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Lost a lighting circuit - fault somewhere tripping MCB

Discussion in 'Electrics UK' started by Grumbler, 10 Nov 2015.

  1. Grumbler

    Grumbler

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    Hi all,

    Have a problem as per title.

    I live in a bungalow with two lighting circuits and one is down. The MCB won't stay live, it just pops immediately. I've ensured all lights are turned off so it's not a bulb issue and just need some advice which order to start my search for the fault.

    I've been working in the loft but not on the wiring, I definitely haven't tripped on or pulled any cables so it's probably most likely a wire is damaged somewhere. I can't see any visible damage and equally can't power the circuit to find a fault.

    Is it a question of just keep remaking the circuit to the individual rooms or is there an easier way to check a downed circuit?


    Also, what are the chances of the MCB itself being at fault (Crabtree B6 61/B06), access to the CU is fine for flicking tripped switches but currently restricted as far as maintenance goes. Will set to and create access if it's worth switching the MCB's around.

    I realise there could equally be a flukish fault in a light switch just when I've been upstairs hence asking for advice on the most likely fault area.

    Oh, should say no nail or screw damage to switch/wall light drops either.

    Many thanks
     
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  3. Grumbler

    Grumbler

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    I've had a really good look in the loft and there's zero obvious damage to any cabling but the wiring for 2 rooms is a right rats nest of multiple junction boxes feeding all the wall lights, it may be worth my time tidying it all up sometime but I really don't see this being a spontaneous issue.

    There are a couple of switches I haven't replaced over time, including an ancient looking 2 way ceiling switch, I may just switch these over for the sake of ruling them out.

    For some reason I feel drawn towards the MCB itself but it'll take some shifting to access it.
     
  4. EFLImpudence

    EFLImpudence

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    Well, for the MCB to trip means you have a short circuit (L to N) or an earth fault (L to E).

    Continued resetting of the MCB is not the way to find the fault.
    Nothing lasts for ever so the MCB might be faulty.
    How do you think powering the circuit would find the fault? Wait and see what melts or catches fire?

    If you cannot see any obvious damage to a cable then it is difficult to know how to help.

    The circuit will have to be tested.
    If you do not know how or do not have the equipment then you will need an electrician.

    Why can you not access the consumer unit?
     
  5. ban-all-sheds

    ban-all-sheds

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    So you've been working in the loft but not on the wiring, you definitely haven't tripped on or pulled any cables, there's no nail or screw damage to switch/wall light drops either, but you think the cause is probably most likely non-spontaneous damage to a wire somewhere.

    :confused:
     
  6. ericmark

    ericmark

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    Step one turn whole consumer unit off and try re-setting the MCB if it will reset unlikely to be MCB if it will not reset with no power then likely it is the MCB. Not a 100% test but about the only test you can do.
     
  7. Grumbler

    Grumbler

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    Didn't mean to provoke the sarcasm but I see where you're coming from. I just meant if I had some but not all lights it would have been easier to find a break for example.

    CU is at the back of a very well packed walk in cupboard. Emptying the cupboard is a fate worse than death.

    Specifically I said I didn't suspect the rats nest of junction boxes to have developed a spontaneous fault. I've been here 10 yrs and it looked ancient then. They're well out of harms way for accidents.





    HOWEVER. I now have lights!!! :D:D:D:D:D:D:D:D

    After a good touch and feel trip all around the loftboard walkway I noticed a glimpse of a cable I'd never seen before. On lifting the board there was a 2 way switch which was being used to effectively convert a 2 way switched light to 1 way. Part of this wiring crossed a joist which the walkway sat on so I gambled there was some damage here, cut the section out and just rejoined "as is".

    Hooorah, lovely lights and for the first time in 2 days I shall see to cook dinner tonight.


    Thanks for the advice anyway guys. rest assured I would have called a sparky if this hadn't worked as to do it "my way" would have involved systematically disconnecting and rejoining the various affected rooms.


    Given this place is 40+ years old I'm thinking about getting a rewire quote in the spring. I'm happy to do all the chasing and making good to keep costs down. Any ideas for a ball park figure to rewire a 3 bed, 2 reception bungalow plus garage in this manner? Standard fittings, no fancy wiring requirments, just a basic rewire. I'm in the midlands.
     
  8. Grumbler

    Grumbler

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    Thanks, I'd found the problem by the time I saw this but your advice is appreciated.


    G
     
  9. ericmark

    ericmark

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    I have been told of rewires in the region of £4k but it is really guess work without seeing the property plus another £1k to empty cupboard with all the stuff and consumer unit in;)
     
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  11. Grumbler

    Grumbler

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    You might regret only asking £1k for the cupboard!
     
  12. ban-all-sheds

    ban-all-sheds

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    Talking of regrets (in case you are unaware)...
    That could end up a cause for regret if you don't agree it with your electrician up front.
     
  13. Grumbler

    Grumbler

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    I'd definitely make sure we're both crystal clear as to what's included in the quote and what I'm doing.

    Are you implying electricians don't like this type of arrangement in general?
     
  14. Iggifer

    Iggifer

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    Well, if you do all the chopping properly, then I don't see as any electrician is going to mind, so long as you discuss it up front - some like doing it!

    The problem arises when people do it without discussing it first, but chop all the boxes out at the wrong height, and cable chases not in the safe zone, because then either a) you gotta do it again or b) he's gotta put it right.

    That just means double the amount of making good afterwards.
     
  15. EFLImpudence

    EFLImpudence

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    Yes, he has to certify that it is done correctly.
     
  16. Grumbler

    Grumbler

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    I see where you're both coming from.

    I know for starters my current sockets and switches are at the wrong heights for current legislation and naturally if I did any of this work it would be to whatever measurements the electrician stipulated in order to certify it.

    Will worry about that as and when but thanks for the valid points.
     
  17. EFLImpudence

    EFLImpudence

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    There is no height requirement for sockets other than common sense.
     
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