Electrical switchgear

and safety:
A concise guide for users

Introduction
This leaflet is aimed at owners and operators of electrical switchgear in
industrial and commercial organisations who have little knowledge and
expertise available in-house on electrical matters. It summarises the
comprehensive advice given in the HSE guide Keeping electrical switchgear
safe, which is aimed at organisations employing electrical engineering
managers and specialists (see Further reading).
The leaflet provides guidance on the managing of three-phase electrical
switchgear with voltage ratings from 400-33 000 volts alternating current
(ac). It covers selection, use, care and maintenance. The equipment covered
includes switchgear using oil, air, sulphur hexafluoride or vacuum as the
interrupting medium. The leaflet deals with circuit-breakers, switches,
switch fuses and isolators and also covers contactors operating at voltages
above 1000 volts alternating current (ac). It does not cover direct current
(dc) switchgear, low-voltage switchgear (voltages up to 1000 volts ac) and
switchgear used on single-phase alternating current (ac) traction systems.
The advice contained in the leaflet will help you to keep your electrical
switchgear safe and comply with The Health and Safety at Work etc Act
1974, the Management of Health and Safety at Work Regulations 1999
and the Electricity at Work Regulations 1989.
In general, switchgear has a proven record of reliability and performance.
Failures are rare but, where they occur, the results may be catastrophic.
Tanks may rupture and, with oil-filled switchgear, this can result in burning
oil and gas clouds, causing death or serious injury and major damage to
plant and buildings in the vicinity. Failures of switchgear can also result in
serious financial losses.
The use of modern switchgear containing sulphur hexafluoride gas and/or
vacuum has removed the hazard of burning oil but inevitably has
introduced other risks that need to be managed. Accident experience has
shown that failure usually occurs at, or shortly after, operation of the

equipment. How switchgear is operated, its condition and the circumstances

existing in the electrical network at the time of operation, can affect its
ability to perform safely.

Managing switchgear
If you use switchgear you are required by law to provide management
systems that will ensure safe operation and minimise the risk of injury.
Such management systems should include the following:

an appropriate system of records;

policies and procedures covering the installation, commissioning,
operation, maintenance and removal of the equipment;
definitions of responsibilities and training requirements for your people;
an auditing regime to monitor and maintain the effectiveness of
procedures.

Records
Check that the records of all switchgear in service, network diagrams and
configurations, including prospective fault level values at every relevant
point on the system, are available and up to date. If no records are found
you will need to prepare these as a matter of urgency.
The switchgear record should include:

a diagram(s) of the electrical network showing the interconnections

between the various plant items including the switchgear and their
location(s);
fault levels at all relevant points;
types of equipment as part of an asset register, which needs to
include details such as manufacturer and type, serial number and
year of manufacture, date of installation, voltage and current rating,
short-circuit rating and type of operating mechanism;

details of operational limitations due, for example, to the possibility

of overstressing;
a maintenance record of each item of switchgear;
the number of fault clearance operations since circuit-breakers were
last maintained (if known);
details of any modifications carried out, for example the fitting of
anti-reflex control handles; and
whether there are arc control devices for oil-filled circuit-breakers.

The basic records in the case of a low-voltage installation may also

contain electrical installation certificates and periodic inspection reports.
See BS 7671 2001: Requirements for Electrical Installations (IEE Wiring
Regulations, Sixteenth Edition).

Policies and procedures

Safety of the equipment
Using the information in the records, you should assess the switchgear and
the electrical network to identify any potential risks and problems. These
can include overstressing of switchgear, presence of equipment having
dependent manual operation, absence of anti-reflex control handles and
inadequate means of protection against fire.
From this assessment you will be able to identify the necessary remedial
action(s) you need to take to ensure that the equipment and systems are
being operated safely.
Actions you may need to take urgently could include:

prohibiting operation of overstressed switchgear when live, including

disabling automatic operation to clear faults on the system. This will
involve adjustments to electrical protection upstream to ensure the
system remains protected;

preventing access to the switchgear when live;

reducing fault levels wherever possible by reconfiguring the network;
prohibiting the operation of dependent manually operated
switchgear when live, except under very carefully controlled
conditions;
replacing overstressed switchgear.

