Safe Isolation Procedure: GS38, EAW Regulations, and Proving Dead

GS38 Requirements for Test Equipment

• CAT rating — test instruments must be rated for the installation category in which they are used. For fixed domestic and commercial installations, CAT III 1000V or CAT IV 600V is required. CAT rating indicates the instrument's ability to withstand transient overvoltages (voltage spikes) without being damaged or causing a flashover.
• Fused test leads — test leads should be fused at an appropriate rating (typically 500mA or 1A) to limit the energy released in the event of an accidental short circuit. Unfused test leads connected to a voltage source can draw very large fault currents in the event of a short.
• Shrouded connectors — the connectors where the test leads plug into the instrument must be shrouded (insulated) to prevent accidental contact with adjacent live terminals.
• Insulated probes — probe shafts must be insulated with only a small tip of metal exposed — no more than 4mm of bare metal at the probe tip. Long bare metal probe shafts create a risk of bridging adjacent terminals.
• Integral prove facility — voltage indicators used for proving dead should have an integral test facility (proving unit function) or should be used with a separate proving unit.

1. 1
   Identify the circuit

   Identify the circuit to be isolated and confirm which protective device controls it. In a well-labelled consumer unit this is straightforward; in an unlabelled or poorly labelled board, plug-in circuit tracers or careful load testing is required. Never assume a label is correct — verify.

2. 2
   Select and prove the voltage indicator

   Select a GS38-compliant voltage indicator. Prove that it is functioning by testing on a known live source — this can be a proving unit, or by testing at the circuit itself before switching off. The indicator must give a positive reading on a known live source before being used to confirm dead.

3. 3
   Isolate the circuit

   Switch off the MCB, remove the fuse, open the isolator, or operate the relevant isolation device. For single-pole MCBs in a domestic consumer unit, this switches off only the live conductor — the neutral may still be connected to the circuit. A double-pole switch ensures both live and neutral are isolated.

4. 4
   Secure the isolation point

   Lock off the isolation device, remove the fuse and carry it, fit an MCB lock-off device, or post a colleague to guard the isolation point. Place warning notices. For multi-operative working, use a multi-lock hasp so each operative has their own lock.

5. 5
   Prove dead at the point of work

   Test at the actual point of work — not just at the consumer unit — to confirm the circuit is dead. Test all conductors: live to earth, live to neutral, neutral to earth. A positive reading on any combination indicates the circuit is not dead — stop and investigate before proceeding.

6. 6
   Prove the indicator is still working

   After proving dead, re-test the voltage indicator on a known live source (proving unit or adjacent live circuit) to confirm it is still functioning. If it does not respond, the "dead" reading in step 5 may have been caused by a faulty instrument — stop work and re-prove with a functioning instrument.

• Electricity at Work Regulations 1989 — Regulations 12 and 13

  The statutory foundation. Regulation 12 requires adequate means for cutting off the supply; Regulation 13 requires precautions to prevent dead equipment from becoming live while work is in progress. Both are absolute duties — no "reasonably practicable" qualification.

• HSE Guidance Note GS38 — Electrical test equipment for use by electricians

  Sets the requirements for test leads, probes, and voltage indicators used in safe isolation — CAT rating, fused leads, insulated probe shafts, shrouded connectors, and integral prove facility. GS38 is the HSE's practical interpretation of what constitutes suitable test equipment under the EAW Regulations.

• IET On-Site Guide (9th Edition, A4:2026) — Chapter 12 / Appendix M

  Chapter 12 of the On-Site Guide provides the ‘Minimum Stages for Safe Isolation’ checklist — a stepwise procedure presented as the minimum that shall be followed before working on any circuit. The OSG also reproduces the key ‘working dead’ principles from HSG85 for practical installer reference. (OSG Reg 12.5)

• HSE HSG85 — Electricity at Work: Safe Working Practices

  HSG85 sets out the HSE's detailed guidance on safe electrical working, including the ‘working dead’ hierarchy — the sequence of steps that must be followed to identify, isolate, secure, and verify dead before work begins. The On-Site Guide incorporates HSG85 principles at Regulation 12.5.

• Remove the fuse — for rewireable fuse boards and old fuse carriers, remove the fuse carrier and carry it in your pocket. No fuse = no current. This is the most common approach for domestic work.
• MCB lock-off device — a plastic clip that fits over the MCB and prevents it from being switched on. Available with a padlock hole so the device can be locked. Suitable for any MCB in a standard consumer unit.
• Padlock on an isolator or switch — purpose-designed isolators and switch-disconnectors often have provisions for a padlock. A padlock provides positive security — the circuit cannot be re-energised without the key.
• Warning notice — a warning notice ("Do not switch on — work in progress") should be attached to the consumer unit or isolation point in all cases, even when a physical locking device is also used. Warning notices alert others to the situation and provide a clear indication of who is responsible for the isolation.

• Multi-lock hasp

  A multi-lock hasp is a steel bar with multiple padlock holes. It is fitted to the isolation point (preventing re-energisation), and each operative working on the circuit fits their own padlock to the hasp. The isolation cannot be removed until all padlocks are removed — which requires every operative to confirm they are clear. Each operative carries their own key; no single person can re-energise the circuit while other padlocks remain.

• Permit to work

  A permit to work is a formal document that identifies the equipment to be worked on, the isolation points that have been locked off, the persons authorised to carry out the work, and the precautions in place. It is signed off by a competent person (the permit issuer) and by the person receiving the permit. Permits to work are required for high-voltage work and are best practice for complex low- voltage work on large installations.