Safe isolation: the full procedure, step by step

Why the law puts this on you personally

Regulation 13 of the Electricity at Work Regulations 1989 requires adequate precautions to prevent equipment being made live while anyone is working on it. Regulation 14 says you must not work on or near live conductors unless it is unreasonable for them to be dead, it is reasonable to work live, and suitable precautions are in place.

In practice that means working dead is the default and working live needs a written justification almost nobody can make for routine domestic or commercial work. The duty sits with the person doing the work, not the employer alone.

Test equipment that actually meets GS38

The HSE guidance note GS38 sets out what test probes and leads must look like. Neon screwdrivers and multimeters on the wrong range are the two items that appear repeatedly in accident reports.

• · A two-pole voltage indicator with fixed leads, not a multimeter
• · Exposed probe tips of no more than 4 mm, ideally 2 mm, with finger barriers
• · Fused leads, insulated to the full length, no cracks or repairs
• · A proving unit, or a known live supply, to prove the indicator before and after
• · Never a neon screwdriver — it relies on current through your body

The sequence, in order

The order matters. Proving the indicator afterwards is what catches an instrument that failed during the test itself.

• · 1. Get permission to isolate and agree the outage with whoever uses the installation
• · 2. Identify the correct circuit or supply from the schedule, and confirm it by switching
• · 3. Isolate at a device capable of securing in the off position
• · 4. Secure the isolation with a lock and a unique key you keep, plus a warning notice
• · 5. Prove the voltage indicator on a proving unit or known supply
• · 6. Test between line and neutral, line and earth, and neutral and earth — all three, at the point of work
• · 7. On three-phase, test all combinations of L1, L2, L3, N and earth
• · 8. Prove the voltage indicator again on the proving unit
• · 9. Only now begin work, keeping the key on you the whole time

Locking off when the device will not take a lock

Older rewireable boards and some switch-fuses have no provision for a padlock. Removing the fuse carrier and keeping it in your pocket, with a warning label fitted, is an accepted approach, but a proprietary lock-off kit with the right adaptor is better and is what an assessor expects to see in your van.

Never rely on a circuit breaker simply being switched off. Someone will switch it back on, and on a shared board they will not know why it was off.

Where it goes wrong on site

The failures are consistent, and none of them are technically difficult to avoid.

• · Isolating the wrong way at a board with an inaccurate or missing schedule
• · Testing line to neutral only, missing a borrowed neutral or a shared circuit
• · Assuming a two-way lighting circuit is dead after isolating one supply
• · Failing to prove the indicator afterwards, so a dead instrument reads as a dead circuit
• · Leaving the lock-off key in the board, or handing it to somebody else
• · Treating PV, battery storage and UPS supplies as if isolating the incomer removes all sources

Battery storage and generation change the picture

An installation with solar PV, battery storage or a standby generator has more than one source. Isolating the DNO supply leaves DC conductors live in daylight, and a battery system can re-energise an installation automatically.

Amendment 4 to BS 7671 gives more attention to this in Chapter 57. Before work, identify every source, isolate each one separately, and lock each one off. Label the board so the next person knows what is there.

Recording it

For most domestic work, a note that safe isolation was carried out is enough. On commercial and industrial sites a permit to work is usual, naming the person isolating, the device, the lock number and the times.

Keep the record. If a dispute arises about who energised what, the permit is the only evidence that protects you.