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Repair SWA Resin Joint

Discussion in 'Electrics UK' started by meb97me, 25 Jan 2016.

  1. meb97me

    meb97me

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    Hi

    We've recently fitted a "Y" branch joint to the SWA cable that feeds our garage to run some power to another out building, however we're now experiencing tripping of the RCCB on out circuit board which can only be cured by the garage MCB being turned off. Having had a search on here one suggestion is that it's possibly a neutral earth short probably caused by water ingress into the joint.

    What I'd like to know is whether anyone got any experience of trying to remove the resin from a joint and how easy was it? and any particular tools that were required.

    We're a bit stuck for cable run space so I'm hoping we'll be able to re do the joint rather than have to chop sections of the cable out

    Many Thanks
     
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  3. 333rocky333

    333rocky333

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    It would be wise to insulation test the cable before condemning the joint, not sure them joints are designed to be re entered, probarly a case of just carefully gnawing away at the resin.
     
  4. bernardgreen

    bernardgreen

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    Also do a full insulation test of the new circuits in the other out building, and any appliance that were plugged in ( but not necessaritly switched on ) when the RCCB tripped.

    Provided the resin Y joint was done properly the chance of it being the problem is much lower than the chance of the fault being elsewhere.
     
  5. Lectrician

    Lectrician

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    Get it tested fully first by a competent person.

    You won't remove the joint. You need to cut the cable and start again.

    If it stops tripping when you turn the MCB soft, it isn't going to be a N to E fault, it would be a L to E fault.

    Many people fail to rough up the sheath and insulation of the cables when doing these joints, doing this provides a key for the resin. It's why they include emery paper in the pack. If you don't, you end up with a smooth cable in a smooth resin, and water will get in.

    If the cables sheath has been damaged and the armours are damp, water can also track into the joint as its curing. You are meant to cut back the cable until it's dry. That could be many meters!
     
  6. Adam_151

    Adam_151

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    I'd aways believed it was to stop the resin running out into the bottom of the pit as it is poured. But that makes sense as well :)
     
  7. bernardgreen

    bernardgreen

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    That is not 100% true. There is the possibility that a Neutral to Earth fault on a circuit with its MCB turned OFF can trip the RCD when there is a load on another circuit protected by the same RCD.
    One has to do a careful check of what loads are in use when the RCD trips and not in use when it doesn't trip.
     
  8. Lectrician

    Lectrician

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    Yes, but they said if the MCB is OFF, the tripping stops. If it was an N to E fault, it would usually carry on nuisance tripping when load was used elsewhere, depending on the impedance of the fault.
     
  9. bernardgreen

    bernardgreen

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    It can be that by co-incidence that both these circumstances apply to mislead the diagnosis of the fault

    1/ the MCB for the suspect circuit is OFF only when the other circuit(s) do not have enough load on them to sneak trip the RCD

    and

    2/ the MCB for the suspect circuit is ON only the other circuit(s) do have enough load on them to sneak trip the RCD
     
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  11. meb97me

    meb97me

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    thank you for the replies

    I should have added that I can reset the RCCB and it will be ok for a while (varies between minutes and hours) but then it will eventually trip again even with the with the RCD in the garage turned off.

    With regards to performing an insulation test if I disconnected the SWA from the fuse board in the garage and also from the main house fuse board then using my multimeter check for continuity between each of the combination of wires that would tell me whether I've got a short in t he joint shouldn't it??

    Thanks
     
  12. stillp

    stillp

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    Your multimeter would find a dead short, but you probably don't have a dead short, just the insulation breaking down under load. You really need a 500V IR tester.
     
  13. meb97me

    meb97me

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    I've just disconnected the SWA from the fuse board at either end and set the resistance to 20M and I got a continuity reading across each combination of wires, would that suggest the whole joint is now swimming in water and shorting the lot ?

    L -> N = 0.62
    N-> E = 0.9
    L -> E = 2.85
     
  14. stillp

    stillp

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    Did you have your fingers clear of the test probes?
     
  15. meb97me

    meb97me

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    yes i used crocodile clips and clipped them onto the wires so fingers were well away
     
  16. Lectrician

    Lectrician

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    Certainly sounds like it. If it is a Y joint, assume all three ends completely disconnected?

    You are going to have to cut the joint out, retest all cables, then rejoint, likely with multiple joints and some extra cable.
     
  17. stillp

    stillp

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    Seems knackered then. :(

    Edit - too slow!
     
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