Permit to work · 9 precautions · 3 critical

Electrical Isolation
permit to work

Work on or near live electrical systems requiring isolation.

These are the precautions the issuer confirms before signing. Each one says what good looks like, when it passes, the regulation it rests on and how it usually fails. Critical precautions are marked: if one cannot be confirmed, the permit is not issued.

Precautions before issue

  1. 1.
    Circuit identified and confirmed
    Critical: a fail stops the work
    What to look forCircuit identified by reference to the up-to-date single-line diagram (SLD) and the schedule of circuits at the distribution board. Circuit traced from origin to point-of-work, not just trusting board labels which are notoriously wrong on retrofitted installations. Confirmation by switching test (open the device, confirm the load drops) or by signal tracer where switching test is impractical. Circuit reference recorded on permit AND on the LOTO lock.
    Acceptable whenSLD <12 months old. Circuit confirmed by switching test or signal trace. Circuit ref written on permit, lock tag, and isolation point label. Independent verification by a second person where the consequences of mis-identification are severe.
    StandardElectricity at Work Regs 1989 reg 13. HSG85 Electricity at work, safe working practices. HSG253 Safe isolation of low-voltage electrical installations.
    Common defectsTrusting board label, old label, circuit re-arranged, wrong circuit isolatedNo SLD, circuit traced by guessworkCircuit "confirmed dead" without switching test, actually fed from a second sourceSub-circuit only confirmed, not the upstream feeder, back-feed via outletCircuit reference not recorded on permit, wrong circuit re-energised at end of works
  2. 2.
    Isolation point identified and locked off (LOTO)
    Critical: a fail stops the work
    What to look forThe selected isolation point genuinely isolates the circuit (not just a control switch, must break supply at the source). Lockable mechanism (hasp, MCB lockout, breaker lockout) applied so the device physically cannot be re-closed. One lock per worker (multi-hasp where multiple workers). Tag identifies the lock owner, contact number, work permit reference, and date. Stored keys stay with the lock owner, not in the office.
    Acceptable whenIsolation point verified to interrupt all live conductors (line + neutral on TN-S, all phases on three-phase). Lockout device proprietary (not cable ties or tape). One lock per worker. Tag completed in full. Multi-lock hasp where >1 worker. Master key under lockable control or destroyed.
    StandardElectricity at Work Regs 1989 reg 12, 13. HSG253. HSG85. BS EN 60204-1 (machinery isolation).
    Common defectsLocal control switch locked, not the isolator, control bypassed and circuit re-energisedCable tie used as a "lock", easily removed by anyoneSingle lock for whole team, first to leave removes lock, others still workingTag illegible or undated, no chain of custody if lock found unattendedMaster key in maintenance office, anyone can overrideThree-phase isolation only on two phases, third still live
  3. 3.
    Lock and tag applied with permit holder details
    What to look forEach working person has their own personal lock and tag, name, photo (ideally), work permit number, mobile number, date of isolation. Tag fixed firmly to the lock or device, not loose. Multi-hasp where multiple personnel, last one out removes their own lock. No "convenience" removal of someone else lock without a documented lock-removal procedure (typically requires multiple signatures and confirmed phone contact with the absent lock owner).
    Acceptable whenPersonal lock per individual. Tag with name, contact, permit ref, date. Multi-hasp where >1 worker. Lock removal procedure documented for absent owner cases (must include attempt to contact, supervisor sign-off, second-person verification of safe-to-remove).
    StandardHSG253. HSG85. BS EN 60204-1.
    Common defectsSingle team lock, group accountability fails when team dispersesLock cut off because operative went home with the keyTag with no contact number, lock found, no owner traceableRe-using same lock-out tag from previous job, date/permit ref wrongTag string broken, lock unidentifiable
  4. 4.
    Isolation proved dead at point of work
    Critical: a fail stops the work
    What to look forGS38-compliant 2-pole voltage indicator (NOT a multimeter, NOT a non-contact volt-stick alone) used at the actual point of work, not at the distribution board. Three-step proving: (1) test indicator on a known live source, (2) test the supposedly-dead conductors phase-to-phase, phase-to-neutral, phase-to-earth, (3) re-test the indicator on the known live source to confirm it has not failed during the test. All three steps recorded on the permit.
    Acceptable whenGS38-compliant 2-pole indicator with finger barriers, fused/current limited probes, max 4mm tip exposure. Three-step prove-dead-prove sequence. All conductors tested L-L, L-N, L-E. Recorded with the indicator serial number on the permit.
    StandardElectricity at Work Regs 1989 reg 14. HSE GS38 Electrical test equipment for use on low voltage electrical systems (4th ed). HSG253.
    Common defectsMultimeter used (not GS38 compliant), exposed probe tip arcs at 415VNon-contact volt-stick used as the only proof, gives false negative on screened cableStep 3 omitted, indicator failed mid-test, "dead" reading was a lieTested at the board, not at the point of work, shared neutral on different circuit liveEarth conductor not tested, earth fault back-feeds line conductorsTest instrument calibration cert overdue
