Wall is live around socket?


Postby Mitch » Sat Sep 08, 2007 7:50 pm

Hi all,

I'm no newcomer to electrics and recently I bought myself a continuity/voltage tester to add to my toolkit.

I have just moved a double socket from its original position surface mounted on the skirting board to a more suitable location 18 inches above the floor (as per regs) and flush mounted it via a sunken metal back box in the wall.

I haven't connected a socket yet as I need to plaster around the area to make good the wall.

So I connected the cable for the socket and a spur cable with some terminal block as a temporary measure.

Of course I had to make use of my new tool so checked for voltage etc.

What alarmed me was that a 2 pole voltage check between phase and the back box showed continuity and a voltage of approx 30 volts. There is now visible sign of a break in the cable insulation and I'd used grommets in the cable access holes.


Even stranger is that the same test between phase and the brickwork around the socket also shows continuity but with a much lower voltage.


I tested the box that the spur connects to (higher up) on the other side of the wall with similar results.

Is this usual?

I've noticed before when using a cable detector that large areas of wall sometimes show up as being live. Is the cable passing voltage via induction to the local building material?

cheers
Mitch
Mitch
Posts: 12
Joined: Sat Sep 08, 2007 7:36 pm

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Postby Mitch » Mon Sep 10, 2007 11:05 am

Well I guess I've worked this one out, doing the 2 pole test I have effectively shorted the phase wire to earth via the metal box or the brickwork. The reduced voltage being the result of the resistance of the localised building material.

A single pole test of the back box shows no sign of voltage which it would if there was a fault.

Doh!
Mitch
Posts: 12
Joined: Sat Sep 08, 2007 7:36 pm


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