Maybe a dumb earth question, but...


Postby RBrad » Wed Oct 17, 2007 7:35 pm

...what 'counts' as earth?

I have just bought a new light to fit in a bedroom. It needs an earth and the old system (1960s ish) has only red/black wire. I can get to this wire in the loft but not back to its rose which is under flooring.

I think I could, therefore, just run an independant wire as earth from the fitting into the loft and then to a suitable earth point. But, what is a suitable earth point?

There are no pipes or other electrical fittings anywhere near in the loft. The house wall is about 1.5m to the right, could I bang a nail into that and attach the wire?

Or is there some other easy way to do it???

Tks in advance

Brad
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Postby BLAKEY1963 » Thu Oct 18, 2007 3:44 pm

[quote="RBrad"]...what 'counts' as earth?

I have just bought a new light to fit in a bedroom. It needs an earth and the old system (1960s ish) has only red/black wire. I can get to this wire in the loft but not back to its rose which is under flooring.

I think I could, therefore, just run an independant wire as earth from the fitting into the loft and then to a suitable earth point. But, what is a suitable earth point?

There are no pipes or other electrical fittings anywhere near in the loft. The house wall is about 1.5m to the right, could I bang a nail into that and attach the wire?

Or is there some other easy way to do it???

Tks in advance

Brad[/quote]

Brad
your wiring could be over 40 years + old and sounds as if a rewire is needed.
The earth required for your your light would be integral to the wiring normaly with a brown and blue now ( new harmonised colours ).
This would go back to the main earthing terminal in your mains board and
give earth fault protection for class one appliances. ( items of equipment
with metal frame work to them ).
normaly in this case of yours a warning sticker would be placed on this circuit advising because of no earth present , class 1 metal frame items should not be connected as they could be a shock risk , in the event of a live conductor touching the frame made of metal.
As for your quest for an earth point , to meet disconnection times now
u would have to directly connect to a cpc ( circuit earth wire ).
Personally i think a earth wire run back to the mains board would be the best option to give u the correct earth loop impeadance value , in order to correctly operate your protective device in the required dissconnection
time .
other than rewiring the lighting circuit and the rest.

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Postby RBrad » Sat Oct 20, 2007 3:54 pm

Thanks for that Blakey, I was worried it may mean a rewire is due but cannot do that at the moment.

On thursday a friend I mentioned this put me on to a retired electrician who said it was not uncommon years ago for individual lighting spurs to not have an earth when the main junction box(in the loft) did. I now intend to find this box and uncover the full truth, as then it maybe only needs a few metres of wire to be replaced.

Thanks again.

Brad
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