New Light Switch Wiring no Earth but old Switches Have Earth


Postby ID015 » Wed Nov 30, 2016 4:37 pm

I didn't like the old light switches so I decided to replace them with new simple one to match the rest of the in the house. I thought the job would have been a simple like for like but in old British houses there are always some surprises.

The current old light switches also have the earth wire connected but the new ones don't have earth in lighting circuit. So the question is, what do I do with the earth wire?

The house is old so wiring is from god knows when and I am afraid that the earth wire was left behind, the other light switches (in modern parts of the house) don't have it. Is it really needed? Can I wire it to the back of the plate?
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Postby kbrownie » Wed Nov 30, 2016 5:20 pm

The earth is very im[important part of the circuit and must be kept continuations throughout. If you have backboxes with an earth terminal, connect to them, if not and the back plate is metallic, it should really be connected to them.
If backboxes are plastic with no terminal then a connector block, should be used.

Most of the new plastic light switch plates do not come with an earth terminal, if the plates where metallic they most be earthed.
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Postby ID015 » Wed Nov 30, 2016 5:45 pm

Thank you - Also after reading a bit more - the current switch is metallic so I understand it must be earthed.
The new switch is simple plastic so I can safely earth the metal back box.

Is it sufficient to earth it to the metal back box via the screw from the light switch plate?

ta
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Postby kbrownie » Thu Dec 01, 2016 7:48 am

If switch plates are plastic with no earth terminal, the metallic backbox is earthed via the earth terminal screw on it.

If the switch plate is metallic, then the swicth plate must be earthed via the earth terminal on the switch.

It is good practice for metallic switch plates to also be bonded across to any metallic backbox, via a short length of earth cable. Although regulation do not require this when at least one of the screw lugs, on the backboxes are rigid. Often you will find one rigid lug and one the is loose that offers some adjustment to the plate position.
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