240v between live and earth

[Malcolmkk]

In my new house which has been recently rewired I went to replace the outside light, in trying to find out where the cable terminated I discovered 240v between Live and earth in addition to live and neutral. This would suggest that a neutral wire or connection is touching earth, probably onto a metal lightswitch or socket back box.
I disconnected a few light switch earth wires and kept checking, with both ends disconnected it showed 0v with live, hopefully this is telling me that the cable is okay. After a few of these I checked a ceiling rose, the earth to the switch was okay, the other 2 cables I assume are the lighting ring, one earth showed 240v with live the other showed 130v with live.
This is confusing so I stopped, should I approach this from the consumer unit on a circuit by circuit basis, if I can't find a solution soon I will call in an electrician.
Any clues or troubleshooting tips before I do this would be appreciated.

 

[davelx]

Neutral and earth are joined, either at the cutout in your house (TN-C-S earthing) or at the local substation (TN-S earthing)


240V between live and earth is normal. If you DON'T see it, then that would suggest a missing earth!

 

[IJWS15]

If you disconnect earth wires from earth you can get strange readings from induced voltages / leakage (which would run to earth if they were connected!

I presume the 130V reading was with the earth wire disconnected from earth.

 

[Malcolmkk]

I never realised that you should have 240v between earth and live, in a way it makes sense now after thinking about it. Previously I have only tested to see if the cables were dead prior to working on sockets or switches so have not come accross this before.
The 130v reading was from an earth wire on the lighting ring when all earth wires from that ceiling rose were disconnected from each other so I am not worried about it, it reads 240v when all connected properly.
Thanks for your replies, I must learn more about the theory of electrics!

 

[davelx]

Have a look here, it will probably help explain it:

//wiki.diynot.com/electrics:earthing_supply_types_and_bonding:earthing_arrangements

 

[securespark]

It's a very minor point, Lectrician, but French for earth is "terre".

I know, being an*l, now...

 

[DESL]

'terra' is from latin

 

[RF Lighting]

Simon, haven't we had this discussion?

 

[Softus]

'terra' is from latin

I thought it was from "Desperate Housewives".

 

[Lectrician]

I thought it was Latin, but changed it to french when there was the last argument about this! Just done a google and it is deffo Latin.

 

[Ratter]

And seperate should be spelt separate but this doesn't detract fom an excellent and informative article.

I probably wouldn't have noticed except you put it in caps!