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How a simple job can go wrong quickly....

Former Community Member
Former Community Member
Not my work before I relate:


Existing 3-ph circuit breaker DB in a shop has a 30 mA 4 pole RCD belatedly fitted in a separate enclosure to provide blanket RCD protection. OK, not ideal.

Electrician asked to install extra 13 A socket-outlet in window during shop hours so padlocks off the circuit's circuit-breaker and proceeds, He lets the circuit neutral and cpc touch when fitting the socket-outlet and out trips the RCD as expected. Resets and shop keeper then announces that the card reader, till, air-con and some lights not working.


All that equipment now duff (technical term!).


For an interesting weekend quiz, what happened?


Without hindsight and the work being done during opening hours, what would you have done differently?


Regards


BOD






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  • 0
    Just to confirm; in the original post, the RCD tripped when the Neutral and the CPC touched. This I would expect. There was NO mention of any such touching of a Live to Neutral or Earth.

    My thoughts are that the 4-pole RCD did not Close the Neutral first or Open it last, as it should have done. Googling 4-pole RCD and looking at the pictures, each I found had the Neutral pole marked with an N. So without seeing the wiring, my guess is that the RCD was not wired correctly and that one of the three Lives was connected to the N Pole (with the corresponding Live out being on the outgoing N) and the Neutral conductor was taken to the unused Live in, with the outgoing Neutral connected to the associated L out.

    So when the RCD tripped, the Neutral lifted first and due to three phase loads being unbalanced, the single phase supply with the now 'duff' equipment on it was now effectively connected phase to phase and reacted accordingly.


    Would guess that if the RCD had ever been tested with the button, then all loads had been switched off first.


    Clive
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  • 0
    Just to confirm; in the original post, the RCD tripped when the Neutral and the CPC touched. This I would expect. There was NO mention of any such touching of a Live to Neutral or Earth.

    My thoughts are that the 4-pole RCD did not Close the Neutral first or Open it last, as it should have done. Googling 4-pole RCD and looking at the pictures, each I found had the Neutral pole marked with an N. So without seeing the wiring, my guess is that the RCD was not wired correctly and that one of the three Lives was connected to the N Pole (with the corresponding Live out being on the outgoing N) and the Neutral conductor was taken to the unused Live in, with the outgoing Neutral connected to the associated L out.

    So when the RCD tripped, the Neutral lifted first and due to three phase loads being unbalanced, the single phase supply with the now 'duff' equipment on it was now effectively connected phase to phase and reacted accordingly.


    Would guess that if the RCD had ever been tested with the button, then all loads had been switched off first.


    Clive
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