Power cable dead or alive conundrum

[Yojevol]

I've been installing a wall mounted heater in our new bathroom (CH a bit lacking) and have encountered an anomaly in the cabling. My plan was to select a suitable power cable in the loft above the bathroom and run a spur from it to an external (to the bathroom) isolation switch and thence to the heater. My non-contact electrical detector pen indicted that the selected cable was coming from the 'house sockets' switch in the consumer unit. That seemed appropriate so i complicated the wiring up.
However the heater wouldn't work. That seemed strange as the pen was indicating power right up to the heater. Must be a faulty heater, thinks I so I took it down, fitted a plug and tested in a kitchen socket - all working as it should.
A little perplexed, I got my basic multimeter out a tested the power cable - ZERO volts, even though the pen indicated LIVE. Tested the meter on other 'house' sockets - fine, 243V.
I tried to find out what the selected cable was serving but this was difficult and unsuccessful as disappeared under a sea of insulation. The power cable is an old one, red/black multi-strand cores.
Today I will complete the job using a different cable which I can see supplies just a single socket in the loft for powering a TV signal booster.
Any suggestions of what might be going on with doubtful cable?
Brian

 

[Phil Pascoe]

That seemed appropriate so i complicated the wiring up.

edit?

 

[imageel]

I've been installing a wall mounted heater in our new bathroom (CH a bit lacking) and have encountered an anomaly in the cabling. My plan was to select a suitable power cable in the loft above the bathroom and run a spur from it to an external (to the bathroom) isolation switch and thence to the heater. My non-contact electrical detector pen indicted that the selected cable was coming from the 'house sockets' switch in the consumer unit. That seemed appropriate so i complicated the wiring up.
However the heater wouldn't work. That seemed strange as the pen was indicating power right up to the heater. Must be a faulty heater, thinks I so I took it down, fitted a plug and tested in a kitchen socket - all working as it should.
A little perplexed, I got my basic multimeter out a tested the power cable - ZERO volts, even though the pen indicated LIVE. Tested the meter on other 'house' sockets - fine, 243V.
I tried to find out what the selected cable was serving but this was difficult and unsuccessful as disappeared under a sea of insulation. The power cable is an old one, red/black multi-strand cores.
Today I will complete the job using a different cable which I can see supplies just a single socket in the loft for powering a TV signal booster.
Any suggestions of what might be going on with doubtful cable?
Brian

Pen testers are notoriously unreliable and as you have found will show live when actually not...
You don't state what the rest of the house wiring looks like however the one you were trying to use is very old -red-black & multi-cored so ~I suspect at some point the place has been re-wired and the old whilst disconnected has been left in place and your pen tester is indicating it as live through inductive coupling to a nearby 'real live' cable.
This is why a lot of electricians don't use pen-testers....

 

[Spectric]

My non-contact electrical detector pen i

Those non contact pens should be banned, also a bathroom is classed as a special location under the regs and only qualified electricians can perform any work in such an area due the high risk possed to occupants. With something like a wall heater it must be approved for use in a bathroom and only fitted in the allowed zone so must have a suitable IP rating and be wired from a two pole isolator switch that is itself powered from a circuit protected by a working RCD. The most important aspect is that you must ensure that the circuit impedances are well within that allowed to guarantee the protective device operates in the event of a fault, a bathroom is a special location because wet skin has a much lower resistance than dry skin so wet naked people in a bathroom are more susceptable to potential electrocution.

Today I will complete the job using a different cable which I can see supplies just a single socket in the loft

How is that single socket supplied, is it part of a ring main or is it a spur ? If it is a spur then you cannot take a spur from a spur.

 

[Spectric]

This is why a lot of electricians don't use pen-testers....

No electrician would be seen with one of those, it would be like a chippy turning up with a plastic hammer. A decent tester would come with a tester to prove the tester is functioning,

ie https://testermans.co.uk/product/fl...c-PxUGGJ6TE9pPhMNZUiPSWeu4gJAAi0n0N84kClagwQW

or if using just a decent tester then always verify it's operation on a known live before use and always prove live before isolation.

 

[Yojevol]

How is that single socket supplied, is it part of a ring main or is it a spur ? If it is a spur then you cannot take a spur from a spur.

The socket has it's own dedicated cable from the CU which is only a metre away. I could run a dedicated cable for the heater from the CU.

Pen testers are notoriously unreliable and as you have found will show live when actually not...
You don't state what the rest of the house wiring looks like however the one you were trying to use is very old -red-black & multi-cored so ~I suspect at some point the place has been re-wired and the old whilst disconnected has been left in place and your pen tester is indicating it as live through inductive coupling to a nearby 'real live' cable.
This is why a lot of electricians don't use pen-testers....

I think you must be right about the inductive coupling. That cable certainly does not appear in thr CU and everything else is working. At least the pen tester is fail safe. It warned me that there is a problem. Tradesmen now prefer them for cable detection
The old cable probably dates from when the bungalow was built in 1968. I'm pretty sure it was all rewired 17 years ago when extensive modifications were carried out. I have found other bits of cable left lying around and covered with a new layer of insulation.

 

[Amplidyne]

Have a read of this. https://www.hse.gov.uk/pubns/priced/gs38.pdf

Particularly section 13 "Single-pole or non-contact live-circuit detectors sometimes referred to as ‘voltage sticks’"

Nothing wrong with them if used properly. And they do have their uses in fault or cable finding. Just as an indication that something is "live" though. and NOT for proving that it is dead.

You should use dedicated two pole test lamps for testing circuits really. They're not sexy at all, but you have the correct tools for other jobs right?

 

[mwinfrance]

If it is a spur then you cannot take a spur from a spur.

Tell that to the french electricians who have wired just about every place I've rented or bought here, and many other "installations that I've seen.

