Another electrical adventure

PS. I have googled and there seem to be mixed opinions about sleeving (especially for red wires).

Much depends on context and what scope there is for confusion. Red does not appear in the harmonised colours anywhere so there is not much scope for it being taken as anything else. So unless you are actually using it for some other purpose where it must be over marked, there is little added value IMHO.

Blue (was line, now neutral), Black (was negative, now live) on the other hand...

Thanks. And can I cut the grommet (not gromet as I have now discovered) to retrofit or it it best practice to disconnect the cables to fit the grommet?

Obviously they're not intended to be snipped, but you see too many backboxes without them fitted.

If you were concerned you could superglue it back together after fitting, I doubt the Part P Taliban would behead you for it ...

As long as it's giving protection from chafing against sharp metal edges then it's doing its job.

You can buy 'grommet strip' which you cut to length:

Nothing to do with Part P, by the way...

Theo

The chances are that once fitted you will not be able to see the cut.

What is the recommendation for plastic surface mount back boxes. When knocking out the plastic to feed through a cable the edge of the plastic is often knife sharp. As a DIYer I always take a file to the hole to at least smooth off the rough razor sharp edge but I've seen videos where the professionals just drive through the plastic with any tool that comes to hand (screwdriver, handle of pliers etc.) and then just fit the plastic box.

Obviously a cut wire cannot short out on a plastic box but the sharp edge could cut through a couple of layer of insulation if the wires are moved, possibly at a later date.

Well, I've got 100 of them so I may as well try it and see.

My experience suggests that house wires *once installed* do not move and get sliced. Installation however is quite another matter, T-shirt available :-(

You can cut them, and a cut grommet will be better than none.

(in fact you can also get grommet strip designed for arbitrary length perimeter holes in metal plates etc).

They certainly don't move if they're plastered into a chase, right up to the box.

Thanks to everyone for the helpful comments.

The cut grommet fitted perfectly. Would you believe that whoever did it before connected the earth wire to the screw that holds the box on to the wall instead of the earthing terminal? I moved it but it was a tight fit.

While best practice would connect earth to the socket, and then have a fly lead to the earth terminal on the box, it is acceptable with a metal back box to rely on the screws to the socket to join the socket and box earth so long as the back box has at least one "fixed" lug.

No, it is a light switch so the screws are connected to the back box only. The earth wire is connected to the box using the screw that fixes the box to the wall. I'm guessing this is probably okay but I would be happier to use the dedicated earthing point where the connection seems to be more secure. I have extended the earth wire using an in-line connector to allow it to fit.

Many metal boxes have a dedicated terminal (in fact some plastic ones as well so there is somewhere to "park" the earth).

Is it a double insulated (i.e. plastic) light switch?

(if so, not much to worry about anyway)

This is the one I intend to use. The problem was that the earth wire was too short to reach the terminal comfortably which I assume is why it was done the way it was but I have now (effortlessly) extended it using an in-line connector.

No, it is made of steel and is. My concern is that the screws could become live if the box became live!

A stray live contacting a poorly earthed back box would make the (contactable) faceplate screws live - at least in older installations where lights don't have RCD protection.

At some previous existence I had a socket like that. The screws gave you a tingle.

Steel is not a guarantee that it is class I - some are class II. (having an earth terminal on the switch would be a clue though!). It should be marked to indicate if it is class II (double insulated).

If it is class one, then the screw holes would normally pass through an earthed bit or metalwork.

The switch is MK plastic with no provision for an earth. The back box is steel and the earth wire was connected to the screw that attaches the back box to the wall instead of the dedicated earthing terminal (because the earth wire was too short). I have now extended the earth wire using an in-line connector and attached it to the earthing terminal. I assume - and hope - this is now okay.