Earthing Light Switch?

[Deleted2797112]

Me again, didn't think I'd be back this quick! I wonder if anyone can advise please?

I'm replacing standard plastic light switches and sockets with some fancypants screwless ones which have a plastic template with the electrical connections mounted on a metal plate then a clip on chrome cover. The instruction sheet has a section for each different type of fitting in this range and the instructions for the sockets, spurs, heavy duty switches, connection unit, dual voltage shaver socket all say to earth the fitting. The instructions for the standard light switch don't mention earthing although the fitting has an earth terminal.

I've opened up an existing two-way light switch - the switch fitting has no earth terminal (because it's plastic?). There is an incoming earth in the switch cable coming from the light. This has been split and attached to a screw on the back box (which is metal) and the earth wire then continues out with the other wires to the next switch downstairs.

So given that the instructions are explicit about earthing everything else but not the light switch, does it need to be earthed and if so, how would I do it?

I got some great help here yesterday after I'd been struggling with a light fitting so thanks for reading! It's much appreciated.

 

[MIH]

I'm not a qualified electrician but I've had personal experience of changing light switches and sockets from plastic to metal and they were being fitted to metal back boxes.

The advice I got at the time, was that you had an earth cable from the earth connection on the switch to the earth connection on the back box.

Don't forget to sheath the earth cable accordingly.

 

[bernardgreen]

The instructions for the standard light switch don't mention earthing although the fitting has an earth terminal.

Earth terminals need to be earthed. That is why they are there.

The CPC ( earth wires ) in the cables should be connected to the earth terminal of the switch to ensure all exposed metal is earthed. It is also a good idea to add an earth wire from the earth terminal on the switch to the earth teminal in the back box to ensure the back box is earthed.

 

[Deleted2797112]

Gosh, that was quick. Thank you!

It just seemed odd that the instructions are explicit about earthing everything else but not the light switches.

I understand how to earth from the back box to the switch but I don't understand how to connect between the earths in the cables to the switch.

As it is now, the incoming/outgoing earth is split in the box and the ends are attached to a small ring connector with a screw attachment to the back box. To earth from the back box to the switch, I'd unscrew this and attach a further sleeved earth connecting the other end to the earth terminal on the switch. How would I separately connect the earth cables to the switch?

 

[echoes]

I'd unscrew this and attach a further sleeved earth connecting the other end to the earth terminal on the switch.

Not best to rely upon a flylead to earth the switch's metal bits, so...

How would I separately connect the earth cables to the switch?

...the better way is to connect the earth wires currently connected to the back box to the switch's earth terminal instead, and then take a flylead from there to the back box.
It is of primary importance to ensure the switch's metal parts are earthed reliably, and the back box is then earthed via the fly lead and/or metal fixing screws. Electrically no different, but much better practice.

 

[riveralt]

The cpc's in main cables that come into the backbox are fastened to the earth lug in the backbox.
You then take a spare piece of cpc - strip it from the same size cable coming into the backbox normally 1mm or 1.5mm - sleeve it in the appropriate green/yellow and attach between the backbox lug and the earth terminal on the metal switch.

Did you know that the cpc (earth) sleeving should be 70/30 between the two colours. But do you know which one should be 70% and which one should 30%?

 

[riveralt]

...the better way is to connect the earth wires currently connected to the back box to the switch's earth terminal instead, and then take a flylead from there to the back box.
It is of primary importance to ensure the switch's metal parts are earthed reliably, and the back box is then earthed via the fly lead and/or metal fixing screws. Electrically no different, but much better practice.

While that is fine for first fix, invariably the cpcs have been cut to fit the backbox lug and will not stretch to the switch cpc terminal.

 

[Deleted2797112]

Ah, OK. I understand now thanks!

There's a tiny bit of slack on the earth cables. I think it will be a bit awkward but I'll give it a go.

 

[echoes]

...the better way is to connect the earth wires currently connected to the back box to the switch's earth terminal instead, and then take a flylead from there to the back box.
It is of primary importance to ensure the switch's metal parts are earthed reliably, and the back box is then earthed via the fly lead and/or metal fixing screws. Electrically no different, but much better practice.

While that is fine for first fix, invariably the cpcs have been cut to fit the backbox lug and will not stretch to the switch cpc terminal.

Good point - thanks!

 

[Paul_C]

Did you know that the cpc (earth) sleeving should be 70/30 between the two colours. But do you know which one should be 70% and which one should 30%?

I think the specification is that any one color should be between 30 and 70% of the surface area, and thus the other color should fill the remaining space. In other words, anything between 30% green/70% yellow and 70% green/30% yellow is considered acceptable, including 60/40, 50/50 etc.

At one time, green seemed to be dominant in most cases, but these days it seems that most manufacturers make the yellow dominant.

 

[Deleted2797112]

Thanks for the help again. I've got the hang of it now. The first one I did, there wasn't enough slack in the earth cable to get to the earth terminal so I did it with the 'fly' to the back box. I managed to do the second one the best practice way. About to tackle the third.

 

[kevindgas]

Not best to rely upon a flylead to earth the switch's metal bits, so...

...the better way is to connect the earth wires currently connected to the back box to the switch's earth terminal instead, and then take a flylead from there to the back box.

It is of primary importance to ensure the switch's metal parts are earthed reliably, and the back box is then earthed via the fly lead and/or metal fixing screws. Electrically no different, but much better practice.

why and why?
don't see that it makes any difference so long as the back box is earthed and any switch is earthed if either/both are metal.

 

[sparkwright]

Not best to rely upon a flylead to earth the switch's metal bits, so...

...the better way is to connect the earth wires currently connected to the back box to the switch's earth terminal instead, and then take a flylead from there to the back box.

It is of primary importance to ensure the switch's metal parts are earthed reliably, and the back box is then earthed via the fly lead and/or metal fixing screws. Electrically no different, but much better practice.

why and why?
don't see that it makes any difference so long as the back box is earthed and any switch is earthed if either/both are metal.

Yes, does it really matter?

I have seen on sockets where the two CPCs (ring for example) have been taken to the metal back box earth terminal, then an earth wire from here to the socket front. Somehow this doesn't seem very good practice.

Back to light switches, you may have something like a 3 gang switch with say 6 earth wires. Due to the earth terminals only being so big, it makes good sense to fit 3 earth wires to the back box, plus a short link from here to the switch, along with the remaining 3 earth wires. 4 wires in each terminal.

 

[echoes]

Thanks for all the comments! We all agree that sound connections between the exposed metal faceplate and the CPC's is what is required, and the exact manner of that depends on practical realities such as space available, number of conductors etc.
(e.g. It may be easier to connect all CPCs in the switch terminal because it's often larger than the back-box terminal.)

The (overcooked) point I was making to the OP is that earthing the switch plate is mandatory, and shall not rely on, e.g. the screw/lug to make the connection. But if the flylead is there, it's rather moot.

 

[ban-all-sheds]

I understand how to earth from the back box to the switch but I don't understand how to connect between the earths in the cables to the switch.

Nor, it seems, do you even understand which is the earth wire.