Power cable dead or alive conundrum

[deema]

When I took over running the Chinese factory that was making earth leakage current detectors and other electrical test equipment the first thing I did was have a random sample of the products tested against primary standards. Everything failed. So donning my best Deer Stalker and pipe with fiddle under arm I began the investigation. Everything seemed fine until we got to the building earth. They knew that the earth was important so had one installed……it was a wire that was imbedded into the wall 6” or 150mm. They proudly told me the building had first class foundations and therefore had a good earth.

A certain ‘high’ value well known brand who makes yellow coloured test equipment when I tested their clamp meters around 20 years ago were only accurate when the conducting wire under test was exactly perpendicular to the clamp, and exactly in the centre. Any other position and it failed its calibration.

The morale being unless you know exactly the quality of the test equipment you are using, and what tests to perform, and exactly what your doing, your basically juggling with a powered up chainsaws, you might get away with it a few times, but eventually it’s going to kill you.

 

[Phil Pascoe]

Travel the world. Power cables tapped off streetlights, joints just taped and covered with an inverted plastic water bottle, fizzing in the rain

20% of India's electricty is stolen, apparently.

 

[Spectric]

The morale being unless you know exactly the quality of the test equipment you are using, and what tests to perform, and exactly what your doing, your basically juggling with a powered up chainsaws, you might get away with it a few times, but eventually it’s going to kill you.

Yes metrology is an amazing subject and understanding the terms used in calibration and the pro's and cons of the different measurement techniques can be really helpful. Even something that to all intents and purposes appears simple such as a weighing scale can become complex once you start looking for high accuracy and repeatability because there is a lot more to it than meets the eyes.

 

[Spectric]

20% of India's electricty is stolen, apparently.

Only 20%, when you see pictures of the street wiring in some of these asian countries it really looks like a free for all.

 

[mwinfrance]

Travel the world. Power cables tapped off streetlights, joints just taped and covered with an inverted plastic water bottle, fizzing in the rain

You've been to Malta pre 1990 too eh..Not Asian , but pre-1990 ( when I was last there ), the phone and power lines were like an Asian country , I was told by someone there in a position to know, that they got their gear from Nice , France, second hand.
,

Only 20%, when you see pictures of the street wiring in some of these asian countries it really looks like a free for all.

 

[Sideways]

You've been to Malta pre 1990 too eh..Not Asian , but pre-1990 ( when I was last there ), the phone and power lines were like an Asian country , I was told by someone there in a position to know, that they got their gear from Nice , France, second hand.
,

That was in Asia in 2010's but yes, I was in Malta in the mid 70's too

 

[Scruples]

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

It is unusual for sockets to be fed via the roof space. They are nomally fed from under the floor on the lower level. What you might have detected is switchline feed in the roof on its way between a switch and an upstairs light. It would be live, as detected by your 'non-contact' device but wouldn't supply 240V because it doesn't have a neutral, it has a return live from the switch.
As there probably won't be a ring main cable in the roof space, you should look to getting a spur from the floor below.

 

[Scruples]

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.

I was an electrician for 30 years and worked for the local electricity board. The board supplied phase-testers and drummond testers tot all of their electricians. The phase-tester (aka non-contact device) was issued, with training on how to use it, and was a useful device when you knew how to use it. The Drummond tester was a 15W bulb and a fuse with prods. When it was connected to a live and neutral, or a live and earth, it would light up. They became less useful as MCBs became the norm since they could trip them.
With all trades, it's not the equipment that's dangerous, it's the user.

 

[Scruples]

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.


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.

Non-contact pens are OK in the right hands but, in this case, the OP thought that a cable in the roof, which showed it was live, was good enough for a spur. As it turned out, it wasn't, but it wasn't the testers fault. It started as a faulty premise that there was a ring main in the roof space.

A homeowner can carry out electrical work on their own premises if they feel competent and get it tested by an approved tradesman.

I agree, a bathroom needs special attention when installing any electrical device. That may be beyond the capability of some householders.

 

[pe2dave]

Having been bitten, I still use a non-contact tester as a 'final check' before touching wires.
A confidence issue. Fluke T130 for actual testing.

 

[Scruples]

I've got one thing to say.
"Pyro"

Like that would be cost-effective. A bit industrial, perhaps?

