New Chrome Lightswitch and Earth Wires

[Pandolf]

Hi there, I've just installed a new chrome lightswitch in my flat. I understand that the earth terminal on the back of the chrome light switch should normally be connected to the green and yellow earth wires in the wall.


My question is this:

In my flat, the green and yellow earth wires are connected to the metal box in the wall that holds all the wiring. The chrome lightswitch screws into this metal box. Do I not need to connect a wire from the switch's earth terminal to the green and yellow earth wires in the wall, because when I connect the chrome faceplate of the switch with metal screws to the metal box it will thereby be connected to the earth wires anyway? (i.e. through the metal screws and metal box)

I'm also wondering what the dangers are of not connecting the earth terminal to the yellow and green wires in any way?

Thanks.

 

[sparkyspike]

If anyone were to undo a live faceplate, there would be a risk of an unprotected metal part unless it was bonded.

NICEIC will not accept unbonded backboxes.

I don't think the Wiring Regulations refer to it directly other than in 411.4.2 which implies that a metal box should be connected to the CPC. It comes down to whether the brass plate screw is an acceptable means of earthing and whether a faceplate which can only be removed with a tool is a safe way of covering an exposed conductive part.

As the plate is connected to the box via the screw, then it is not protecting anyone from direct contact from the backbox only as much as the screw is also bonding the backbox.

Most people put a platescrew in their mouths whilst fixing back a faceplate. This will inevitably lead to corrosion of the screw and a poor contact.

 

[GaryMo]

NICEIC will not accept unbonded backboxes.

Yes they will, assuming there's at least one fixed lug.

 

[sparkyspike]

NICEIC will not accept unbonded backboxes.

Yes they will, assuming there's at least one fixed lug.

Not where I live they won't. Just goes to show it's a matter of opinion.

 

[GaryMo]

Perhaps show them their own book (their own opinion?), NICEIC Snags and Solutions - Earthing and Bonding. Then point them towards Snag 21.

 

[Pensdown]

My question is this:

In my flat, the green and yellow earth wires are connected to the metal box in the wall that holds all the wiring..

The chrome lightswitch screws into this metal box.

Do I not need to connect a wire from the switch's earth terminal to the green and yellow earth wires in the wall, because when I connect the chrome faceplate of the switch with metal screws to the metal box it will thereby be connected to the earth wires anyway? (i.e. through the metal screws and metal box)

Yes you do. Your light switch is an exposed conductive part so it must have an earth connection to protect people even if it's un-screwed from the back box.