Earthing back box

[Johan2218]

Hi, for some inlnunk reason when I opened up a double socket I could see that it wasn't directly earthed to the metal back box.
I know that it is "effectively" earthed via the socket screws but thought it was best practice to directly earth the back box to the socket. Having checked the rest it seems several are missing this.
I would normally strip the earth wire out of a 2.5 mm cable, earth sleeve it and use that... but was just wondering if the similar thinner earth wire from a 1.5 mm lighting cable would be equally acceptable to use?
Many thanks

 

[ktuludays]

Yes, that should be fine

 

[SimonH2]

For some sockets (eg surface mounted metalclad) it's required, but for the normal metal box in a plastered wall it's optional. The reasoning is that the box itself isn't accessible unless you remove the accessory - and when you remove the accessory you are exposing other risks as well which you should be aware of (if you aren't, then you shouldn't be doing it).
The only accessible parts linked to the backbox are the screws - which will be earthed by the metal strap integral to most sockets. For plastic switches, where they have no earth strap earthing the screws, there's usually no earth terminal and so an earth terminal in the backbox will be used to terminate the CPC(s).
But personally, I earth the boxes - usually with a bit of 6491X.

 

[Johan2218]

Thank you both.
The question really is, when using a wire to earth such as 6491x, does it matter if it's 1.5mm rather than 2.5mm?
Thanks

 

[Risteard]

Use the same csa cpc as that in the cable.

Exception to this for me is 6mm^2 T&E cable from the Free State (I.S. 201) as it has a 6mm^2 cpc.

 

[Johan2218]

Okay thanks...it was asking because for some reason I seem to have lots of 1.5mm earth wire.
So had hopes to safely get away with that.

 

[SimonH2]

That's fine. Our 2.5mm² T&E has a 1.5mm² CPC - so need to go larger than that.
Even if the T&E had a 2.5mm² CPC, it's hard to imagine a reasonable scenario in which a 1.5mm² wire wouldn't do the job. It'll only come into play in the presence of a fault - and all the faults I can think of will be handled by the CPC connected to the socket itself EXCEPT for when someone has the socket removed from the box, and then they should know what they are doing anyway.

 

[Johan2218]

Hi Simon,

That's good to hear... thanks very much.

I will use the extra earth wire from a load of stripped 1.5mm cable.

Again, many thanks
John

 

[EFLImpudence]

I would say that a thing which is not actually required at all does not have a minimum size.