This document provides guidance on selecting current transformers (CTs) for monitoring electrical systems, including:
1. Determine the monitoring point and whether the conductor can be disconnected to use a solid core CT.
2. Measure the conductor diameter and use that to determine the appropriate CT style (solid core, split core, etc.) and models.
3. Determine the necessary CT rating by considering the upstream breaker/fuse size and maximum current the conductor can handle. Select a CT with a primary rating at least 20% higher.
4. Choose the appropriate CT ratio (primary to secondary amps) based on the selected model and necessary rating. Looping conductors through multiple times can alter the ratio.
This document provides guidance on selecting current transformers (CTs) for monitoring electrical systems, including:
1. Determine the monitoring point and whether the conductor can be disconnected to use a solid core CT.
2. Measure the conductor diameter and use that to determine the appropriate CT style (solid core, split core, etc.) and models.
3. Determine the necessary CT rating by considering the upstream breaker/fuse size and maximum current the conductor can handle. Select a CT with a primary rating at least 20% higher.
4. Choose the appropriate CT ratio (primary to secondary amps) based on the selected model and necessary rating. Looping conductors through multiple times can alter the ratio.
This document provides guidance on selecting current transformers (CTs) for monitoring electrical systems, including:
1. Determine the monitoring point and whether the conductor can be disconnected to use a solid core CT.
2. Measure the conductor diameter and use that to determine the appropriate CT style (solid core, split core, etc.) and models.
3. Determine the necessary CT rating by considering the upstream breaker/fuse size and maximum current the conductor can handle. Select a CT with a primary rating at least 20% higher.
4. Choose the appropriate CT ratio (primary to secondary amps) based on the selected model and necessary rating. Looping conductors through multiple times can alter the ratio.
This document provides guidance on selecting current transformers (CTs) for monitoring electrical systems, including:
1. Determine the monitoring point and whether the conductor can be disconnected to use a solid core CT.
2. Measure the conductor diameter and use that to determine the appropriate CT style (solid core, split core, etc.) and models.
3. Determine the necessary CT rating by considering the upstream breaker/fuse size and maximum current the conductor can handle. Select a CT with a primary rating at least 20% higher.
4. Choose the appropriate CT ratio (primary to secondary amps) based on the selected model and necessary rating. Looping conductors through multiple times can alter the ratio.
KELE www.kele.com USA 901-937-4900 International 901-382-6084
CURRENT TRANSFORMER SELECTION GUIDE DETERMINE MONITORING POINT IN SYSTEM Can conductor be disconnected to slide into A solid core (one-piece) CT? MEASURE LARGEST DIAMETER OF CONDUCTOR OR BUS YES NO DETERMINE CT STYLE Model Description RL or AL SFT SHT *Non-stock items Use Model If diameter is less than in (cm) 2 5 7 8 Call Kele 0.50 (1.3) 1.00 (2.5) 2.00 (5.1) 2.75 (7.0) over 2.75 (77.0) SOLID CORE (5A Secondary) SPLIT CORE 500, 501, 600, 601, 603, 603D, SCT 5A Secondary 500, 501, 600, 601 1A Secondary 603, 603D, 600 601, 500 MEASURE LARGEST DIAMETER OF CONDUCTOR OR BUS Use Model Use Model If diameter is less than in (cm) If diameter is less than in (cm) If diameter is less than in (cm) 600 1.5 x 5 (3.8 x 12.7) 601 4 x 4 (10.2 x 10.2) 500 3.5 x 6.5 (8.9 x 16.5) 501 3.5 x 11 (8.9 x 28.0) Note: Bus bar may fit diagonally Note: Bus bar may fit diagonally 603 603D 600 500 601 DETERMINE CT RATING DETERMINE MAXIMUM AMPS BY 1. Size of upstream breaker, 2. Size of upstream fuse, or 3. Maximum current conductor can carry (Refer to National Electrical Code Tables: 310-16 through 310-19) 4. Analysis of last 12 months demand billing can be used to determine maximum kW ( consider possible load growth) Use 80% of the above value in selecting the CT ratio primary amps. SELECT THE RATIO TO USE MORE READILY AVAILABLE CT's Note: CT ratio = maximum primary amps followed by the secondary amps Example: 500:5 = 500 maximum primary amps and 5 secondary amps Select the ratio code from the catalog page of the selected style (round up if between two sizes). CT sizing can be changed by looping the monitored conductor through multiple times. Example: A 200:5 CT with conductor doubled becomes a 100:5 or with conductor through 4 times becomes a 50:5 (limited to #8 wire or smaller) The burden in VA is the allowable load on the secondary of the CT. This consists of the sum total of the wiring and all connected devices. For a long secondary cable runs or to make burden calculations, contact Kele or visit www.kele.com. Round Square with base* Square without base* 0.5 x 1.5 (1.3 x 3.8) 1.5 x 1.5 (3.8 x 3.8) 1.5 x 5 (3.8 x 12.7) 3.5 x 6.5 (8.9 x 16.5) 4 x 4 (10.2 x 10.2) 0.333V Secondary SCT Series Use Model SCT-1250 SCT-2000 1.25 x 1.25 (3.2 x 3.2) 2 x 2 (5.1 x 5.1) Note: Bus bar may fit diagonally NOTE: Except for SCT Series, the above dimensions are approximately 0.5" less than the CT hole size for ease of installation.