  5. 5.
    Earthing applied where required
    What to look forFor HV (>1kV) work or where stored capacitance exists (long cables, capacitor banks, motor windings) earthing leads applied at point of work after proving dead. Earth lead is rated for prospective fault current, applied with a hot stick where HV. Discharge stick used on capacitor banks before earthing. Earths stay applied for the duration of work and removed only by the original applier.
    Acceptable whenHV earthing leads sized to short-circuit rating (typical 25-50kA for 1 sec). Hot stick or insulated rod for application. Capacitors discharged with discharge stick before touch. Earths applied at all sources of supply (e.g. both ends of a cable that could be back-fed).
    StandardElectricity at Work Regs 1989 reg 13. HSG230 Keeping electrical switchgear safe. ENA G81 (DNO operational practice). BS 6626 (HV switchgear maintenance).
    Common defectsNo earths on long cable, induced voltage from parallel circuitsEarths applied at one end only, back-feed energises the conductorsCapacitor bank not discharged before earth applied, flashoverEarths removed by a different person than applier, chain of accountability lostSingle phase earthed on a three-phase HV system
  6. 6.
    Adjacent live equipment identified and barriered
    What to look forWhere the work area also contains live conductors (e.g. neighbouring distribution board, busbar above, adjacent feeder), live parts are physically barriered or insulated to prevent inadvertent contact. Insulating mats, screens, blankets to BS 921 or EN 61112. Warning notices "DANGER LIVE" facing the worker. Approach distances per HSG85 maintained.
    Acceptable whenAdjacent live separated by physical barrier OR maintained approach distance per HSG85 (LV: arm reach minimum, HV: per voltage class, 0.7m at 11kV, 1.0m at 33kV, 2.0m at 132kV). Insulating screens to BS 921 or EN 61112. "Danger Live" notices.
    StandardElectricity at Work Regs 1989 reg 14, 15. HSG85. BS 921 / EN 61112 insulating screens.
    Common defectsLive busbar above the work, not screened, tool dropped onto itAdjacent panel cover removed for cooling, live exposed at arm reachApproach distance not maintained at HV, flashover at <0.7m on 11kVInsulating mat used as a screen but not rated for the voltage"Live" warning sign behind the worker, not facing the work direction
  7. 7.
    Insulated tools available
    What to look forHand tools insulated to EN 60900 (rated 1000V AC / 1500V DC). Insulation intact, no nicks, splits, or melted-through layers. Insulated for the actual voltage worked on (1000V tools NOT suitable for 11kV work, HV requires hot sticks and live-line tools). Insulating gloves EN 60903 of appropriate class (Class 0 = 1kV, Class 2 = 17kV, etc.) tested in the last 6 months for HV.
    Acceptable whenEN 60900 insulated hand tools, intact. EN 60903 gloves tested 6-monthly for HV use. Voltage rating of tools and gloves >= system voltage. Inspected pre-use.
    StandardEN 60900 insulated hand tools. EN 60903 insulating gloves. Electricity at Work Regs 1989 reg 4(4).
    Common defectsInsulated screwdriver with chip in the insulation, flashover at the chip1kV tools used on 11kV equipment, under-ratedGloves overdue for 6-monthly retest, dielectric strength unknownGlove inflated test failed (pinhole) but glove still in serviceWedding ring or watch worn, bridges live to earth
  8. 8.
    Competent person carrying out work (qualified electrician)
    What to look forPerson doing the work holds appropriate qualification: 18th Edition (BS 7671) for installation work, City and Guilds 2391 for inspection and testing, NICEIC / NAPIT / Stroma scheme membership, ECS Gold card. For HV: SAP / Operating Authorisation, AP15 / EUSR HV authorisation. Competence is task-specific, a domestic electrician is not competent on industrial three-phase, an LV person is not competent on HV.
    Acceptable whenQualifications match the task class (LV/HV/installation/maintenance/test). Scheme membership current. Site-specific authorisation (AP / SAP / Operating Authorisation) for HV work. CSCS card matches role.
    StandardElectricity at Work Regs 1989 reg 16. HSG85. ESC Best Practice Guides. ENA G81/G89.
    Common defects18th Edition holder doing HV work, not authorisedTrainee unsupervised, qualified person off-siteAuthorised Person (AP) authorisation lapsed, performing HV switching anywayDomestic electrician on commercial three-phase TPN board, under-qualifiedScheme registration lapsed, work non-notifiable in error
  9. 9.
    Test instruments in calibration
    What to look forVoltage indicator, multifunction tester, insulation tester all carry a current calibration certificate (typical 12-month interval). Calibration sticker on the instrument shows next-due date. Pre-use functional check: voltage indicator proves on a known live source per GS38 step 1 / step 3. Insulation tester gives expected reading on a known good and a known short.
    Acceptable whenCalibration <12 months old (some manufacturers / standards specify 6 months). Cal sticker visible. Pre-use prove-test on known source. Cal certificate available on site or electronically retrievable.
    StandardHSE GS38. HSG253. ISO/IEC 17025 (calibration laboratories). UKAS-traceable calibration.
    Common defectsCal sticker peeled off, interval cannot be confirmedInstrument dropped, recalibration not done, readings driftInstrument used past cal-due date, readings court-inadmissible if challengedVoltage indicator pre-use prove not performedInsulation tester used on energised circuit, instrument damaged, cal voided

