Strange cable found in my wall

wcavanagh · 12 Aug 2011

Hi All,

Starting some work on my new house (new to me). Started to sink a 1 gang back box into the hall way for the thermostat.

On scanning the wall my detector was showing live mains, but nothing was on that wall, no light switch or sockets close at all.

After some careful plaster removal I found this rather strange black cable, it reminds me of the figure 8 shotgun cable used by Sky. After some investigation is only become live when the 6A lights breaker was switched on, it runs vertical from ceiling down to floor.

Untitled

wcavanagh
12 Aug 2011
1

In the living room, I have had some plaster taken off for some damp work, and the same cable type was found cut but not live. Checked a couple of light switches, they all have normal twin and earth.

Untitled

wcavanagh
12 Aug 2011
1

Any ideas?

sparkwright · 12 Aug 2011

Do you have any concrete floors?

It may be a type of cable that is designed to go in concrete floors.

Or it may not.

riveralt · 12 Aug 2011

Here's another guess - old bell wire/ telephone cable?
Or even speaker cable.

What is the conductor made of?
And what size would you say it is?

wcavanagh · 12 Aug 2011

Hi,

Don't think so the same kind of wire is in the living room by the fireplace,this one is 1/3rd up the stairs. The outa dia of the cable is about 5 mmm with two cores, about 1mm, the bridge section that links the two cores is about 5mm wide.

Will take up the floor upstairs tomorrow and see if I can find the top.

Really odd.

wcavanagh · 12 Aug 2011

Only solid floor is kitchen, all rest are suspended timber

riveralt · 12 Aug 2011

How are you testing that the cable becomes live when you energise the 6amp lighting circuit?

wcavanagh · 13 Aug 2011

With my fluke volt stick and also the AC setting on my stud detector

bernardgreen · 13 Aug 2011

If it is redundant cable disconnected but left in place then it is unlikely ( but not impossible ) that it can become dangerously live. (*)

If the redundant cable runs close to the new and active cables then it may become apparently live to high impedance testers by voltages being capacitively induced in it from the new active cabes.

(*) Test for live using a low impedence volt meter ( or a test lamp ) to know if it is connected to the live supply and is therefor dangerously live or that it merely appears to be live due to induced voltages which will be reduced to practically zero by any applied load.

wcavanagh · 13 Aug 2011

Hi,
No other cables within 1m, I will check with multimeter today.

Got to love these little surprises, lol

Cheers

flyingsparks · 13 Aug 2011

Looks like an old rubber cable to me. Could have been left in and connected to a feed somewhere when the property was re wired in the past.

bernardgreen · 13 Aug 2011

wcavanagh said:
No other cables within 1m, I will check with multimeter today.

It is under floor boards where the old and the new may share the same notches in joists that the most capactive coupling occurs.

wcavanagh said:
Got to love these little surprises, lol

Not always " love ", not when they are really live from a nail through old and new cables. ( which my cousin found in a house )

OwainDIYer · 13 Aug 2011

looks like Maconite cable which has a very distinctive 0--0 shape.

Dates pre World War Two.

Would that correspond with the age of the house?

wcavanagh · 13 Aug 2011

Thanks All,

It runs diagonal too, madness.

House was built 1930

0--0 is 100% the shape, and feels rubble like.

Found it connected into the lighting circuit. It is now disconnected

I will be getting the whole house re-wired anyway,

Cheers,
All

wcavanagh · 13 Aug 2011

Thanks All,

It runs diagonal too, madness.

House was built 1930

0--0 is 100% the shape, and feels rubble like.

Found it connected into the lighting circuit. It is now disconnected

I will be getting the whole house re-wired anyway,

Cheers,
All

mattylad · 13 Aug 2011

You can say that again....

OH -you did

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Strange cable found in my wall

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