(Sorry if this has been covered before but I couldn't easily find anything by searching.)

When installing 3-pin sockets into the metal boxes embedded in the wall should I also link the earth connector on the back of the socket to the metal box using a short piece of earth cable? (This is what I have seen at a UK DIY website). But my metal boxes have no connectors. I asked a guy at the electrical department of a Global store and he said connect it to one of the 2 screws that fastens the socket unit into metal box. Is this correct/safe practice or not? I am using Siemens Delta Azio sockets and switches.

How about the switch - does that also have to be earthed to the box?

Thanks.

JB.

It's certainly good practice to earth the metal back box even if you have PVC conduit, the main reason is to stop the screws becoming live if you clip a live cable when tightening.

That said, it's rarely done here and all the plastic outlets and switchplates on common sale have concealed screws so even less of a danger.

Note that if you have metal faced outlets / switchplates then grounding them is vital for safety, usually one would ground the box, the plate is then grounded via the fixing screws but look at your outlets to see what arrangements are made.

If you have no connection point a small self-tapper drilled into the back of the box will do a fine job, put a ring crimp on the earth pigtail if you're feeling professional.