Table 62.2. If
the enclosure surface may be installed in either a vertical or horizontal plane, the vertical bending moment
value is to be used.
Exception: For an end-of-line enclosure see the Exception to 62.13.3.1 the bending moment need
only be 150 pound-inches (16.9 Nm).
Table 62.2
Bending moment
Normal mounting Bending moment, pound-inches (Nm)

plane of enclosure Conduit size,
surface inches Metallic conduit Nonmetallic conduit
Horizontal All 300 (33.9) 300 (33.9)
Vertical 1/2 3/4 300 (33.9) 300 (33.9)
1 up 600 (67.8) 300 (33.9)
Note The test may be terminated prior to attaining the values specified if the deflection of the conduit exceeds 10 inches (254
mm) for a 10 foot (3.1 m) length of conduit.
62.14 Knockouts
62.14.1 If knockouts are incorporated in an enclosure made of polymeric material, they shall remain in
place when subjected to a force of 20 pounds (89 N) applied at right angles by means of a mandrel with
a 1/4-inch (6.4-mm) diameter flat end. The mandrel shall be applied at the point most likely to cause
movement of the knockout.
62.15 Abnormal operation
62.15.1 When tested in accordance with 62.15.2 there shall be no ignition of the enclosure material,
exposure of live parts, emission of flame or molten metal nor glowing or flaming of the combustible
material upon which the equipment is mounted. The disturbance shall be confined by the enclosure.
Exception: See 62.15.3.
62.15.2 The equipment is to be operated under the most adverse condition of abnormal operation such
as stalled-rotor, blocked-armature of relay, burnout of transformer or operation with current-carrying parts
short-circuited, and the like. During the test, the equipment is to rest on white tissue paper on a softwood
surface and is to be operated continuously until the ultimate results have been determined. In most cases,
continuous operation will be necessary until constant temperatures are reached.
62.15.3 Warping, shrinkage, expansion, or cracking of the enclosure materials is acceptable, as is any
emission of flame or molten metal through an opening normally provided in the enclosure not an opening
that occurs as a result of this test.
62.16 Resistance to ignition
62.16.1 A polymeric material shall not ignite when subjected to at least 30 high-current arcs for V-5
material and 60 arcs for HB material in accordance with the High-Current Arcs Ignition Test described in
the Standard for Polymeric Materials Short Term Property Evaluations, UL 746A. The electrodes are to
be positioned on the surface of the material during the test. Additional consideration shall be given when
the equipment is protected by an overcurrent device rated more than 30 amperes.
Exception: Materials not meeting the requirement in 62.16.1 may be additionally evaluated by
interrupting the available energy current, voltage and power factor of the device itself 30 times for V-5
material and 60 times for HB material on the surface of the material without ignition of the enclosure.
62.16.1 revised June 2, 1998
62.17 Creep and overcurrent
62.17.1 If the continuity of the grounding system relies on the integrity of a polymeric enclosure, various
samples shall be subjected to creep tests conducted at various oven-conditioning temperatures and
overcurrent tests shall be conducted at 200 percent of the rated current of the branch-circuit-protective
device.
63 Class 2 Power Sources and Circuit Tests
63.1 General
63.1.1 For Class 2 power sources and circuits, the tests described in this section, the sequence of
conducting the tests and the number of samples for each test is specified in Table 63.1. A sample may
be used for more than one test if it is not damaged in a previous test. If a test results in damage to the
power source, additional samples may be necessary to complete the test series. Unless otherwise
specified, each test is to be conducted at the supply voltage specified in Table 63.2.

Table 63.1
Test sequence and number of samples
Number of
Test sequence Paragraph reference Test samplesa
1 63.3.1 Open-circuit secondary voltage 3
2 63.4.1 63.6.2 Output circuit and power 3
3 63.7.1 63.7.3 Calibration of overcurrent-protective devices 3
4 63.8.1 63.8.3 Rated secondary output 3
5 63.9.1 Rated output heating 1
6 63.10.1 Dielectric voltage withstand 1
7 63.11.1 63.11.3 Component breakdown 1 or more
8 63.12.1 63.12.7 Overload heating 1 or more
9 63.13.1 Repeat dielectric voltage withstand 1 or more
10 63.14.1 63.14.2 Overload of overcurrent- or overtemperature- 3
protective devices
11 63.15.1 63.15.2 Endurance of automatic reset overtemperature- 3
protective devices
a The same samples are to be used for these tests in the sequence indicated; however, if any nonreplaceable protective device
opens or a coil burns open as permitted in 63.4.2 63.8.1 and 63.12.2 63.13.1, additional samples are to be used for the
remaining tests. These additional samples need not be subjected to the preceding tests.
Table 63.2
Values of test voltage
Rated primary voltage Test voltage

120 or less 120a,b
121 219 Rated voltagea
220 240 240
254 277 277
440 480 480
550 600 600
a If the rated voltage is expressed as a range, the maximum voltage of the range is to be used.
b If a transformer is rated less than 110 volts and is not intended for use on a 110 120 volt circuit, the transformer shall be
marked as indicated in 69.4 and the test voltage is to be the rated voltage.
63.1.2 For the output current and power test, calibration of overcurrent protective devices test, overload
heating test, overload of overcurrent- or overtemperature-protective devices test, and endurance of
automatic reset overtemperature protective devices test specified in this section, all exposed dead metal
parts of the power source are to be connected to the live pole least likely to strike ground through a
3-ampere non-time delay type fuse. The power source is to be connected to a circuit having 20-ampere
branch-circuit protection. The power source is to be supported on a tissue paper covered softwood
surface, and is to be covered with a double layer of cheesecloth conforming to the outline of the power
source. The cheesecloth is to be bleached untreated cotton cloth running 14 15 square yards per pound
(26 28m2/kg) and for any square inch a count of 32 threads in one direction and 28 in the other direction
(for any square centimeter, 13 threads in one direction and 11 in the other direction).
63.1.3 During the tests mentioned in 63.1.2, a risk of fire or electric shock is considered to exist if any of
the following occur:
a) Opening of branch-circuit protection;
b) Opening of grounding fuse;
c) Charring of cheesecloth;
d) Emission of flame or molten material from the transformer enclosure;
e) Development of any opening in the enclosure that exposes live parts at a potential of more
than that specified in Table 63.3 to any other part or to ground;
f) Noncompliance with the repeat dielectric voltage-withstand test in 63.13.1;
g) Exceeding the applicable values in Tables 63.3 and 63.4; or
h) Rise of the temperature on the enclosure exceeding 60C (108F).
Exception: The temperature rise on the enclosure during the test may be greater than 60C but
not greater than 125C (225F), if the transformer open-circuits without the emission of flame or
molten material and without other evidence of risk of fire, electric shock, or injury to persons, in
less than 1 hour after the primary winding is energized.
63.1.4 If a portion of an isolated-limited-secondary or electronic circuit is connected to low-voltage

field-wiring terminals, one set of samples is to be subjected to the shorted-secondary test described in
49.5 and a second set of samples is to be tested as specified in this section, but with the load applied at
the equipment output terminals. The energy level at the equipment output terminals, the temperatures
measured, and opening of the overcurrent protective device shall comply with the requirements for a
Class 2 power source.
Table 63.3
Maximum voltage
Alternating voltage, direct voltage, Fundamental frequency,

and combinations thereof, where the (fo) hertz Peak volts
change in instantaneous voltage for Wet contact likely to
a duration equal to 5 percent of the occurb
period of the fundamental frequency Instantaneous More than
of the waveform is:a Row voltage polarity but Less than No Yes
Column 1 2 3 4 5
0 3 60 30
3 4 55 27.5
4 5 50 25
5 6 45 22.5
6 7 40 20
7 8 35 17.5
For any duration, greater than: 8 9 30 15
9 10 25 12.5
A. 20 volts where wet contact 10 200 24.8 12.4
is not likely to occur, or
A does not reverse 200 300 26 13
300 400 28 14
B. 10 volts for locations 400 500 31 15.5
where wet contact is likely to
occur
500 600 34 17
600 700 37 18.5
700 800 41 20.5
800 900 46 23
900 1000 51 25.5
1000 1400 56 28
1400 60 30
B reverses Values to be determined by an investigation
For all durations, not more than: C does not reverse Any 60 30
A. 20 volts where wet contact 30 V peak
is not likely to occur, and and 42.4 Vd
60 V peak peak-to-
B. 10 volts for locations and 84.8 Vc peak
where wet contact is likely to peak-to-
occur D reverses Any peak
NOTES
1 The peak output voltage is to be measured with the input voltage applied in accordance with Table 38.1.
2 The allowable voltage is not specified for the possible nonrepetitive transient wave during initial manual turn-on or turn-off of
the power source or equipment.
a The change in instantaneous voltage at 5 percent of the period of the fundamental frequency of the waveform is to be
determined by taking any 18-degree segment along the waveform and determining the change in instantaneous voltage in that
segment. See Figure 63.1
b Wet contact likely to occur applies to parts of outdoor equipment, such as automatic lawn sprinkling systems, and indoor
equipment, such as controls for bathroom plumbing equipment.
c For a sinusoidal wave, 84.8 volts peak-to-peak equals 30 volts rms.
d For a sinusoidal wave, 42.4 volts peak-to-peak equals 15 volts rms.
Figure 63.1
Sine wavea,c
a Values of the sine for angles from 0 to 180
b Eighteen-degree segment if started at zero.
c The 18-degree segment may be measured anywhere along the wave, and is to include any angle from 0 to 360.
Table 63.4
Current and power limitations
Inherently limited power source overcurrent Not inherently limited power source
Circuit characteristics protection not required overcurrent protection required
Circuit voltage (volts) 0 20 Over 20 but Over 30 60 Vd 0 15 Over 15 but Over 20 but
not more than not more not more
30 than 20 than 60
Power limitation (volt- 350 250 250
amperes)a
Current limitation 8 8 150/Vmax 1000/Vmax 1000/Vmax 1000/Vmax
(amperes)b,c
Maximum overcurrent 5 5 100/Vmax
protection (amperes)
Power source nameplate
ratings
Power (watts or 5 Vmax 100 100 5 Vmax 5 Vmax 100
volts-amperes)c
Current (amperes)c 5 100/Vmax 100/Vmax 5 5 100/Vmax
NOTES
1 In all cases the applied primary voltage is to be as indicated in Table 63.2.
2 Root-mean-square value for voltage and current.
a Maximum volt-ampere output after 1 minute of operation regardless of load, and overcurrent protection, if used, bypassed.
When current-limiting impedance evaluated for the purpose is used, the current-limiting impedance shall not be bypassed.
b Maximum output current after 1 minute of operation under any noncapacitive load, including short circuit, and with overcurrent
protection, if provided, bypassed. When current-limiting impedance evaluated for the purpose is used, maximum output current
after 5 seconds of operation with current-limiting impedance not bypassed.
cV
max is the maximum output voltage (rms) with rated input voltage applied.
d This column pertains only to waveforms which do not reverse in polarity. See Figure 63.4.
63.2 Ambient air temperature
63.2.1 The tests described in this section are to be conducted in an ambient air temperature within the
range of 21 30C (70 86F), except that the rated output heated test with or without standard fuses,
but without other forms of overcurrent and overtemperature protectors may be conducted in an ambient
temperature of 10 40C (50 104F).
63.3 Open-circuit secondary voltage
63.3.1 The open-circuit voltage between any two secondary output terminals of a power source shall not
be more than the value specified in column 5 of Table 63.3 for the indicated frequency, with or without
any combination of interconnected secondary terminals when the primary is energized in accordance with
the voltage specified in 63.1.1.
Exception No. 1: The open-circuit voltage between multiple sets of secondary output terminals may
exceed the values in column 5 for the indicated frequencies when secondary terminals are interconnected,
if the following conditions are met:
a) The open-circuit voltage between any two terminals is not more than the values in column 5
for the indicated frequency when no connections are made between secondary terminals, and
b) The power source is marked in accordance with the interconnection of limitations in 74.9.
Exception No. 2: The open-circuit voltage between any two secondary output terminals with or without any
combination of interconnected secondary terminals may be more than the values in column 5, but not
more than the values in column 4 for the indicated frequencies if the product is marked for not wet contact
use in accordance with 75.8.
Exception No. 3: The open-circuit voltage between multiple sets of secondary output terminals may
exceed the values in column 4 for the indicated frequencies when the secondary terminals are
interconnected, if the following conditions are met:
a) The open-circuit voltage between any two output terminals is not more than the values in
column 4 for the indicated frequency when no connections are made between secondary
terminals, and
b) The power source is marked with both the interconnection limitations specified in 74.9 and the
wet-contact limitations specified in 75.8.
63.3.2 With regard to Table 63.3, the change in instantaneous voltage for all durations equal to 5 percent
(360 degrees 0.05 = 18 degrees) of the period of the fundamental frequency (fo) of the waveform is
determined in the manner shown in Figure 63.2. The 18 degree time interval is to be located anywhere
along the horizontal axis that the greatest voltage change takes place. For a sine wave, this occurs when
the 18 degree time interval is centered about a zero-crossing point. For a saw-tooth wave, this occurs for
any 18 degree interval which includes the retrace interval. For other waveforms, the interval may not
include a zero-crossing point. Each 18 degree segment must be examined to locate the interval of
greatest voltage change.
Figure 63.2
Eighteen-degree segments of common waveforms
NOTES:
For waveform A the maximum change in instantaneous voltage for 5 percent of the fundamental frequency period is determined as
follows:
V = V2 V1
= (42.4) (sin 171) (42.4) (sin 189)
= (42.4) (0.156) (42.4) (minus 0.156)
= 6.63 + 6.63
V = 13.26 volts
For waveform B, the maximum change in instantaneous voltage for 5 percent of the fundamental frequency period is determined as
follows:
V = V2 V1
= 84.8 0
V = 84.4 volts
This is an unacceptable waveform because the voltage change exceeds the 60 volt limit listed in column 4 of Table 63.3, where the
waveform does not reverse in polarity.
63.3.3 Whether or not the instantaneous voltage reverses in polarity is determined as shown in Figure
63.4.
63.3.4 Figure 63.5 shows examples of acceptable waveforms where the instantaneous voltage does not
reverse in polarity and the change in instantaneous voltage is more than 20 volts if wet contact is not likely
and more than 10 volts if wet contact is likely. The maximum acceptable voltage is a function of the
fundamental frequency (fo) of the waveforms as shown in Table 63.3. The maximum acceptable voltage
for locations where wet contact is likely is half that allowed for locations where wet contact is not likely.
63.3.5 Figure 63.6 shows examples of acceptable waveforms where the instantaneous voltage does not
reverse in polarity and the change in instantaneous voltage is not more than 20 volts if wet contact is not
likely and not more than 10 volts if wet contact is likely. The maximum acceptable voltage is 60 volts peak
if wet contact is not likely and 30 volts peak if wet contact is likely.
63.3.6 Figure 63.7 shows examples of acceptable waveforms where the instantaneous voltage reverses
in polarity and the instantaneous voltage is not more than 20 volts if wet contact is not likely and not more
than 10 volts if wet contact is likely. The maximum voltage allowed is 60 volts peak and 84.8 volts
peak-to-peak if wet contact is not likely and 30 volts peak and 42.4 volts peak-to-peak if wet contact is
likely.
63.4 Maximum current of inherently limited power source
63.4.1 The effective value (rms value of the periodically time-varying voltage or current) is to be used in
the calculations for current and power.
Figure 63.3
Eighteen-degree segment of irregular waveform
NOTE:
For the nonsinusoidal waveform shown, the maximum change in instantaneous voltage for 5 percent of the fundamental frequency
period is determined as follows:
V = V1 V2
= 0.62 42.4 0 (taken graphically)
= 26.3
Because the voltage change exceeds 20 and the waveform does reverse polarity, an investigation would be required to determine
if the waveform is acceptable as indicated in row B of Table 63.3.
If the change in instantaneous voltage was not more than 20 volts, see row D of Table 63.3.
Figure 63.4
Polarity determination
Figure 63.5
Waveforms of same polarity with large V
Figure 63.6
Waveforms of same polarity with small V
Figure 63.7
Waveforms with polarity reversal
63.4.2 The output current of a power source intended to be inherently power limited shall be tested as
described in 63.4.3 63.4.9. See the flow chart in Figure 63.8. The results are acceptable if after 1 minute
of operation the current does not exceed the values specified in Table 63.4 for inherently limited power
sources.
63.4.3 Unless the power source is marked in accordance with 74.9, multiple secondary windings or output
terminals, if any, are to be interconnected to produce maximum current. Under the conditions described
in 63.1.1 63.1.4 and 63.4.5, a resistance load is to be determined that produces the largest initial value
of current (including short circuit). The secondary winding(s) is to be loaded with this value of resistance,
and the power source is to be energized as described in 63.1.1 63.1.4 while at room temperature.
63.4.4 The impedance of the short circuit measuring circuit in the secondary is not to be more than 0.03
ohms. If the secondary winding of a transformer is provided with leads or a flexible cord, 1 foot (305 mm)
of each lead or the cord is to be included in the short circuit.
63.4.5 If operation of a protective device exposes the power source to the effects of arcing contacts, the
value of current at such operation shall not exceed 10 amperes.
63.4.6 If during this test the current is interrupted by a resettable or replaceable protective device, the test
is to be repeated with the protective device shorted.
63.4.7 If the current is interrupted by a nonresettable, nonreplaceable protector or by coil burnout, other
samples are to be tested by attempting to continuously adjust the resistance load to hold the current for
1 minute just above the value specified in Table 63.4.
Figure 63.8
Test flow chart
(Continued)
Figure 63.8 (Contd)
IO = Current at opening
IF = Current at 1 minute
I2 = Current in Sample of Set No. 2
IExp = Extrapolated current at 1 minute
a = 63.4.6
b = 63.5.1
c = 63.4.1
d = 63.4.4
e = Table 63.4
f = 63.4.5
g = 63.4.7
h = 63.4.8
63.4.8 If the current described in 63.4.7 exceeds the value specified in Table 63.4 after 1 minute of
operation, a third sample is to be tested with the resistance load adjusted to provide an initial current
midway between the maximum initial obtainable value and the value specified in Table 63.4. The value of
resistance is not to be further adjusted during the test. The results are not acceptable if after 1 minute of
such operation the output current exceeds the applicable values in Table 63.4.
63.4.9 If the current in the test described in 63.4.8 again results in the current being interrupted, another
sample is to be tested as described in 63.4.8 with the initial current adjusted to midway between the initial
current recorded during the test in 63.4.8 and the value specified in Table 63.4. During this test, a
recording of current versus time is to be obtained. If the current is again interrupted before 1 minute of
operation, the recorded curve of current versus time is to be extrapolated to 1 minute by a smooth curve
that is judged to best match the measured data. The results are acceptable if the extrapolated value of
current, after 1 minute, does not exceed the applicable values in Table 63.4.
63.5 Maximum current of not inherently limited power source
63.5.1 If the power source is not an inherently limited power source, it shall be tested as described in
63.4.2 63.4.9. The results are not acceptable if the maximum current exceeds the applicable values in
Table 63.4 for not inherently limited power sources.
63.6 Maximum power of not inherently limited power source
63.6.1 The maximum obtainable power output shall not exceed the applicable value in Table 63.4.
63.6.2 Protective devices are to be shorted out during this test. Unless marked in accordance with 74.9,
multiple secondary windings, if any, are to be interconnected to produce maximum power output. The
maximum output power is to be determined by simultaneous voltage and current measurements with the
variable resistance connected to the output terminations. Starting with the device at room temperature, the
measurements are to be made within 2-1/2 minutes.
Table 63.5
Maximum acceptable time to open
Maximum time for overcurrent

