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

N2 terminal on 50A Mk dipole switch overheats

Discussion in 'Electrics UK' started by kez1, 18 Dec 2018.

  1. kez1

    kez1

    Joined:
    9 Apr 2012
    Messages:
    230
    Thanks Received:
    2
    Country:
    United Kingdom
    Have 10.8Kw shower attached to 50A Mk Switch.
    Outward apperance of switch is fine but switch used to get warm during use.
    Noticed neon light flickering so pulled switch, peeled wires back to new and replaced with another MK 50 A dipole switch.

    Photos show N2 terminal was overheating and had partially melted blue sheathing around it.
    Ideas what has caused this?


    IMG_20181218_051320.jpg IMG_20181218_051431.jpg IMG_20181218_051946.jpg IMG_20181218_051957.jpg IMG_20181218_052002.jpg IMG_20181218_052035.jpg IMG_20181218_052109.jpg IMG_20181218_052113.jpg IMG_20181218_052122.jpg IMG_20181218_052127.jpg
     
  2. Jackrae

    Jackrae

    Joined:
    20 Nov 2012
    Messages:
    2,186
    Thanks Received:
    366
    Location:
    Dumfriesshire
    Country:
    United Kingdom
    Loose screw, faulty switch (unlikely as heat seems to be from termination rather than switch contact) or more likely blue insulation partially trapped under screw so decreasing current carrying capacity of termination. Can I suggest careful removal of blue wire end to see if there was trapped insulation.
     
    • Thanks Thanks x 1
  3. Sponsored Links
  4. kez1

    kez1

    Joined:
    9 Apr 2012
    Messages:
    230
    Thanks Received:
    2
    Country:
    United Kingdom
    Terminal screw was tight when I first removed wires / switch from wall.

    Blue N2 wire is stripped back 2 - 3 mm beyond where the grub screw bites when fully pushed in as far as it will go, so seems no blue insulator from the wire was under the grub screw.

    Looking carefully at the wire it seems very good contact was made by grub screw with one strand and a bit of contact with one other strand but not apparently with the other strands.
    Grub screw certianly seemed tight when removed. Had to apply a bit of pressure to all 4 grub screws to get them out.

    IMG_20181218_102705.jpg IMG_20181218_102744.jpg
     
    Last edited: 18 Dec 2018
  5. Jackrae

    Jackrae

    Joined:
    20 Nov 2012
    Messages:
    2,186
    Thanks Received:
    366
    Location:
    Dumfriesshire
    Country:
    United Kingdom
    The 'earth' terminal looks pretty green suggesting ingress of water; but even that wouldn't result in gross overheating of the neutral terminal.
    You can see the plier marks on the cable end, caused by the sparky twisting the strands together. Clamping screws can only bear on one or two strands but if the wires are twisted, which yours were, then the strands effectively form a 'solid' conductor. I looks like a not-fully-tight termination. Once the termination has been suitably 'cooked' the screw would probably be tight due to products of heat (oxides)
     
    • Thanks Thanks x 1
  6. Sponsored Links
  7. AndyPRK

    AndyPRK

    Joined:
    4 Jan 2009
    Messages:
    5,510
    Thanks Received:
    534
    Location:
    Herefordshire
    Country:
    United Kingdom
    maybe best not to twist the wires, for better contact ?
     
  8. DIYnot Local

    DIYnot Local

    Joined:
    3 Sep 2019
    Country:
    United Kingdom

    If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

    Select the supplier or trade you require, enter your location to begin your search.


    Are you a trade or supplier? You can create your listing free at DIYnot Local

     
Loading...

Share This Page