Further actions you may need to take (the urgency of which will depend
on the results of your assessment) could include:

replacing overstressed switchgear;

when possible, replacing the closing mechanism for dependent
manually operated switchgear. When this is not possible, you will
need to replace the switchgear;
fitting anti-reflex handles;
improving measures for protection against fire.

If you do not have sufficient technical expertise in-house to carry out an

assessment and decide on the appropriate actions, you should take advice
from and employ suitably competent persons/organisations, such as:

electricity distribution companies;

switchgear manufacturers;
switchgear maintenance companies with particular expertise in older
types of switchgear;
consulting organisations specialising in switchgear.

Once you have decided on the actions you need to take, you should
develop a plan and timetable to carry them out.

Operating procedures
You should develop operating procedures and select the appropriate
category of people for the activities needed for operating, inspecting,
repairing, maintaining and testing the switchgear. In all cases, the people
you employ will require the appropriate knowledge of the safety rules and

will need to know how to apply the safety documents. You will also need
to tell them their responsibilities to ensure safety and for safe working.
Their level of knowledge of the switchgear could range from a general
understanding to detailed technical knowledge depending upon the duties
you expect them to have.
Electricity distribution companies, training companies, switchgear
manufacturers and technical services companies may employ people who
are adequately trained and competent to operate the network and
maintain the switchgear. Where you have little knowledge and expertise
available in-house on electrical matters, one option is to employ them to
do some or all of these activities. You should certainly consider employing
someone in-house who is competent to deal with emergencies.
To ensure that the different activities that are associated with switchgear
are performed competently and to the safety rules, it is also important to
define different categories of people, for example competent and
authorised persons. This allows you to clearly define the duties that are
expected of them, and what they are not authorised to do. Training
courses can be prepared to meet the requirements of these categories.

Safety rules and safety documents

You should develop and implement safety rules and a safety documents
scheme (for example use of limitation-of-access and permit-to-work forms)
because they are fundamental to safety in the use, care and maintenance of
plant. The correct use of the safety rules and safety documents is essential.

Responsibilities and training

People operating, inspecting, maintaining and testing your switchgear will
need to be made familiar with the procedures, safety rules and safety
documents (particularly for high-voltage switchgear). You will also need to
tell them their responsibilities to ensure safety and safe working.

As a user of switchgear you are required by law to ensure the people you
have selected to be competent persons or authorised persons receive the
necessary training so that they are able to carry out their duties in safety
and without risk to health. The following organisations offer a full range
of training courses, from general appreciation of site access and
responsibilities through to detailed courses on operations, safety and
maintenance practice:

electricity distribution companies;

training companies;
switchgear manufacturers;
technical services companies.

Auditing regime
It is very important that you implement an auditing regime to ensure that
the procedures you have developed are being operated properly. It should
also include means to identify and rectify defects in the systems (need for
training or retraining etc).

Inspecting and maintaining

switchgear
You should regularly inspect, maintain and test all switchgear and its
environment, for example the switchroom. In all cases you should do this
in accordance with the manufacturers instructions.
This leaflet cannot cover in detail those aspects of inspection and maintenance
particular to each type of switchgear (oil, sulphur hexafluoride and/or
vacuum). Also, materials such as oil and sulphur hexafluoride have their
own requirements for handling, cleaning, avoidance of contamination,
disposal and recycling. There are also hazards associated with their use.

Inspection
You should inspect substations regularly. During the inspection work you
should prioritise any remedial actions as follows:

immediately (this should always be the case when security of the

substation enclosure has been interfered with);
earliest possible opportunity;
next scheduled maintenance.

