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I managed to damage two wires/cables: tv/internet and a power wire.

There were three of power wires: a blue, a black and a green/yellow. I've damaged the black one, but just a little bit.

When the drill hit it, the power went out. I used a heat-shrinkable sleeve and some insulating tape; Is this sufficient to restore the wire to full power? Is it dangerous to keep it that way? Should I use a junction box to fix it? It's in a brick wall, so that wouldn't be very easy.

burned wall showing wires

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    i.imgur.com/0RMSXcv.png There were two tubes, the grey one with the tv/internet cable and the blue one with the electrical wires. The damaged black wire is currently outside the blue tube, after being "patched"; the two other ones are inside. – mnib Mar 17 '17 at 21:52
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    Ok, next question: is your circuit breaker a regular circuit breaker or something more modern like an AFCI breaker? An AFCI breaker will have a Test button on it, just like a GFCI outlet – Machavity Mar 17 '17 at 21:59
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    Mine has a test button, 300mA. – mnib Mar 17 '17 at 22:12
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So it sounds like the AFCI breaker did its job and saved you from a potentially nasty jolt. The AFCI detects the arc (i.e. your metal drill bit contacting the live wire) and cuts the power.

If the wire wasn't severed, you can probably get away with just wrapping the wire in electrical tape and then wrapping the whole scar. If the wires were severed, you can use an inline splice to reattach them without a box.

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    The wire might have been severed, but if so it was almost nothing. The exposed area is about 1mmx3mm or something. I can see the copper but I don't even know how much of it the drill took, if anything at all. For now I'll leave it like that, but I just might call an electrician and replace the whole wire. Thanks. – mnib Mar 18 '17 at 11:09
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    How would an electrician "replace the whole wire"? Can the wires in this sort of conduit be pulled from one box to another? – Jim Stewart Mar 18 '17 at 12:26
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    @JimStewart Depends on the conduit and how many bends the conduit has. This looks like flexible conduit, which might make that difficult. But conduit at least means it's not stapled to the studs – Machavity Mar 18 '17 at 14:37
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    A wire doesn't have to be severed to cause problems. A damaged wire accumulates heat more quickly under load to to the additional resistance. It's very important that you know that the conductor is undamaged. – isherwood Apr 4 '17 at 16:47
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Wiring codes may have a thing or two to say about fixing wires with electrical tape and burying that part in plaster. This may be noncompliant and possibly illegal where you live.

You’re lucky that the damaged wire is in a conduit—it should be possible to pull in a new wire, which is the safest way of fixing this.

Disconnect power before you do anything.

Now find out where the damaged wire begins and ends—likely at the next switch, wall outlet or junction box.

Then, determine the gauge of the wire and be sure to get a replacement wire of equal gauge.

Now, disconnect both ends of the wire. Attach the new wire to one end of the old one (e.g. by stripping a bit of the outer sheath of the new cable, forming hooks from the leads and securing them with tape—you don’t want the junction to come loose or get caught). Then start pulling gently at the other end of the wire, while another person feeds the new wire into the conduit.

When you have the old wire out and the new one in, cut, strip insulation and reconnect. Double-check all connections before you power up again.

One last word: if you really feel you needed instructions as detailed as these, consider getting a professional electrician to do this operation for you. Remember electricity can kill you or set your house on fire if you don’t know what you’re doing.

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