Permits to Work · Mandatory · Construction
Permit to Work — Electrical Isolation
The Electrical Isolation Permit controls work on or near electrical systems by confirming that circuits have been isolated, locked off, and proved dead before work commences. It records the isolation points, lock-out/tag-out details, and the competent person who verified the dead state. Re-energisation must only occur after all personnel are clear and the permit is formally cancelled.
Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. Electricity at Work Regs 1989 remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.
| EAW Reg 13 | Dead working is the default — the Electricity at Work Regulations 1989, Regulation 13, requires that equipment is made dead before any work is carried out on or near it, unless it is unreasonable in all circumstances for it to be dead |
| LOTO procedure | Lock-Out/Tag-Out — the isolation device must be locked in the off position and tagged with the name of the person who applied the lock; the lock must only be removed by that person |
| Proving dead | GS38 three-step test: (1) test the proving unit on a known live source, (2) test the isolated circuit to confirm dead, (3) re-test the proving unit on the known live source to confirm it is still working correctly |
| Multiple workers | Where more than one person is working on the isolated system, each worker must apply their own personal padlock to the isolation point — the circuit cannot be re-energised until every lock is removed |
| Live working exception | Regulation 14 — live working is permitted only where it is unreasonable for the equipment to be dead, it is reasonable to work live, and suitable precautions are taken; this is a narrow exception, not a routine practice |
1. Dead Working as the Default: EAW Regulation 13
The Electricity at Work Regulations 1989 establish a clear hierarchy for electrical safety. Regulation 13 requires that adequate precautions are taken to prevent danger where work is carried out on or near electrical equipment that has been made dead. The underlying principle is absolute: equipment must be made dead before work is carried out on it. Live working is only permitted under the narrow exception in Regulation 14, where all three conditions are met simultaneously.
The electrical isolation permit is the formal mechanism through which dead working is authorised and controlled. It documents the specific circuit or equipment to be isolated, the method of isolation, the lock-out/tag-out procedure, the proving dead test results, and the persons authorised to work on the isolated system. The permit ensures that no circuit is re-energised while anyone is still working on it, and that the isolation is formally removed only when all work is complete and all workers have withdrawn.
The legal framework combines the Electricity at Work Regulations 1989 (the primary legislation), the Management of Health and Safety at Work Regulations 1999 (risk assessment), CDM 2015 (contractor duties), and the HSE guidance notes GS38 (Electrical test equipment for use by electricians) and HSG85 (Electricity at work: safe working practices). Regulation 29 of the EAW Regulations imposes personal criminal liability on duty holders, making electrical safety offences among the most seriously prosecuted in health and safety law.
Never assume a circuit is dead — PROVE it
Switching off a circuit breaker or removing a fuse is not the same as proving a circuit dead. Circuits can be back-fed from alternative supplies, generators, solar panels, or parallel circuits. Labels on distribution boards may be incorrect or out of date. The only way to confirm that a circuit is dead is to carry out the GS38 three-step test with a proving unit at the point of work, after the isolation has been applied. The three-step test must be carried out every time — there is no exception for circuits that were tested earlier, circuits that have been dead for a long time, or circuits that someone believes to be dead based on prior experience.
2. Isolation PTW Required Content
The electrical isolation permit must contain the following fields. Each must be completed and verified before the work is authorised. The permit is circuit-specific — a separate permit is required for each distinct isolation.
| Field | Required content |
|---|---|
| Circuit or equipment identification | Precise identification of the circuit, equipment, or system to be isolated: distribution board reference, circuit number, cable route, voltage, and phase configuration; cross-referenced to as-built drawings where available |
| Reason for isolation | Clear description of the work to be carried out on the isolated system: installation, modification, repair, testing, or inspection; reference to the supporting RAMS |
| Point of isolation | The specific device used to achieve isolation: circuit breaker, switch-disconnector, fuse carrier, or isolator; physical location identified; confirmation that the isolation device is capable of being locked in the off position |
| Lock-out/tag-out (LOTO) applied | Confirmation that a personal padlock has been applied to the isolation device by the person carrying out the work; tag attached recording the name of the lock owner, the date and time of application, and the permit reference number; where multiple workers are involved, each worker has applied their own lock |
| Proving dead test (GS38 three-step) | Step 1: proving unit tested on a known live source and confirmed working; Step 2: proving unit applied to the isolated circuit at the point of work and confirmed dead on all phases and neutral; Step 3: proving unit re-tested on the known live source and confirmed still working; all three steps recorded with the instrument serial number |
| Earthing applied (where required) | For high-voltage systems or systems with significant stored energy: confirmation that temporary earths have been applied to the isolated conductors at the point of work; earth connections verified and secure |
| Caution notices posted | Danger and caution notices posted at the point of isolation and at the point of work; notices must state that the circuit is isolated, identify the permit holder, and warn that the locks must not be removed by anyone other than the lock owner |
| Boundaries of work defined | The exact scope and boundaries of the permitted work clearly defined: which conductors, which equipment, which sections of the installation; any adjacent live equipment identified and barriers or insulating covers applied where necessary |
| Competence of workers confirmed | Confirmation that all persons carrying out work on the isolated system hold the appropriate level of electrical competence: designated as competent persons under the EAW Regulations; hold relevant qualifications (e.g. JIB ECS card, City and Guilds 2391, 18th Edition BS 7671); competence verified before the permit is issued |
| Restoration and close-out | Procedure for restoring the circuit to service: confirmation that all work is complete and the installation is safe to re-energise; all workers withdrawn and all personal locks removed; proving unit test to confirm safe to re-energise; permit formally closed with signatures of the permit holder and the issuer |
3. Common Mistakes
No proving dead test carried out at the point of work
Switching off a circuit breaker is isolation. Proving dead is a separate and essential step that must be carried out at the point of work, not at the distribution board. The GS38 three-step test confirms that the circuit is genuinely dead at the location where work will be carried out. Without this test, there is no assurance that the correct circuit has been isolated, that back-feeding is not occurring, or that stored energy has dissipated. This is the single most common failure in electrical isolation.
