I recently replaced a plastic light switch with a brass victorian type. Coming from the ceiling were 2 x red wires and an earth, which connected securely to the metal mounting box.
Question: There is an earth terminal on the back of the brass faceplate. Do I need to connect this to the earth on the back box?
Thanks, Bruce
No, as the securing screws to back box will suffice.
Unless the back box is plastic, in which case, connect the earth to the terminal on the switch plate instead of parking it in the terminal on the backbox.
Tsssss!
If the back box has at least one fixed (non-sliding) lug, then it's considered that the fixing screws are sufficient to earth the box *from* the accessory.
I wouldn't dream of doing it the other way around with a brass accessory. IMO, the OP should earth the switch properly.
Will
Yes. The metal box is then still earthed when the screws holding the switch are undone.
John
You need to connect the cable earth to the back of the brass faceplate. You can also run a flying lead from the faceplate earth to the backbox. This isn't usually required, but is often taken as a sign of a conscientous installer.
Don't do it the other way, though. The circuit earth should go directly to the accessory, not the backbox. It was only run this way before because the existing white plastic switch won't have had an earth terminal.
Christian.
Thanks. But as 3rd Earl says... don't the brass connecting screws in effect make an earth connection from the brass faceplate to the metal back box, to which is connected the supply earth. Same as a flying lead, really.
I always turn the power supply off before I unscrew any switch face plates.
Thanks, Bruce
Not reliable enough. You want the secure connection to the faceplate and the dodgy connection to the backplate. The screws rust and can end up with a high earth impedence. In the event of an earth fault, this could be high enough to cause a fire. Unlikely, I know, but not best practice.
I don't. Nor do many others. I might want the lights on when decorating behind the faceplate.
Christian.
Curiosity question.
What do you do when the earth is too short? ie someone has cut it just long enough to reach the earth terminal of the backbox but it will not reach the earth terminal on the metal faceplate.
A flylead must still be used from the backbox terminal to the metal faceplate but would it pass an inspection?
IMHO it would even though it is not the preferred method of installation
Adam
Surely the main protection here is to prevent the plate becoming live due to fault in switch/loose wiring, the earth return needs to have a low enough impedance to trip breaker/blow fuse (as with all metal cased appliances), as such I would have thought it essential to have this plate earthed. Many people do not switch off when loosening screws and pulling forward the plate when decorating - I can see a loose live wire being pulled out the terminal to rest on the back of the plate when the plate is released, in this situation the screws are removed and no earth in place, will give a shock(maybe severe/fatal) when plate is grabbed - likely fault/severe consequence = high risk, worth a short length of wire + earth sleeve.
By opening the (single pole) MCB perhaps? If so remember that you ought to treat the neutral as a live conductor as well - hence you still want the back box earthed even if the screws are removed.
Personally I would say it is OK, provided there is a flying lead and no reliance on the screws. I'm not an inspector, though!
Christian.
Its advisable, but in practice if you use metal screws these have the same effect.
The earth connection on the face plate is important if, like me, you have plastic dryfit backing boxes...
Crimp on an extension. and sleeve the crimp G&Y.
The recommendation is to take the protective conductor to the accessory and loop that to the back box. This is because of the poor quality of the terminal in most metal "plaster" boxes. The brass terminals in old MK boxes were OK but most of the others are horrible , fill up with plaster and corrode easily. If you have enough length you can loop it without a join.
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