Rated secondary potential, volts Secondary test current, amperes protective device to open, minutes
20 or less 10 2
20 or less 6.75 60
21 and over 200/Vmax 2
21 and over 135/Vmax 60
63.7 Calibration of overcurrent-protective devices
63.7.1 A one-time or manually-resettable overcurrent-protective device, provided as part of a not

inherently limited Class 2 power source, shall operate to open the circuit in not more than the time
indicated in Table 63.5 when the power source is delivering the specified secondary current. The
protective device may be located in either the primary or secondary circuit. The results are acceptable if
there is no emission of flame or molten metal from the power source enclosure and no other evidence of
a risk of fire or electric shock as described in 63.1.2 and 63.1.3.
63.7.2 To determine if an overcurrent-protective device complies with the requirement in 63.7.1, the
power source is to be allowed to deliver the test current to a resistive load, with the primary connected to
a circuit as described in 63.1.1 63.1.4 and 63.2.1.
63.7.3 If there is more than one secondary or if the secondary winding has accessible taps, sufficient
tests shall be conducted to determine that for any winding or partial winding, the protective device will
open within the applicable time specified in Table 63.5.
63.8 Rated secondary output
63.8.1 A power source marked with a secondary current rating shall be capable of delivering its rated full
load secondary current continuously. If not marked with a secondary current rating, a power source shall
be capable of delivering its marked secondary volt-ampere rating continuously.
63.8.2 To determine whether a power source complies with the requirement in 63.8.1, a power source is
to be tested with a variable resistor and an ammeter connected to the secondary or output terminals, and
the primary connected to a circuit in accordance with 63.1.1 63.1.4 and 63.2.1. The resistor is to be
adjusted until the rated full-load secondary current or power is drawn. The power source is to be mounted
so that the primary terminals or leads are on top. After 15 minutes of operation, the load is to be
readjusted, if necessary, to return the current or power to the full load value. The circuit is to be energized
for 1 hour without further adjustment. The results are acceptable if, at the end of the 1 hour period, the
output current or power is not less than 90 percent of the rated value, and the overtemperature or
overcurrent protective device does not open.
63.8.3 With reference to 63.8.2, if a power source has two secondary windings, both windings are to be
operated simultaneously, with each secondary winding independently loaded.
63.9 Rated output heating
63.9.1 The test described in 63.8.1 63.8.3 is to be continued without further adjustment until
temperatures become constant. The temperature rise shall not exceed the applicable values specified in
Table 40.1.
63.10 Dielectric voltage withstand
63.10.1 A power source shall be subjected for 1 minute to the application of a 60 hertz essentially
sinusoidal potential with the unit at the maximum operating temperature reached in the rated output
heating test described in 63.9.1. The results are acceptable if there is no dielectric breakdown. The
applied potential is to be:
a) As described in Dielectric voltage-Withstand Test, Section 47;
b) For a Class 2 power source, 2500 volts between the primary and secondary circuits;
c) One thousand volts plus two times the sum of the secondary voltages between the secondary
windings unless considered as a single winding as described in the Exception No. 1 to 36.4.2; and
d) Five hundred volts between a secondary circuit and accessible dead metal parts.
63.11 Component breakdown
63.11.1 Components in the equipment shall be subjected to the test described in 63.11.2 and 63.11.3.
There shall be no emission of flame or molten metal or a risk of fire or electric shock as described in 63.1.2
and 63.1.3 while operating as in the rated output heating test.
63.11.2 The components in the equipment, such as diodes, resistors, transistors, capacitors, and the like,
are to be shorted or opened, one at a time. The equipment is to be energized and operated continuously
as described in 63.1.1 63.1.4 and 63.2.1 until ultimate conditions are observed, including opening of a
thermal cutoff or a similar device, for 7 hours if temperatures stabilize or cycling of an automatically reset
protector occurs, or for 50 cycles of resetting a manually reset protector. During this test the grounding
means, if provided, is to be connected directly to ground.
63.11.3 The test shall be followed by a dielectric voltage-withstand test, as required by 63.13.1.
Exception: The dielectric voltage-withstand test need not be conducted on a component that has been
evaluated in accordance with 36.5.1.
63.12 Overload heating
63.12.1 A transformer shall be subjected to the overload heating tests described in 63.12.3 63.12.7,
under the conditions specified in 63.1.1 63.1.4 and 63.2.1. A protective device that is relied upon to open
the circuit as a result of the test is to be one that has been investigated and found to be acceptable for
this purpose. If the same insulating system is used in a group of transformer models, only those models
having the maximum volt-ampere rating, the minimum volt-ampere rating, and an intermediate
volt-ampere rating need be tested.
63.12.2 The results are acceptable if:
a) The temperature rise of the coils by the resistance method at the end of 7 hours is not more
than 105C for coils having Class 105 insulation or 135C for coils having Class 130 insulation,
Exception: The temperature rise may exceed these values if the test is continued on three
samples for 15 days. If the test is interrupted by a protector or a burnout, additional samples are
to be tested with the other conditions described in Table 63.6 and 63.12.3 63.12.7.
b) There is no emission of flame or molten metal from the transformer enclosure, and
c) There is no other evidence of risk of fire or electric shock as described in 63.1.2 and 63.1.3 (a)
(g) and, with the output terminals shorted, 63.1.3(h).
Table 63.6
Test loading conditions
Condition Secondary winding load

A Load used for final sample in tests described in 63.4.2 63.5.1
B Rectifier to cause half wave rectified short circuit
Ca IR +0.75 (IA IR)
Da 50
Ea 25
Fa 20
Ga 15
Ha 10
Ia 5
Note:
IA = Current at end of 1 minute obtained on final sample of the output current test.
IR = Rated current.
aFor conditions (C-1), rated current (18R) plus indicated percent of difference between A (I A ) and rated current.
63.12.3 One sample of a transformer is to be operated for 7 hours under each condition described in
items A I as shown in Table 63.6.
63.12.4 For the sequence of tests described in items A I of Table 63.6, if a test for a particular condition
continues for 7 hours without a coil or a protective device opening, the remaining tests need not be
conducted. If a coil or protective device opens during a particular 7-hour test, the test is to be discontinued
and the next test in sequence is to be conducted, until a test condition continues for 7 hours. All samples
used for the tests are to be subjected to the evaluation criteria described in 63.12.2 while in the heated
condition.
63.12.5 For the purpose of these requirements, each secondary winding tap other than a center tap, and
each primary winding tap intended to supply power to a load, is considered to be the equivalent of a
secondary winding.
63.12.6 If a power source is equipped with more than one set of output terminals or secondary windings,
each of the secondary windings or sets of terminals is to be loaded for each condition specified in Table
63.6 with the other windings or set of terminals loaded to rated current. The secondary windings or output
terminals are to be loaded to rated current before the abnormal condition is introduced; and the loads
other than the one connected to the circuit to be overloaded, are not to be readjusted thereafter.
63.12.7 For the loading conditions, a variable resistor is to be connected across the secondary winding.
The tests described in items A H of Table 63.6 are to be continued for 7 hours unless a winding of the
power source or a protective device opens in a shorter time. In conducting the tests described in items C
H of Table 63.6, the variable resistance load is to be adjusted to the required value as quickly as
possible and readjusted, if necessary, 1 minute after application of voltage to the primary winding.
63.13 Repeat dielectric voltage withstand
63.13.1 Following the overload-heating test, a power source shall comply with the requirements of the
dielectric voltage-withstand test described in 63.1.2.
Exception: The voltage between primary and secondary need not exceed 1000 volts plus twice the
primary test voltages specified in Table 63.2.
63.14 Overload of overcurrent- or overtemperature-protective devices
63.14.1 A protective device for a not inherently limited power source, other than a fuse, thermal cutoff, or
a device as covered in 63.15.1 and 63.15.2, provided as a part of a power source, shall make and break
the circuit for a total of 50 cycles of operation with the power source connected and loaded in accordance
with 63.4.2, 63.4.3, and 63.5.1. The results are acceptable if there is no emission of flame or molten
material from the power source enclosure, or other evidence of a risk of fire or electric shock as described
in 63.1.2 and 63.1.3, and the overcurrent protective device is operable at the end of the test.
63.14.2 In the test of a manual-reset device, the device is to be reset as soon as possible after opening;
however, if the device will not reset within 1 hour after opening in any cycle, the test is to be stopped and
the device considered inoperable.
63.15 Endurance of automatic-reset overtemperature-protective devices
63.15.1 An automatic-reset overtemperature-protective device on an inherently limited power source shall

be subjected to an endurance test by connecting it to a source as specified in 63.1.1 63.1.4 and 63.2.1
with the secondary loaded as described in 63.4.2 63.6.1 to produce the maximum possible current
through the automatic reset device. The power source is then to be allowed to operate for 15 days. The
results are acceptable if:
a) There is no emission of flame or molten material from the power source enclosure,
b) There is no other evidence of a risk of fire or electric shock as described in 63.1.2 and 63.1.3,
and
c) The protective device remains operable.
Exception: If maximum possible current results in interruption of an overcurrent-protective device, the

power source is to be tested starting with a load that causes a current of 110 percent of the overcurrent
device rating. The load current is to be increased or decreased, as necessary, in increments of 2 percent
until a current is reached at which the overcurrent device does not open.
63.15.2 A supplementary automatic-reset protector used in addition to the protector specified in 36.6.2 for
a not inherently limited power source shall also comply with the requirement in 63.15.1.
64 Isolated-Limited Secondary and Non-Class 2 Circuits Tests
64.1 Equipment that has a transformer supplying an isolated-limited-secondary circuit or an electronic

circuit that is not Class 2 is to be tested in accordance with 49.2 49.5.
MANUFACTURING AND PRODUCTION TESTS
65 Details
65.1 General
65.1.1 The manufacturer shall provide regular production control, inspections, and tests on the devices
mentioned in 65.1.2 65.1.4.
65.1.2 For a refrigeration pressure-limiting control, water-heater temperature-limiting control, water-heater

temperature-regulating control with a maximum temperature setting of more than 77C (170F),
water-heater temperature-regulating control set at a temperature no higher than 60C (140F),
temperature-limiting or combination temperature-regulating and -limiting control, time-delay or thermal
relay that responds to a pressure- or temperature-limiting control, electric-baseboard-heater
temperature-limiting control, oven door lock control, self-cleaning oven temperature control, and hot
tub/spa water temperature-regulating or temperature-limiting control, the program shall include at least the
following:
a) Calibration verification and adjustment of set point under prescribed conditions and following a
prescribed method;
b) A 1-minute dielectric voltage-withstand test at 1000 volts plus twice rated voltage, or a
1-second test at 120 percent of that voltage; and
c) Determination that a manually reset control complies with the requirements in 12.1 and 12.3
when conducted under a prescribed procedure unless such compliance is not dependent upon
control of close manufacturing tolerances.
65.1.3 For the production dielectric voltage-withstand testing mentioned in 65.1.2(b), the requirement for
a 500 volt-ampere or larger transformer as specified in 47.1.12 may be waived if the high-potential testing
equipment used maintains the specified high-potential voltage at the equipment for the duration of the test;
for example, the equipment is provided with a voltmeter to measure directly the applied output potential.
65.1.4 For an automatic cycling control, such as a shunt-heater, bimetal-heater, hot-wire, or similar
mechanism for control of a surface unit on an electric range, the program shall include at least the
following:
a) Verification of continuity and design performance of each 100 percent of production

thermal element, after energization of the heater (burn-in) for a period of time; and
b) A dielectric voltage-withstand test as described in 65.1.2(b) and 65.1.3.

