Earthing

shifty · Posted: Mon Apr 18, 2005 9:56 pm Post Subject: Earthing

I want to fit a new ceiling light in my living room,the new light that I have bought is made of metal and so has a earth terminal on it. However there is no earthing on my lighting circuit. Can this light be fitted or should I change it for one without an earth.

ban-all-sheds · Posted: Mon Apr 18, 2005 10:37 pm Post Subject:

You need to change it, or provide an earth.

Are you sure though that there is no earth, and that it's not just been cut back? What do you see at light switches, other light fittings and the CU?

If the circuit really does have no earth, do you know how old your wiring is?

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plugwash · Posted: Tue Apr 19, 2005 8:33 am Post Subject:

if you find a cut back earth there is a significant chance that it doesn't actually connect to anything.....

shifty · Posted: Tue Apr 19, 2005 9:40 pm Post Subject:

No earth on the circuit, ceiling rose wired in old red and black multi stranded . Would it be acceptable to earth the light to copper pipe in attic?

ninebob · Posted: Tue Apr 19, 2005 11:18 pm Post Subject:

'Fraid not. You're looking at a rewire of at least the lighting circuit. How old is the rest of the wiring?

ban-all-sheds · Posted: Tue Apr 19, 2005 11:23 pm Post Subject:

shifty wrote:

No earth on the circuit, ceiling rose wired in old red and black multi stranded .

Past its sell-by...

Quote:

Would it be acceptable to earth the light to copper pipe in attic?

Absolutely not!

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shifty · Posted: Wed Apr 20, 2005 5:37 pm Post Subject:

Does this mean that I have to rewire the lighting circuit fully or can I run an earth from the rose that I want to use back to the board (and if so what size would this need to be).

I appresiate that a full rewire would be the best thing to do but lots cheaper just to earth the light that I want. Anyway thank you all for your advice so far.

ban-all-sheds · Posted: Wed Apr 20, 2005 5:42 pm Post Subject:

shifty wrote:

Does this mean that I have to rewire the lighting circuit fully or can I run an earth from the rose that I want to use back to the board (and if so what size would this need to be).

4mm²

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andy · Posted: Wed Apr 20, 2005 6:20 pm Post Subject:

shifty wrote:

I appresiate that a full rewire would be the best thing to do but lots cheaper just to earth the light that I want. Anyway thank you all for your advice so far.

but do you know what condition the wiring is in? it may have extremely low insulation resistance, your sockets may not be earthed. you probably wont have an RCD (altho quite a few houses dont)

mapj1 · Posted: Wed Apr 20, 2005 11:22 pm Post Subject:

It is permissible to earth just the offending light, but the condition of the cable in other ways needs to be considered. Is it cloth, rubber or PVC insulated?
Anything except PVC nowadays is suspect until passed by a 500V insulation test. Some early PVCs have a problem of 'green gunge' as the plasticiser leaches, and the copper is attacked.
Some 1970s copper shortage 2.5mm ring mains have a 1mm earth core that fails to discriminate against a 30A fuse under certain embarassing fault conditions, and as Andrew mentions an RCD is now required on all new sockets that might reasonably be used to feed outdoor equipment.
It is probably worth getting someone who can check these details to give the installation a once over in the not too distant future, even if you do just run a separate earth for this light.

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