Earth wire for light fitting?

Alhex · Posted: Tue May 10, 2005 3:02 pm Post Subject: Earth wire for light fitting?

I recently purchase a new ligtht fitting with metal frame. As all lighting circuit is old there is no earth available. Can I run an earth wire from a socket in the room above to feed the light?
Many thanks for your help.

andy · Posted: Tue May 10, 2005 3:21 pm Post Subject: Re: Earth wire for light fitting?

Alhex wrote:

I recently purchase a new ligtht fitting with metal frame. As all lighting circuit is old there is no earth available. Can I run an earth wire from a socket in the room above to feed the light?
Many thanks for your help.

best get a earth from the same circuit or take a single earth from the CU to light. altho using an earth from the sockets is better than no earth

ban-all-sheds · Posted: Tue May 10, 2005 3:45 pm Post Subject:

Does the light need an earth? Just because it is metal that doesn't mean it does...

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Alhex · Posted: Tue May 10, 2005 6:55 pm Post Subject: thanks for previous reply

Yes it does need an earth it is a legal requirement. I spoke to a bloke in an electric shop and he tell me that I really should not use the same circuit as a socket to connect the earth from.
Is there any risk? (now that I have done it)

Also there is a conduit around the old wiring. The conduit should normaly be earthed. What is the best and easiest way to go about checking this out.
Thank you

ban-all-sheds · Posted: Tue May 10, 2005 7:11 pm Post Subject: Re: thanks for previous reply

Alhex wrote:

it is a legal requirement.

Why do you say that?

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Alhex · Posted: Tue May 10, 2005 7:57 pm Post Subject:

If there is a fault and the casing is live I could fry just changing a bulb so it would have to be earthed. I got the legal bit from a retired electrician. Any metal pendant and other need earthing

mapj1 · Posted: Thu May 12, 2005 3:10 pm Post Subject:

Earth needed ONLY if the cables in side the metal housing are not double insulated. Nowadays many are, for just that reason.
And it never was 'legal' just a very good idea.
Borrowing earths is frowned upon, as it may be removed in maintainance to the other circuit, and not realised. However, its much better than no earth at all.

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Alhex · Posted: Thu May 12, 2005 4:31 pm Post Subject:

Many thanks for all your comments.

Cheers

ban-all-sheds · Posted: Thu May 12, 2005 10:28 pm Post Subject:

Seriously - check the fitting. If it says that it's double insulated, or has a symbol of two squares, one inside the other, not only does it not need an earth, it must not be earthed.

Your retired electrician friend has given you dangerously inaccurate general advice that does not apply to all metal light fittings.

If there is no indication that it is double insulated, and it has earth terminal, then yes it must be earthed.

If there is no indication that it is double insulated, and it has no earth terminal, then don't use it.

Is it new, and CE marked?

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jtaunton · Posted: Fri May 13, 2005 10:15 am Post Subject:

ban-all-sheds wrote:

Seriously - check the fitting. If it says that it's double insulated, or has a symbol of two squares, one inside the other, not only does it not need an earth, it must not be earthed.

What are the implications of trying to earth something that is double-insulated ?

mapj1 · Posted: Fri May 13, 2005 10:36 am Post Subject:

In practice it is unlikely to be a problem, but you are not using it as the makers intended, so guarantees are affected, and it may no longer pass the flash test of the insulation that makers would have performed to certify as double insulated. However, that alone does not make it any more dangerous than it was before.
If making up fittings for home use, I'd recommend double insulated construction plus earth.
The most dangerous thing is to think you have earthed it, but to have connected to an earth that doesn't actually go back to true earth - in old lighting circuits this can occur. The floating wire can then pick up a voltage by capacitive couling to adjacent wiring, causing all sorts of unpleasantness. So having got an earth, using a meter on ohms and a long wander lead, make sure it really does connect back to the board.

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ban-all-sheds · Posted: Tue May 17, 2005 11:15 am Post Subject:

mapj1 wrote:

In practice it is unlikely to be a problem, but you are not using it as the makers intended, so guarantees are affected, and it may no longer pass the flash test of the insulation that makers would have performed to certify as double insulated. However, that alone does not make it any more dangerous than it was before.

I think it does. A 100% earth-free environment is the safest there is. We have earthing, and bonding, because this is very difficult to arrange in practice, so protection from indirect contact becomes essential. But earthing something unnecessarily just introduces more earths into an environment, and so lowers overall safety.

Consider this concept: Would you feel more, or less, safe if you had a cable permanently running between your body and your MET?

If less, then you should also feel less safe the more earthed metal there is in your environment....

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