65.2 Marked-off position
65.2.1 In order to determine that the requirements for a control having or intended to have a marked-off
position as specified in 11.5 11.12 are maintained in production, the manufacturer shall provide a regular
control program inspection, and tests as required on such devices.
66 Grounding Continuity
66.1 Equipment that has a power-supply cord having a grounding conductor shall be tested, as a routine
production-line test, to determine that grounding continuity exists between the grounding blade of the
attachment plug and accessible dead metal parts of the equipment that are likely to become energized.
66.2 Only a single test need be conducted if the accessible metal selected is conductively connected by
design to all other accessible metal.
66.3 Any acceptable indicating device, such as an ohmmeter, a battery-and-buzzer combination, or the
like, may be used to determine whether the equipment complies with the requirements in 66.1.
RATING
67 General
67.1 Temperature-indicating and -regulating equipment shall be rated in volts, and, as appropriate for the
intended use, also in horsepower, amperes, amperes resistive (or resistance only or noninductive),
volt-amperes or watts, or any combination thereof. The rating of a device shall include the current in
amperes if the wattage rating is not a close indication of the volt-ampere input. The rating shall indicate
whether the device is for direct or alternating current and, for an alternating-current device, the number of
phases and, if necessary, the frequency, except that a single-pole or other device obviously intended only
for single-phase use need not include the phase rating.
67.2 A contact device intended for control of a solenoid coil of a relay contactor, valve, or the like shall
be rated in volts and volt-amperes using the sealed value and shall be marked in accordance with 69.10
69.12.
67.3 Normal pilot-duty ratings for alternating current are 125, 360, and 720 volt-amperes; and for direct
current 57.5, 120, and 250 volt-amperes; but other ratings may be used.
67.4 Other than as noted in 67.5 67.9, a device intended to control a motor shall be rated in accordance
with one of the following:
a) The device may be rated in horsepower only;
b) The device may be rated in horsepower and, in addition, may be rated in full-load and
locked-rotor current provided the relationship between the three values is in accordance with
Table 45.1 and Table 45.2 or 45.3, whichever is applicable; or
c) If the device is intended to control a motor rated 2 horsepower (1.5 kW) or less, the device may
be rated in full-load current that need not correspond with that in the applicable Table 45.2 or 45.3,
and in locked-rotor current six times the rated full-load current if alternating-current and ten
times the rated full-load current if direct-current. The device may be marked with a lesser
locked-rotor current rating, but tests shall be conducted at the values specified.
67.5 Except for equipment rated 265 or 277 volts, a refrigeration controller or a wall-mounted room
thermostat intended to control a compressor motor may be rated in accordance with 67.4 or shall be rated
in horsepower and in full-load and locked-rotor current. The full-load current rating may be greater than
the equivalent of 2 horsepower (1.5 kW), and the locked-rotor current rating need not be six times the
full-load current rating for control of an alternating-current motor. Current ratings shall be plainly marked
to indicate that they apply only to a hermetic compressor motor and shall be separated from other ratings
to distinguish them from those ratings.
67.6 A device intended to control a single phase, alternating-current motor rated 265 or 277 volts, 2
horsepower (1.5 kW) or less or an equivalent current rating shall be rated in full-load current and in
locked-rotor current. The device may be marked with a locked-rotor current rating less than six times
full-load current, but tests are to be conducted at six times the full-load current rating. If the rated full-load
current is in accordance with note b to Table 45.3, the device may also be rated in horsepower. See
69.13.
67.7 A refrigeration controller or a wall-mounted room thermostat rated 265 or 277 volts single-phase,
alternating current, that is intended to control a compressor motor and that may also control a
conventional motor shall be rated in accordance with 67.6 and may also have a rating of 2 horsepower
(1.5 kW) or less or an equivalent current rating for a hermetic compressor motor. The locked-rotor
current rating and test current need not be six times the full-load current rating. See 69.13.
67.8 The ratings of a component device intended only for installation as part of other equipment need not
comply with 67.4 67.7 and may exceed 2 horsepower (1.5 kW) or the equivalent at 265 or 277 volts,
single-phase, alternating current. See Exception No. 2 to 69.1.
67.9 Unless intended for permanent mounting and intended for the control of a stationary, industrial-type
air heater, a room thermostat shall not have a rating of more than 300 volts.
67.10 A time-delay or thermal relay that responds to a limiting control shall be assigned a maximum
ambient-air-temperature rating and timing ratings. The ratings are to include:
a) Maximum ambient air temperature,
b) The range of ambient temperatures to which the normal timings apply,
c) Normal time-to-close and time-to-open, and
d) Manufacturing tolerances, such as a plus-or-minus percentage of time.
67.11 The requirements specified in 67.10 (c) and (d) may be combined and expressed as time ranges
or minimum operating time between stages on closing and opening. Tolerances shall be within that
specified for the device function. See Table 38.3.
68.1 The electrical ratings of a power source shall include the primary voltage and frequency, all
secondary voltages and frequencies, and the capacity of each secondary winding in volt-amperes. For
continuous direct current and nonsinusoidal voltages, the peak voltage shall be included.
68.2 The secondary voltage rating of each secondary winding or terminal of a power source shall not
exceed the values specified in columns 4 or 5 in Table 63.3 at the specified frequencies.
68.3 The secondary volt-ampere rating of a power source winding shall not be more than five times the
secondary voltage rating; and the current rating, in amperes, shall not be more than 5, or 100 divided by
the secondary voltage rating, whichever is less.
68.4 The sum of the volt-ampere ratings of all secondary windings of a power source shall not exceed
100.
MARKING
69 General
69.1 Temperature-indicating and -regulating equipment shall be plainly and permanently marked with the:
a) Manufacturers name, trademark, or other descriptive marking by which the organization

responsible for the equipment may be identified,
b) A distinctive catalog number or the equivalent, and
c) The electrical rating.
Exception No. 1: A product intended only for factory installation in end-use equipment need not be marked
with a rating.
Exception No. 2: A product intended only for installation as part of other equipment need not be marked
with a rating if a different catalog designation is employed for each different rating.
69.2 A distinct catalog number or suffix for each design or function shall be marked on the product.
69.3 A room thermostat having one or more ratings of more than 300 volts shall be marked: In a circuit
of more than 300 volts, for use with stationary, industrial air heaters only, or with an equivalent wording.
As an alternative, the marking may be: For use with stationary, industrial air heaters only.
69.4 A transformer or other device rated less than 110 volts (primary) and not intended for use on a 110
120 volt circuit shall be marked: For use only on ___ volt circuits. The blank space is to be replaced
with the intended voltage.
69.5 Information necessary for the proper operation of the equipment, for a definite mounting position that
is required but not obvious, for the selection of heaters for overload relays or thermostat anticipation, and
for the setting of controls and the like shall be permanently marked on the equipment.
Exception: Equipment that must be mounted in a definite position in order to function properly may have
the directions for mounting either marked on the equipment or on an instruction sheet supplied with the
equipment.
69.6 If a manufacturer produces or assembles temperature-indicating and -regulating equipment at more

than one factory, each finished item of equipment shall have a distinctive marking, which may be in code,
by which it may be identified as the product of a particular factory.
69.7 An enclosure that has been investigated in accordance with 7.13.1 shall be marked Raintight or
Rainproof as appropriate. Also, see 14.15.
69.8 A control intended for outlet box mounting shall be so marked, except that such marking may be
omitted if the intended mounting is obvious.
69.9 A control that is acceptable for use with a specific remote control or another specific part of a control
or appliance shall be marked accordingly, and the marking location shall be in accordance with 73.1
73.3.
69.10 With reference to the requirement in 67.2, a contact device intended for control of a solenoid coil
of a relay contactor, valve or the like, that is rated in volts and volt-amperes using the sealed value shall
be marked Pilot Duty.
69.11 For an alternating-current pilot-duty rating that has an inrush rating differing from ten times the
sealed value, the inrush rating shall also be marked.
69.12 A pilot-duty rating may be marked in amperes, instead of volt-amperes, if both the sealed and
inrush ampere values are used.
69.13 With reference to the requirements in 67.6 and 67.7, the conventional motor rating and the
hermetic compressor motor rating shall be plainly marked and shall be separated to distinguish them from
each other.
69.14 A controller intended to comply with the requirement in Exception No. 1 to 28.1.1, shall be marked
with the maximum control-circuit protective-device rating corresponding to the size of control-circuit wire
used within the equipment.
69.15 A controller intended to comply with Exception No. 3 of 28.1.1 or Exception No. 4 of 28.1.3 shall
be marked with the maximum control circuit protective device rating used in the Short Circuit Test, Section
50.
69.16 With reference to the requirements in 28.1.1 and 28.1.2, there shall be a marking near a fuseholder
provided for a supplementary fuse specifying the voltage and current rating of the replacement fuse. The
marking shall indicate the designation of the fuse but may include or equivalent. A marking specifying
the maximum fuse rating to be used shall be provided near a fuseholder for other than a supplementary
fuse that will accept a fuse having a higher current rating than specified in Table 28.1.
69.17 With reference to the requirements in 28.1.3, a controller shall be marked with the maximum
voltage and current rating of the branch-circuit overcurrent-protective device corresponding to the size of
the internal wire.
69.18 A manually reset limiting control shall be marked Manually Reset 1 (or 2), or M1 (or 2). See
Reset Mechanism Limiting Control, Section 12.
Exception: The manual reset information need not be marked on a component intended only for factory
installation in end-use equipment if a different catalog number is employed for each manually reset type.
69.19 Equipment (including a motor operator) employing a motor shall be marked Thermally Protected
Motor if such protection is provided in accordance with 40.8 or Impedance Protected Motor if the motor
either has been investigated for impedance protection or the temperature of the motor does not exceed
the limits specified in Table 40.1 when stalled. The word Motor may be omitted if the marking is on an
enclosure identifiable as a motor.
Exception No. 1: The foregoing marking is not required for a clock-type motor.
Exception No. 2: For a motor rated 100 watts or less, the marking may be T.P. for a thermally protected
motor or Z.P. for an impedance-protected motor.
69.20 A control that has been investigated for use in agricultural environments involving excessive dust
(but below explosive or ignitable concentration), water, and corrosive atmospheres shall be marked: For
Use in Agricultural Buildings, or the equivalent.
69.21 Equipment rated and tested in accordance with 50.3.1 shall be marked in accordance with the
applicable short-circuit withstand marking requirements in the Standard for Industrial Control Equipment,
UL 508.
70 Wiring
70.1 Wiring terminals shall be marked to indicate the proper connections for the power supply, load, and
control circuit connections, and the like, or a wiring diagram coded to the terminal marking shall be
securely attached to the device.
Exception: The terminals need not be marked if the wire connections are plainly evident, as for a
2-terminal switching device.
70.2 A terminal for the connection of a grounded conductor shall be identified by means of a metallic
plated coating substantially white in color and shall be readily distinguishable from the other terminals, or
proper identification of the terminal for the connection of the grounded conductor shall be clearly shown
in some other manner, such as on an attached wiring diagram. If wire leads are provided, the lead
intended to be grounded shall have a white or natural gray color and shall be readily distinguishable from
other leads.
70.3 A single white terminal in other than a single-pole device for the connection of an ungrounded
conductor is not acceptable, but two or more terminals may be white if it does not make any difference
how line connections are made, it is obvious which terminal is intended for the connection of the grounded
conductor, or the line connections are plainly indicated on a wiring diagram.
70.4 A device incorporating two or more separate circuits that are capable of being connected to separate
power supplies but that are intended to be connected to a common power supply shall be marked: All
circuits must have a common disconnect and be connected to the same pole of the disconnect, or with
an equivalent wording. The wiring diagram of the device shall illustrate a typical connection of the various
circuits connected to the common power supply.
70.5 If a motor that is connected to the same branch circuit as another motor or heating load group
installation is to be installed remote from the controller, the marking on the controller shall specify the
rating of the motor, the size of conductors supplying it, and a statement that a disconnect is required in
the circuit between the controller and the motor and in sight of the motor.
70.6 A control employing a special fitting for the connection to a specific wiring system shall be marked
to indicate that it must be installed with such a wiring system.
70.7 A device that is acceptable for installation in a nonmetallic-enclosed wiring system only shall be
marked to indicate that it must be installed with such a wiring system.
70.8 Equipment having field-wiring terminals shall be marked as follows or with equivalent wording:
a) Use Copper Conductors Only if the terminal is acceptable only for connections to copper
wire;
b) Use Aluminum Conductors Only or Use Aluminum or Copper-Clad Aluminum Conductors