You should include the following items in the inspection schedule:

switchgear environment (switchroom access and surrounds,

including fence and external walls if outdoors), signs of water getting
in/dampness, signs of unauthorised access and/or interference,
condition of firefighting equipment and warning notices, and general
housekeeping;
signs of abnormal conditions such as high temperature, smell of hot
substances or ozone, presence of smoke, signs of fresh leakage of oil
or compound, distortion and evidence of sooting on enclosures;
general condition of switchgear, such as corrosion, evidence of leaks,
fluid levels, presence/condition of labels, padlocks and key exchange
interlocks, condition of instruments and protection equipment;
condition of ancillary equipment such as batteries and chargers,
control panels etc.

Maintenance
You should do this at regular pre-determined intervals by, for example,
time-based preventative maintenance - see below. You should also do it,
particularly in the case of oil-filled circuit-breakers, immediately after it has
operated to switch off an electrical fault in the network. Certain types of
switchgear (such as that using sulphur hexafluoride and vacuum) are
sometimes designated or described as low maintenance. However, you
should not interpret this to mean that no maintenance is required.

Time-based preventative maintenance

This system of carrying out maintenance at regular, pre-determined
intervals has been in use for many years. You decide the frequency of
maintenance from factors such as:

the type of switchgear;

whether it uses oil, sulphur hexafluoride or vacuum interruptors;
its age; and
how often it is operated.

You should also take the maintenance history of the switchgear into
account. You should keep records for each item so you can identify aspects
such as deterioration in the condition of the equipment. You can then
adjust the period between each maintenance accordingly.

Selecting new, replacement or

refurbished switchgear
When your assessment shows that switchgear needs to be replaced you
should consider the following options, taking advice as necessary.

Replacing the switchboard in its entirety

This has the advantage that a completely new switchboard installation will
use the latest designs on offer from manufacturers.

Replacing/refurbishing switchgear in the existing

installation
You will have a number of options:

replace the individual switchgear units (moving and fixed portion);

refurbish the switchboards or individual switchgear units;
retrofit the switchgear (this usually applies to circuit-breakers).

Factors to take into account before selecting

switchgear
Before you can decide you need to obtain assurance that the high-voltage
insulation components of the busbar system, current transformer
chambers, cables and terminations etc have adequate remaining life to
justify the costs of partial replacement, refurbishment or retrofitting. It is
essential that an overall assessment of the switchgear is carried out. This
includes a condition assessment of the high-voltage insulation by using
partial discharge measurement techniques and the evaluation of available
test data and relevant standards. Where circuit-breakers are under
consideration, you also need to consider the:

condition of the secondary wiring, protection and control

equipment;
interlocking and earthing arrangements in relation to current safety
standards;
short-circuit ratings;
venting arrangement (where appropriate);
rating of the existing (fixed) equipment is adequate to ensure the
replacement equipment can be used to its full rating.

The availability of spares plays a role in the decision process. You should
ensure that both strategic items (eg bushings, current transformer
chambers, cable boxes, operating mechanisms) and routine maintenance
items (eg arcing contacts, turbulator inserts, gaskets, tripping and closing
coils) are available. Do this by contacting the original equipment
manufacturers, their successor companies (if no longer trading) or small
specialist engineering companies.
Only then can you evaluate the economics of refurbishment/retrofit against
replacement.

10

Second-hand equipment
You can buy second-hand switchgear from companies specialising in the
recovery of redundant switchgear and in its refurbishment for re-sale. But
you need to be sure you only deal with reputable and experienced
organisations. Such organisations are required to provide documentation
on the use and maintenance of the equipment they sell. This would
include information originating from the original equipment
manufacturers. The companies supplying the refurbished equipment
should ensure all relevant items are dealt with during overhaul, upgrades,
modifications etc. However, you could employ an independent consultant
to oversee the contract. This can be a worthwhile safeguard against
purchase of unsuitable equipment that might turn out to be not fit for
purpose.

Measures to limit fires

Failure of switchgear can lead to fires and where oil-filled equipment is
involved the incident can be major. A serious incident not only poses
potential fire and smoke risks to people in the vicinity and to the building
fabric but may also affect other plant. You should therefore carefully
consider the measures you need to take and put in improvements where
necessary. There are a number of techniques that can be used singularly or
in combination to mitigate the effects of a fire and limit smoke spread.

