Earthing a light switch-do I have to find a lighting earth

[consciouspnm]

I need to earth a light switch so I can replace it with a metal version. After a bit of struggling inside the walls I've got a single earth cable to a nearby switched fused spur, can I use this earth or do I have to struggle on to the nearest earthed light switch?

 

[Spark123]

The earth needs to be from the lighting circuit, if your wiring doesn't incorporate an earth core then might be time to look towards rewiring.

 

[steve1811uk]

Surely it is still better to be earthed in some way rather than not earthed at all. A total rewire may not be feasible. Experts please comment on this. Steve.

 

[consciouspnm]

Most of the sockets and switches are wired in singles in 20mm PVC conduit. I can just about get to an inspection box several metres away by removing a downlight, but if it's not the same conduit or it branches off somewhere else the only way to get to it would be to take down the ceiling as I've got a flat roof.

...and the walls are made of laminated plywood so I cann't put any holes in them without replacing the entire panel.

 

[bernardgreen]

Surely it is still better to be earthed in some way rather than not earthed at all. A total rewire may not be feasible. Experts please comment on this. Steve.

You are right to ensure the switch is earthed. But ALL metal switch back boxes need to be earthed including those with plastic face plate as the two screws which hold the switch in place would become live if the back box became live due to loose wires or damaged cables.

If there is no earth wire in the cable to the switch then there is no garantee there is an earth wire to other parts of the lighting circuit for lights and switches.

If you have any lights with exposed metal, a flourescent light for example, then without a earth wire they could become live.

 

[Spark123]

You also need to be able to identify which conductors belong to each circuit, i.e. if someone was to disconnect the phase+neutral+earth conductors at the consumer unit for the ring, there is a risk that in the event of a fault the switch can become live or the person working on the system may get a shock from touching the disconnected earth.
I'm still of the frame of mind each circuit should have its own CPC in its correct terminal in the consumer unit.

 

[consciouspnm]

You are right to ensure the switch is earthed. But ALL metal switch back boxes need to be earthed

The back boxes are plastic.

 

[securespark]

Experts please comment on this. Steve.

Sorry, Spark123, you're obviously not an expert!

The NICEIC (for what they're worth) advise that if a lighting circuit has no cpc, there are two options: Rewiring, or adding a cpc from the consumer unit, and take it round the circuit, following closely the existing cables. If you can't do that, your best option is to bite the bullet & rewire.

 

[bernardgreen]

You are right to ensure the switch is earthed. But ALL metal switch back boxes need to be earthed

The back boxes are plastic.

Which suggests it is a recent up-grade, in which case it should be wired in twin and earth. Did someone cut short the ""un-neccessary"" earth wire in the when they fitted the plastic box.