Only if the terminal is acceptable only for connection to aluminum wire; or
c) Use Copper or Aluminum Conductors or Use Copper, Copper-Clad Aluminum, or Aluminum

Conductors if the terminal is acceptable for connection to either copper or aluminum wire.
70.9 Equipment provided with a wire connector for field-installed wiring as covered in the Exception No.
1 to 16.2.1.6, shall be marked to specify that the connector provided is to be used in making the field
connection.
70.10 A control with direct-current motor ratings that does not comply with the requirements in 16.2.1.1(d)
shall be marked with the following or the equivalent: Do Not Connect to a Rectifier of the Single-Phase
Half-Wave or Full-Wave Type.
70.11 An outlet-box mounted device that does not have an equipment grounding terminal or lead
provided on the device as shipped shall be marked:
a) Mount This Control Only To A Grounded Metallic Box, or the equivalent; or
b) With a statement indicating which pressure wire connector or component terminal kits are
acceptable for use with the device. The device shall readily accept the field provided means of
connection. A terminal kit shall be provided with installation instructions and be marked with the
part number and manufacturer.
71 Calibration Setting
71.1 The set point shall be indicated in a recognizable and legible manner using standard units of
measurement on a:
a) Water-heater temperature-limiting control,
b) Water-heater temperature-regulating control having a maximum temperature setting of more

than 77C (170F),
c) Temperature-limiting control,
d) Electric-baseboard-heater temperature-limiting control,

e) Oven-door-lock control,
f) Self-cleaning oven temperature control, and
g) Hot tub/spa control.
Exception No. 1: A component intended only for factory installation in end-use equipment need not be
marked with a set point if a different catalog designation is employed for each different set point.
Exception No. 2: In place of standard units, the letter L or F, indicating open-on-rise and close-on-rise,
respectively, together with the functioning temperature in degrees F may be used; for example, L110 to
indicate open-on-rise at 110F.
71.2 The operating cutout pressure of a refrigeration-controller pressure-limiting device shall be

marked on the control in pounds-per-square-inch-gauge (psig). For a fixed setting control, the marked
value shall be that of the setting. For an adjustable setting control the marked value shall be the maximum
setting permitted by the normal adjusting means, and shall be indicated as Maximum.
Exception No. 1: The operating pressure on a component device intended only for installation as part of
refrigeration or air-conditioning equipment need not be marked if a different catalog number is employed
for each different operating cutout pressure.
Exception No. 2: If the operating pressure is obvious by reading a dial for various adjustments and a
legible dial-scale subdivision is provided for each 5 percent of the maximum adjustable setting, the
maximum adjustable setting need not be specifically marked.
71.3 A time-delay or thermal relay see 38.5.1 and Table 38.3 shall be marked with the time-calibration
and tolerance ratings as specified in 67.10 or a different catalog number, or the equivalent, shall be
assigned and marked for each different time-calibration and tolerance ratings.
72 Elevated Air Temperature
72.1 A control rated for use in an elevated air temperature in accordance with 40.3 and note a to Table
40.1 shall be marked to indicate the maximum allowable ambient air temperature.
72.2 If, in accordance with note a to Table 40.1, any point within a terminal box or compartment of certain
controls, internal wiring, or the wires intended for supply connections attains a temperature higher than
60C (140F), the control shall be marked with one of the following statements or the equivalent:
a) For supply connections, use No. ____ AWG or larger wires rated for at least ____ C (____
F), or
b) For supply connections, use Type NM-B or NMC-B nonmetallic sheathed cable with No. ____
AWG or larger wires.
The AWG size indicated in the marking shall be the size of the conductors used in conducting the normal
temperature test, and the temperature value shall be in accordance with Table 72.1. The wire size need
not be specified if No. 14 AWG wire was used for the test. The statement shall be legible and located so
that it will be clearly visible during installation and examination of the supply-wiring connections.
Table 72.1
Terminal box marking
Temperature attained during test at points within terminal box or

compartment, or on wires intended for supply connections Temperature marking
61 75C (142 167F) 75C (167F)
76 90C (168 194F) 90C (194F)
72.3 With regard to note a of Table 40.1 and to 72.2, if the supply-connection area is located so that it is
obvious that the supply wiring can be properly located and maintained away from parts of the device
operating at temperatures higher than 60C (140F), a marking, clearly visible during installation and
examination of the supply-wiring connections, may be used to indicate the area in which the supply wiring
and splices should be located after the splice is made.
73 Location
73.1 All markings shall be permanently attached to the device and shall be legible and prominent and,
except as noted in 73.2 and 73.3, shall be located so that they will be visible after installation of the
equipment. Markings shall be visible during the phase of installation, use, or inspection for which they are
intended to apply. Markings of a cautionary nature or reflecting some special use or restriction shall be at
least as prominent as the general or informational markings such as those used for ratings.
73.2 Marking is not required to be located on the outside of an enclosure, if it is readily visible by opening
a door or removing a cover after installation. A marking that is not visible unless the cover is removed is
acceptable only if the installation wiring will not be disturbed by removing the cover and if the marking is
visible at the time it is needed.
73.3 On outlet-box-mounted devices a marking designating the material used for the conductors, and all
required markings shall be visible with the device mounted on the outlet box.
Exception: A marking of required wiring and installation instructions may be visible upon removal of the
device from the outlet box.
74 Cautionary Markings
74.1 If more than one disconnect switch is provided to disconnect all power within a control assembly or
compartment, the assembly or compartment shall be marked with the word CAUTION and the following
or the equivalent: Risk of Electric Shock More than one disconnect switch is provided. Disconnect all
power to the device before servicing.
74.2 The marking required by 74.1 shall be in letters not less than 1/8 inch (3.2 mm) high and shall be
in a permanent location on the outside of the device or on a stationary fixed, nonremovable part inside
the device. The warning marking placed inside the cover or on the connection diagram attached to the
inside of a cover is not acceptable.
74.3 A wall-mounted room thermostat, room humidistat, or the like shall be marked with the word
CAUTION and the following or the equivalent: High voltage Disconnect power supply before
servicing. Such marking shall be prominent and located where visible at the time of exposure of live parts
to persons, and may be on the mechanism, but not inside the cover.
74.4 A live heat sink or other part likely to be mistaken as dead metal and exposed to persons as
specified in 23.1.8 and 23.1.9 shall be marked with the word CAUTION and the following or the
equivalent: Risk of Electric Shock Plates (or other word describing the type of part) are live
Disconnect power supply before servicing. The marking shall be in letters at least 1/8 inch (3.2 mm) high
and shall be located on the live part so as to make the risk known before the part is likely to be touched.
74.5 A cautionary marking that is required to be permanent shall be located on a part that cannot be
removed without impairing the operation or appearance of the equipment.
74.6 A marking that is required to be permanent shall be molded, die-stamped, paint-stenciled, stamped
or etched metal that is permanently secured, or indelibly stamped or pressure-sensitive labels secured by
adhesive that is found to be acceptable for the application when subjected to the tests described in
Permanence of Marking Test, Section 60. Ordinary usage, handling, and storage of the device are to be
considered in the determination of the permanence of the marking.
74.7 A cautionary marking intended to instruct the operator shall be legible and visible by the operator
during the normal operation of the appliance. A marking giving servicing instructions shall be legible and
visible when such servicing is being performed.
74.8 A cautionary marking shall be prefixed with the word CAUTION, WARNING, or DANGER in
letters not less than 1/8 inch (3.2 mm) high. The remaining letters of such marking, unless specified
otherwise in individual marking requirements, shall not be less than 1/16 inch (1.6 mm) high.
74.9 A power source with multiple secondary windings with total output voltage exceeding the values in
column 4 or 5 in Table 63.3 or with total output current or power exceeding the limit specified in 63.4.2
and 63.6.1, respectively, shall be marked with the word WARNING and the following statement or the
equivalent: Risk of Electric Shock or Fire. Do Not Interconnect Secondary Windings. See 36.2.3.
74.10 A 2-wire, 220 250 volt product intended for connection to a circuit operating at 150 volts or less
to ground shall be marked with the word DANGER and the following or the equivalent: To Reduce the
Risk of Electric Shock Do not connect to a circuit operating at more than 150 volts to ground.
74.11 A 3-wire, 3-phase, 220 250 volt product intended for connection to a circuit operating at 150 volts
or less to ground shall be marked with the word DANGER and the following or the equivalent: To
Reduce the Risk of Electric Shock Do not connect to a circuit operating at more than 150 volts to
ground.
75.1 A Class 2 power source, a controller containing such a power source, or a controller that switches
or consumes Class 2 power is to be marked as stated in 74.9 and 75.2 75.9, as appropriate.
Exception: If the possible risks contemplated in 74.9 do not exist, and if the Class 2 power source,
circuitry, and load are entirely within factory-wired equipment, the marking is not required.
75.2 A Class 2 power source shall be marked Class 2.
75.3 If a low-voltage device or part of the equipment is intended to be wired in the field to become only
part of a Class 1 circuit or a Class 2 circuit wired with Class 1 wire, the terminals of the device or part of
the equipment shall be marked accordingly.
75.4 A low-voltage switching or power-consuming device or part of the equipment that is intended to be
wired in the field to become part of a Class 2 circuit only shall be marked accordingly.
75.5 A low-voltage device or part of the equipment that is acceptable for connection to either a Class 1
or a Class 2 circuit is not required to be so marked.
75.6 If wiring instructions are provided with the device or equipment, they shall not conflict with the
75.7 Equipment having two or more Class 2 circuits arranged as described in 36.2.3 shall be marked in
accordance with 74.9.
75.8 If a secondary voltage rating of a Class 2 power source exceeds the acceptable limit where wet
contact is likely to occur (immersion not included), it shall be marked: Restrict Load Circuit to Locations
Where Wet Contact Is Not Likely to Occur, or NEC Class 3 Wiring Must Be Used, or the equivalent.
75.9 If the open-circuit secondary voltage of a power source exceeds the values specified in column 5 in
Table 63.3 for the specified frequencies, but is not more than the values in column 4, the power source
shall be marked in accordance with 75.8.
76 Instructions
76.1 For equipment having a 2-blade, polarized attachment plug, the following instructions, or the
equivalent, shall be provided: To reduce the risk of electric shock, this equipment has a polarized plug
(one blade is wider than the other). This plug will fit in a polarized outlet only one way. If the plug does not
fit fully in the outlet, reverse the plug. If it still does not fit, contact a qualified electrician to install the proper
outlet. Do not change the plug in any way.
76.2 For equipment having a grounding-type attachment plug, the following instructions, or the
equivalent, shall be provided: To reduce the risk of electric shock, this product has a grounding type plug
that has a third (grounding) pin. This plug will only fit into a grounding type power outlet. If the plug does
not fit into the outlet, contact a qualified electrician to install the proper outlet. Do not change the plug in
any way.
SPECIAL-PURPOSE DEVICES
77 Scope
77.1 These requirements cover special-purpose devices the design and function of which necessitate
specific constructional and performance requirements to judge their acceptability.
78 Fan/Heat Sequencers
78.1 Scope
78.1.1 These requirements cover a fan/heat sequencer that is a multiple-circuit device to be used alone,
or a multiple- or single-circuit device that is intended to be used with other devices to sequentially control
a fan and heater or heating elements in electric central air-heating equipment.
78.1.2 These requirements do not cover additional tests that are required for a heat sequencer or similar
device that responds to a limit control to de-energize heaters to reduce the likelihood of unsafe
temperatures.
78.1.3 A device that is not involved in the sequence of operation between a fan and a heating element
or elements is not investigated as a fan/heat sequencer, and need not comply with the requirements in
this section of the standard.
78.1.4 These requirements do not cover additional tests, different tolerances, or the like, required for a
fan-delay control.
78.2 General
78.2.1 A fan/heat sequencer shall comply with the applicable requirements in Sections 1 74
supplemented by and, in some cases amended by, the requirements given in this section.
78.2.2 The sequence of operation of the fan circuit to that of any heating circuit in a fan/heat sequencer
shall be such that the fan circuit is energized at any time that any heating circuit is energized. This
sequence of operations shall be met for the most severe manufacturing tolerance and drift as a result of
the endurance test of the device or devices to be employed on the heating equipment. The sequence of
operation between different heating circuits is not specified.
78.2.3 Whether a device complies with the requirement in 78.2.2 is to be determined by combining the
assigned product tolerances with the greater of the absolute drift or percent drift in calibration and then
comparing the time data thus obtained for the fan circuit with all heater-element circuits.
78.2.4 The required sequence of operation shall be attained by:
a) Different timings of fan and heater-element controls,
b) A mechanical arrangement,
c) A combination of the means specified in (a) and (b), or
d) An equivalent construction.
78.2.5 It may be necessary to test ganged or stacked fan/heat sequencers as combinations, rather than
as individual units.
78.2.6 The sequence of operation of the fan and heater contacts shall not depend upon the operation of
a motor unless stalling of the motor in any position does not affect the sequence of operation.
78.2.7 An electronic or solid-state circuit used in a fan/heat sequencer shall perform acceptability in a
reliability evaluation.
78.2.8 A setting that affects the sequence of operation shall be sealed or factory-secured in accordance
with the requirements in Means for Calibration, Section 13.
78.3 Performance
78.3.1 General
78.3.1.1 To determine whether the sequence of operation is acceptable, a fan/heat sequencer is to be

