The correct sequence for proving a circuit dead before you work on it. Non-negotiable.
Electricity at Work Regulations 1989HSE GS38BS 7671 Reg 537
More people are hurt working on circuits they believed were dead than on circuits they knew were live. Safe isolation removes the belief and replaces it with proof. The sequence below is the one that stands up in an investigation: identify, isolate, secure, prove dead, and prove your tester on a known source both sides of the test.
Why the sequence matters
A voltage indicator that reads zero tells you one of two things: the circuit is dead, or your indicator is faulty. You cannot tell which from the reading alone. That is why proving the instrument on a known live source — before and after you test the isolated conductors — is not optional. It is the step that turns a zero reading into evidence.
This is a legal duty, not a courtesy
Regulation 14 of the Electricity at Work Regulations 1989 prohibits work on or near live conductors unless it is unreasonable for them to be dead. In practice that means: isolate, prove dead, and only then work.
The right test kit
Use an approved two-pole voltage indicator (a 'voltage tester' to GS38), not a non-contact pen and not a multimeter on the wrong range. The tester should have fused or current-limited probes, finger guards, and no more than 4 mm of exposed metal tip.
You also need a proving unit (or a known live supply), a lock-off device to suit the isolator, your own padlock with a unique key, and a caution notice.
Why not a multimeter?
A multimeter left on a resistance or current range can read 0 V on a live circuit, and its leads rarely meet GS38. Two-pole voltage indicators are purpose-built for the job and fail safe.
The procedure, step by step
1
Identify the circuit
Confirm exactly which circuit or supply you are isolating, using the schedule, the labelling and, where needed, a proving trace. Isolating the wrong way switches off someone else's work, not yours.
2
Isolate
Switch off and isolate at the point that removes supply to the circuit — the MCB/RCBO, the main switch, or an upstream isolator. A plug-and-socket connection is only isolation if you can keep the plug under your control.
3
Secure the isolation
Lock off the isolating device with a device and padlock, keep the only key on you, and fit a caution notice so nobody re-energises the circuit.
4
Prove the tester works
Check your voltage indicator on a proving unit or a known live source. It must clearly indicate voltage.
5
Prove the circuit dead
Test every combination at the point of work: line–neutral, line–earth, and neutral–earth (and between phases on three-phase). All must read dead.
6
Re-prove the tester
Return to the proving unit and confirm the indicator still works. Only now do you know the earlier zero readings were real.
Prove–test–prove
Remember it as prove the tester, test the circuit, prove the tester again. If the tester fails the final check, every dead reading is void — start over with a working instrument.
Traps that catch people out
Borrowed supplies: a circuit can be fed from more than one source (a shared neutral, a two-way lighting strap, a standby generator or inverter). Prove dead at the point of work, not just at the board.
Solar PV and batteries: the DC side is live in daylight and the a.c. side can back-feed. Isolate both, and treat PV strings as live even when isolated.
Capacitive charge: motors, PFC capacitors and long cable runs can hold a charge after isolation. Allow discharge and confirm dead.
Neutral is not safe: a disconnected neutral on a live circuit can sit at line potential. Always test to neutral as well.
Reference material for qualified electrical work. Figures follow BS 7671 and the IET On-Site Guide unless stated; always confirm against the current edition and the standard that applies to your installation.