I've been called back to a job where I have put in a ring main.. I've used metal clad face plate and back boxes. When wiring all I have simply done is used the incoming earth and terminated to the face plate and used the out going earth to terminate to the back box. Their saying that both earths should be in the face plate with a separate fly lead going off to the back box. Surely terminating 3 2.5mm earth into one terminal there is more chance of it coming loose? Is this a regulation??
Earth bonding to metal clad back box?
- Thread starter traineelectrician
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The two earths MUST go into the terminal on the socket.
What you have done is create the dangerous situation of the earth to some sockets relying on the screw holding a faceplate to the back box.
When those screws become loose sockets down stream from that socket will not have an effective earth.
What you have done is create the dangerous situation of the earth to some sockets relying on the screw holding a faceplate to the back box.
When those screws become loose sockets down stream from that socket will not have an effective earth.
Thanks. So in effect when you unscrew the face plate off from the back box the earth continuity is broken in the ring making it a danger..
Yes that is the danger
The fixing screws can become loose with normal use meaning the earth continuity can be broken before the front plate is noticable loose. Corrosion of the box lug can affect the conductivity as well hence the reccomendation for the link wire between face plate and box.
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Great.. Thanks, that makes sense. I shall make sure to do it in future works!
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You should also go back and fix it in previous works.
Who taught you to do it that way?
Who supervised your work?
Who did the inspection & testing?
Who signed the EIC?
The faceplate should not be unscrewed unless the circuit is isolated anyway.
But the cpc might be shared between several circuits. More likely on older work getting updated where a lighting circuit without earth might have an earth taken from a nearby socket.
I don't think that using the mounting screws for this is a secure connection hence imo is in violation of fundamental principles of the regs.
I know there is an allowance using a metal back box where the back box isn't accessible to use the mounting screws to earth the back box from a socket front but not vice versa, however is not applicable using metal clad surface mounted accessories anyway.
3 lots of 1.5mm or 2.5mm into a terminal isn't that difficult, a decent brand of socket may even have two CPC terminals.
I know there is an allowance using a metal back box where the back box isn't accessible to use the mounting screws to earth the back box from a socket front but not vice versa, however is not applicable using metal clad surface mounted accessories anyway.
3 lots of 1.5mm or 2.5mm into a terminal isn't that difficult, a decent brand of socket may even have two CPC terminals.
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