subjected to the following tests in the order given:
a) Initial time-calibration test I;
b) Initial time-calibration test II at different ambient air temperatures and voltages;
c) Endurance; and
d) Time-calibration after endurance.
78.3.2 Bimetal-heater design
78.3.2.1 A bimetal-heater hot-wire, or similar fan/heat sequencer shall be time calibrated as specified in
78.3.3.1 78.3.7.1.
78.3.3 Initial time-calibration test I
78.3.3.1 The operating times determined in the initial time-calibration tests shall be within the assigned
production tolerances.
78.3.3.2 Initial time-calibration tests shall be conducted on separate samples having the shortest,
average, and longest rated time settings, and on samples of different assigned production time tolerances,
to represent the intended variations in a line of devices. One test is to be conducted on each sample; or,
at the manufacturers request, the time setting is to be recorded as the average of three tests.
78.3.3.3 For the time-to-close calibration-verification test, the device is to remain at room temperature
with the bimetal heater de-energized, until conditions have stabilized. The bimetal heater is then to be
energized at rated voltage, and the time for each load circuit to close is to be determined and recorded.
The current through the load circuit is to be a value sufficient for detection purposes.
78.3.3.4 Room temperature is to be nominally 25C (77F), except that if the timing is severely affected
by ambient air temperature, the manufacturers specified ambient-air-temperature range is to be used.
78.3.3.5 For the time-to-open calibration-verification test, the device is to be at room temperature as
noted in 78.3.3.3 with the bimetal-heater energized at rated voltage and:
a) Maximum rated current through all load-circuit contacts, or
b) A detection current through the load contacts if current does not affect timing.
78.3.3.6 When thermal equilibrium is attained, the bimetal heater is to be de-energized, and the time for
each load circuit to open is to be determined and recorded.
78.3.4 Initial time-calibration test II
78.3.4.1 Additional initial time-calibration-verification tests shall be conducted using the method described
in 78.3.3.3 78.3.3.6 except that the test conditions shall be:
a) Rated bimetal-heater voltage and an ambient-air temperature of 0C (32F);
b) Rated bimetal-heater voltage and an ambient-air temperature equal to the maximum rating,
but not less than 66C (151F);
c) Eighty-five percent of rated bimetal-heater voltage and room temperature; and
d) One hundred-ten percent of rated bimetal-heater voltage and room temperature.
78.3.4.2 Under each of the four conditions specified in 78.3.4.1, the fan/heat sequencer shall comply with
the requirement in 78.2.2.
78.3.4.2 revised May 4, 2001
78.3.5 Endurance
78.3.5.1 An endurance test preceded by an overload test as described in Overload Test, Section 45, shall
be conducted on one sample having the highest heating effect from the bimetal-heater, at maximum
current and at maximum rated ambient temperature. The heater is to be cycled using rated ambient
temperature and rated voltage. The endurance test on fan and heater contacts in a fan/heat sequencer
system shall be 30,000 cycles of operation conducted at a maximum rate of 1 cycle per minute as
specified in note a or b to Table 46.1. Only one pole of a multistage device is to be loaded, unless loading
of the other poles contributes to timing differences. Additional overload and endurance tests are to be
conducted on separate samples for additional ratings, or the like. These samples need not be calibrated,
unless such ratings contribute to timing differences.
78.3.6 Dielectric voltage withstand
78.3.6.1 The device shall be subjected to a dielectric voltage-withstand test in accordance with the
requirements in Dielectric voltage-Withstand Test, Section 47.
78.3.7 Time-calibration-verification time after endurance
78.3.7.1 The sample subjected to the endurance test shall be recalibrated using the method specified for
the initial time-calibration test I. The test results are to be judged as described in 78.2.2 and 78.2.3.
78.3.8 Other design
78.3.8.1 A fan/heat sequencer of a design not contemplated by these requirements, such as a

motor-drive, multiple-cam type, a device with a mechanical staging arrangement, or a
temperature-operated type, shall be tested in a manner appropriate for its design to obtain the results
contemplated by 44.3 44.10 or 78.3.3.2 78.3.7.1.
78.3.8.2 A mechanical arrangement or other feature shall sequence the fan and heater-element
operation, both before and after the endurance test, to comply with the requirements in 78.2.2 and 78.2.3.

78.4 Mechanical and production tests
78.4.1 A fan/heat sequencer shall be subjected to the manufacturing and production tests described in
Details, Section 65.
78.5 Rating
78.5.1 Each fan/heat sequencer or circuit shall be assigned a maximum ambient-air-temperature rating
and timing ratings. For a multicircuit device, the time-calibration rating of concern is that of the fan circuit
with respect to any or all heater circuits. The ratings are to include:
a) Maximum ambient-air temperature;
b) The range of ambient temperatures to which the normal timings apply;
c) Normal time-to-close and time-to-open; and
d) Manufacturing tolerances, such as a plus-or-minus percentage of time.
78.5.2 The requirements specified in 78.5.1 (c) and (d) may be combined and expressed as time ranges
or minimum operating time between stages on closing and opening.
78.6 Marking
78.6.1 A fan/heat sequencer shall be marked with the time-calibration and tolerance ratings as specified
in 78.5.1 unless a different catalog number, or the equivalent, is assigned and marked for each different
rating.
79 Fluorescent-Lamp-Ballast Protectors
79.1 Scope
79.1.1 These requirements cover automatically reset thermostats intended to be employed in fluorescent
lamp ballasts for overtemperature protection.
79.2 General
79.2.1 A fluorescent-lamp-ballast protector shall comply with the applicable requirements in Sections 1
74 supplemented by, and in some cases amended by, the requirements given in this section.
79.3 Construction
79.3.1 The means for calibration shall comply with the requirements in Means for Calibration, Section 13.
79.3.2 Spacings between parts of opposite polarity, different circuits, or exposed dead metal parts shall
be in accordance with column F of Table 32.1.
79.3.3 Spacings between parts of the same polarity specified in notes e and g to Table 32.1 do not apply.
79.4 Performance
79.4.1 Initial calibration-verification
79.4.1.1 The opening temperature of a protector shall not differ by more than 5C (9F) from the rated
opening temperature.
79.4.1.2 One sample of the protector shall be tested in accordance with 44.5 44.7. Opening of the
protector shall be determined by any means that does not pass more current through the protector than
3 percent of the rated protector current, or 0.010 ampere, whichever is less.
79.4.2 Endurance test
79.4.2.1 The sample subjected to the initial calibration-verification test shall be used for the endurance
test. The protector shall make and break a load of twice the rated current, having a 40 50 percent power
factor, at rated voltage for 10,000 cycles of operation. The cycling rate shall be in accordance with note
a or b to Table 46.1. There shall be no electrical malfunction, mechanical damage to the device, or undue
burning, pitting, or welding of the contacts. See Overload Test, Section 45 and Endurance Test, Section
46 for general test methods.
79.4.3 Repeated calibration
79.4.3.1 The same sample used in the initial calibration-verification and endurance tests shall be
subjected to a repeated calibration-verification test using the test procedure described in 79.4.1.2.
79.4.3.2 In the repeated calibration-verification test the opening temperature shall not be more than 5C
(9F) more than the opening temperature recorded during the initial calibration-verification test.
79.4.4 Overload test
79.4.4.1 A previously untested sample shall be used for the overload test. The protector shall make and
break a load having a 40 50 percent power factor at rated voltage, for 1000 cycles of operation. The
test current shall be four times the rated current, but not less than 20 amperes at 120 volts. There shall
be no electrical malfunction, mechanical damage, or undue burning, pitting, or welding of the contacts.
See Overload Test, Section 45 for general test methods.
Exception: A protector rated less than 5 amperes at 120 volts need not complete 1000 cycles of
operation if it fails in the open position, and if two additional samples, tested in the same manner, also fail
in the open position.
79.4.5 Limited-short-circuit test
79.4.5.1 When a protector is tested as described in 79.4.5.2 there shall be no ignition of the cotton
indicator or any other evidence of a risk of fire such as emission of flame or molten metal during or after
the test.
Exception: The limited-short-circuit test may be waived if the test is to be conducted on the protector
when it is installed in a ballast.
79.4.5.2 Three previously untested samples are to be subjected to a limited-short-circuit test. The test is
to be conducted at 5 percent of the rated voltage of the protector with the protector in series with a
20-ampere nonrenewable fuse having design characteristics such that it will not open in less than 12
seconds when carrying 40 amperes. The circuit is to limit the current to 200 amperes, measured without
the protector in the circuit. The power factor of the circuit is to be 0.9 1.0 unless a lower power factor
is agreeable to those concerned. The protector is to be connected in the circuit by two 3-foot (0.91-m)
lengths of No. 14 AWG copper wire. Cotton is to be wrapped around the protector during the test. Each
protector is to be subjected to one test in which the short circuit is closed on the protector.
79.4.5.3 If the protector cycles during this test and if the cotton is not ignited the test is to be continued
until the protector permanently opens the circuit or until the fuse opens.
79.5 Manufacturing and production tests
79.5.1 A protector shall be subjected to the manufacturing and production tests specified in Details,
Section 65.
79.6 Marking
79.6.1 A protector shall be marked in accordance with the applicable requirements in General, Section
69.
Exception: The electrical rating need not be marked.
79.6.2 The marking of the set-point temperature shall be as specified in Calibration Setting, Section 71.
Exception: A distinctive catalog designation may be used in lieu of a separately marked set-point
temperature.
80 Control-Circuit Temperature-Limiting Devices for Temperature Protection of Enclosures of

Motors and Generators for Use in Hazardous Location
80.1 Scope
80.1.1 These requirements cover automatically reset temperature-limiting devices intended to be installed
in motors and generators for use in hazardous locations, and to be connected in the motor-control circuit
to limit enclosure temperatures.
80.1.2 These requirements cover devices that are to be connected into a 3-wire, start-stop, push-button
control circuit, so that manual restarting is required.
80.1.3 These requirements do not cover:
a) A device connected directly in the motor or generator circuit,
b) A device intended to limit the motor- or generator-winding temperatures, or
c) An auxiliary temperature-limiting device in the motor- or generator-control circuit that is not

relied upon to limit the enclosure temperatures, unless agreeable to the manufacturer.
80.2 General
80.2.1 A control-circuit temperature-limiting device shall comply with the applicable requirements in
Sections 1 74 supplemented by and, in some cases amended by, the requirements given in this section.
80.3 Construction
80.3.1 Means for calibration
80.3.1.1 The means for calibration shall comply with the requirements in Means for Calibration, Section
13.
80.3.2 Spacings
80.3.2.1 Spacings between parts of opposite polarity, different circuits, or grounded or exposed dead
metal parts, shall be in accordance with column A or D of Table 32.1.
80.3.2.2 Spacings between parts of the same polarity specified in notes e and g of Table 32.1 do not
apply.
80.4 Performance
80.4.1 Initial calibration-verification
80.4.1.1 A control-circuit temperature-limiting device is to be tested at the ambient-air temperature or at

temperatures consistent with its intended use.
80.4.1.2 One sample of the device is to be tested in accordance with the requirements in 44.5 44.7.
The opening temperature of the device shall not differ by more than 5C (9F) from the rated opening
temperature.
Exception: The initial calibration-verification tolerance may differ by 5C (9F) from the rated opening
temperature if acceptable in the end-use product.
80.4.2 Overload
80.4.2.1 The sample subjected to the initial calibration-verification test shall be used for the overload test.
A device shall, in sequence, carry the inrush current of a moving armature load, then break (only) the
normal (sealed) current of an electromagnetic load of rated value at 110 percent of the voltage specified
in Table 38.1 for 50 cycles of operation. See 45.4. A new sample may be used for each overload-test
potential for which the device is rated. There shall be no electrical malfunction, mechanical damage to the
device, or undue burning, pitting, or welding of the contacts.
80.4.2.2 The load is to consist of an electromagnet representative of the magnet-coil load that the device
is intended to control. For an alternating-current device, the power factor is to be 0.35 or less and the
inrush current is to be ten times the normal current unless the normal (sealed) and inrush ampere ratings
are separately specified in 80.6.1 and 80.6.2. The test shall be conducted with the contactor free to
operate; for example, not blocked in either the open or closed position.
80.4.3 Endurance
80.4.3.1 The sample subjected to the initial calibration-verification and overload tests is to be used for the
endurance test. A device shall, in sequence, carry the inrush current of a moving-armature load as
described in 80.4.2.2, then break (only) the normal (sealed) current of an electromagnet load of rated
value at the voltage specified in Table 38.1 for 10,000 cycles of operation. A new sample may be used for
each endurance-test potential for which the device is rated, except that each device is to be subjected to
the appropriate overload test before the endurance test is conducted. There shall be no electrical
malfunction, mechanical damage to the device, or undue burning, pitting, or welding of the contacts.
Exception: For a device tested by making and breaking the load during the overload and endurance
tests, the endurance test may be 6000 cycles of operation.
80.4.4 Repeated-calibration-verification test
80.4.4.1 The sample used in the initial-calibration-verification, overload, and endurance tests is to be
subjected to a repeated-calibration-verification test using the test procedure described in 80.4.1.1 and
80.4.1.2.
80.4.4.2 In the repeated-calibration-verification test, the opening temperature shall not vary from the
as-received opening temperature by more than 5 percent of the maximum set-point Fahrenheit
temperature, or by more than 5C (9F) whichever is greater, except as noted in 44.4 and 54.6.
80.4.5 Dielectric voltage withstand
80.4.5.1 A device, in which there are parts of opposite polarity, different circuits, or grounded or exposed
dead metal parts, is to be tested in accordance with Dielectric voltage-Withstand Test, Section 47.
80.5 Manufacturing and production tests
80.5.1 A device is to be subjected to the manufacturing and production tests specified in Details, Section
65.
80.6 Rating
80.6.1 A device shall be rated in volts, alternating- or direct-current, or both, and in volt-amperes pilot
duty; or for alternating-current in amperes normal (sealed) and amperes inrush. For a pilot duty rating
stated as volt-amperes, the value to be used is the product of the normal (sealed) amperes and the
voltage.
80.6.2 Normal pilot-duty ratings for alternating-current are 360 and 720 volt-amperes, and for
direct-current, 137.5 and 275 volt-amperes. Other ratings may be used if at least 360-volt-amperes normal
(sealed) for alternating-current and 137.5 volt-amperes for direct-current.
80.7 Marking
80.7.1 General
80.7.1.1 A control-circuit temperature-limiting device shall be marked in accordance with the applicable
requirements in General, Section 69.
80.7.2 Calibration setting
80.7.2.1 The marking of the set-point temperature shall be as specified in Calibration Setting, Section 71.
81 Single-Operation Devices
81.1 Scope
81.1.1 These requirements cover single-operation thermostats for use in appliance temperature-limiting
applications. Such a thermostat is designed so that once the thermostat has been actuated it cannot be
reset manually and will not automatically reset.
81.1.2 A single-operation device is to be tested to determine that the contacts will not reclose
automatically at either 0C or minus 35C as specified by the manufacturer. The acceptability of the
temperature at which the device does reclose is to be investigated in the end-use application.
81.1.3 A device that recloses at a temperature above 0C is to be investigated as an automatically reset

