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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. 



Parents
  • 0
    To test a downstream RCD without firing off the upstream one, use the neutral of the upstream supply as the 'earth' for the tester. Having first verified supply polarity ! The RCD under test sees the imbalance when the button is pressed, as current flows out of the RCD live and does not come back via the neutral, the upstream RCD sees equal and opposite L-N currents and does not trip.


    It may be the non-tripping RCD is faulty, or it may be that the two RCDs are a too close in rating, and one is nearer the centre of permitted performance, and the other nearer the edge. If they have identical spec, say both 30mA instant, then  which goes first will always be a toss up.

    Or it may be that the upstream RCD is already taken near to the brink of tripping by other loads and needs less to take  it over the edge.

    What are the two RCD types and ratings, and what is the level of  standing leakage ?
Reply
  • 0
    To test a downstream RCD without firing off the upstream one, use the neutral of the upstream supply as the 'earth' for the tester. Having first verified supply polarity ! The RCD under test sees the imbalance when the button is pressed, as current flows out of the RCD live and does not come back via the neutral, the upstream RCD sees equal and opposite L-N currents and does not trip.


    It may be the non-tripping RCD is faulty, or it may be that the two RCDs are a too close in rating, and one is nearer the centre of permitted performance, and the other nearer the edge. If they have identical spec, say both 30mA instant, then  which goes first will always be a toss up.

    Or it may be that the upstream RCD is already taken near to the brink of tripping by other loads and needs less to take  it over the edge.

    What are the two RCD types and ratings, and what is the level of  standing leakage ?
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