LOT/General/TBT-LOT-008

Verification of Isolation (Proving Dead)

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Verification of Isolation (Proving Dead)

Toolbox Talk Record

Ref: TBT-LOT-008  |  Issue: 1  |  Date: March 2026
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What?

  • Proving dead means testing that an isolated system is genuinely de-energised before work begins.
  • Isolation alone is not enough — the system must be verified as dead using appropriate test instruments.
  • Electrical proving uses a voltage tester that has itself been proved on a known live source.
  • The test sequence is: prove the tester works, test the circuit, prove the tester works again.
  • This three-step proving sequence ensures the tester was functioning correctly throughout the test.
  • Mechanical proving confirms that stored energy such as pressure, spring, or gravity has been released.
  • The Electricity at Work Regulations 1989 Regulation 14 requires systems to be dead before work begins.
  • Voltage indicators with self-test features are preferred but must still be proved on a known source.
  • Failure to prove dead has caused fatal electrocutions and unexpected machinery start-ups on UK sites.
  • Only a competent person should carry out proving dead tests using calibrated, approved instruments.

Why?

Prevent electrocutionWorkers have been killed by touching circuits they believed were isolated but which were still live due to untested isolation.
Legal requirementThe Electricity at Work Regulations 1989 and HSE Guidance Note GS38 require proving dead before any electrical work begins.
Stored energy riskMechanical, hydraulic, and pneumatic systems can retain lethal energy even after the power source is disconnected.
Do Don't
  • Always prove dead using the three-step test sequence before starting work.
  • Prove your voltage tester on a known live source before and after testing.
  • Use approved test instruments that comply with HSE Guidance Note GS38.
  • Verify all phases, conductors, and neutral are dead, not just one phase.
  • Confirm mechanical stored energy has been released or safely restrained.
  • Apply earths or short-circuit devices after proving dead where required.
  • Record the proving dead test result on the permit to work.
  • Repeat proving dead if there is any interruption to your work period.
  • Ensure your test instruments are calibrated and within their service date.
  • Only allow competent persons to carry out proving dead procedures.
  • DON'T assume a circuit is dead because the isolator is in the off position.
  • DON'T use a tester that has not been proved on a known live source first.
  • DON'T skip the final prove step after testing the circuit being worked on.
  • DON'T use non-contact voltage detectors as the sole means of proving dead.
  • DON'T start work on any system until proving dead is confirmed and recorded.
  • DON'T test only one phase and assume the others are also de-energised.
  • DON'T use damaged, expired, or uncalibrated test instruments for proving dead.
  • DON'T allow anyone other than a competent person to carry out these tests.
  • DON'T forget to check for stored energy in capacitors and backup supplies.
  • DON'T rely on indicator lights or control panel status to confirm isolation.

See also: LOTO Awareness | Electrical Isolation
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