RCD Nuisance tripping

Discussion in 'General DIY' started by brendabarratt, 8 Jun 2002.

This topic originated from the How to page called RCDs - Your questions answered.

  1. brendabarratt

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    My RCD regularly trips out for no apparent reason.

    How can I prevent this whilst I the house is empty during my four week holiday?

    Are there RCDs that automatically reset themselves using battery power if it's safe to do so? This is no less safe that the manual resetting I do after a trip.
     
  2. amtodd

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    No, there aren't any motorised trips.
    Theory is if a trip trips something is wrong with your wiring, the load or the trip itself. Investigate the fault.

    Could be the trip itself is faulty. If it is an MCB rather than an RCD, they're really cheap (about £5).

    Check the loading of the circuits. Basically anything that is turned off when the RCD trips draws current whilst working. It could be collectively these are drawing more current that the RCD is rated for, which is causing it to trip. This is dangerous as overloaded circuits catch fire - but they usually trip out the MCB first.

    You could have a wiring fault. If the amount of current going down the live is different to the amount of current going down the neutral by >30mA, the trip will go. This is to stop you getting electrocuted if the live wires get loose and touch metal things. Unfortunately it also trips if you have a neutral to earth connection.

    Pay attention to what happens just before the trip goes. eg If the turning the washing machine, kettle, iron, and oven all on at the same time, it might be an overload. if the trip only goes when one item is used, it might be faulty. If it's entirely random, it may well be the trip itself.
     
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  3. AnonymousImport

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    a new board consumer unit went in last year. no problem. i live in s.w. cornwall so we get rough weather from time to time. 3 months ago, when the weather started turning, the rcd (80mA) would trip. i switched off all the circuits on the board to see what was causing the problem, the trip still does not go on, it only switches back on when the isolation fuse (between the meter and unit) is switched off. i have no outside electrics (apart from what is coming into my house from the pole outside). we have a spike earth rod. if we have reasonable weather, no problem. i checked the roof space and no wet is getting onto the electrics that i can see. any ideas ?
     
  4. AnonymousImport

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    As an electrician I came across a similar problem when installing a new consumer unit which incorporated rcd protection.

    On that occassion the rcd would not close even when all outgoing circuits were isolated but would if the supply side of the rcd was isolated.

    In this case the problem was simply a faulty rcd and a replacement corrected the problem.So that is worth a try,use a 100milliamp s type time delayed.

    I did some research on nuisance tripping and it can be caused by problems in the supply.I,m afraid that would mean contacting the supplier,check on any charges but they do have a responsibility to provide a certain standard of supply. Its a complicated subject (harmonics) and they would really be the pople to turn to.

    It is very unlikely that the weather is causing the problem on you,re side.If all cicuits are isolated so that no current is flowing out of the rcd there can be no imbalance.
    An earth rod does become a more efficient earth in wet ground conditions but it would still require a current flow out from the rcd to have any effect.

    Hope this helps,I would be interested in the result.
     
  5. As discussed in the forum the nuisance tripping could be due to the fact that the RCD sensitivity is more than the collective standing leakage current of the down stream circuits. To tackle this problem, either a low sensitivity RCD could be installed on the main with a high sensitivity one for the smaller circuits. If the tripping issue still persists, a delayed trip type RCD could be tried out. Schenider Electric -Square D, has a special 200 mS trip time RCDs. The ordinary RCDs would trip within 40 mS.

    P.G. Sreejith
    Electrical Safety Division
    Cholamandalam AXA Risk Servicves
    INDIA
     

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