LOT/General/TBT-LOT-008

Verification of Isolation (Proving Dead)

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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.

Prevent electrocution	Workers have been killed by touching circuits they believed were isolated but which were still live due to untested isolation.
Legal requirement	The Electricity at Work Regulations 1989 and HSE Guidance Note GS38 require proving dead before any electrical work begins.
Stored energy risk	Mechanical, hydraulic, and pneumatic systems can retain lethal energy even after the power source is disconnected.

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See also: LOTO Awareness | Electrical Isolation

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