Safe isolation is a legal requirement under the Electricity at Work Regulations 1989. This guide covers the prove-isolate-secure-prove sequence, HSE GS38 requirements for test instruments, locking off, multi-lock hasps, and the correct method for proving dead.
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Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.
The short answer
Safe isolation follows a prove-isolate-secure-prove sequence: identify the circuit, prove your GS38 voltage indicator works on a known live source, switch off and isolate, secure the isolation point with a lock or by removing the fuse, prove dead at the point of work testing all conductor combinations, then re-prove the indicator still works. It is a legal duty under Regulations 12 and 13 of the Electricity at Work Regulations 1989.
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01 · Safety Procedure Guide
The sequence, in one line
Identify → prove the indicator → isolate → secure → prove dead at the point of work → prove the indicator again.
Six steps, in that order, every time. The legal duty is Regulations 12 and 13 of the Electricity at Work Regulations 1989. BS 7671 makes sure a suitable means of isolation is there to use, and HSE Guidance Note GS38 covers the instrument you prove dead with.
Safe isolation is not a recommendation. The Electricity at Work Regulations 1989 (the EAW Regulations) place duties on employers, the self-employed and employees to ensure electrical work is carried out safely, and safe isolation is the foundation of working dead. Two regulations do most of the work:
Where necessary to prevent danger, suitable means — including, where appropriate, methods of identifying circuits — shall be available for cutting off the supply of electrical energy to any equipment and for the isolation of any equipment. Regulation 12(2) then defines isolation as disconnection and separation from every source of electrical energy in such a way that the disconnection and separation is secure. Locking off is not an add-on to isolation; it is part of what the word means.
Adequate precautions shall be taken to prevent equipment that has been made dead, in order to prevent danger while work is carried out on or near it, from becoming electrically charged during that work where danger may thereby arise. In practice that means locking off, warning notices and proving dead at the point of work.
Neither regulation is qualified by ‘so far as is reasonably practicable’. Regulation 29 of the EAW Regulations does provide a defence of having taken all reasonable steps and exercised all due diligence — but that is a defence argued at trial, not a relaxation of the duty on site. A breach is prosecuted under the Health and Safety at Work etc. Act 1974: on indictment, an unlimited fine and up to two years’ imprisonment for an individual. Beyond that, an electrical accident — particularly a fatality — has consequences that no penalty describes.
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02 · Safety Procedure Guide
Is GS38 statutory?
No — GS38 is HSE guidance, not law. The duty it interprets is.
GS38 has no legal force of its own and is not an Approved Code of Practice. What is statutory is Regulation 4(4) of the EAW Regulations: equipment provided to protect people working on or near electrical equipment shall be suitable for the use for which it is provided, be maintained in a condition suitable for that use, and be properly used. GS38 is the HSE’s published account of what ‘suitable’ means for test leads, probes and voltage indicators — so working outside it is not automatically an offence, but it leaves you proving suitability some other way, usually after an incident.
GS38, ‘Electrical test equipment for use by electricians’, sets out what the HSE regards as suitable test equipment for use during safe isolation and electrical testing. IET Guidance Note 3 reinforces it directly, stating that the testing safety procedures detailed in GS38 shall be observed when using electrical test equipment.
The measurement category tells you how close to the supply origin an instrument and its leads can safely be used. The closer to the origin, the larger the transient overvoltage the equipment has to survive.
| CAT rating | Where it applies | Typical use |
|---|---|---|
| CAT II | Appliances and equipment downstream of a socket-outlet | Plug-in loads |
| CAT III | Fixed installation wiring — distribution boards, final circuits, socket-outlets | Most fixed-wiring work |
| CAT IV | The origin of the installation — supply intake, meter tails and main switch | Origin / intake work |
For most fixed installation work a CAT III 1000 V or CAT IV 600 V instrument with matching leads is appropriate. The whole set-up carries the rating — instrument, leads and probes — and the lowest-rated component sets the safe limit. BS 7671 applies the same logic to the installation itself: Regulation 537.2.3 requires devices for isolation to be designed for overvoltage category III or IV.