 

[Sideways]

I think that was his point. Pyro's a bit of a faff so could be seen as a downside of doing industrial work which is otherwise satisfyingly "proper".

 

[Amplidyne]

Like that would be cost-effective. A bit industrial, perhaps?

A lot industrial I'd say, and not particularly cost effective.
But then it's virtually indestructible, and isn't a fire risk (Well as long as it's installed and fused properly)

TBH, I look at most house wiring as a bodge.
It works, and it's safe, but it's done for the cheapest, like pretty well everything is in houses, particularly new ones.

 

[Yojevol]

It is unusual for sockets to be fed via the roof space. They are nomally fed from under the floor on the lower level. What you might have detected is switchline feed in the roof on its way between a switch and an upstairs light. It would be live, as detected by your 'non-contact' device but wouldn't supply 240V because it doesn't have a neutral, it has a return live from the switch.
As there probably won't be a ring main cable in the roof space, you should look to getting a spur from the floor below.

It's a bungalow and all rewired using the loft space. That would have been cheaper than lifting all the floorboards. The rogue cable is difficult to investigate fully because it dissappears under loft flooring. I have traced one end as it drops down to to a chimney breast which once housed an oil fired warm air CH system. This is long gone having been replaced with a gas system.

 

[MikeJhn]

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.

Most barn conversions (hundreds in France) only need one socket and one light circuit with compliance for EDF to instal a supply not forgetting they fit their own current limiting RCD, radial circuits if 2.5mm (20amp MCB) can have twelve sockets attached to them in near any configuration, if in 1.5mm (16amp MCB) only eight sockets allowed, but only all MCB's must be supplied off an RCD, only eight circuits to each RCD, white goods to be on a dedicated radial, soon mounts up. Domestic three Phase is common.

 

[Spectric]

Pyro's a bit of a faff so could be seen as a downside of doing industrial work

Yes the good old MICC but not as common now since you can get cables like Prysmian FP200 for your fire alarm circuits.

 

[mwinfrance]

Domestic three phase was common,.We had it in this house.Then EDF and the mairie decided that they would bury the incoming supply in as many roads as possible in the village ( lot of towns and villages are doing this ) , for "aesthetic reasons" *. They offered mono, or keep the three phase at much higher cost on the standing charge ( abonnment ), the mairie and EDF also wanted to remove the poles that the three phase lines were on. We went for mono on cost grounds. The only 3 phase gear I had left after closing the big atelier was a medium size compressor ( which I could , and did rig to run as mono ) and a large Juki industrial sewing machine ( which I rigged for mono too ). Finally when they had dug up the road and moved most of us to mono, they left the poles up anyway, as they need them to run the fibre on**. Some fibre is being buried, much is being run on the old EDF poles. Out in the country the outlying farms and buildings are still often 3 phase, but EDF are getting very picky about supplying three phase to properties that will be residential only. My immediate neighbour works as a subcontractor for them on their domestic supply installation side, another runs one of the EDF teams who work on the really big industrial and agri installations that they do.

* This is a private road, access ( but no "right of way" , is over our property ) so we could have told them no, but as all the neighbors further into the road, at that time wanted to lose the poles ( there are now fewer neighbours ) we said OK.The huge increase in the standing charge to be able to keep three phase was also very persuasive. We are right on the coast, in rural areas inland, there is still more 3 phase.

** yes they could have buried the conduit for the fibre, or run it along the EDF tubes,.But as it is a private road the mairie didn't want to pay for that. They refused to let me pay for it. So, they can't run the fibre underground for us. Same stupid thinking affects over half of the village, so the poles cannot come down in many places.

 

[Scruples]

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...)

Does that happen a lot in Oz, then? Loss of a neutral is a very bad circumstance but, fortunately, doesn't happen often here.

 

[Scruples]

Yes the good old MICC but not as common now since you can get cables like Prysmian FP200 for your fire alarm circuits.

And, of course, MICC is rather a specialist cable, not really something a DIYer would try. On the other hand, if the OP lives in a building likely to have mice or rats...

 

[Scruples]

You've been to Malta pre 1990 too eh..Not Asian , but pre-1990 ( when I was last there ), the phone and power lines were like an Asian country , I was told by someone there in a position to know, that they got their gear from Nice , France, second hand.
,

Hong Kong - Kowloon street electrics were a bit ropey too.