Repairing mouse-nibbled cables (twin without earth)

If a mouse can get at it, it is accessible. So use a junction box.

Shouldn't be done. You have knowingly installed a length of cable with no working circuit protective conductor - even worse, you have installed a cable with a cpc and not connected it.

Either replace the whole run back to a proven working cpc, or as a mitigating measure pick up an earth from somewhere (preferably on the same circuit) and run it to the location in 10mm green/yellow.

Cables should be clipped or clamped each side of the joint. Unless you have a handy joist to clip to, this suggests using an enclosure with strain relief.

Owain

Why? I've always thought that crimps or/and soldering were the "weapon of choice"

The cable goes to a light switch - would you *really* have chased out the wall to replace the whole cable? I was surprised to find a cable without a CPC but I suspect it's one of many in the lighting circuits. A re-wire is probably due in the future. - even worse, you have installed a cable with a cpc and not connected it. This is the bit I was unhappy about. The practical choice was to wrap the damaged cable in self-amalgamating tape or replace the damaged section.

They're clipped to a joist (unlike 99% of the wiring and the many tens of JBs that are littered about between the joists)

They might give some advantages if done properly using quality materials, and skill. But far more chance of cocking it up than a JB. Crimps vary wildly in quality. I've seen some made out of baking foil. And seen some results of attempts to solder things.

If it's /just/ the switch drop, then that's actually fairly favourable, as you can connect T&E above the ceiling and prove continuity around the rest of the circuit.

The light switch should of course be a plastic one, and some would suggest using insulated screws or insulated caps over the screwheads, and there should be a label at the CU.

Owain

Should you firstly not try to stop the problem reoccurring ie exterminate the mouse problem and stop them gaining access to the wiring? Brian

I'm intrigued how old the twin with no earth might be also. I guess one could run separate earths, and actually many forms of join should be fine in my humble opinion, but probably not exactly true to the current specs Surely there has to be provision for repairs not total rewire jobs. Brian

Are you certain repairing an existing installation that once conformed to regs isn't allowed?

If you're worried about having an ECC on a short length of replaced cable, simply pull it out.

The original problem sounded worse than it actually is.

"once conformed to regs" is a red herring, as even bare wire on cleats once conformed to regs.

I would also coil up sufficient spare new T&E in the ceiling to allow the switch drop to be replaced at a future date without needing a join.

Owain

I'll try, but with a house like this I think that's going to be a challenge, even without cats that seem to have "taken" to the country life ;-)

Generally, unused cores should be tied to earth if possible. In cases where that is not possible, then ideally they could be terminated in some way to prevent them from being able to make accidental contact with anything else. So terminating in a bit of chock block or in an insulated butt crimp (with nothing in the other side) would meet the requirements. Leaving a length of earth folded back in some earth sleeving is also commonly done (although not totally compliant)

Any of those are seen as preferable to clipping the earth wire off tight against the stripped outer since it means it could be brought into service later if the circumstances changed.

Insulated Crimps and heat shrink is acceptable in most cases.

Thanks, I hadn't seen those labels before, unfortunate that they're sold in packs of 100 - anybody want to buy 99 labels? ;-) (I'll print a suitable label unless I find smaller quantities somewhere)

If I find any more cables that have just had the outer insulation nibbled I think I'll wrap them with self-amalgamating tape rather than splicing-in a new piece of cable and sleeving with heat shrink. I wonder whether mice prefer self amalgamating tape or PVC insulation ... ?

It has the advantage of working when there is no free end to thread through the heat shrink!

On a lighting circuit, probably mid fifties to 1966 or slightly after.

Any work on a lighting circuit without an earth is going to be dodgy - there is no way to do much with it to current standards.

The earth doesn't usually go to the fitting. It doesn't really do much at all in the standard loop in system.

The difficulty is that new work has to be to current standards, and this one of those cases where you can't really do it. So its going to be a bodge either way unless you rewire the circuit.

Or label it as not connected on both ends.

An RCD would be an effective way of gaining adequate safety for lighting circuits only, but it's not regs compliant so you can't do that.

NT