03 · Safety Procedure Guide
The sequence must not be shortened or reordered. It rests on one principle: the voltage indicator has to be shown to be working, both before and after it is used to declare a circuit dead.
Identify the circuit to be isolated and confirm which protective device controls it. In a well-labelled board this is straightforward; in an unlabelled one, use a plug-in circuit tracer or careful load switching. Never take a label at face value — verify it. Regulation 12 of the EAW Regulations specifically includes methods of identifying circuits within the "suitable means" it requires.
Select a GS38-compliant two-pole voltage indicator. Prove it works on a known live source — a proving unit, or the circuit itself before you switch off. It must give a positive indication on a known live source before you can rely on it to confirm anything is dead.
Switch off the breaker, withdraw the fuse, or open the isolator. A single-pole MCB breaks only the line conductor, leaving the neutral connected. BS 7671 Regulation 461.2 allows this in TN-S and TN-C-S systems where protective equipotential bonding is installed and the neutral is reliably connected to Earth; on a TT or IT system, isolation requires all live conductors to be disconnected.
Lock off the device, fit an MCB lock-off clip, or withdraw the fuse and keep it on you, and add a warning notice. Regulation 12(2) of the EAW Regulations makes the security of the disconnection part of the definition of isolation. Where several operatives are working, use a multi-lock hasp so each holds their own lock.
Test at the actual point of work, not just at the board. Test every conductor combination — line to neutral, line to earth, neutral to earth. Any indication on any combination means the circuit is not dead: stop and investigate before going any further.
Re-test the voltage indicator on the proving unit or a known live source. If it no longer responds, the dead reading in step 5 proves nothing — stop, replace the instrument and start the proving sequence again.
Work can now proceed. The locking device and warning notice stay in place until the work is finished and the circuit is ready to be re-energised — and it is re-energised by the person who isolated it, after checking nobody is still working on it.
04 · Safety Procedure Guide
Safe isolation sits across statutory law, HSE guidance and the BS 7671 ecosystem. No single document holds all of it — BS 7671 itself does not set out a safe isolation procedure at all. These are the documents that do.
The statutory foundation. Regulation 12 requires suitable means for cutting off the supply and for isolation, and defines isolation as a secure disconnection and separation. Regulation 13 requires precautions to stop dead equipment becoming live during work. Regulation 4(4) requires the protective equipment you use — including test instruments — to be suitable, maintained and properly used.
The HSE’s practical account of suitable test equipment: measurement category, fusing, insulated probes, shrouded connectors and the means of proving the indicator. Guidance, not law, but the reference point against which your kit will be judged.
The HSE’s detailed guidance on safe electrical working, including the key principles of the working dead procedure. It also places responsibility on managers to establish a system of rules and procedures wherever electrical work is carried out — a duty that stays with the premises management even when contractors are engaged. Free to download from the HSE.
Appendix M is where the On-Site Guide puts its safe isolation guidance, reproducing the key principles of the working dead procedure from HSG85 and stressing that modern installations may have more than one source of supply. The Guide’s requirements for the isolation devices themselves sit separately at Section 5.1.
For inspection and testing: where testing does not require the equipment or part of an installation to be live, the installation or part shall be made dead and safely isolated before the test is performed. Guidance Note 3 also requires the absence of voltage to be verified after isolation, and the GS38 procedures to be observed.
Guidance on the management of electrical safety and safe isolation procedures for low voltage installations. Referenced by both the On-Site Guide and Guidance Note 3 as recognised best practice, and free to download.
05 · Safety Procedure Guide
Choosing the right instruments is not just about compliance. Substandard test leads are one of the most common causes of electrical accidents in the trade — and Guidance Note 3 requires the condition of probes and leads to be checked before any live test.