Questions people ask

When is a electrical isolation permit needed?

Work on or near live electrical systems requiring isolation. A permit is the right control when the work is high risk, time-limited and depends on specific precautions being in place before it starts and being kept in place while it runs. It does not replace the RAMS; it sits on top of it for that shift. Guidance, not legal advice.

Who issues a permit to work?

An authorised person who is competent for that type of work and is not the one doing it. They walk the job, confirm each precaution, sign the permit, and hand it to the person in charge of the work, who accepts it by signature. Two names, two signatures, a start time and an expiry.

How long is a permit valid?

One shift, or a shorter stated period. If the conditions change, the permit is suspended, not stretched. A new day is a new permit, walked and signed again, because the site is not the same site it was yesterday.

What does critical mean on a precaution?

3 of the 9 precautions here are marked critical. If a critical precaution cannot be confirmed, the permit is not issued and the work does not start. The rest can be conditioned or noted; the critical ones cannot.

How is the permit closed out?

The person in charge hands it back when the work stops, the issuer checks the area is left safe, and both sign the close-out. For hot works that includes the fire watch period after the last spark. The closed permit is kept with the job file.

Issue it on a phone, close it out on a phone

The same 9 precautions with the guidance a tap away, issuer and acceptor signatures, start and expiry times, suspension, close-out and a branded PDF in the job file. 14 days free.

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