Light Switch Replacements - Earth

ChilliBob

Hey guys, I have a messy set of four light switches next to each other in my kitchen - all different types! Arrgh! 


Three are metal and one is plastic, all have metal screws and metal back boxes.

I have switched the power off and looked behind all four, most are just a case of carefully following the existing wiring like for like, however, on the plastic, which I will replace for metal, I think it's best practice if I earth it.

I can see what I believe to be the earth wire in the backbox, so my assumption is I just connect this to the earth part of the new metal socket - as per the other metal sockets.

This is the mess I want to correct!


This is an existing metal socket, the dimmer, with the earth wire.


This is the plastic socket


And in the plastic socket's backbox is this, I presume, earth wire.



Have I missed anything here? Seems to all make sense from what I can see. Oh and the two switch two way one is a bit mental!.. Will need to label the cables very clearly as I remove them one by one!



Thanks for reading

Risteard

Not merely "best practice" - it's mandatory that Class I accessories be Earthed.

CliveOfIndia

ChilliBob said:

however, on the plastic, which I will replace for metal, I think it's best practice if I earth it.

And in the plastic socket's backbox is this, I presume, earth wire.

Any metal "fitting", for want of a better word, must be earthed.

ChilliBob said:

I can see what I believe to be the earth wire in the backbox, so my assumption is I just connect this to the earth part of the new metal socket - as per the other metal sockets.

Well ...... as far as it goes, the answer is yes.

But there's two things you really must check.  Firstly, the earth wire you can see, is that part of the same 3-core cable that the live & neutral are coming from?  That's pretty easy to check yourself.

Secondly, is the "other end" of that earth wire connected correctly into the CU?  That's probably going to be rather more tricky for a DIY-er to confirm (and you REALLY don't want to poking around inside the CU unless you absolutely 100% know what you're doing).

Realistically .... you're probably safe to assume it's connected up at the CU end (there'd be no reason for it not to be).  But there's always an outside chance that a previous owner has made a cowboy job of something, somewhere along the line.

ChilliBob

Risteard said:

Not merely "best practice" - it's mandatory that Class I accessories be Earthed.

Thanks, I'd read something on a YouTube video that it was 'best practice'. As you can tell I'm far from an expert. Some other observations from my research..

1. It's quite common for home owners to discover their metal switches aren't earthed like this (I seem to recall some in a past house

2. Somewhere said, which seems odd, the metal screws into the metal back box acted as an earth...

3. Not earthing is more of a risk if somebody takes the switch off without isolating it at the consumer unit - it's not as if the metal surrounding the switch is live if you touch it!

ChilliBob

CliveOfIndia said:

ChilliBob said:

however, on the plastic, which I will replace for metal, I think it's best practice if I earth it.

And in the plastic socket's backbox is this, I presume, earth wire.

Any metal "fitting", for want of a better word, must be earthed.

ChilliBob said:

I can see what I believe to be the earth wire in the backbox, so my assumption is I just connect this to the earth part of the new metal socket - as per the other metal sockets.

Well ...... as far as it goes, the answer is yes.

But there's two things you really must check.  Firstly, the earth wire you can see, is that part of the same 3-core cable that the live & neutral are coming from?  That's pretty easy to check yourself.

Secondly, is the "other end" of that earth wire connected correctly into the CU?  That's probably going to be rather more tricky for a DIY-er to confirm (and you REALLY don't want to poking around inside the CU unless you absolutely 100% know what you're doing).

Realistically .... you're probably safe to assume it's connected up at the CU end (there'd be no reason for it not to be).  But there's always an outside chance that a previous owner has made a cowboy job of something, somewhere along the line.

I shall inspect further, probably tomorrow, and take another picture. Essentially it's two double back boxes here, and all the other switches are earthed in the same way. 

I don't quite get why the homeowner previous to us used a plastic switch when everything else in the house is metal.

If it wasn't as expected, and it was wired up and then switched on at the consumer unit would it sense a fault and trip? Hence me knowing its wrong?

Lastly, how would a sparky, or anyone else for the matter, be able to trace a cable in a wall back to a consumer unit?! - it's not like they're surface mounted cables. Just curious really, not something I intend to do! 

Ectophile

ChilliBob said:
Lastly, how would a sparky, or anyone else for the matter, be able to trace a cable in a wall back to a consumer unit?! - it's not like they're surface mounted cables. Just curious really, not something I intend to do! 

Continuity tester, with a very long lead.  The fancy instruments they will use have this, but so do almost all digital multimeters of the sort you can buy for a few pounds.

If you have a multimeter, try switching it to continuity.  Then push the probes onto the screws that hold in the switches.  If there is continuity between the screws of all the switches, then it's likely that the earth is actually connected at the other end.

ChilliBob

Ectophile said:

ChilliBob said:
Lastly, how would a sparky, or anyone else for the matter, be able to trace a cable in a wall back to a consumer unit?! - it's not like they're surface mounted cables. Just curious really, not something I intend to do! 

Continuity tester, with a very long lead.  The fancy instruments they will use have this, but so do almost all digital multimeters of the sort you can buy for a few pounds.

If you have a multimeter, try switching it to continuity.  Then push the probes onto the screws that hold in the switches.  If there is continuity between the screws of all the switches, then it's likely that the earth is actually connected at the other end.

My Dad had a multimeter, so yeah I could try this. So basically.. 

Set multi meter to cont
Switch off lights at the consumer unit
Unscrew plastic switch 
Put each probe into screw holes on the back box. 

What I'm *not sure* there is what the expects behaviour would be.. Edit: just read up on this, I sort of half understand it! 

molerat

ChilliBob said:

I don't quite get why the homeowner previous to us used a plastic switch when everything else in the house is metal.

Looking at the earth wire just left dangling in the back box I suspect they quickly replaced a metal switch with what they could find cheaply, the plastic switch having nowhere to connect the earth to.

ChilliBob

molerat said:

ChilliBob said:

I don't quite get why the homeowner previous to us used a plastic switch when everything else in the house is metal.

Looking at the earth wire just left dangling in the back box I suspect they quickly replaced a metal switch with what they could find cheaply, the plastic switch having nowhere to connect the earth to.

You may be right. I suspect, based on one light being absent, and these being gu10s, LED they probably had a dimmer on it or something which messed things up!

I just looked on the lounge, also a metal dimmer, also earthed in the same way. 

I know the electrics were redone in this house about 14 years ago when it was completely gutted, by one of the previous owners electrician mates - one of those situations where the person doing up the house was in the building trade and knew people to do other bits like electrics, carpentry etc