Single padlock used for multiple workers
Where more than one person is working on an isolated system, each worker must apply their own personal padlock to the isolation point. A single padlock controlled by a supervisor does not provide individual protection — the supervisor may remove the lock while a worker is still in contact with the system. Multi-lock hasps are available for this purpose, allowing multiple padlocks to be applied to a single isolation device. The circuit cannot be re-energised until every individual lock has been removed by its owner.
Relying on distribution board labels that are incorrect
Distribution board schedules are frequently inaccurate, particularly in existing buildings where circuits have been modified over time. Isolating a circuit based solely on the label at the distribution board, without verifying the circuit identity at the point of work, can result in the wrong circuit being isolated while the target circuit remains live. Circuit identification must be confirmed by testing, not by reading a label.
Live working treated as a routine option
Live working under Regulation 14 is a narrow exception, not a routine practice. All three conditions must be met simultaneously: it must be unreasonable for the equipment to be dead; it must be reasonable in all the circumstances for the work to be done live; and suitable precautions (including appropriate test equipment, insulated tools, and barriers) must be in place. Live working for convenience, to avoid the disruption of isolating a circuit, does not satisfy the first condition. The default is always dead working.
No formal permit close-out before re-energisation
Re-energising a circuit without formally closing the isolation permit is extremely dangerous. The permit must be closed only after every worker has confirmed that their work is complete, that they have withdrawn from the system, and that they have removed their personal padlock. The issuer must verify that the installation is safe to re-energise before the circuit is restored. Re-energising without this process can result in electrocution of a worker who is still in contact with the system.
5. Frequently Asked Questions
What is the GS38 three-step test?▾
GS38 is the HSE guidance note on electrical test equipment for use by electricians. The three-step test is the procedure for confirming that a circuit is dead: (1) test the proving unit (voltage indicator) on a known live source to confirm the instrument is working; (2) apply the proving unit to the isolated circuit at the point of work to confirm it is dead on all phases and neutral; (3) re-test the proving unit on the known live source to confirm the instrument is still working. If any step fails, the test is invalid and must be repeated with a different instrument. The three-step test must be carried out every time an isolation is applied, without exception.
Can a supervisor remove another worker's padlock?▾
No. Under a properly operated LOTO system, each padlock can only be removed by the person who applied it. This is the fundamental safeguard that prevents a circuit being re-energised while someone is still working on it. If a padlock needs to be removed and the owner is not available (e.g. they have left site), a formal lock-removal procedure must be followed: the permit issuer must verify that the lock owner is not on site, confirm that no one is working on the system, and document the removal. Cutting a lock without this procedure is a serious breach of the safe system of work.
When is live working permitted?▾
Live working is permitted under Regulation 14 of the Electricity at Work Regulations 1989 only when all three conditions are met simultaneously: (1) it is unreasonable in all the circumstances for the equipment to be dead (e.g. the work requires the circuit to be live for diagnostic testing); (2) it is reasonable in all the circumstances for the work to be done live (considering the nature and magnitude of the risk); and (3) suitable precautions are taken (insulated tools, barriers, appropriate test equipment, a competent person, and an emergency plan). Live working for convenience or to avoid disruption does not satisfy condition (1). Any decision to work live must be documented with a specific live-working risk assessment.
Does the permit apply to low-voltage circuits as well as high-voltage?▾
Yes. The Electricity at Work Regulations 1989 apply to all voltages. Low-voltage circuits (typically 230V single phase or 400V three phase on UK construction sites) are fully capable of causing fatal electrocution. The isolation permit, LOTO procedure, and proving dead test apply to all circuits regardless of voltage. The additional requirement for temporary earthing at the point of work is generally applied to high-voltage systems, but the core LOTO and proving dead procedure is the same for all voltages.
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