This may be a obvious question, but I am currently replacing plastic light switch face plates with metal ones; so far I have been earthing straight to the earth terminal on the face plates. Does it matter that I am not also earthing the the metal back box?
My logic is surely it's more important to earth the face plate itself, but have seen online that you should really earth both.
The Belt and Braces Rule, would make it sensible to earth to both. But the requirements allow you to only terminate the switch plate, if you have a rigid fixing lug to screw plate on to the backbox. If both fixing lugs a movable/adjustable, then you must earth both plate and switch.
The most important thing to do, when installing metallic plates, is not only to connect the earth (CPCs) but also to actually establish that a path to earth is present and continuous. Otherwise connecting that bit of cable would be pointless and by swapping plates you have introduced a potential danger.
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