Help with wiring?

[Ihatemondays]

Hi, my cousin has had a new pump fitted to her boiler. There was no other work carried out. The fitter said that he got an electric shock from the 'earth' from the room thermostat (twin and earth cable)

I investigated, and found that there was 240 volts in both the brown and the green/yellow cable from the thermostat. I take it that is not normal, but am unsure as to how the thermostat works - is it just an electric switch controlled by the dial? If so, therre should no reason for 240 volts in the earth cable.

Can anyone confirm my opinion? Any suggestions? Is the thermostat faulty?

The heating works OK, and so does the water. Thanks guys!

 

[Fluffster]

It is not an earth thermostats have constant live , switched live and neutral.
You should not be working on any cabling live esp if not qualified.
Pete

 

[JohnD]

1) Be sure to test using a multimeter not a neon screwdriver. If you do not have one already you can buy one for less than £10 in your high street.

2) have a look at both ends of the cable to see what the G&Y is connected to. Maybe someone has connected it to Phase by mistake.

3) If that's not what's happened, disconnect the G&Y at both ends and see if it is still live. If it is then there is a fault in the cable - quite possibly someone has stuck a nail through it when putting a picture up, or something like that.

4) At the Boiler end, the G&Y ought to be connected to all your other earths, so that even if there was a fault, it should not become live without blowing the fuse.

Edited:
Fluffster may be correct - look at the terminals on the thermostat. If it is not an earth then it must not be sheathed G&Y, sheath it at both ends in red or brown.

 

[oilman]

Its a common problem in central heating circuits. The "earth" is often used as a live conductor, and it is often not indicated as such. Another problem is that using the earth in a t&e cable means there is only single insulation and not double.

From an acedemic point of view, the cable ought to be changed to a 4-core or a control cable if no earth is used.

A neon screwdriver is very useful, my opinion.

Fitter is obviously not familiar with central heating installations.

 

[Ihatemondays]

Thanks for the replies. I'll let her know and get it checked out.