Drill hit a cable

thousands of amps makes it fairly obvious :)

You won't need anything like 4". If you're not upto speed with this, crimping & soldering require equipment & skill that won't be worth investing. Simpler to use a connector, preferably one suitable for inaccessible joints. These kind of incidents are sometimes the cause for a new socket in an odd place.

By noticing the arc in the hole being drilled and the burnt drill bit end.

Yes, that is how I'd do it. However it does seem a strange place to rout a cable, near a window like that where you would put a curtain rod. It might be a good policy to take a cheap cable finder around and look for other things like this before you drill a hole!

Brian

I suspect that my mother's 1960s house it somewhat like that. Not a spare cm of slack cable to pull. Undo a light fitting rose and its almost like all the cables to it are on an extended spring and they will withdraw back from the fitting by a few inches. Try changing a socket and they original electricians left enough wire in the back box to just be able to get to the screws to remove the cable. I suspect that they were trying to use as little cable as possible and probably used the shortest distances for the runs.

Brian Gaff snipped-for-privacy@gmail.com wrote

Not when its a cable to an external light.

Specially when there is an obvious external light nearby.

How deep did the drill go before hitting this cable. Could it be just the other side of dot and dab plasterboard or was the drill deeper into block or brick?

If it is going to be buried in plaster, then it needs to be a maintenance free connector. These are somewhat more bulky and so will need an enclosure of some kind for protection. Also many of the more common ones are single ended (i.e. both wires go in the same end - so you need some slack wire).

One option would be Wago 221 series splices:

Above a curtain, powered from a lighting circuit?

Worth noting that 150mm adjacent to a corner also counts as a safe zone

- so drilling near a ceiling should involve a little more caution:

Yup definitely.

Yup - it needs to me "maintenance free" - so traditionally crimped, soldered, or welded. However modern sprung terminal connectors are also usually acceptable. You need some additional enclosure round the connection like heat shrink or a box - but preferably not mummified in insulating tape!

As John has said only specific connectors can be used in a non-maintenance location. The alternatives are to use crimp or solder.

There is a solder seal type but I can't see any reference for them being suitable for T+E cables:

I said sometimes, not always. If the op did want a socket there one could fit a 2A round pin one.