Here we have an example of one of the problems of our shallow light-switch boxes (this is the standard depth of 1/2 inch).

The arcing which has taken place here could have been due to a loose wire or skinned insulation, but from the location of the marks, my money is on a conductor being trapped and nicked as the switch was jammed into the box.

Oh, and there's also a code violation here as well.

Paul,
whats that stray 6491x doing in that box?

Britspark

Hmm,
I'm guessing that the Code violation has something to do with either the box not being Earthed or if that 3-Core is a 2-Way switch wire, the green wire should be a different colour.

I wish we could get ahold of cable with colors like that here for 240v circuits and switch loops. No more recoloring white wires!

Funny you don't have it there in the USA, but they do make a 12/2 Red/Black NMD-90 for the Canadian market, and it is rather common in the home centers I've been in. It was I think originally made for wire in 240V heaters, but I have seen it used for other 240V loads and switchloops.

Larry you can get it here, just no one stocks it, and rarely ever uses it because tape or 3-wire is much faster, and cheaper than special order wire.

The violation has to be the single red wire going up. What was it for? Added three way?

The green was actually connected to the earth terminal on the box -- I'd already removed it before taking the pictures (it's actually the bare earth conductor with green sleeving on the end).



For the benefit of non-UKers:
6491X = Single-insulated cable of the type normally pulled into conduit.


You've got it! The added single was on the switch common with the red/black in the cable used as travelers.



Strictly speaking that black wire should have been remarked red, as black is (was) our neutral color.

We have cable with two red conductors, intended specifically for use on switch loops, although in my experience it's very rarely used.

Unfortunately neither red/black nor red/red will be available for much longer as we change over to the new brown/blue color code.

That single 6491x cable should be a double insulated single. If that was used, and the box was wired neatly and laid in carefully the job would of been ok.

The real problem, of course, is stamped on the inside of the box:



j/k!