Drill hit a cable

Dig a hole in the wall, cut-out damaged cable, splice-in new cable, insulate, repair wall, paint wall.

The damage site will be a random mess of insulation, deposited metal & charred plastic. Glooping it would not be safe. Dig the cable out & rejoin it properly.

With a new place, the best you could hope four would be a cable under a bit of capping - very difficult to pull in new.

Excavate (carefully) the area around the hole with SDS and chisel bit (or bolster and lump hammer). Cut out section of damaged cable crimp in new section, and cover in heat shrink tubing. Make good with plaster etc.

On one occasion a friend did this.

I gained access below after pulling up some floorboards where I pulled a new cable in the channelling in the wall to replace the old.

If it's the cable to the outside light it's probably run in the cavity, which may be full of insulation. If it is the outside light and with loft access, perhaps... remove the light, attach firmlya new piece of cable to the end of the cable that attached to the light, pull the old cable with the new cable attached back through from the loft until you see the new cable. By this stage you will have already pulled to damaged cable back. Cut the old cable at the damaged section and splice/join the new cable to that position.

Pulling through may be a two man job. One person gently pulling and the other feeding the new cable trough the hole so it doesn't get damaged such as the insulation being cut by the sharp edge of the hole in the brick/block.

take a chance

Thanks very much all. Once they have dug out the damaged area, how would they splice/ crimp the new cable in place? I am assuming they expose say 10cm of the cable cut it out and then replace with a circa 10cm bit of T&E joined somehow top and bottom to the existing cable. Is that correct?

How do you know you hit a cable, as opposed to the drill itself tripping the circuit, for some reason. Maybe someone ran the plug socket the drill was using off the light circuit, that could do it.

Buried wires should go vertically up or down, if there isn't a light or switch directly below, I wouldn't assume there is a wire. Possibly worth getting a device to detect concealed wires.

Otherwise, you need to dig it out and investigate.

What are the rules for splicing a buried cable. I seem to remember you can use Wago connectors, but not the old screw blocks ( I think they were called choc blocks).

Here is the full process:

When the two cable ends almost meet, you can probably get away with just the one joint, since the crimps themselves will add a very small amount of length (2mm - 3mm) to the wires.

So I would expose 150mm of cable and assess the damage. If there is drill damage in just one place you can cut the cable cleanly at that point and strip back the outer insulation 25mm both ways. Place the heatshrink over one of the cut ends, then crimp the three wires with insulated butt crimps. Slide the heatshrink into place and shrink it, then make good.

If the damage is a bit more spread out, you might need to expose a bit more, cut out the damaged section, and crimp in a short new extra bit of cable.

(normally it is easier to get the overall heatshrink in place if you stagger the crimps so they don't all bunch up - however that can be harder to achieve in cases like this).

Should being the operative word. I've seen unplastered walls with diagonal cables.

Or horizontally in teh permitted areas. Of which this this was probably one.

Drilling for a curtain rail suggests maybe running horizontal close to the ceiling.

I'd solder and use heat shrink, but double ended crimps well wrapped in PVC tape should work. Big danger is wet plaster/filler popping an RCD/MCB

Yes, I was wrong, thank you for the correction.

This site seemed helpful:

However, running a horizontal wire, directly above a window, seems like an accident waiting to happen.

Great thanks very much. To answer the wiring questions. I haven't seen it but from what I can gather the curtain rail was being out up in an upstairs bedroom and the outside light is nearby. The switch that controls the light is on the ground floor so I assume they hit the cable running from the light to the switch. With no sockets or switches below where they were drilling I guess they assumed it would be clear.

There is a concrete or metal lintel above an opening and the wire wouldn't necessary pass through that.

Which wouldn't be a problem.

This house had a diagonal cable to the cooker point, and that was as built, so I guess the whole estate was wired like that.