control.
81.2 General
81.2.1 A single-operation device shall comply with the applicable requirements in Sections 1 74
supplemented by, and, in some cases amended by, the requirements given in this section.
81.3 Operation mechanism
81.3.1 There shall be no means to permit resetting of a single-operation device, such as a hole in the
body over the bimetal.
81.4 Construction
81.4.1 Means for calibration
81.4.1.1 The means for calibration shall comply with the requirements in Means for Calibration, Section
13.
81.4.2 Spacings
81.4.2.1 Spacings between parts of opposite polarity, different circuits, and live parts and grounded or
exposed dead metal parts, shall be in accordance with the values specified in column A, D, E, or F of
Table 32.1, depending upon the intended use.
81.4.2.2 Spacings between parts of the same polarity specified in note e or g of Table 32.1 shall apply
depending upon the intended use.
81.5 Performance
81.5.1 General
81.5.1.1 A single-operation device shall be subjected to the tests described in 81.5.2.1 81.5.6.1 in the
order in which they are presented.
81.5.2 Calibration-verification test I
81.5.2.1 Ten samples of the thermostat shall be subjected to a calibration-verification test as required by
Temperature Test, Section 40 to determine the average opening and closing temperature. The opening
temperature of the devices shall be within the calibration limits specified in Calibration-Verification Test,
Section 44. A thermostat that recloses at either below 0C or below minus 35C as specified by the
manufacturer is acceptable.
81.5.2.2 The samples are to remain at the maximum reclosing temperature for at least 7 hours and the
contacts are to be checked to be sure they are open.
81.5.3 Conditioning test
81.5.3.1 The contacts of ten samples of a single-operation device shall remain closed when conditioned
for 720 hours at the following temperatures:
a) For a control rated 300F (149C) or less, the greater of 6 percent or 12F below the
Fahrenheit set-point temperature;
b) For a control rated 400F (204C) to 301F (149C), 8 percent below the Fahrenheit set-point
temperature; or
c) For a control rated more than 400F, 10 percent below the Fahrenheit set-point temperature.
81.5.4 Calibration-verification test II
81.5.4.1 The ten samples subjected to the conditioning test are to be recalibrated. Opening temperatures
shall be within the limits specified in Calibration-Verification Test, Section 44. Reclosing temperatures
shall remain below 0C or minus 35C, as specified by the manufacturer.
81.5.5 Overload and endurance tests
81.5.5.1 One sample of a single-operation device with a specified reclosing temperature below 0C, but
not below minus 35C, is to be subjected to a 50-cycle overload test and a 6000-cycle endurance test
make and break performed in a reduced ambient chamber. The tests are to be conducted as described
in Overload Test, Section 45 and Endurance Test, Section 46.
81.5.5.2 Ten samples of a single-operation device with a specified reclosing temperature below minus
35C are to be subjected to a 1 cycle overload test breaking the circuit only as described in Overload
Test, Section 45.
81.5.5.3 There shall be no electrical or mechanical breakdown; malfunction that could cause the contacts
to remain closed; or welding or undue burning or pitting of the contacts.
81.5.6 Dielectric voltage-withstand test
81.5.6.1 All samples are to be subjected to a dielectric voltage-withstand test as described in Dielectric
voltage-Withstand Test, Section 47.
81.6 Manufacturers inspection and test program
81.6.1 The manufacturer shall provide a regular control program, inspection, and tests for
single-operation devices. The program shall include at least the following:
a) Parts of single-operation devices shall be examined for workmanship, materials, and finish to
determine that they are free from fabrication flaws and are within design tolerances;
b) A calibration test shall be conducted under prescribed conditions and following a prescribed
method; and
c) Devices shall be subjected to a 1-minute dielectric voltage-withstand test at 1000 volts plus
twice rated voltage, or a 1-second test at 120 percent of that voltage.
81.6.2 For the production dielectric voltage-withstand testing specified in 81.6.1(c), the requirement for a
500 volt-ampere or larger transformer as specified in 47.1.12 may be waived if the testing equipment used
is such that it maintains the specified high potential at the equipment for the duration of the test; for
example, if the transformer is provided with a voltmeter to measure directly the applied output potential.
81.7 Ratings
81.7.1 A device shall be rated as specified in General, Section 67.
81.8 Marking
81.8.1 A device shall be marked in accordance with the applicable requirements in General, Section 69.
81.8.2 The marking of the set-point temperature shall be as specified in Calibration Setting, Section 71.
82 Thermal Protective Devices for Lighting Fixtures
82.1 Scope
82.1.1 These requirements cover thermal protective devices, including thermal protectors and
self-heating thermal protectors (SHTP), intended for use in lighting fixtures. Thermal protective devices
shall comply with the applicable requirements in Sections 1 73 supplemented by and, in some cases
amended, by the requirements in this section.
82.2 Enclosures
82.2.1 A SHTP that is intended to be installed such that all splices, terminals, and current-carrying parts
are not enclosed by the fixture shall be provided with its own integral enclosure that encloses all splices
and current-carrying live parts in metal, glass, ceramic, porcelain, or a polymeric material that complies
with requirements for fixed equipment in Polymeric Materials Tests, Section 62.
Exception No. 1: A polymeric enclosure complying with the security of mounting means test specified in
82.9.11 need not comply with the crush and impact tests specified in Polymeric Materials Tests, Section
62 and need only be temperature index rated mechanically without impact for the maximum operating
temperature.
Exception No. 2: Molded phenolic and similar thermosetting polymeric materials need not be subjected to
the flammability of enclosure test specified in 62.2, if it has a minimum flammability class of V-2 in
accordance with the Standard for Tests for Flammability of Plastic Materials for Parts in Devices and
Appliances, UL 94.
82.3 Accessibility
82.3.1 A thermal protective device provided with an integral enclosure shall not permit the accessibility
probe shown in Figure 7.1 to contact current-carrying parts. An accessibility barrier provided to restrict
access to current-carrying parts when installed in accordance with the manufacturers instructions shall
comply with the requirements in 82.3.2 82.3.5.
82.3.2 An accessibility barrier shall be constructed of:
a) Metal (ferrous, aluminum, brass, zinc, or copper) minimum 0.016 inch (0.4 mm) thick;
b) Glass, porcelain, or ceramic minimum 1/8 inch (3.2 mm) thick;
c) Impregnated glass fiber sleeving at least 0.01 inch (0.3 mm) thick that is rated for the
temperature involved;
d) Vulcanized fiber minimum 0.028 inch (0.71 mm) thick; or
e) A polymeric material that complies with 82.3.3.
Exception: An accessibility barrier may be of a thickness less than that specified if it complies with the
82.3.3 A polymeric material used to form an accessibility barrier shall:
a) Be rated for at least the maximum operating temperature of the barrier in the fixture;
b) Be classified at least HB in accordance with the Standard for Tests for Flammability of Plastic
Materials for Parts in Devices and Appliances, UL 94; and
c) Comply with minimum property and test requirements in the Standard for Polymeric Materials
Use in Electrical Equipment Evaluations, UL 746C.
82.3.4 The minimum properties are maximum assigned performance level category 2 (30 seconds
ignition time) for hot wire ignition (HWI) and maximum assigned performance level category 1 (60 arcs)
for high-ampere arc ignition (HAI). The barrier shall additionally be subjected to the mold stress relief test
specified in 62.11.1.
82.3.5 An accessibility barrier need not be of the minimum thickness specified in 82.3.2 if the application
of a force of 10 pounds (44.5 N) over an area of 1 square inch (6.45 cm 2 ) on the barrier does not result
in:
a) Permanent distortion of a metal barrier,
b) Temporary displacement of a metal barrier that results in a reduction in spacings, or
c) Breaking or cracking of a glass, porcelain, ceramic, or polymeric barrier.
Exception: Permanent or temporary distortion of a polymeric barrier is acceptable if parts required to be

inaccessible continue to be inaccessible in accordance with 82.3.1 both during and after the application of
the force.
82.4 Open hole
82.4.1 An open hole provided in the enclosure of a thermal protective device that is not intended to be
enclosed by a part of a fixture shall comply with the ventilating opening requirements in 7.10.2 (b) and (g).
82.5 Insulating materials
82.5.1 A polymeric insulating material shall comply with one of the following:
a) The applicable electrical insulation requirements specified in the Standard for Polymeric
Materials Use In Electrical Equipment Evaluations, UL 746C;
b) The Standard for Extruded Insulating Tubing, UL 224, for at least the maximum voltage and
operating temperature involved; or
c) The requirements specified in 32.2.14.
Exception: Vulcanized fiber need not comply with the requirements in (a) (c) if it is used as an
insulating bushing, a washer, a separator, or a barrier and is not relied upon as the sole support material
where voltages are greater than 30 volts rms.
82.6 Wiring connections
82.6.1 All wiring connections shall comply with 19.18, 19.19, and 82.6.2.
82.6.2 All external leads of a thermal protective device that are intended for field connection shall be
provided with a strain relief means that does not transmit stress to internal connections when tested in
accordance with 82.9.2.1 and 82.9.2.2.
Exception: A strain relief means separate from the internal connection means need not be provided if:
a) The internal connection means is by a mechanical assembly, such as:
1) A lead passing through a hole in a printed wiring board and soldered in place,
2) A rivet,
3) A crimp, or
4) A rivet and crimp connection; and
b) The connection complies with the strain relief test in 82.9.2.1 and 82.9.2.2.
82.7 Mounting hardware
82.7.1 A securement means provided as an integral part of a thermal protective device shall be such that
the device cannot be readily removed without the use of a tool or other means that requires more than
unintentional contact to release the device from where it is mounted.
82.7.2 External parts of a thermal protective device shall be free of sharp edges and burrs that could cut
insulating materials that may come into contact with it when used as intended.
82.8 Spacings
82.8.1 Electrical spacings between parts of opposite polarity, different circuits, or exposed dead metal
parts shall be in accordance with column F of Table 32.1.
Exception: Spacings between parts of the same polarity specified in notes e and g to Table 32.1 do not
apply.
82.9 Performance
82.9.1 General
82.9.1.1 A thermal protective device is to be subjected to the following tests, as applicable. The tests are
to be conducted at a room ambient of 77 9F (25 5C) or as specified. Immediately preceding a test,
all materials involved in the test are to be at room ambient.
82.9.1.2 A thermal protective device is to be tested as rated for use with a tungsten load, a ballast load,
high-intensity-discharge load, or any combination of these loads. For testing, a high-intensity-discharge
lamp load may be represented by a ballast load. See also Fluorescent-Lamp-Ballast Protectors, Section
79.
82.9.2 Strain relief test
82.9.2.1 Strain relief for field wiring leads provided as an integral part of a thermal protective device is to
be tested by the application of a 20 pound (89 N) pulling force on the wires for 1 minute. For strain relief
provided in accordance with 82.6.2, the result is acceptable if the pull is not transmitted to terminals,
splices, or internal wiring. For strain relief provided in accordance with the Exception to 82.6.2, the result
is acceptable if the stress to individual connections does not cause internal parts to be displaced such that
the normal operation of the thermal protective device may be affected.
82.9.2.2 In testing in accordance with 82.9.2.1, the pull is to be applied to the wire in a direction
perpendicular to the plane of the entrance to the device. For strain relief provided in accordance with
82.6.2, the conductors are to be severed immediately adjacent to the terminals or splices, and movement
of any wire more than 1/16 inch (1.6 mm) at the point where it is severed is not acceptable. For strain
relief provided in accordance with the Exception to 82.6.2, the conductors are not to be severed.
82.9.3 Resistance test
82.9.3.1 The resistance of the heater in 3 previously unenergized SHTPs shall be measured by a suitable
ohmmeter in the unheated condition and then as specified in 82.9.3.2 and 82.9.3.3 with the device in the
unheated condition and the heated condition. The internal resistance of the 3 SHTPs shall not differ by
more than 5 percent of the average resistance of all 3 devices for each test method (ohmmeter or voltage
drop) and test condition (heated and unheated) specified. The average resistance of the internal
resistance in a heated condition may differ by more than 5 percent of the average resistance measured
in the unheated condition.
82.9.3.2 Each SHTP shall be connected to a source of supply adjusted to rated voltage, as illustrated by
Figure 82.1.

