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Fatal Incident - Safe Isolation failure?

jbrameld

What do we think on this incident, reported a bit differently in these two locations:

Whilst very sad and no-one should lose their life in the workplace (or anywhere else) I can't help thinking that an engineer of 30 years' experience should have been familiar with safe isolation procedures, and perhaps these were not followed.  There are of course many unreported possibilities such as multiple supply sources not identified but if you follow the mantra of poking a verified test device probe in before anything else (like your fingers or a screwdriver….), then your chances of falling victim are much reduced.

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    When I was taught safe isolation twenty years ago we were taught to prove live before proving dead, so:

    • Prove the circuit LIVE using the two pole tester, checking L-N, L-E and N-E to ensure correct polarity, also the two pole tester works correctly
    • Isolate the circuit and secure it.
    • Prove the circuit DEAD using the two pole tester, checking L-N, L-E and N-E.
    • Prove the tester still works using a known live supply, such as the incoming terminals of the isolation switch or a proving unit.

    That way there’s less risk of testing between two conductors or terminals both with the same voltage on them or between a live and a disconnected conductor and not identifying an issue. 

    Consider the theoretical situation where the isolating device somehow disconnected N and PE but left L connected…

    (there are a few devices that deliberately switch PE, from some in-line RCDs to PME_style EV controllers to islandable on-site generation, so perhaps not an entirely implausible situation, let alone the complete idiot-wired setups where they get three wires into three terminals but not necessarily in the right order….)

       - Andy.

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    When I was taught safe isolation twenty years ago we were taught to prove live before proving dead, so:

    • Prove the circuit LIVE using the two pole tester, checking L-N, L-E and N-E to ensure correct polarity, also the two pole tester works correctly
    • Isolate the circuit and secure it.
    • Prove the circuit DEAD using the two pole tester, checking L-N, L-E and N-E.
    • Prove the tester still works using a known live supply, such as the incoming terminals of the isolation switch or a proving unit.

    That way there’s less risk of testing between two conductors or terminals both with the same voltage on them or between a live and a disconnected conductor and not identifying an issue. 

    Consider the theoretical situation where the isolating device somehow disconnected N and PE but left L connected…

    (there are a few devices that deliberately switch PE, from some in-line RCDs to PME_style EV controllers to islandable on-site generation, so perhaps not an entirely implausible situation, let alone the complete idiot-wired setups where they get three wires into three terminals but not necessarily in the right order….)

       - Andy.

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