"live" brick wall

  laurie53 09:03 18 Oct 07

I was going to put a picture up in the bedroom last weekend, and as usual I ran my metal/power detector over the wall to check it.

I was amazed to find that the whole wall was “live”

Like most my detector has different tones for metal and power, and while the metal warning did not operate, the power one did, over the whole of the wall, top to bottom, side to side.

The wall is a gable end, shared by four rooms – the bedroom, bathroom, kitchen and living room, standard brick construction built in the fifties. It has no embedded wiring or pipework, bathroom pipes are surface mounted.

At first I thought it might be a Tetra signal from the police station opposite, but none of the other rooms show this result, nor does anywhere else in the house.

Any possible explanations?

  Monument 12:13 18 Oct 07

Brick, mortar, paper plaster do not conduct electricity. So my guess in one of two things.

1. Dodgy detector
2. The wall is very damp and that is condcuting electricity from a power supply.

  laurie53 13:24 18 Oct 07

Good points, but a dodgy detector would show up all over not just on one wall, and a damp wall would show the same effect in all four rooms, at least to some degree.

I think there would also be some other evidence that the wall was damp.

  Forum Editor 23:38 19 Oct 07

These detectors are notorious for it. Presumably you've touched the wall, and discovered that it's not live at all.

If the wall has no power cables on it and no pipework it can't be live, at least not at mains voltage. Presumably if it was built in the 1950's and it's a gable end it will be a cavity construction?

  laurie53 07:35 20 Oct 07

Update - I've now tried another detector, with the same result.

That's a bit worrying.

  jack 08:51 20 Oct 07

Cavity Wall houses built in the fifties[as mine was] frequently had the mains distribution simply 'dropped' from floor to floor though the cavity.
A few years ago an electrician re cabling a house near by resorted to removing bricks from an end wall simply to tack an existing run.
So is it possible your may be the same and earlier work has 'found' a run and breached the insulation?

  Fruit Bat /\0/\ 20:16 21 Oct 07

Any sockets - spurs - or power connections of any sort on the bedroom wall or on the wll in the room below?

  Forum Editor 20:27 21 Oct 07

that jack's suggestion may be the answer. He's right to say that early cavity walls were an attractive proposition for electricians wanting to get their cables from one floor to the next, and not just electricians - plumbers sometimes ran water mains in the cavities as well.

It's possible that a metal cavity tie could abrade the insulation on a cable, and cause a live reading in a wall, but it's hard to see how this would happen without some movement on the cable, unless mice or squirrels have eaten away the insulation. There would have to be quite a sequence of unlikely events for it to happen like this, but it's certainly possible.

  laurie53 21:30 21 Oct 07

I think I confused the issue by using the term "live".

My detector simply shows that there is a ac voltage present. It may well be fully contained within insulation. My query is that instead of appearing in a limited area, where you can actually trace the cable/conduit run, it is present over the whole wall of just one room, but not in any other room which shares that wall.

I think my next step is to get a ladder and see if I get the same result outside, on the other side of the wall.

  jack 11:59 22 Oct 07

Laurie's last post gives the answer I suspect.
It is the norm for cabling to be vertical whether in conduit or not in plaster or in cavity.
What you seem to have is a horizontal tun which will indeed show presence along a wall rather than up/down over a limited area.

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