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Caravan RCD trip power connections

Paul R
Dear all , a holiday question


I have an acquaintance who asks why his IET 18th Edition RCD tester when plugs it in to the Local RCD (<30mA/300mS) , the primary supply RCD trips (that is further up the AC supply line) , rather than the caravan’s, so in effect nullifying the test.

Is this because the Primary Supply RCD  is monitoring a small standing current from other connections and the Local RCD needs to be tested by using the Local Earth at the unit ? ( which is not so easily accessible). 


Are there any other thoughts please ? 


Paul , Swindon LN IET. 



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    gkenyon:

    See Fig A722 in Amendment 1:2020.



    BS7671:2018:Amd1


    That's the arrangement I pictured it in my mind to get the RCD to trip under test using an isolation transformer, it takes away risks associated with broken PEN conductors, but surely has to reintroduce some risk, but I suppose an EV is not double insulated like an electric razor and a hell of a lot bigger and there's not much of an option to solely rely on the isolation transformer.


    By now we could have took the RCD out of the caravan, bench tested it and put it back in again ?


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  • 0
    gkenyon:

    See Fig A722 in Amendment 1:2020.



    BS7671:2018:Amd1


    That's the arrangement I pictured it in my mind to get the RCD to trip under test using an isolation transformer, it takes away risks associated with broken PEN conductors, but surely has to reintroduce some risk, but I suppose an EV is not double insulated like an electric razor and a hell of a lot bigger and there's not much of an option to solely rely on the isolation transformer.


    By now we could have took the RCD out of the caravan, bench tested it and put it back in again ?


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