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Lighting circuit continually trips on RCD breaker but not on MCB breaker

Discussion in 'Electrics UK' started by kez1, 4 Apr 2019.

  1. kez1

    kez1

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    New BG domestic box has been fitted.

    Everything in box works ok, without tripping, except the led lighting circuit, which trips RCD every time wall switch is activated.

    Lighting circuit trips either B6 RCD it is connected to, or larger in line 63A RCD.

    LED lighting circuit works Ok when MCB is used in place of RCD.

    Any ideas?
     
    Last edited: 4 Apr 2019
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  3. Taylortwocities

    Taylortwocities

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    1.Have you checked where you(someone) has connected the neutral of the lighting circuit?
    2. Have you checked/tested for shared neutrals?
    3. What are your IR measurements for that circuit.?

    Also, can we check some of your terminology., you say 6A RCD. Do you mean RCD, or do you mean something else?
    Also (surely you know this) that the only significant trip figure on your 63A device is 30mA??
     
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  4. AndyPRK

    AndyPRK

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    SO if every/most lights in the house trip the RCD, you need to check the neutral wire in the new CU.
    If it's only 1 light or stair light that causes the RCD to trip, it maybe how the stair light is wired. Search "borrowed neutral" on youtube etc
     
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  5. ericmark

    ericmark

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    As said B6 RCD seems wrong, B6 RBCO or B6 MCB yes. Even with old tungsten bulbs I have had a water leak cause the glass to crack and the globe fill with water, which was still there some 4 months latter when I got home from work in the Falklands my wife had gone all that time without dinning room lights.

    I would get back who ever fitted the box, a RBCO should not be fed from a RCD however I have two RCD's and it is not unknown when resetting one for the other one to trip, and with 32A circuits switching the circuit on the inrush can cause it to trip so may no be a fault with installation, however step one before fitting a consumer unit with RCD replacing one without RCD protection is the measure the insulation resistance using 500 volt to high light any potential problems before starting, however if the fault is after a light switch or the switch its self this would be easy to miss.

    30 mA is approx 7 watt, so a 5 watt bulb could be wired to wrong neutral and the RCD not always trip, where with tungsten we never used such small bulbs so it would trip every time, so as said look for borrowed neutrals, in the main with lights it's actually a borrowed live where some one has used two core cable between switches instead of 3 core and earth and borrowed the live from another switch on the plate.
     
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  6. kez1

    kez1

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    63A or 6A trips when lighting circuit switch is activated. Photo of breakers attached.
     

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  7. EFLImpudence

    EFLImpudence

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    What do you mean by "led lighting circuit"?
    Is only one led light on the circuit - or a lot of led lights and no other lights?

    The B6 is an MCB - Miniature Circuit Breaker.

    What does that mean?

    If it trips the MCB and/or the RCD then you have a live to earth fault somewhere.
     
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  9. EFLImpudence

    EFLImpudence

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    Can we have a picture of all the circuit breakers?
     
  10. flameport

    flameport

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    By who? What testing was done?
    Has this problem occurred at the same time the new box was fitted?
     
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  11. ericmark

    ericmark

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    Your description is not that good, so trying to read between the lines, I am going to ignore the 63A RCD (30 mA) for the moment as likely tripped by a spike from the B6 MCB when that trips. So for the MCB to trip it needs either 7A for a long time or 30A for 10 ms the latter is the more likely, and to get that drain yet some times hold makes me think a capacitor charging, as anything else would either clear its self or be always there.

    So I would think some where a bulb has a faulty circuit and since we know the LED bulb uses a capacitor to limit current it seems likely it is a bulb at fault, or bulbs if from same batch.

    So set one remove all bulbs, and see if the MCB trips, it should not trip if my idea is correct, so assuming it does not trip, replace bulbs one at a time, one hopes then you will find the faulty bulb?

    I have not heard of this fault before, so trying to use logic as to what it may be, feed back is appreciated.
     
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  12. JohnW2

    JohnW2

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    Do the LED lights have removable bulbs/lamps?

    Kind Regards, John
     
  13. Taylortwocities

    Taylortwocities

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    Get whoever fitted and certified the CU to fix the problem.
     
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  14. DIYnot Local

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