 

[Dabop]

Have a read of this. https://www.hse.gov.uk/pubns/priced/gs38.pdf

Particularly section 13 "Single-pole or non-contact live-circuit detectors sometimes referred to as ‘voltage sticks’"

Nothing wrong with them if used properly. And they do have their uses in fault or cable finding. Just as an indication that something is "live" though. and NOT for proving that it is dead.

You should use dedicated two pole test lamps for testing circuits really. They're not sexy at all, but you have the correct tools for other jobs right?

Plus when 'testing for dead' there is a 'required' test procedure, needing both a tester (2 connector) and a 'test unit' for the tester- the correct procedure is test the tester, test the circuit, then test the tester again...
Many think 'why bother doing all that'- there's a reason they call it testing for dead... screw it up and thats what you will be...

(these type of regs are literally written in blood- people have died from it, and thats why you test the tester both before and after the test...)

What happens if the circuit you are testing has a major fault, with hundreds of volts above the correct line voltage that blows up your tester???- the second 'test the tester' will show your tester is now a 'Norwegian Blue Parrot' and that you shouldn't proceed with touching that circuit until you can positively check that it is actually dead...

(Any electrician who is working in the industry would already be well aware of this...)

 

[Spectric]

Tell that to the french electricians who have wired just about every place I've rented or bought here, and many other "installations that I've seen.

I think you will find that they are radials being in Europe, only the Uk adopted Ring mains so maybe all ok.

It is very important to prove dead and that your action has isolated the circuit especially when working in industrial facilities where you have many circuits and the potential for cross feeds.

 

[Amplidyne]

You can have radials in this country as well.

Rings will carry heavier loads for the cable size.

As you say, checking that everything is dead before any work is essential. I've seen "isolated" houses with power still on them from next door via lighting due to the wrong circuit being picked up where there is a room over next door, let alone industrial stuff, that has had all sorts done to it.

It's something to never take for granted because the switch is off.

As always, if you're not sure, get somebody who is to do the work.

 

[Spectric]

Rings will carry heavier loads for the cable size

That is because the load is carried by two cables, a major issue with rings in that if one conductor becomes O/C then the load is now carried by just one cable so often becomes overloaded. Because it is not a short circuit the fault current is in excess of the cable capacity but not high enough to trip the protective device and so it gets hot, at some point potentially hot enough to cause a thermal event especially if it is laying under the floor boards in a load of detritus left by builders.

 

[mwinfrance]

I've seen loads of radials here with spurs off them, and some with spurs off the spurs that are on the radials, back at the box, a breaker , or fuse, rated for a light. French wiring on old properties has to be seen to be believed. New build is different, EDF won't put the power on if their inspector doesn't like anything.

 

[Amplidyne]

That is because the load is carried by two cables, a major issue with rings in that if one conductor becomes O/C then the load is now carried by just one cable so often becomes overloaded. Because it is not a short circuit the fault current is in excess of the cable capacity but not high enough to trip the protective device and so it gets hot, at some point potentially hot enough to cause a thermal event especially if it is laying under the floor boards in a load of detritus left by builders.

Yes, and that's one reason I'm not that keen on rings really. Never used them in industry, (although I'm sure they do get used) only domestic really. I believe they were first used to combat the shortage of copper after WWII, at least I think that's what we were told.

 

[Spectric]

I've seen loads of radials here with spurs off them,

By definition a radial will always be a radial, if you take another socket of a radial it is still a radial, the difference in the uk using a radial or ring is that there is a fuse in the plug, I can remember talking with @MikeK about the wiring in Germany and no fuses in plugs.

 

[mwinfrance]

Difference of terminology , I bow to your greater knowledge of electricity. I always thought of extras off a radial as spurs.But I see what you mean.Yes no fuses here either, and sometimes none after the initial breaker which is after the meter. Two houses down from us was wired like that by a ship's cook ( dead now, looked like Mr Creosote ) , who ( according to the old lady who owned the house "knew a bit about electrics and did her place cheap for cash ) Meter with 30 amps incoming to breaker wit a 500 milli trip, which fed into two brown plastic connector strips ( one live , one neutral ).these were done with short bits of bare copper wire along one side so as to "spread the leccy" .On the other side the wires out went out ( in a "radial system" ) to lights, sockets, central heating etc. No earth anywhere.

Our house had no earth either when we arrived, a friend of my now dead mother in law had wired the place, he did at least but in a box with what I took to be breakers,( in a cupboard at ceiling height in a dark part ) but they turned out to be fuse holders that pivot out towards you. He'd later redone her bedroom wiring to put a pull switch near the repositioned bed. A socket was in the way of the new siting for the bed, so he removed it and stuffed the wires back behind the plaster board with a bit of black tape around each bare end , didn't disconnect them at the box though,.he then covered the hole with a dab of plaster. Done back in the 90s. Got myself a hefty "bang" ( not my first ) when I removed the plaster "bung" with a non insulated tool. same guy put a two pin socket and switch handily between the hand basin and the shower, easily reachable from the shower.

Rented a place once here ( longere* split into two ) where the meter cupboard ( with no door , just a bit of flowery curtain ) was where they kept the shotguns and rifles and ammo.That was 3 phase , with almost everything ( luckily not much more than lights and a shaver socket and a few wall sockets ) , was on the same phase,.The others had a light and a socket on each. Electrics done by the local doctor and his brother, they each owned half of the longere.

* long stone built farm building used as accommodation, old with thick stone walls.

Just few of the "horrors" I've seen here.

Some very strange masony ( cement block work ) currently being done on our neighbour's house.

Anyone who has lived in France for a while ( 35 years in my case ) will have seen lots of really dodgy electrics, and building, plumbing, carpentry etc.

Yet they also have "les compagnons du devoir".