06 · Safety Procedure Guide
Proving dead — confirming a circuit is not live at the point of work — is the step that everything else exists to support. An approved two-pole voltage indicator is the correct instrument for it. A multimeter can be a secondary check, but not the primary one.
| Factor | Two-pole voltage indicator | Multimeter |
|---|---|---|
| Proving dead | Designed for it — the HSE’s preferred instrument | Secondary check only, never on its own |
| Input impedance | Lower — rejects capacitive coupling | High, typically around 10 MΩ — can show a phantom voltage |
| Range selection | None — a clear go / no-go indication | May auto-range, with a settling delay |
| Prove before and after | Integral prove facility or a separate proving unit | Relies on a separate known live source |
The two failure modes to understand are the reason for the preference. A multimeter on the voltage range has an input impedance of around 10 megohms, high enough that capacitive coupling from adjacent cables can produce a readable voltage on a conductor that is genuinely dead — which trains people to distrust a real warning. And an auto-ranging meter takes a moment to settle, so a reading taken immediately after the probes land can be wrong. A two-pole indicator has a lower impedance, no range to select and a clear go / no-go indication.
At the point of work, one test is not enough. For a single-phase circuit with line, neutral and earth, test all three combinations:
Any indication on any combination means the circuit is not dead — stop and investigate. Borrowed neutrals, shared CPCs and second supplies all leave conductors live with the controlling device off. BS 7671 Regulation 537.1.2 requires a durable warning notice wherever an item of equipment or enclosure contains live parts connected to more than one supply; on an unfamiliar installation, do not assume that notice was ever fitted.
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07 · Safety Procedure Guide
Once the circuit is isolated, the isolation point has to be secured. Switching the MCB off is not enough — someone else can switch it back on without knowing anyone is working. Regulation 12(2) of the EAW Regulations builds security into the definition of isolation, and BS 7671 Regulation 462.3 requires devices for isolation to be designed or installed so as to prevent unintentional or inadvertent closure.
| Method | Best suited to |
|---|---|
| Withdraw the fuse or carrier and keep it | Rewireable and cartridge fuse boards; single-operative domestic work |
| MCB lock-off clip with padlock | Standard MCB consumer units where there is no fuse to remove |
| Padlock on the isolator or switch-disconnector | Boards and equipment with built-in provision for a padlock |
| Multi-lock hasp | More than one operative on the same circuit or item of plant |
| Lockable enclosure or cupboard | Plant rooms and intake rooms — recognised by Regulation 462.3 |
A notice — ‘Do not switch on, work in progress’, with your name on it — goes on the board alongside whatever physical device you have fitted, every time. It tells the next person what is happening and who owns the isolation.
BS 7671 requires notices in its own right, too. Regulation 514.11.1 requires a durable warning notice in each position where there are live parts that cannot be isolated by a single device, indicating the location of each disconnector. Regulation 537.1.2 requires a warning notice wherever an installation, item of equipment or enclosure contains live parts connected to more than one supply, positioned so that anyone about to gain access is warned of the need to isolate every supply. Those notices are your first clue that a board is not as simple as it looks.
08 · Safety Procedure Guide
The duty to isolate comes from the EAW Regulations; BS 7671 makes sure the means of isolation you rely on exists, is fit for the job and can be secured. BS 7671 defines isolation as the function intended to make dead, for reasons of safety, all or a discrete section of the installation by separating it from every source of electrical energy — wording that lines up closely with Regulation 12(2). Chapter 46 and Section 537 set out where isolation devices go and how they must behave.
