No earth on ring main ?!

[pdunn]

I've just replaced a couple of 3 pin sockets on a 1970's ex-council house in Scotland. There were only live and neutral wires - are the socket boxes earthed behind the plasterboard and how common is this - I've never seen it before ? Can I reliably test for earth by putting an ohm-meter from an earth pin to a water tap ?

Thanks, Peter

 

[Taylortwocities]

In many houses of this age, the wiring is run in steel conduit and this provides the earth. Have a look at where the wires enter the box, you may see a brass collar and just two wires (red and black) with no outer covering. Thats a fair bet that you have conduit.

To test if it is earthed, TURN ALL OF THE POWER OFF.
Then, using a long lead. test from the back box to the earth terminal at the fuseboard, not a water tap. The tap may not be earthed, or may be supplied by plastic pipe!

 

[RF Lighting]

It sounds like you probably have a steel conduit installation, with the conduit supplying the earth. This was a fairly common installation style for 70s council houses.

It would be a good idea to take an earth fault loop impedence test at each socket to prove the earth, as corrosion or a loose bush can lead to a failed earth. (A seperate earth wire is run in the conduit these days to prevent this happening)

It would also be a good idea to fit a link from the back box to the socket front, as you are currently relying on the socket screws for your earth.

 

[pdunn]

.. for the rapid response. Now go & enjoy 'hogmanay' !!

All the best for 2008.

Peter