INTRODUCTION

This guide gives information on safe working procedures for the isolation of the supply of electrical energy to electrical equipment. The example illustrated below shows the minimum steps required to isolate the final circuits supplied by a single-phase consumer unit.

STEP 1

Check it is safe and acceptable (with the occupier/user) to isolate. If the isolator is an off-load device, remove the load. Open the means of isolation for the circuit(s) to be isolated and secure the isolating device in the open position with a lock or other suitable means.

STEP 2

Prove the correct operation of a suitable voltage detection instrument*, against a known voltage source, such as that illustrated

*Guidance on voltage detection instruments is given in HSE Guidance Note GS 38 – Electrical test equipment for use by electricians.

STEP 3

Using a voltage detection instrument, check that there is no dangerous voltagepresent on any circuit conductor to be worked on. It is important to confirm that conductors are not energised, for example, due to a wiring fault. Check terminal voltages between (1) earth and line, (2) neutral and line (as shown) and (3) earth and neutral.

STEP 4

Prove the voltage detection instrument again against the known source to check that it was functioning correctly when the circuit(s) were tested for the presence of voltage.

NOTES

• In practice the equipment being worked on is likely to be remote from the consumer unit, for example, a socket outlet located remotely from the means of isolation. In this case it is necessary to check that all the socket outlet contact terminals are dead.

• When checking for a voltage between an earth terminal and live (including neutral) terminals, the test probe should make contact with the earth terminal first, to reduce the risk of the remaining probe becoming live.

• The example illustrated shows the minimum steps required to isolate the final circuits supplied by a single-phase consumer unit. The consumer unit includes an isolator and circuit-breakers. When circuits are protected by fuses enclosed in a distribution board, remote isolation of the supply to the distribution board may be required.

• HSG85 Electricity at work safe working practices gives detailed guidance on devising safe working practices for people who carry out work on or near electrical equipment. 

• The Electricity at Work Regulations 1989 require precautions to be taken against the risk of death or personal injury from electricity in work activities. Regulation 12 requires that, where necessary to prevent danger: a suitable means is available for cutting off the supply of electrical energy to any electrical equipment, and isolation of any electrical equipment. 

• The Health and Safety Executive booklet HSR25 – Memorandum of guidance on the Electricity at Work Regulations 1989 is intended to help duty holders meet the requirements of the Regulations.