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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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  • 0
    ebee:

    Can`t we cheat that one in a similar manner?

    At best it will only check the RCD itself is working under those conditions (Fake TNC-S) and not the actual conditions on site but hey ho better than not testing at all methinks


    The testing would only be "site conditions" if the unit is tested at the site it's being used at, which won't be the case for many touring caravan periodics (or "service checks"), and pre-delivery or pre-use inspections of mobile and transportable units.


    Also, as I said earlier, do we need to worry about the actual cpc being part of the test, particularly considering that 

    (a) we check earth continuity anyway and

    (b) for additional protection, the fault path doesn't necessarily include the cpc.


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  • 0
    ebee:

    Can`t we cheat that one in a similar manner?

    At best it will only check the RCD itself is working under those conditions (Fake TNC-S) and not the actual conditions on site but hey ho better than not testing at all methinks


    The testing would only be "site conditions" if the unit is tested at the site it's being used at, which won't be the case for many touring caravan periodics (or "service checks"), and pre-delivery or pre-use inspections of mobile and transportable units.


    Also, as I said earlier, do we need to worry about the actual cpc being part of the test, particularly considering that 

    (a) we check earth continuity anyway and

    (b) for additional protection, the fault path doesn't necessarily include the cpc.


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