| Regulation | Requirement |
|---|---|
| 462.1.201 | A main linked switch or linked circuit-breaker shall be provided as near as practicable to the origin of every installation as a means of switching the supply on load and as a means of isolation. A main switch intended for operation by ordinary persons, for example in a household installation, shall interrupt both live conductors of a single-phase supply. |
| 462.2 | Every circuit shall be provided with isolation means for all live conductors, except as detailed in Regulation 461.2. Provision may be made for isolating a group of circuits by a common means if the service conditions allow this. |
| 462.3 | Devices for isolation shall be designed and/or installed so as to prevent unintentional or inadvertent closure. The examples given are: located within a lockable space or lockable enclosure; padlocking; located adjacent to the associated equipment. |
| 462.4 | Where residual electrical energy is potentially present, suitable means shall be provided for its discharge, with a warning label giving the discharge time before the enclosure can be safely opened where relevant. |
| 537.2.3 | Devices for isolation shall be designed for overvoltage category III or IV — the exception being the plug of a plug and socket-outlet combination identified in Table 537.4 as suitable for isolation. |
| 537.2.6 | Means of isolation shall preferably be a multipole switching device disconnecting all applicable poles, although single-pole devices situated adjacent to each other are not excluded, subject to Regulation 461.2. |
| 537.2.7 | Each device used for isolation shall be clearly identified by position or durable marking to indicate the installation or circuit it isolates. |
| 514.11.1 | A durable warning notice shall be fixed in each position where there are live parts which are not capable of being isolated by a single device. The location of each disconnector shall be indicated unless there is no possibility of confusion. |
Section 537 sets the device-level requirements, and Table 537.4 — ‘Guidance on the selection of protective, isolation and switching devices’ — is the lookup that tells you which device does which job, against which product standard. Two points from it are worth carrying around. A device only counts as suitable for isolation where it is marked with the symbol for isolation, IEC 60617 identity number S00288. And on a TT or IT system, isolation requires disconnection of all the live conductors, neutral included — the single-pole allowance in Regulation 461.2 is a TN-S and TN-C-S concession, not a general one.
The requirements do not stop at selection. Regulation 537.2.7 requires every isolating device to be clearly identified, by position or durable marking, to show what it isolates — which is exactly the circuit identification Regulation 12 of the EAW Regulations calls for, and the reason an unlabelled board is a safe isolation problem as well as a paperwork one.
Part 6 assumes dead working as the default. Regulation 642.1 states that inspection shall precede testing and shall normally be done with that part of the installation under inspection disconnected from the supply, and Regulation 641.4 requires precautions to be taken to avoid danger to persons and livestock, and damage to property and installed equipment, during inspection and testing. Guidance Note 3 puts the same duty in procedural terms at Regulation 1.1.
Recording the isolation and the instruments used is part of completing an EIC or EICR. For the wider inspection workflow, see the inspection and testing course.
09 · Safety Procedure Guide
On larger commercial and industrial installations, where several operatives work on the same plant, isolation needs a structure around it: multi-lock hasps and a permit to work. The On-Site Guide makes the same point for modern domestic and small commercial work — an installation with solar PV, battery storage or a generator may have more than one source of supply, and isolating the incoming supply does not necessarily make the installation dead.
A steel bar with multiple padlock holes, fitted to the isolation point. Every operative working on the circuit fits their own padlock and keeps their own key. The isolation cannot be released until the last lock comes off, so no one person can re-energise the circuit while anybody else is still working.
A formal document identifying the equipment, the isolation points that have been locked off, the people authorised to do the work and the precautions in place, signed by the issuer and by the person receiving it. Required for high voltage work and standard practice for complex low voltage work on large installations.
Where an installation, item of equipment or enclosure contains live parts connected to more than one supply, BS 7671 Regulation 537.1.2 requires a durable warning notice so that anyone gaining access is warned of the need to isolate every supply, unless an interlocking arrangement isolates all the circuits together. Prove dead after isolating each source, not after the first.
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10 · Safety Procedure Guide
Safe isolation happens on every job, every time. There is no exemption for a quick job, and a circuit is not dead because a switch is off — the switch may be the wrong one, the circuit may be fed from two places, or there may be a borrowed neutral. Prove it dead before you touch it.
The EIC and EICR both include sections for the test instruments used. Complete them — they are the record that suitable, GS38-compliant equipment was used on that job, on that date, and Regulation 4(4) of the EAW Regulations puts the burden of showing suitability on you.
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