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Caravan RCD trip power connections

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. 



Parents
  • Different question same subject.


    Tonight I nipped into a house where there’s an RCD tripping issue. I put a Megger earth leakage clamp meter around the tails and when I opened the jaws one of the RCDs tripped. Obviously the meter tails are upfront of the RCD, but I tried it another three times and each time the RCD tripped when I opened the jaws. I have not figure out why at the moment, I am going back to do more testing and I am assuming there’s a neutral to earth fault on a RCD protected circuit.


    Any thoughts on why opening the clamp meter jaws trips the downstream RCD?


    Andy B.
Reply
  • Different question same subject.


    Tonight I nipped into a house where there’s an RCD tripping issue. I put a Megger earth leakage clamp meter around the tails and when I opened the jaws one of the RCDs tripped. Obviously the meter tails are upfront of the RCD, but I tried it another three times and each time the RCD tripped when I opened the jaws. I have not figure out why at the moment, I am going back to do more testing and I am assuming there’s a neutral to earth fault on a RCD protected circuit.


    Any thoughts on why opening the clamp meter jaws trips the downstream RCD?


    Andy B.
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