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Exploding Lightbulb and MCB

Discussion in 'Electrics UK' started by gooseacre, 14 Oct 2010.

  1. gooseacre

    gooseacre

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    Everyone,

    The lightbulb in the main light fitting in my living room exploded yesterday when I pressed the switch to turn it off before I went to bed. It tripped the MCB. The circuit has lights on it - in my living room, hall, kitchen and utility room.

    Now the MCB will not switch back on. I have tried turning the complete supply off and the MCB switch will not flip over to on - was going to see if I turned it on and then the mains supply back on whether it would trip again.

    Does this sound like just the MCB is faulty? If so can I change it myself without calling in an electrician?

    Thanks in advance for any thoughts.
     
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  3. viewer

    viewer

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    Some MCBs need to be turned off after tripping before they will reset. They look 'off' but are in a seperate tripped position. If still not successful check wiring, especially in rose & pendant.
     
  4. DIYDANDY

    DIYDANDY

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    Have you tried pushing further toward the off position before turning on again?
     
  5. gooseacre

    gooseacre

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    I have checked the ceiling rose and pendant - have even removed it. Looks fine.

    Have just checked the MCB switch again as suggested - pushing all the way down. The switch is "floppy" when I try pushing it back up - the others have some physical resistance before they "engage" in the on (up) position.
     
  6. vsynth

    vsynth

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    Yup it's a gonner.
     
  7. Steve

    Steve

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    The resistance you feel is the spring-loaded contacts. They are spring loaded, so that even if you push the lever very slowly, the contacts will make or break quickly to avoid any arcing. Yours has clearly failed.
     
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  9. pjcomp

    pjcomp

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    Have you removed the exploded lamp? If a lamp fails, the MCB trips because it detects a fault. If you leave the lamp in place the fault can still be there so the MCB won't reset. Having said which, as the others have said in this case it sounds like a dead MCB.

    PJ
     
  10. ericmark

    ericmark

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    You asked if you can change yourself. In the main the answer would be not recommended as it will involve removing the front of the consumer unit and even when switched off since the main switch is part of the same consumer unit there are live parts you could touch especially if any covers are missing. Also according to model often you need to remove other MCB's in order to replace one.

    However the old Wylex fuse consumer units did have a conversion to MCB and with these units the MCB simply unplugs. So there are some models where you could easy DIY the MCB change. But many it is really a job for an electrician.

    Also of course there may be other faults and an electrician would also locate and correct any other faults like a faulty bulb holder.
     
  11. gooseacre

    gooseacre

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    Thanks all for replies. Decided to call an electrician as I could not see how to remove the MCB without removing the cover and in case there were other faults.

    Changed MCB and now fixed for £45.
     
  12. plugwash

    plugwash

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    IIRC when you try to reset a MCB or RCD against a fault you typically feel the normal stiffness right up to the last minuite when you hear it trip out again and then the handle goes floppy.

    If you have pushed the handle on a MCB as far in the off direction as it will go and it stays floppy the MCB is shot (regardless of what other faults there may be).
     
  13. Adam_151

    Adam_151

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    ^^^

    Also sometimes it can happen where you feel the spring resistance up to a point and then all of a sudden it feels like it becomes dis-engaged and goes floppy, but before the device has come close to closing. Its normally pretty easily (except on rcbos*) to tell device failure apart from closing onto a fault :LOL: ... also seen breakers that physically jam in the open position and trying to move them simply resets in the toggles snapping off...these were early generation MCBs though and probably hadn't been moved since they were installed

    *sometimes the electronics inside seem to fail in such a way that you can push it on properly and it'll feel like it was closed properly, but then it'll trip itself straight back off even with no load connected
     
  14. kai

    kai

    When a MCB breaker interrupts a fault current greater than its rated fault capacity, often 6kA for a typical domestic MCB, the mechanism becomes ruined, and you won't be able to reset the breaker, even with the power isolated...

    In that case it's time to buy a new one... :LOL: :LOL: :LOL:
     
  15. DIYnot Local

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