Confirming light switch is earthed

[consciouspnm]

I've got a light switch which is wired in 1.5mm T & E, but having traced the cables to the point them come down from the ceiling, the light switch appears to have been moved across the the wall by around 300mm and there is no earth in the original set of cables. The original cables are singles in pvc conduit.

How can I confirm the earth in the switch is actually connected to something?

 

[ricicle]

An earth continuity test or earth fault loop impedance test.

 

[Chivers7]

How can I confirm the earth in the switch is actually connected to something?

What type of test equipment have you got?

If you've got a low reading ohm meter than as ricicle says

A resistance measurement from a known good earth (MET) and the one your worried about would give you an indication. A long "wander" lead ie reel of cable may help.

 

[consciouspnm]

I've got a digital multimeter but can go and buy anything else I need. There's a socket on the ring main directly below the switch so are you saying probe the earth on that and the earth on the switch?

 

[Chivers7]

I've got a digital multimeter but can go and buy anything else I need. There's a socket on the ring main directly below the switch so are you saying probe the earth on that and the earth on the switch?

Sounds like a good plan. Measure the resistance across the two if it's really low then the earths present if not further investigations required, but be careful.

 

[bernardgreen]

First measure for a voltage between the good earth and the suspect earth. That way you protect the ohms range of your meter if the suspect earth has a voltage on it from somewhere.

Any voltage present will be sign there is no reliable earth.

 

[consciouspnm]

I'm getting 50v AC between the earth on the socket and the metal backbox of the switch, if I remove the probe from the known earth (so just the one on the switch) I get around 15v AC so I guess it's not connected to anything.

 

[RF Lighting]

No it sounds like a floating earth, IE not connected at the other end, and the 50V you are reading is an induced voltage.