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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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    BS 7671 in general requires the settings of RCDs to be coordinates so that downstream RCDs are unlikely to trip.


    HOWEVER, that are certain cases where this is not possible.


    For example, in this case, BS 7671 has a safety requirement for all socket-outlets to be protected by a 30 mA non time-delayed RCD, as well every circuit in the caravan that's plugged into those socket-outlets.


    Because the devices have the same rating (30 mA, non time-delayed) to meet BS 7671 requirements, either RCD might have a faster response, so either may trip before the other.


    In these situations, the only way to test the downstream RCD (the one in the caravan) properly, is to use what is known as the "up/down" or "upstream/downstream" method ... IF that is supported by the test equipment manufacturer.



     
    Of course, this isn't as simple as "plug in and hit the test button", and requires the devices under test meet IP2X/IPXXD with covers removed, and test equipment and test leads to comply with HSE Guidance Note GS38.


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  • 0

    BS 7671 in general requires the settings of RCDs to be coordinates so that downstream RCDs are unlikely to trip.


    HOWEVER, that are certain cases where this is not possible.


    For example, in this case, BS 7671 has a safety requirement for all socket-outlets to be protected by a 30 mA non time-delayed RCD, as well every circuit in the caravan that's plugged into those socket-outlets.


    Because the devices have the same rating (30 mA, non time-delayed) to meet BS 7671 requirements, either RCD might have a faster response, so either may trip before the other.


    In these situations, the only way to test the downstream RCD (the one in the caravan) properly, is to use what is known as the "up/down" or "upstream/downstream" method ... IF that is supported by the test equipment manufacturer.



     
    Of course, this isn't as simple as "plug in and hit the test button", and requires the devices under test meet IP2X/IPXXD with covers removed, and test equipment and test leads to comply with HSE Guidance Note GS38.


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