Compartmentation
You can separate substation plant items by fire-resisting barriers to limit the
extent of any fire to the item affected, but it is important this does not
inhibit any venting that may be required to safeguard against explosion.
Also, if you have automatic fire extinction or control then
compartmentation is useful.

11

Control and extinction

Fire-extinguishing systems use extinguishing mediums such as halon and
carbon dioxide. Halon is not an ideal choice because of environmental
considerations but its use may be necessary in areas where fire hazards are
particularly severe and could affect adjacent plant.
These systems require the flooding of fire compartments and often are
arranged to operate automatically on detection of a fire. You should ensure
that secure measures to make the system non-automatic are available for
use by people before entering the protected area. Suitable warning notices
and instructions should be prominently displayed at the point(s) of access
to the area. These instructions should also be included in the safety rules.
You should also review the use and provision of portable fire extinguishers
and the procedures for checking these and any permanent systems. Where
problems are identified in design, operation or during inspections you
should ensure corrective actions such as replacement, recharging and
relocation etc are taken.

Fire prevention and detection

The most appropriate control measure is prevention. Strategies you should
consider are:

good management of the plant items, for example careful control of

workmanship. There is a greater likelihood of an incident occurring
after replacement or maintenance of equipment;
careful monitoring of any degradation of oil and dielectric insulation;
reduction of possible ignition sources;
good housekeeping.

An appropriate automatic fire detection system could provide the electrical

plant room or area with early fire detection and alarm features. This could
also be linked with a control/extinction system to provide fast-response fire
suppression or control.

12

Further reading
Keeping electrical switchgear safe HSG230
HSE Books 2002 ISBN 0 7176 2359 9
BS 6626: 1985 Code of Practice for maintenance of electrical switchgear
and controlgear for voltages above 1 kV and up to and including 36 kV
British Standards Institution
BS 6423: 1983 Code of Practice for maintenance of electrical switchgear
and controlgear for voltages up to and including 1 kV
British Standards Institution
BS 7671: 2001 Requirements for Electrical Installations (IEE Wiring
Regulations, Sixteenth Edition)
Institution of Electrical Engineers (see Other sources of advice for address)

13

Further information
British Standards are available from BSI Customer Services,
389 Chiswick High Road, London W4 4AL
Tel: 020 8996 9001 Fax: 020 8996 7001
Website: www.bsi-global.com
HSE priced and free publications are available by mail order from
HSE Books, PO Box 1999, Sudbury, Suffolk CO10 2WA
Tel: 01787 881165 Fax: 01787 313995
Website: www.hsebooks.co.uk
(HSE priced publications are also available from bookshops and free
leaflets can be downloaded from HSEs website: www.hse.gov.uk.)
For information about health and safety ring
HSEs Infoline Tel: 08701 545500 Fax: 02920 859260
e-mail: hseinformationservices@natbrit.com or write to
HSE Information Services, Caerphilly Business Park, Caerphilly CF83 3GG.

14

Other sources of advice

British Electrotechnical and Allied Manufacturers Association (BEAMA)
Westminster Tower
3 Albert Embankment
London
SE1 7SL
Tel: 020 7793 3000
Fax: 020 7793 3003
The Institution of Electrical Engineers (IEE)
PO Box 96
Stevenage
SG1 2SD
Tel: 01438 767328
Fax: 01438 742792
e-mail: sales@iee.org.uk

15

This leaflet contains notes on good practice which are

not compulsory but which you may find helpful in
considering what you need to do.
This leaflet is available in priced packs of 5 from
HSE Books, ISBN 0 7176 2187 1.
Single free copies are also available from HSE Books
Crown copyright This publication may be freely
reproduced, except for advertising, endorsement or
commercial purposes. First published 04/03.
Please acknowledge the source as HSE.
INDG372
04/03
C150
Printed and published by the Health and Safety Executive