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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
    A mobile caravan owner or user cannot really test a RCD in anyway other than by pressing its built in test button.


    Using a Very basic loop polarity and RCD tester  may trip the upfront RCD in the fixed installation first, which won’t prove the caravan works. So long as one of the RCDs works you can sleep easy on your trip away, as you know at least one of the devices works.


    Testing the caravan RCD is going to involve dismantling the consumer unit, as Graham pointed trying to trick the RCDs by playing with the earthing arrangement is not straightforward for a big lump of metal that introduces alternative earth paths, so is not easy to isolate within the installation for testing.


    Going back to the “PAT” analogy when insulation testing a caravan because of reported RCD tripping I just unplug it and put the installation tester croc clips across the pins of the plug testing the caravan and its flex in one go, then move on from there.


    Don’t overthink things, the user just needs to press the test buttons on the RCDs and check both of them.


    Andy B.
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  • 0
    A mobile caravan owner or user cannot really test a RCD in anyway other than by pressing its built in test button.


    Using a Very basic loop polarity and RCD tester  may trip the upfront RCD in the fixed installation first, which won’t prove the caravan works. So long as one of the RCDs works you can sleep easy on your trip away, as you know at least one of the devices works.


    Testing the caravan RCD is going to involve dismantling the consumer unit, as Graham pointed trying to trick the RCDs by playing with the earthing arrangement is not straightforward for a big lump of metal that introduces alternative earth paths, so is not easy to isolate within the installation for testing.


    Going back to the “PAT” analogy when insulation testing a caravan because of reported RCD tripping I just unplug it and put the installation tester croc clips across the pins of the plug testing the caravan and its flex in one go, then move on from there.


    Don’t overthink things, the user just needs to press the test buttons on the RCDs and check both of them.


    Andy B.
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