1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

slightly exposed live wire behind plug socket

Discussion in 'Electrics UK' started by ravsaidha, 19 Nov 2017.

  1. ravsaidha

    ravsaidha

    Joined:
    18 Nov 2017
    Messages:
    15
    Thanks Received:
    0
    Country:
    United Kingdom
    There was a slight nick and clearly something exposed which is why it short circuited. But he had checked the wire itself and was happy with it all before placing a sleeve. He actually didn’t seem that fussed with it and just felt it was touching metal which is why it just needed to be covered...
     
  2. ban-all-sheds

    ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    69,787
    Thanks Received:
    2,857
    Location:
    London
    Country:
    United Kingdom
    You would not be the first person to encounter an electrician who is not very good.

    IF the wire when live made contact with an earthed back box then it WILL have been damaged, and that's all there is to it.
     
  3. mattylad

    mattylad

    Joined:
    27 Apr 2008
    Messages:
    5,983
    Thanks Received:
    329
    Country:
    United Kingdom
    The Op stated that the power was off and has not said it has shorted at all. So the scenario where making a live contact is not applicable here.

    That's all there is to it too.
     
  4. ravsaidha

    ravsaidha

    Joined:
    18 Nov 2017
    Messages:
    15
    Thanks Received:
    0
    Country:
    United Kingdom
    Well when I tried turning the mains on the fuse kept tripping. Not sure if that makes a difference?

    Obviously bit worried if the electrician has just done a bodge job
     
  5. Jackrae

    Jackrae

    Joined:
    20 Nov 2012
    Messages:
    1,951
    Thanks Received:
    318
    Location:
    Dumfriesshire
    Country:
    United Kingdom
    The black material evident in the photograph comes from burning and the burning comes from arcing which also causes depletion of copper, so in simple terms the copper is damaged. Add to that the fact that "the fuse kept tripping" suggests either excessive current (fuse or MCB) or an earth-fault if RCD protected. But an earth fault resulting in an RCD trip probably would not result in any burning.
     
  6. John D v2.0

    John D v2.0

    Joined:
    26 Aug 2016
    Messages:
    5,609
    Thanks Received:
    750
    Country:
    United Kingdom
    Agreed with the above, someone did that in our place at some point and the screw was obliterated at the end and there was a lot of black. But it was just sitting there exposed for a long time without I'll effect.
    In reality the thin bit of the wire may get too warm and further damage the insulation if there's a lot of current in that part of the ring. But there are probably a lot in service like that.
     
  7. ban-all-sheds

    ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    69,787
    Thanks Received:
    2,857
    Location:
    London
    Country:
    United Kingdom
    There probably are. But there should not be any which have been ministered to by a professional electrician.
     
  8. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    41,025
    Thanks Received:
    2,543
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    I'm not sure why you are trying to make that distinction.

    We effectively know that the problem arose because of an L-E fault (earthed screw/box touching live conductor), and exactly the same current would have flowed through that fault (until a protective device stopped it) whether or not the circuit were RCD protected. I therefore wonder why you are saying that burning would not be likely if there was RCD protection (but likely without RCD protection) - are you thinking that an RCD would limit the fault current to a shorter duration than would an MCB, or what?

    Kind Regards, John
     
  9. Jackrae

    Jackrae

    Joined:
    20 Nov 2012
    Messages:
    1,951
    Thanks Received:
    318
    Location:
    Dumfriesshire
    Country:
    United Kingdom
    I stand corrected but from a semantic stand-point "probably" isn't the same as "not be likely".
    What I was endeavouring to suggest was that a "minor" L-E fault (ie a 'leakage') might trip an RCD specifically if the current wasn't high enough to trip an MCB or blow a fuse.
     
  10. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    41,025
    Thanks Received:
    2,543
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    Fair enough. It wasn't actually the semantics of 'how likely' that I was questioning.

    Given that the evidence (both circumstantial and visible) is that the problem was a full-blown L-E 'short' (not a 'minor leakage'), I was concerned that what you wrote might perpetuate the common misconception in a good few people's minds that an RCD can somehow limit the magnitude of L-E current (to 30mA or whatever) - whereas, as you will know, all it can limit is the duration of whatever fault current is flowing.

    Kind Regards, John
     
  11. John D v2.0

    John D v2.0

    Joined:
    26 Aug 2016
    Messages:
    5,609
    Thanks Received:
    750
    Country:
    United Kingdom
    I don't agree there is guaranteed to be damage at the site of the short. If the fault was created when the power was off, and was creating a fault of negligible impedance, then there would be little voltage across the fault and therefore little heat generated.
    Otherwise we would be suggesting to replace the whole circuit every time the MCB tripped.
    If in the other hand, as in my case, the fault presumably had a relatively high impedance, there would have been a lot of heat and damage until the wire fuse or wire or screw parted.
    Don't forget that the let through of an MCB at 5xIn wouldn't actually be that great.
     
  12. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    41,025
    Thanks Received:
    2,543
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    Indeed. However, I don't think it's being suggested that heating of the cable, in general, is a problem - after all, the requirements of ADS are deemed to leave the cable unscathed. I think it is being suggested that the local damage can result from localised heating ('in the fault') due to a fault of non-negligible impedance and/or arcing at the point of the fault.

    Kind Regards, John
     
Loading...

Share This Page