Figure 82.1
Circuit connections for parameter measurements

82.9.3.3 The internal resistance shall be calculated based on the voltage and current measurements
taken within 30 seconds of energizing the circuit and at three hours after energizing the circuit.
82.9.4 Temperature test
82.9.4.1 A SHTP shall be tested as described in 82.9.4.2 82.9.4.4 employing the measurement
methods described in Temperature Test, Section 40. During the test, the temperature at any point shall
not be sufficiently high to present a risk of fire, to damage any materials employed in the device, or to
attain temperature rises in excess of the temperature rises specified in Table 40.1.
82.9.4.2 A SHTP is to be installed in a 6 by 6 by 6 inch (152 by 152 by 152 mm) box constructed of 1/2
inch (12.7 mm) thick Grade A D fir plywood. A SHTP with measurement thermocouples attached is to
be inserted through an open hole in the box such that the back of the body of the device is flush with the
outside of the box. The open hole in the box is to have dimensions only as large as necessary to
accommodate the protector (snug fit). The open hole is to be located in the side of the box such that it is
centered horizontally and the top of the open hole is 1 inch (25.4 mm) below the top of the box.
82.9.4.3 The box is to be completely filled (flush with the top of the box) with expanding polyurethane
foam. A 1/2 inch (12.7 mm) thick plywood top is to be provided on the box.
82.9.4.4 A SHTP is to be connected to two separate supply sources. One supply source is to be adjusted
to rated voltage and connected through the integral thermal protector across the maximum rated lamp
load. The other supply source is to be connected to the SHTP heater and adjusted to the maximum
voltage that will not result in the integral thermal protector cycling within 7-1/2 hours (this usually will result
in operating the heater at less than rated voltage). If the thermal protector will not trip within 7-1/2 hours
at rated voltage and under the test conditions specified, two 4 inch square and 1-3/4 inch deep (102 by
102 by 44.5 mm) trade size metal outlet boxes are to be secured to the wood test box over the base of
the SHTP as shown in Figure 82.2. A length of No. 12 AWG Type THHN wire is to be arranged as shown
and secured in place by RTV sealant. With the supply voltage to the SHTP heater at rated voltage, the
box heater conductors are to be energized by a low voltage source of supply with the supply adjusted to
the maximum current that will not result in the thermal protector cycling within 7-1/2 hours. The lamp load
is to be located such that any heat produced by it will not affect the operation of the thermal protector.
Figure 82.2
Temperature test setup
82.9.5 Temperature calibration-verification
82.9.5.1 The cutout temperature of a thermal protector, including the integral thermal protector of a
SHTP, shall not differ by more than 5C (9F) from the rated cutout temperature or by more than 5 percent
from the rated Fahrenheit cutout temperature, whichever is greater.
82.9.5.2 A previously unenergized thermal protector is to be tested as specified in 44.6 and 44.7 to
determine the cutout temperature. The thermal protector is to be representative of a production thermal
protector that has been produced and calibrated within the same tolerances permitted in factory
production.
82.9.6 Time calibration-verification
82.9.6.1 The cutout time of 3 SHTPs tested as specified in 82.9.6.2 and 82.9.6.3 shall not differ by more
than 30 percent of the average cutout time if the average time is less than 3 hours, or 10 percent of the
average cutout time if the average time is 3 hours or greater.
82.9.6.2 Three previously unenergized SHTPs are to be tested under the same test conditions specified
for the temperature test in 82.9.4.2 82.9.4.4 with the internal heater of the SHTP connected to the rated
supply voltage and, if necessary, the outlet box heater.
82.9.6.3 The test conditions are to be the same for each SHTP tested, including the supply voltages to
the SHTP and the supply voltage to the outlet box heater.
82.9.7.1 The thermal protector subjected to the initial temperature calibration-verification, 82.9.5.1 and
82.9.5.2, is to be used for the overload test, and shall function as intended at the conclusion of the test.
A protector with a tungsten rating is to make and break a tungsten-filament lamp load for 50 cycles of
operation. For a tungsten-filament lamp load, the test cycle is to be minimum 1 second on and minimum
55 seconds off. A protector with a ballast or high-intensity-discharge rating is to make and break a ballast
load for 50 cycle of operation. The test current is to be 150 percent of the rated current, or 4.5 amperes,
whichever is greater. The voltage is to be 120 volts or the rated voltage, whichever is higher. See
Overload Test, Section 45 for the general test method.
82.9.7.2 If a wattage-rated device has wattage ratings with more than one voltage, a test at the highest
voltage is considered to be representative of tests at the lower voltages. However, if the device has a
higher wattage rating at the lower voltage than at the higher voltage, tests are to be conducted at the
highest and lowest voltages.
82.9.8.1 The thermal protector subjected to the overload test, 82.9.7.1 and 82.9.7.2, is also to be
subjected to the endurance test. A protector with a tungsten rating is to make and break a
tungsten-filament lamp load of rated current at rated voltage or 120 volts, whichever is greater, for 10,000
cycles of operation. The cycling rate is to be one cycle per minute with a minimum on period of 1 second
and a minimum off period of 55 seconds. For a protector with a ballast or high-intensity-discharge rating,
the test is to be conducted in accordance with the endurance test in Fluorescent-Lamp-Ballast Protectors,
Section 79. There shall be no electrical malfunction, mechanical damage to the device, nor welding,
undue burning, or pitting of the contacts.
82.9.8.2 At the conclusion of the endurance test, the thermal protector used in the endurance test is to
be subjected to the applicable calibration-verification tests in 82.9.5.2 82.9.7.2.
82.9.8.3 The results of the temperature calibration-verification, 82.9.5.1 and 82.9.5.2, on the thermal
protector used in the endurance test is considered acceptable if the cutout temperature does not rise
above the cutout temperature in the initial temperature calibration test by more than 5C (9F), or by more
than 5 percent of the rated Fahrenheit cutout temperature, whichever is greater.
82.9.9.1 A thermal protective device shall comply with the applicable requirements in Dielectric
voltage-Withstand Test, Section 47. A thermal protective device with a polymeric enclosure with no
accessible metal parts is to be tested with aluminum foil wrapped around the enclosure.
82.9.10 Abnormal operation tests
82.9.10.1 General
82.9.10.1.1 All abnormal tests are to be conducted with the thermal protective device lying in a relatively
horizontal position on a tissue covered pine board that is in a horizontal position or mounted as intended.
Previously unenergized devices are to be subjected to each abnormal test.
82.9.10.2 Short circuit
82.9.10.2.1 Three thermal protective devices are to be subjected to a short circuit test. Each device is to
be connected to a branch circuit supply with a power factor of 0.9 1.0, available current as specified in
Table 82.1, and adjusted to the maximum rated voltage for the device. A nonrenewable fuse that will not
open in less than 12 seconds while carrying twice its rated current, rated for the maximum intended
branch circuit amperes, 10,000 amperes fault current, and voltage-rated equal to or greater than the
maximum rated voltage of the thermal protective device is to be connected in series between the supply
and the thermal protective device. The conductor between each side of the branch circuit supply and the
thermal protective device are to be No. 8 AWG and are to be 4 feet (1.2 m) long. That part of a device
that could protrude into the concealed space of a building and any openings in the device are to be
wrapped with a layer of surgical cotton. The device is to be operated with the output of the device
connected to the grounded supply conductor, until the fuse opens or some part of the thermal protective
device is permanently open-circuited. The test setup is illustrated in Figure 82.3.
Table 82.1
Short-circuit currents
Branch circuit capacity at which device is intended to be

used (amperes) Circuit capacity (amperes)
20 200
30 1000
40 3500
50 5000
MARCH 4, 1999 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 171
Figure 82.3
Short circuit test setup
82.9.10.2.2 During and after the test, there shall be no ignition of the cotton. After the test, the thermal
protective device shall be permanently open-circuited; or if still functional, the cutout temperature shall not
rise above the cutout temperature in the initial temperature calibration-verification, 82.9.5.1 and 82.9.5.2,
by more than 10C (18F).
82.9.10.3 Overvoltage
82.9.10.3.1 Three SHTPs are to be subjected to an overvoltage test. Each SHTP is to be connected to
a supply circuit that has been adjusted to 10 percent above the rated nominal voltage of the device. Rated
nominal voltages are 120, 208, 240, 277, and 480. The SHTP is to be operated for 7-1/2 hours and is to
be caused to cycle (by an external heat source if necessary) 5 times during the 7-1/2 hours. During each
cycle, the SHTP is to be de-energized no more than 5 minutes.
82.9.10.3.2 After the conclusion of the test, the resistance of the heater shall be within 5 percent of its
value before the test, and the cutout temperature of the device shall not rise above the initial cutout
temperature by more than 5C (9F), or more than 5 percent of the rated Fahrenheit cutout temperature,
whichever is greater, when subjected to temperature calibration-verification, 82.9.5.1 and 82.9.5.2.
82.9.10.4 Thermal cycling
82.9.10.4.1 Three SHTPs are to be subjected to a thermal cycling test. Each SHTP is to be connected to
a source of supply adjusted to rated voltage and connected to a rated load. The supply is to be cycled on
and off such that the device is energized for one hour and then de-energized for the next hour and
repeated for a total of 1000 hours.
82.9.10.4.2 At the conclusion of the test, the resistance of the internal heater shall be within 5 percent of
its value before the test; and the cutout time of the device shall be within 5 minutes of the initial cutout
time as determined by subjecting the SHTP tested to the initial time calibration-verification, 82.9.6.1
82.9.6.3.
82.9.11 Security of mounting means tests
82.9.11.1 Load
82.9.11.1.1 Three SHTPs provided with an integral enclosure for mounting to a fixture are to be subjected
to a load test. Each SHTP shall withstand a 5 pound (2.27 kg) static load on any surface that is likely to
be exposed after installation, without cracking, breaking the SHTP, or displacing it from its original position
on a surface representative of the surface to which it is intended to be mounted. The load is to be applied
by hanging a 5 pound weight from the part of the SHTP most likely to dislodge it from its mounting with
the SHTP mounted as intended.
82.9.11.2 Impact
82.9.11.2.1 Three SHTPs provided with an integral enclosure for mounting to a fixture are to be subjected
to an impact test. Each SHTP shall withstand a 1 foot-pound (1.4 Nm) impact on any surface that is likely
to be exposed after installation, without cracking or breaking the SHTP, or damaging the SHTP such that
the SHTP could not be reinserted in the mounting hole, if dislodged, and would not comply with the load
test, 82.9.11.1.1, when mounted on a surface representative of the surface to which it is intended to be
mounted. The impact is to be applied by a 2 inch (50.8 mm) diameter sphere weighing 1.18 pounds (0.54
kg). The impact is to be applied to the SHTP enclosure in a downward direction.
MARCH 4, 1999 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 172A
82.10 Manufacturing and production-line tests
82.10.1 The manufacturer shall provide regular production control and inspections on each device and
perform the following tests at the intervals specified:
a) For a thermal protector, including a thermal protector intended for integral mounting in a SHTP,
temperature calibration-verification on 100 percent of production;
b) For a SHTP, a one minute dielectric voltage-withstand test at 1000 volts plus twice rated
voltage or a one second test at 120 percent of that voltage is to be conducted on 100 percent of
production;
Exception: A SHTP with no dead metal parts likely to become energized need not be subjected
to this test.
c) For a SHTP, after the device is assembled, measurement of the resistance of the internal
heater on 100 percent of production; and
d) For a SHTP, a time calibration-verification is to be conducted under a prescribed procedure.

172B TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 MARCH 4, 1999

82.10.2 The time calibration-verification is to be as specified for the time calibration-verification in 82.9.6.1
82.9.6.3. The temperature calibration-verification is to be conducted under the same test conditions
specified in 82.9.5.1 and 82.9.5.2, temperature calibration-verification. The production line dielectric
voltage-withstand test is to be conducted under the same test conditions as specified in Dielectric
voltage-Withstand Test, Section 47, and 65.1.3 for the dielectric voltage-withstand test. The
production-line resistance measurement is to be determined by an ohmmeter.
82.11 Ratings
82.11.1 A thermal protective device shall be rated in volts, alternating current frequency, and, as
applicable, watts tungsten, ballast, high-intensity-discharge, or any combination. The rating shall also
include the cutout temperature.
82.11.2 The rating shall include the maximum branch circuit rating in accordance with 82.9.10.2.1 if
intended for use on a branch circuit rated more than 20 amperes.
82.11.3 In addition to the rating specified in 82.11.1 and 82.11.2, the rating on a SHTP shall include the
internal heater resistance and the cutout time.
82.12 Markings
82.12.1 Each thermal protective device shall be permanently marked with:
a) The manufacturers name, trademark, or other descriptive marking by which the organization
responsible for the equipment may be identified,
b) A distinctive catalog number or the equivalent, and
c) The cutout temperature.
Exception: The cutout temperature need not be marked if a different catalog designation is employed for
each different cutout temperature.
83 Controllers for Solar-Energy Systems
83.1 Scope
83.1.1 These requirements cover controls for solar-energy systems (hereinafter referred to as solar
controllers).
83.1.2 A solar controller shall comply with the applicable requirements in Sections 1 74 supplemented,
and, in some cases amended, by the requirements in this section.
83.1.3 A solar controller that incorporates a cord and plug, a receptacle outlet, or both, is limited to use
with portable appliances, and shall be marked as specified in 83.3.2.
83.2 Supply connections
83.2.1 Permanently connected
83.2.1.1 A permanently connected solar controller shall be provided with supply-connection means in
accordance with 16.1.1 16.2.3.5.
83.2.2 Cord connected
83.2.2.1 CORD AND PLUG A solar controller not intended to be permanently connected to the supply
circuit shall be provided with a length of flexible cord and an attachment plug. The cord shall be Type S
or SJ, or equivalent, and shall be not more than 12 feet (3.7 m) long. The cord and plug shall be:
a) Sized for the electrical rating of the controller in accordance with 16.3.1; but the cord shall
not be smaller than No. 18 AWG (0.82 mm2),
b) Provided with a grounding contact conductor in accordance with Grounding, Section 21 and
Bonding of Internal Parts, Section 22, and
c) Made of materials having the necessary resistance to rain and sunlight if the cord will be
subjected to weather during intended use.
83.2.2.1 revised May 4, 2001
83.2.2.2 STRAIN RELIEF The strain-relief means and bushing shall comply with the requirements in
16.4.2.1 16.4.3.6.
83.2.2.3 RECEPTACLE A receptacle outlet shall be of the grounding type, and be sized for the rating
of the load.
83.3 Marking
83.3.1 A solar controller shall be marked in letters at least 1/16 inch (1.6 mm) high with the following or
equivalent: Controller, Accessories, and the Controlled Equipment Must Be Wired and Connected in
Compliance with the Installation Instructions.
83.3.2 A controller as specified in 83.1.3 shall be marked in letters at least 1/16 inch (1.6 mm) high with
the following or the equivalent: For Use Only With a Portable Appliance.
83.4 Instructions
83.4.1 A solar controller shall be provided with installation and operating instructions. The instructions
shall include information on proper wiring and connection to the supply, accessories, controlled
equipment, and sensing circuits.
84 Temperature-Regulating Thermostats for Household Drip-Type Coffee Makers
84.1 Scope
84.1.1 These requirements cover automatic temperature-regulating thermostats for use in household
drip-type coffee makers.
84.1.2 A temperature-regulating thermostat shall comply with the applicable requirements in Sections 1
74, supplemented by, and in some cases amended by, the requirements in this section.
84.1A Glossary
84.1A.1 Set-Point Temperature Rating (Ts-p) The temperature at which the thermostats electrical load
switching contacts change state upon temperature rise. For adjustable thermostats the Set-Point
Temperature Rating (Ts-p) is the temperature at which the thermostats electrical load switching contacts
change state, upon temperature rise, with the thermostat adjusted to the maximum temperature setting.
This rated value is a nominal figure of a temperature range. The range is defined by the allowable
tolerances specified in Section 84.4.
84.1A.1 added May 4, 2001
84.1A.2 Operating Temperature - Initial (Top-init) A temperature, measured during the initial calibration
verification test, at which the thermostats electrical load switching contacts change state upon
temperature rise. If multiple trials of the initial calibration test are conducted, this value is the arithmetic
average of up to three trials.
84.1A.2 added May 4, 2001
84.1A.3 Operating Temperature - Final (Top-fin) A temperature, measured during the repeated
calibration verification test conducted after the overload and endurance test sequence, at which the
thermostats electrical load switching contacts change state upon temperature rise. If multiple trials of
the final calibration test are conducted, this value is the arithmetic average of up to three trials.
84.1A.3 added May 4, 2001
84.1A.4 Maximum Normal Use Temperature Rating (Tmax) The maximum temperature permitted on
the thermostats sensing surface during normal operation of the coffee maker. This temperature is equal
to or greater than Ts-p.
84.1A.4 added May 4, 2001
84.1A.5 Maximum Dry Operation Temperature Rating (Tdry) The maximum temperature permitted on
the thermostats sensing surface during abnormal (dry) operation of the coffee maker. This temperature
is equal to or greater than Tmax.
84.1A.5 added May 4, 2001
84.1A.6 Reset Temperature (Treset) A temperature at which the thermostats electrical load switching
contacts change state upon temperature fall. This value is a performance-based value noted during the
overload and endurance test. This temperature need not be declared by the manufacturer. Calibration
verification tolerances are not applied to Treset.
84.1A.6 added May 4, 2001
84.2 Construction
84.2.1 The insulation material of a temperature-regulating thermostat shall have a performance level
category (PLC) value of 3 or less [comparative tracking index (CTI) value of 175 or higher].
84.3 Performance
84.3.1 Initial calibration-verification test
84.3.1.1 The Operating Temperature-Initial (Top-init) of a temperature-regulating thermostat shall not vary
from the Set-point Temperature Rating (Ts-p) by more than the tolerance specified in Table 84.3.1.1.
84.3.1.1 revised May 4, 2001
Table 84.3.1.1
Temperature Tolerances
Table 84.3.1.1 revised May 4, 2001
Ts-p Tolerance to the maximum fahrenheit Ts-p

