Voltage on brass light switch

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I touched the brass light switch in my front room today and it felt like it was vibrating,on further investigation I have found that the switches are not earthed the earth cable has been connected to the back plate but there is no continuity to earth,if I put my meter to earth and the switch cover I get 125v,also if I put one probe on the earth in the ceiling rose and the other end to earth I get 125v. I have a modern consumer unit with rcd protection and electrics were checked 2 years ago and I'm pretty confident nothing has disturbed /damaged the wiring since.
Why is there 125v present and why did it not trip the consumer unit out ?

p.s it's a front room with two ceiling roses and two switches one with a double dimmer
 
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and the other end to earth
Was this earth true earth or the main earth at the CU ?

If it was the earth at the CU then the CPC (earth wire) of the lighting circuit has gone open circuit. Other circuits may also have lost their CPC.

If it was true earth ( a ground rod or similar ) then it my be the entire CPC (earth wire) system in the house is no longer connected to earth.

If a TT system relying on a earth rod then the connection to the earth rod is the first thing to check.

It is is PME or other system that relies on an "earth" provide by the supply cable then visually check connection from CU to the cut out on the incoming cable.
 
I used the earth from a socket,it only seems to be a problem on the lights in the frontroom,if i check continuity from the earth point in the light switches to earth in a socket there is none but i get 125v.We dont have a earth rod it uses the incoming earth which seems ok.the earth in the ceiling roses are connected to earth.

Ps i have just for a quick check i stuck a srewdriver into the soil outside and put my meter on one end connected to earth pin in a outside socket there seems to be continuity
 
Also the voltage goes when i turn off the downstairs lights trip switch on the consumer lights.
 
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If it was the earth at the CU then the CPC (earth wire) of the lighting circuit has gone open circuit.
Assuming it was ever connected in the first place. I've seen more than one lighting system where additions have been made and all the earths interconnected between the new lights and switches, but the feed has been taken from an older lighting circuit which never had an earth, so the earth conductors on the new extension have never actually been connected to earth.
 
If it was the earth at the CU then the CPC (earth wire) of the lighting circuit has gone open circuit.
Assuming it was ever connected in the first place. I've seen more than one lighting system where additions have been made and all the earths interconnected between the new lights and switches, but the feed has been taken from an older lighting circuit which never had an earth, so the earth conductors on the new extension have never actually been connected to earth.

I have checked between earth in sockets and the other light switches and all appears to be ok,when we had electrics checked i can remember the electricain checking the earthing for the lights,we also had the earth bonding done at the same time.
 
It almost certainly sounds like youve got a floating CPC and the voltage you are reading will be an induced voltage.

You need to trace the CPC. It should be contiuous all the way back to the earthing bar in your consumer unit.

Yours will have a break in it. It could be a connection somewhere which has gone bad, or it might be that the CPC has never been connected due to it being supplied from an old circuit somewhere.

Without being there it's very difficult to give advice as to where the fault will lie.
 
I was thinking along the lines of the above that the voltage was being induced into the cable,strange thing is nothing has really changed and the wiring is in pretty good shape,I have a feeling that it may have been that way for some time and probably was like that when the electricican checked it four years ago.

Any way thanks all, i have turned off the downstairs lighting cct and have a electrician coming out soon.
 

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