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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
    Sparkingchip:



    I don't view it as a "trick" it does however require dismantling of the installation and it cannot be done with some portable RCD devices such as plug in RCD adapters.




    Yes it can be done very safely with PRCDs using plug-in test adaptors, provided there's a socket-outlet at the other end (so, plug-in RCD, or RCD plug on an extension lead).


    This technique should also work for testing at double SRCDs where the RCD element is shared between the two outlets ... but of course not for testing the SRCD itself: to test the SRCD you'd have to pop the green wire with a probe on the incoming N.


    A double socket-outlet is not always necessary, provided you choose two socket-outlets on the same circuit downstream of any RCD, it won't trip whilst you test the PRCD.


    Certainly this gets higher marks from a H&S advisor to the measurement at a CU approach.




     



    From the original post, I was specifically exploring how to do the RCD test by plugging the tester in, rather than dismantling the installation. The answer is use the test button on the RCD apart from when annual servicing is being carried out, then the cover needs to come off the consumer unit.




    Perhaps not... thinking about it, you could also use this PRCD test technique with a wander lead in place of the green lead to actually test the RCD in the caravan: Replace the PRCD in the diagram with the socket-outlet in the caravan, and plug the caravan, via a "connect my caravan to a socket-outlet in my PME installation at home" adaptor, in the other outlet of the double socket-outlet.

     

     


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  • 0
    Sparkingchip:



    I don't view it as a "trick" it does however require dismantling of the installation and it cannot be done with some portable RCD devices such as plug in RCD adapters.




    Yes it can be done very safely with PRCDs using plug-in test adaptors, provided there's a socket-outlet at the other end (so, plug-in RCD, or RCD plug on an extension lead).


    This technique should also work for testing at double SRCDs where the RCD element is shared between the two outlets ... but of course not for testing the SRCD itself: to test the SRCD you'd have to pop the green wire with a probe on the incoming N.


    A double socket-outlet is not always necessary, provided you choose two socket-outlets on the same circuit downstream of any RCD, it won't trip whilst you test the PRCD.


    Certainly this gets higher marks from a H&S advisor to the measurement at a CU approach.




     



    From the original post, I was specifically exploring how to do the RCD test by plugging the tester in, rather than dismantling the installation. The answer is use the test button on the RCD apart from when annual servicing is being carried out, then the cover needs to come off the consumer unit.




    Perhaps not... thinking about it, you could also use this PRCD test technique with a wander lead in place of the green lead to actually test the RCD in the caravan: Replace the PRCD in the diagram with the socket-outlet in the caravan, and plug the caravan, via a "connect my caravan to a socket-outlet in my PME installation at home" adaptor, in the other outlet of the double socket-outlet.

     

     


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