q: impact of NOT connecting earth to Light connection block

[lstoner]

Thanks again for all your replies. In summary then:

- The existing old wiring cannot be 1930's as it looks in pretty good shape ( just no earth )
- Wiring the light in without an earth IS a big no no
- Using an earth from a nearby [new] light circuit is ok, but if I knew what I was doing then I'd be able to rewire the circuit.
- It helps that I'm no where near the bathroom, especially the shower circuit

q1: If i'm just running an earth, what cable would you recommend ? I'm assuming there are different specs of earth wire.

q2: Given that I don't know what CPC stands for, should I go near the wiring at all ?

 

[andy]

CPC is the fancy name for earth. it means circuit protective conductor. use 1.5mm single core earth between the lights

 

[Damocles]

Always with safety issues, everything is a question of degree. Once upon a time someone must have decided that lighting circuits did not need an earth. Though at the same time it was felt sockets did. This probably quite correctly reflects the greater danger from things plugged in than those screwed in place. Brass light switches have always been popular in up-market situations. I don't know if you were expected to provide an earthed lighting circuit if you used metal switch plates, at the time when your non earthed lighting circuit was installed.

Big no-no is something like invading someone else's country and killing lots of people. Adding an unearthed light fitting is more of a small no-no in my way of looking at it. Unearthed metal light fittings have been in use since electricity was invented with a relatively small death toll.

But having said all that, yes you should supply an earth somehow. It is better to provide one by grabbing one from a different circuit than not to have one. There has been a bit of discussion, but it seems quite possible it would pass inspection if you did only this. It might not be ideal, but I think it would not be considered unsafe.

A 2.5mm green and yellow should be big enough. This is bigger than the size in the lighting circuit, but that makes it a bit stronger.

It does not matter if you do not know what CPC stands for. It might be a good idea though to read up about it, make sure you understand how your wiring works and the normal cables, ratings which are used for what you want to do.

Oh, and the full time professionals don't understand all of it either.

 

[ban-all-sheds]

there are a couple of important facts here

1: the lighting cable will generally be longer and is very unlikely to be significantly shorter than the shower cuircuit cable.
2: cable of 6 times the CSA (the CPC in 10mm T&E is 6mm isn't it) has significantly less than 6 times the current capacity.

The same situation arises when you've got multiple circuits in the same enclosure - perfectly in accordance with the regs if properly labelled - e.g. wall lights spurred off a socket circuit and taken to a 2-gang switch. You're going to take both cpcs to the back box and/or faceplate, aren't you....

 

[brown-nought]

A 2.5mm green and yellow should be big enough.

Are you sure a single 2.5mm cable run without mechanical protection is allowed? I thought it needed to be 4mm?

I understood there can be reactance problems when you run the earth and phase via separate paths and this is why it’s recommended to run them in close proximity.

 

[securespark]

You're a bunch of bean muggers....

CPC= Circuit Protective Conductor
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