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Discuss RCBO trip test query - Testing wrong or is there a fault? in the Looking for Domestic Electricians? area at ElectrciansForums.co.uk.

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  1. Robert M.
    Offline

    Robert M. New EF Member

    Location:
    Hamilton
    Business Name:
    DPM Ltd.
    Hi,

    Can anyone please explain why my friend's 30mA trip RCBOs passes the trip test (e.g. x5 is less than 40ms) when the test is done at the consumer unit but fails when the test is done at the sockets.

    Is he doing something wrong or is there a fault somewhere (the RCBO or the circuit?

    Thanking you in anticipation.
     
  2. Flanders
    Offline

    Flanders Regular EF Member

    Location:
    Tamworth
    If there is any load on the circuit then you can get false readings
    Rcds should be tested with no load in the circuit.
     
    • Agree Agree x 3
  3. stevethesparks
    Offline

    stevethesparks Electrician's Arms

    Location:
    Northampton
    That's absolutely correct.
    It just makes you wonder if they will work properly in an actual earth fault situation.
     
  4. Flanders
    Offline

    Flanders Regular EF Member

    Location:
    Tamworth
    I beleave its the way the tester works to simulate the fault , if there is already leakage on the circuit, for example a fridge or computers , thats when the tester gives the false readings .
     
  5. Pete999
    Offline

    Pete999 Forum Mentor

    Location:
    Northampton
    Business Name:
    None
    Are you not testing the actual RCD, not the circuitry?
     
  6. stevethesparks
    Offline

    stevethesparks Electrician's Arms

    Location:
    Northampton
    Yes, if there are other loads you might expect the rcd/rcbo to trip before its supposed to due to the cumulative effect, but there are also times when they won't trip at all when tested end of circuit.
     
  7. Midwest
    Offline

    Midwest Electrician's Arms

    Location:
    Oxfordshire
    Has he done an insulation resistance test?
     
  8. UNG
    Offline

    UNG Forum Mentor

    Location:
    Nr Wigan, Lancs
    I would suggest ramp testing the RCD

    Had this problem a little while ago fitted a new consumer unit and everything tested ok, went back 6 months later to do some additional work and the RCD would not trip on the 1x test and the 5x result was a bit close to the limit when tested at a socket same tests at the CU gave satisfactory results although I was not too happy so decided to ramp test at the CU and the socket and both results were very similar with an indicated trip current of 35ma. The result after a phone call to the manufacturer was a replacement RCD in the post

    I now always ramp test RCD's before any other tests and I have had quite a few that trip above the rated tripping current
     
    • Like Like x 2
    • Informative Informative x 1
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