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While fixing the extractor hood yesterday, I accidently hit a wire when drilling and exposed the copper. The wires are too tight to get some kind of a box in there and putting an electrical tape may be too fiddley.
Any advice will be greatly appreciated even if you believe hiring a tradesman is a better option.

See the pictures attached:

close-up of exposed copper

overall picture of the situation

close-up with fingers for size comparison

Edit: after repair by the pro:

repair1

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    related – bummi May 5 at 10:48
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    Where are you on this planet? – ThreePhaseEel May 6 at 0:38
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    Of course, previous owners of the house may have installed cables in ways counter to regulations, so even outside these zones you should check in future. – Martin Bonner supports Monica May 6 at 10:17
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    To state the obvious, do not touch it! – dalearn May 6 at 12:20
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    @MartinBonner Are those regulations international or are you just guessing where OP lives? – pipe May 6 at 15:05
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A DIY repair may be possible, though ugly, even if the wires are trapped so you cannot pull through any extra length or a replacement length of cable. Attach a 1-gang box to the wall in exactly the right place so you can cut the cable and bend the ends upwards into that box from below on opposite sides. Join Live to Live, Neutral to Neutral and Earth to Earth using screw connectors and short pieces of wire to bridge the gap. The bridging wire must be the same gauge as the cable ... easiest source is a bit of offcut cable, probably 2.5mm, and the screw connectors must be rated for 30A if that's a ring main. Put an informative label inside the lid to help anybody wondering what the heck it is, and screw the lid on. You now have an accessible junction box as required by the rules, that looks like an old socket box that's been blanked off.

THe lesson for the future is to invest in a buried cable detector device, and to always use it before drilling holes in walls. These detectors aren't expensive., compared to calling out an electrician....

  • 1
    So the work was finally done by a pro and thank you all for your suggestion. Here are some pic on the final result. Lesson learnt for next time are - invest in good cable detector, start with an assumption that there is a wire underneath where you are drilling and switch off the electric supply if possible. I have an RCD so chances of starting a fire was less but its good to be careful. – user1607035 May 8 at 10:00
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Obviously, safety considerations like isolating that circuit are paramount, and note that even if that circuit's breaker is off, then the neutral touching earth can still trip the Earth Leakage Circuit Breaker...

Find the socket / box that that wire goes to, disconnect it, then pull it out from the other end (which you need to find - either in the roof space or under the upstairs floor) then replace it.

If the copper has been damaged then just covering over with tape may not be safe.

Looking at the plastic cover, this looks like you are in the UK. You can hope that the wire is not totally trapped somewhere...

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    @user1607035 Even is the copper is still partially intact, it is still unsafe, as a "smaller" wire will heat quicker than the other parts, and normally your breakers will prevent the wire from heating up and catching fire, but those are not rated for an effective smaller wire size – Ferrybig May 5 at 18:27
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    If the wire is "totally trapped somewhere", you could just leave it in the walls but disconnect it. – BlueRaja - Danny Pflughoeft May 6 at 11:38
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    @J... "main service wire" ? It has been established that this is in the UK, and that is likely to be 2.5mm^2 cable which is either part of a ring-main circuit or possibly a spur from a ring-main circuit. Without further detail I cannot say. – Solar Mike May 6 at 12:05
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    @J... cooker supply maybe, but the main service cable to the property is not that type, at least, in every property in the UK I have worked in... – Solar Mike May 6 at 12:15
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    Ummmm FIRST kill the breaker which feeds this line! – Carl Witthoft May 7 at 15:16
14

Given the size and location of the wire, It looks like you hit the range feed which may draw upto 50 amps. Such high current applications require greater care in making connections such as splices. in general there are two safe approaches to repairing this damage. The easiest but most expensive (since you have conduit and assuming that it is continuous) is to pull the wire out, repair the conduit and pull new wire. A cheaper variation if local code allows hidden splices is to cut the damaged location in the wire and crimp slice (with a good crimper, probably hydraulic given the wire size). The other option is to put in a splice box with a splice rated for the current.

I do not recommend just repairing the insulation as you have damaged the copper and ranges are a high current appliance.

By the way you are quite fortunate not to have started a fire as if you had hit both wires . . .

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    "quite fortunate not to have started a fire" or facilitated your early demise, I.E. death. – Alaska Man May 5 at 17:28
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    I know of no devices rated for hidden splicing of cables >20A. – ThreePhaseEel May 5 at 18:47
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    OP is in the UK. All senses of amperage, wire sizes, and normal circuit layout you might have in the US will be wrong. Voltage is doubled, current is halved, and circuits are usually laid out in rings, which divides the wire size in two again from what you'd be used to. The size of this cable suggests it is probably the main feeder for the residence. – J... May 6 at 12:00
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    UK wiring code always has or had a fuse or (usually) circuit breaker "upstream" to protect the cable from overload. So no fire, just a big spark. Modern installations always have an earth leakage detector of some sort that will disconnect the supply if any significant current (>30mA) escapes to earth, such as through a person. This will almost always trip before a lethal shock is delivered, though it is unwise to count on that. – nigel222 May 7 at 13:39
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Insulated crimped connections are allowed in the UK, and considered maintenance-free so they can be concealed. A proper ratchet crimper is essential. The whole should then be wrapped in self-amalgamating tape.

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    Thank you all for your comments. My local electrician recken its a 30 min job and he is going to place a 'maintenance free box' and the hole can then be filled. – user1607035 May 6 at 8:32

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