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Damaged electric cable - Best way to repair?

Discussion in 'Electrics UK' started by M1AK, 1 Sep 2021.

  1. M1AK

    M1AK

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    Hi All,

    Just needed some advice.

    A carpenter is currently replacing doors in my house and whilst replacing door frames he found that there was a unprotected bunch of cables that he accidently hit. It has damaged the sheath.

    We didn't realise at the time, but it was powering a plug socket in the loft and it tripped a RCD and thats how we realised.

    Replacing the cable is too labour intensive and costly (involves alot of removal and redecorating /plastering work with the way they are situated).

    Is it perfectly okay to repair this section and what would you use? I am competent with vehicle electronics and would happily use heatshrink and electrical tape but not sure in home electrics.

    Any recommendations, as I'd like to repair it properly and safely, as replacing it is not feasible. It is a small cut on the sheath gone through to potentially one cable. The plug socket only powers the shower pump in the loft.

    TIA
     
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  3. securespark

    securespark

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    You say it is a small cut to the sheath and the insulation of one conductor, but if the RCD tripped there must have been contact between earth and one other.

    In which case there could easily be more damage.

    Then there's the matter of whether the cable is sited in the correct zone and if not, what to do to make it safe(r).
     
  4. oldbutnotdead

    oldbutnotdead

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    If the cables are buried in a corner (where 2 walls meet) then 150mm of that corner is a safe zone, your chippy should have been a bit more alert & in theory he is responsible for fixing it properly.
    In real life, if the mend is going to be buried it needs to be maintenance free. Crimps are ok (but need to be crimped properly, not with the cheap tatty crimp pliers we all own). Not 100% sure whether solder and sleeve is acceptable. Wagos and a small box buried in the wall might be the least controversial method.
    If the cables aren't in a safe zone you'd be wise to rectify that- easiest way is to set a backbox in the wall (vertically in line with the cables) where the join is & put a blank faceplate on- that'll create a safe zone and allow you to use terminal block on the repair.
     
  5. Harry Bloomfield

    Harry Bloomfield

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    An adequately soldered and insulated joint is acceptable.
     
  6. M1AK

    M1AK

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    Hi All,

    Thanks for the replies. So the wiring is probably pre-2000s and isn't to current standards. I don't think it is 150mm away from the door frame. Basically you have two door frames and a wall in between that is probably 100mm in width. The doors are next to the frame but one wire (this damaged one) was trapped in some plaster where as the others were hanging freely. I don't feel it was the chippys fault tbh, it was unavoidable.

    Just to be clear when the fuse tripped we put it back on and it has stayed on and been working fine and still is. But when I mentioned this we went on a hunt and found the damaged sheath. I think a screwdriver hit into it and possibly went through the sheath, and possible made contact with one of the cables within the twin and earth. No cable appears to be broken so I'm a bit reluctant to cut and join. I wanted to sort the insulation out whilst in situ without cutting into it (if that is feasible from a safety point of view).
     
  7. oldbutnotdead

    oldbutnotdead

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    If the wall between the doors runs at 90 degrees to the wall the doors are in then there's your corner- where walls join at a corner, the first 150mm of each wall is a cable safe zone.
    Let us hypothesise your screwdriver incident.
    Option 1- the screwdriver has nicked live or neutral, the RCD tripped because fault current ran through whoever was holding the metal bit of the screwdriver. That person would have noticed the shock but there is unlikely to be damage to the CPC.
    Option 2- as above but the screwdriver made a circuit between either phase conductor and the earth conductor. Unlikely any shock would have been felt, may be damage to Cpc.

    Your big problem is if the earth core has been severed or significantly nicked. Testing is the answer (and not with a multimeter, you'll need a Megger or similar to check insulation resistance and a high current/low resistance tester to make sure the CPC is still capable of safely carrying the fault current of the circuit).
     
  8. bernardgreen

    bernardgreen

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    If there is no slack in the cable then it is going to be very difficult id not impossible to get enough overlap of bare copper for a solder joint or crimp joint.

    You are going to have to remove quite a lot of plaster to get access to enough of the cable to make a joint and then repair the hole. Doing the job properly ( new cable ) will be a larger plastering job but be a safer electrical repair.
     
  9. M1AK

    M1AK

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    So I managed to pull the wire out a bit, it has enough flex. Please see photo attached.

    You can see the red wires sheathing has split slightly and there is a slight graze to the copper earth, which you can see shining through in the pic.

    The cable looks whole so I didn't want to do a cut and join but don't know if it's safe to do a good old electric tape job.

    Hope this brings the damage to light more.

    Any thoughts?
     

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  11. flameport

    flameport

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    No.

    That requires a professional electrician to repair.
    You can't fix this yourself.
     
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  12. M1AK

    M1AK

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    So I called one electrician and he said electrical tape is fine and that is how he would repair it. I've called another who is coming out to me as he didn't inspire me with confidence and frankly I can do that myself.

    Question is how should that be repaired in the ideal situation? Except for replacing the cable . I ask just so I know he has done a proper job.
     
  13. sparkwright

    sparkwright

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    It's damaged far too much to think about just wrapping tape around it.

    It LOOKS like it's tucked in the gap between the door frame and wall, where the architrave would go?

    Correct?

    If so, it's very wrong to have it there - one reason being prone to damage from screws from hinges, and latches and all that stuff.

    As there is a gap, you do have room to do a repair.

    You could use crimps and heat shrink.

    You will also need a short length of the same type of cable, as you will have to cut out the damaged section.

    You need a decent crimping tool, not those cheap auto crimping tools.

    Of course, all this would have to be classed as temporary repair as those cables are in a dangerous place, and need replacing and re-routing somewhere safe.
     
  14. M1AK

    M1AK

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    A bit further back, but yes you are correct. The builder replaced the doors and architraves and this is why this happened. I agree, it doesn't seem to be in the right place which is why I don't blame the builder to be fair.

    I had a emergency leccy out who made it safe temporarily using some push wire connectors and in a junction box for now. It looks like it will need to be rerun or properly joined but something he couldn't do.

    He checked the RCD with a megger as someone mentioned too and all is okay.

    Thanks for all the replies and help. Appreciated.
     
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  15. flameport

    flameport

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    If you described the problem as
    then that's the kind of answer you might expect.

    The damage in the photo is NOT 'a small cut'.

    It's been sliced open over a significant length, the inner insulation has been damaged, at least one of the copper conductors has been damaged, and there is arc damage as evidenced by the blackened mess on the inner insulation and outer sheath.
    The fact that something tripped means at least 2 of the wires made contact.

    The absolute best case is several inches of that cable being removed, and a new section being spliced in.
    More likely is removing and replacing a much longer section, or disconnecting that cable entirely and installing a new supply to the shower pump from elsewhere.
     
  16. M1AK

    M1AK

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    Thanks for the replies. So after a nightmare of trying to find a leccy who will actually do it (5 in total declined as they are so busy) I managed to find someone who said rewiring is not necessary.

    He basically put an accessible flush box with a blanking plate on top and joined the wires. Whilst he was in his van I took a picture of the cables and he has joined it with some orange connectors. I did ask him about these and he said they are as good as crimping and it's in a accessible box now so it is fine. Is this a acceptable repair?
     

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  17. Taylortwocities

    Taylortwocities

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    Looks good to me. I assume that a blanking plate will go on top?
    That is a good thing as it will alert future trades people of the presence of cables!
     
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