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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
    That neons NE & LE is best with a high value resistor LN too.

    Gives a missing N or E indication by striking both neons.


    We used to make such as homemade polarity testers a few years back.


    From memory (So I might be wrong, check it first) I think it might have been 220K ohms, therefore 3 x resistors (22K ohms) one each in series with the neons to give LE and NE the just a resistor for LN. This meant a missing N or E would effectively have 2 x resistors in series with the neon, it strikes a bit duller but still as noticable (or not!) as the neon.

    Of course, if you have room on a socket, you could double up those neons and resistors just to give a little more resiliance to component failure.

    Probably not much better than the outlawed "Mains Tester Screwdriver" but I suspect even the those might have saved a few from harm.

    So top marks to MAPJ1 for adding this bit of advice
Reply
  • 0
    That neons NE & LE is best with a high value resistor LN too.

    Gives a missing N or E indication by striking both neons.


    We used to make such as homemade polarity testers a few years back.


    From memory (So I might be wrong, check it first) I think it might have been 220K ohms, therefore 3 x resistors (22K ohms) one each in series with the neons to give LE and NE the just a resistor for LN. This meant a missing N or E would effectively have 2 x resistors in series with the neon, it strikes a bit duller but still as noticable (or not!) as the neon.

    Of course, if you have room on a socket, you could double up those neons and resistors just to give a little more resiliance to component failure.

    Probably not much better than the outlawed "Mains Tester Screwdriver" but I suspect even the those might have saved a few from harm.

    So top marks to MAPJ1 for adding this bit of advice
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