Back box screw threads

[m0t]

I'm decorating my dining room at the moment and needed to remove the light switch.

I popped the little plastic covers over the screws and realised the normal slotted machine screws had been replaced with large wood screws. Not sure why because the whole house was rewired 3 years ago and the back boxes were new. Normal machine screws now won't fit.

I wanted rid of the plastic screw covers because I don't like the way they look and I suspect they were only put on by the sparky to hide the wood screws. They don't colour match the mk switch and nothing else in the house has them.

How can I fix this without removing the back box (the wall has just been plastered).

 

[JohnW2]

Normal machine screws now won't fit. ... How can I fix this without removing the back box (the wall has just been plastered).

If the holes are now too big for standard M3.5 machine screws, one can often get away with squeezing the lug )with pliers etc.) so as to make the hole oval, and then rethreading with a cheapo M3.5 re-threader (basically a tap in a plastic handle, widely available), and then using the normal machine screws.

Kind Regards, John

 

[m0t]

Cheers, I'll give that a go

 

[securespark]

If it is sill too big, you will have to rethread for M4's.

http://www.westfieldfasteners.co.uk...PYG9ajDV9urA-o3D7WoSxR9ciBOXdNAirEaAnk08P8HAQ

 

[flameport]

Another option is to remove the lugs completely, drill holes in the back of the box and thread those. Longer screws will be required.
Or get two extension studs, cut the long threaded part off and fix those in place of the old lugs using epoxy.

 

[SimonH2]

Or, epoxy a 3.5mm nut on the back of the lugs ? Tricky to avoid getting the epoxy in "the wrong place" - I guess putting a lightly greased screw through would help - and also provide a means of holding the nut in pace while the epoxy sets.

 

[JohnW2]

Or, epoxy a 3.5mm nut on the back of the lugs ? Tricky to avoid getting the epoxy in "the wrong place" - I guess putting a lightly greased screw through would help - and also provide a means of holding the nut in pace while the epoxy sets.

... but then don't rely on faceplate screws to earth a backbox!

Kind Regards, John

 

[SimonH2]

... but then don't rely on faceplate screws to earth a backbox!

I don't. But then, if the box isn't exposed, earthing it isn't critical, and if it is exposed then earthing it via the screws isn't permitted.

 

[JohnW2]

I don't.

Nor do I, but it seems that many do.

But then, if the box isn't exposed, earthing it isn't critical, and if it is exposed then earthing it via the screws isn't permitted.

What "doesn't permit" it? In any event, as has been discussed before, although people shouldn't be taking faceplates off 'live', some do, and even a (normally) non-exposed box could theoretically become a hazard if not earthed (particularly since pulling the faceplate forward has been known to yank out the L conductor, which may then touch the box).

Kind Regards, John

 

[Iggifer]

Have never used them myself, but sound ideal in this situation where the lugs are destroyed

https://backboxsaver.com/

 

[SimonH2]

What "doesn't permit" it?

I assume a requirement for an exposed back-box to be properly earthed, together with the fairly common belief that the socket screws alone aren't a reliable earth - especially when the socket is removed.

In any event, as has been discussed before, although people shouldn't be taking faceplates off 'live', some do, and even a (normally) non-exposed box could theoretically become a hazard if not earthed (particularly since pulling the faceplate forward has been known to yank out the L conductor, which may then touch the box).

But then, if someone is taking a fitting off live - one hopes they are sufficiently technically competent to realise the risks (such as having a live wire suddenly make a bid for freedom) and mitigate them. I know that's perhaps a bit of wishful thinking ....

 

[JohnW2]

I assume a requirement for an exposed back-box to be properly earthed, together with the fairly common belief that the socket screws alone aren't a reliable earth - especially when the socket is removed.

Yes - but, as you say, that is a 'common belief', and (since you spoke of 'not permitted') I was wondering whether you knew of any corresponding regulatory requirement.

But then, if someone is taking a fitting off live - one hopes they are sufficiently technically competent to realise the risks (such as having a live wire suddenly make a bid for freedom) and mitigate them. I know that's perhaps a bit of wishful thinking ....

Yes, definitely 'wishful thinking', I would have said

Kind Regards, John