Up to 300F (149C) 10F (6C)
301 to 400F (149.5 to 204C) 4 percent
Greater than 400F (204C) 5 percent
84.3.1.2 One sample of the thermostat is to be tested in accordance with 44.5 44.7.
84.3.2.1 The sample of the temperature-regulating thermostat subjected to the initial

calibration-verification test, 84.3.1.1 and 84.3.1.2, is to be subjected to an overload test at rated voltage
consisting of making and breaking a current of 150 percent of the rated value at a unity power factor for
50 cycles of operation. During each cycle of operation, the thermostat is to be exposed to a temperature
range from the Reset Temperature (Treset) to the Maximum Normal Use Temperature Rating (Tmax). There
shall be no electrical or mechanical breakdown, no loosening of parts, and no undue burning, undue
pitting, or welding of the contacts.
84.3.2.1 revised May 4, 2001
84.3.3.1 The temperature-regulating thermostat that has been subjected to the overload test is to be
subjected to an endurance test as described in 84.3.3.2 and 84.3.3.3. There shall be no electrical or
mechanical breakdown, no loosening of parts, and no undue burning, undue pitting, or welding of the
contacts.
84.3.3.2 The endurance test is to consist of making and breaking the rated current at a unity power factor
at rated voltage for 100,000 cycles of operation. During the first 5,000 cycles of the endurance test, the
thermostat is to be exposed to a temperature range from the Reset Temperature (Treset) to the Maximum
Dry Operatation Temperature Rating (Tdry). During the remaining 95,000 cycles of the test, the thermostat
is to be exposed to a temperature range from the Reset Temperature (Treset) to the Maximum Normal Use
Temperature Rating (Tmax).
84.3.3.2 revised May 4, 2001
84.3.3.3 The temperature-regulating thermostat is to be operated by alternately heating and cooling the
sensing surface. The thermocouple for measuring the temperature of the sensing element and the
insulating materials is to be located at the periphery of the thermostat face that normally is in contact with
the part being sensed. The manufacturer may supply the test sample with the thermocouple attached.
84.3.3.3 revised May 4, 2001
84.3.4 Repeated calibration-verification test
84.3.4.1 The sample used in the overload and endurance tests is to be subjected to a repeated
calibration-verification test using the test procedure described in 84.3.1.2.
84.3.4.2 In the repeated calibration-verification test the Operating Temperature-Final (Top-fin) shall not
vary from the Operating Temperature-Initial (Top-int) in the initial calibration test by more than 5 percent of
the maximum Fahrenheit Set-point Temperature Rating (Ts-p) or by more than 5C (9F), whichever is
greater.
84.3.4.2 revised May 4, 2001
84.3.5.1 A temperature-regulating thermostat having parts of opposite polarity, different circuits, or

grounded or exposed dead metal parts shall comply with the applicable requirements in Dielectric
voltage-Withstand Test, Section 47.
84.4 Ratings
84.4.1 A Set-point Temperature Rating(Ts-p), a Maximum Dry Operation Temperature Rating (Tdry), and
a Maximum Normal Use Temperature Rating (Tmax) shall be assigned by the thermostat manufacturer.
84.4.1 revised May 4, 2001
84.5 Markings
84.5.1 A temperature-regulating thermostat shall be marked in accordance with the applicable

requirements in General, Section 69. The markings shall be legible at the conclusion of the endurance
test.
84.5.2 The Set-point Temperature Rating (Ts-p) shall be marked as specified in Calibration Setting,
Section 71. The markings shall be legible at the conclusion of the endurance test.
84.5.2 revised May 4, 2001
JUNE 2, 1998 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 A1
APPENDIX A
Standards for Components
Standards under which components of the products covered by this standard are evaluated include the
following:
Title of Standard UL Standard Designation
Attachment Plugs and Receptacles UL 498

Capacitors UL 810
Capacitors for Radio- and Television-Type Appliances, Across-the-Line, Antenna-Coupling and
Line-by-Pass UL 1414
Cord Sets and Power-Supply Cords UL 817
Fittings for Cable and Conduit UL 514B
Fuseholders UL 512
Fuses for Supplementary Overcurrent Protection UL 198G
Grounding and Bonding Equipment UL 467
Industrial Control Equipment UL 508
Marking and Labeling Systems UL 969
Metallic Outlet Boxes UL 514A
Motors, Electric UL 1004
Nonmetallic Outlet Boxes, Flush-Device Boxes, and Covers UL 514C
Overheating Protection for Motors UL 2111
Plastic Materials for Parts in Devices and Appliances, Tests for Flammability of UL 94
Polymeric Materials Fabricated Parts UL 746D
Polymeric Materials Long Term Property Evaluations UL 746B
Polymeric Materials Short Term Property Evaluations UL 746A
Polymeric Materials Use in Electrical Equipment Evaluations UL 746C
Printed-Wiring Boards UL 796
Protectors for Use in Electrical Equipment, Supplementary UL 1077
Sleeving, Coated Electrical UL 1441
Switches, Special-Use UL 1054
Systems of Insulating Materials General UL 1446
Tape, Polyvinyl Chloride, Polyethylene, and Rubber Insulating UL 510
Terminal Blocks UL 1059
Terminals, Electrical Quick-Connect UL 310
Thermal Cutoffs for Use in Electrical Appliances and Components UL 1020
Time-Indicating and -Recording Appliances UL 863
Transformers, Specialty UL 506
Tubing, Extruded Insulating UL 224
Valves, Electrically-Operated UL 429
Wire, Flexible Cord and Fixture UL 62
Wire Connectors and Soldering Lugs for Use With Copper Conductors UL 486A
Wire Connectors for Use With Aluminum Conductors UL 486B
Wires and Cables, Rubber-Insulated UL 44
Wires and Cables, Thermoplastic-Insulated UL 83
A2 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - UL 873 JUNE 2, 1998

JUNE 2, 1998 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - CRG 873 CRG1
CANADIAN REQUIREMENTS COMPARISON GUIDE CRG 873
UL AND CANADIAN STANDARDS FOR TEMPERATURE-INDICATING AND

-REGULATING EQUIPMENT
CRG2 TEMPERATURE-INDICATING AND -REGULATING EQUIPMENT - CRG 873 JUNE 2, 1998
Product Category: Temperature-Indicating and -Regulating Equipment

UL Category Control Number: SDFY7, SDFY8, XAPX7, XAPX8
UL Standard:
Standard for Temperature-Indicating and -Regulating Equipment
UL 873
Eleventh Edition
Canadian Standard:
Temperature-Indicating and -Regulating Equipment
CAN/CSA-C22.2 No. 24-93
Eighth Edition
This Canadian Requirement Comparison Guide is only intended to identify Canadian requirements that
must be applied in addition to the requirements in the UL Standard to obtain a C-UL Mark. The guide is
not intended to replace a thorough review and comparison of the requirements applicable to the product
category as contained in the applicable UL and Canadian Standards. Where requirements are not
specifically addressed, compliance with the requirements in the UL Standard satisfy the requirements in
the Canadian Standard.
The actual requirements applied for a C-UL product investigation may differ from those identified in this
guide based on the specific features, characteristics, components, materials, or systems used in the
product.
CRG: 873
Issue No.: 1
Issue Date: June 2, 1998
Revisions of this guide will be made by issuing revised or additional pages bearing their date of issue. A
Canadian Requirement Comparison Guide is current only if it incorporates the most recently adopted
revisions, all of which are itemized on the transmittal notice that accompanies the latest set of revision
pages for the Guide.
The following outlines the requirements contained in CSA C22.2 No. 24-93 that are in addition to the
requirements in UL 873 that must be met in order for a product to bear the appropriate UL Marking. UL
provides a certification program for products that meet the Canadian requirements. The c-UL Mark
provides assurance that the product as evaluated by UL, complies with the appropriate Canadian
requirements.
Copyright 1998 Underwriters Laboratories Inc.

Requirements Topics CSA Clause Comparison

Scope 1.3 Scope includes extra-low voltage (Canadian Electric Code (CEC))
Class 2 room thermostats with anticipators.
Controls for use in household 3.2 Additional requirements are specified for controls in CSA C22.2 No.
electric ranges 61.
Weatherproof enclosure 4.2.7 An enclosure intended to be used outdoors shall comply with the
requirements in CSA C22.2 No. 94.
Field wiring terminal parts 4.7.2 The size of a screw used as the terminal shall not be less than No.
10 if it is intended for use with copper conductors larger than No. 12
AWG.
Leads 4.7.5 Leads of devices used as components in other assemblies shall not
be smaller than No. 22 AWG.
Wire-bending space 4.10.1 Wire-bending space requirements are specified for No. 14 AWG and
4.10.2 larger conductors in the CEC.
Tip-switches 4.14.5 A gravity type tip switch employed as part of an appliance thermostat
shall be tested per Clause 6.6.6 to determine operation at any
temperature setting.
Adhesives 4.19 Parts of enclosures or insulating liners secured by adhesives shall
comply with test program in Clause 6.18.
Bonding and Grounding 4.21 Bonding conductor size requirements are different and are specified in
CSA C22.2 No. 0.4. A ground lug terminal is required for all
applications (including household). Steel conduit connections are not
acceptable as a sole means for grounding.
Markings 5.1 (l) Safety controls rated for temperatures below 0C shall be marked with
the low temperature rating for which the controls have been
investigated.
5.8 The temperature rating of field wiring (105C maximum), shall be
marked per Clause 5.8 and the CEC.
5.9 A date code marking is required.
Table Continued

5.12 If a wall mounted thermostat complies with the requirements in
Clause 6.4.10, the thermostat shall be marked SUITABLE FOR
INSULATED WALLS.
Line Voltage Wall Mounted 6.4.10 Line voltage wall thermostats for an insulated building wall shall be
Thermostat tested while mounted in the test fixture for the temperature test and
Fig. 5 marking per Clause 5.12.
Overload Test 6.7.1 For non-motor load rating, the test shall be conducted at 120% of
both rated voltage and rated current of the non-motor load.
6.7.4 For pilot duty load rating, the test shall be conducted at 120% of rated
voltage.
Conditioning of Safety Controls 6.8 Conditioning as follows:
a) first, conditioned at minus 40C for at least 6 hours;
b) then, conditioned at room temperature for 24 hours;
c) then, conditioned at maximum rated temperature for 1

hour;
d) then, subjected to the Endurance Test, Clause 6.9.
Hydrostatic Pressure Test 6.19.1 to 6.19.3 Hydrostatic Pressure Test shall be conducted on all pressure controls.
Manual-Reset Limit Controls, 6.23.5 Test all manual reset limit controls for 30 N reset-force requirements.
Strength of Reset
Extra-Low Voltage Thermostats 7 Requirements for extra-low voltage (Class 2) wall thermostats are
with Heat Anticipators specified in Clause 7.
Fan/Heat Sequencers:
a) Operation at 8.4 Operation within 5 minutes at 85 percent of rated voltage is required.
minimum normal
voltage and
temperature
b) Operation at 8.6 Operation at 110 percent of rated values at 50C for 48 hours is
maximum normal required.
temperature and
overvoltage
c) Endurance Test 8.8 250,000 cycles for safety controls; 100,000 cycles for all other types
of controls.
Table Continued

Fluorescent-Lamp Ballast 9.1 Covers normal-reset and automatically reset thermostats.
Protection
9.4 6 samples may be required. The samples shall be subjected to the
endurance test with an overload of 4 times the rated current at 0.75
power factor.
a) manually-reset type 50 cycles;
b) automatically reset type 10,000 cycles.


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UL 873

Underwriters Laboratories Inc. (UL)

UL Standard for Safety for Temperature-Indicating and -Regulating Equipment, UL 873

Eleventh Edition, Dated December 22, 1994

Copyright 2001 Underwriters Laboratories Inc.

This Standard consists of pages dated as shown in the following checklist:

1-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . May 4, 2001

173 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . December 22, 1994

Standard for Temperature-Indicating and -Regulating Equipment

First Edition August, 1942

December 22, 1994

An effective date included as a note immediately following certain requirements

Revisions of this Standard will be made by issuing revised or additional pages

COPYRIGHT 1979, 2001 UNDERWRITERS LABORATORIES INC.

No Text on This Page

22.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

40 Temperature Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76A

62.7 Resistance to hot-wire ignition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .118

MANUFACTURING AND PRODUCTION TESTS

84 Temperature-Regulating Thermostats for Household Drip-Type Coffee Makers . . . . . . . . . . . .175

Standards for Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1

CANADIAN REQUIREMENTS COMPARISON GUIDE CRG 873

UL AND CANADIAN STANDARDS FOR TEMPERATURE-INDICATING AND -REGULATING

No Text on This Page

a) Refrigeration Controllers Humidistats for factory installation on or in refrigeration equipment;

d) Controls for Factory Installation on or in Appliances

2) Electric water-heater controls intended to regulate or limit water temperature.

3) Other controls including door-interlock thermostats for self-cleaning ovens; baseboard

1.8 A humidistat is investigated in the same manner as a thermostat.

2.3 EQUIVALENT SELF-HEATING THERMAL PROTECTOR A SHTP that is identified as being

2.4 ISOLATED-LIMITED-ENERGY CIRCUIT A circuit derived from an isolated secondary winding of

2.8 SELF-HEATING THERMAL PROTECTOR (SHTP) A thermal protective device consisting of a

2.10 THERMAL PROTECTOR A thermal protective device consisting of a temperature sensitive

4.2 A component is not required to comply with a specific requirement that:

b) Is superseded by a requirement in this standard.

7 Frame and Enclosure

No Text on This Page

7.2 Accessibility of live parts

7.2.2 An opening in an enclosure of a control is acceptable if an accessibility probe as illustrated in Figure

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Note: All length dimensions in millimeters

7.2.5 Deleted effective August 28, 1995

7.5 Cast metal

7.6 Sheet metal

Exception: A room thermostat shall be as specified in 7.9.3.

a) Single sheet with single formed flanges formed edges,

b) A single sheet that is corrugated or ribbed,

With supporting frame or equivalent

Without supporting framea With supporting frame or equivalent reinforcinga

d) Resistance to combustion and to ignition from electrical sources;

e) Dielectric properties, insulation resistance, and resistance to arc tracking; and

7.9 Room thermostats

a) An opening shall not be provided in a compartment or part of an enclosure that contains

b) No openings shall be located in the mounting surface of an enclosure.

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