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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
    Possible, but a reverse polarity supply on 3 phase is very hard not to notice, and while near the origin  shorting L1 to N does indeed over-volt L2-N and L3-N, you do not need to be many metres down the line for most of the volt drop to be in the final cct.

    It could be a 4 pole RCD and breaking neutral first.


    In TNC-s shorting CPC to N on a final circuit bypasses the neutral coil of the RCD - unless you bypass the phase coil too, I expect a trip.
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  • 0
    Possible, but a reverse polarity supply on 3 phase is very hard not to notice, and while near the origin  shorting L1 to N does indeed over-volt L2-N and L3-N, you do not need to be many metres down the line for most of the volt drop to be in the final cct.

    It could be a 4 pole RCD and breaking neutral first.


    In TNC-s shorting CPC to N on a final circuit bypasses the neutral coil of the RCD - unless you bypass the phase coil too, I expect a trip.
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