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Old 19th Nov 2018, 6:27 pm   #1
Welsh Anorak
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Default Neon tester vs dodgy wiring

Hi
Hope this is in the right place!
My partner who is painting and decorating a house called to say she's had a mild shock from a metal switch faceplate. I went along and sure enough my trusty neon screwdriver lit up dimly. It turns out several light switches on the ground floor are between 70 and 200v above true earth.
I'd say the wiring is about 25 years old, but has been 'improved' by these metal switches and sockets. It has an RCCB which works in the good area of the house, and all cross-bonding has been done.
I tried earthing the light switch in question via a milliammeter to a good earth - around 10mA drawn and all was well - except the others were still live!
So I'm in a bit of a dilemma. The work she's doing is for an acquaintance who lives abroad and the house is to be let out in two weeks. I let them know about the shock and they said the electrics had had a clean bill of health 12 months ago. Looking under the bonnet there's the usual enthusiastic DIY approach - faceplates earthed but not the back boxes and the odd bit of rubber cable (no earth). This ties in with the general state of repair of the house.
I can't in all conscience let them rent the house without insisting they get this sorted, but if I was in the position of the electrician I'd be suggesting a rewire which won't go down at all well. I'm not Part P so this is not something I want to get involved with, especially as it'll be a floorboards up job.

Is any leakage permissible? Any ideas or suggestions?
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Old 19th Nov 2018, 6:34 pm   #2
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Default Re: Neon tester vs dodgy wiring

If it's going to be rented out then the landlord will need to fork out for a proper electrical inspection and remedial work as necessary. Anything else is asking for trouble.
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Old 19th Nov 2018, 6:45 pm   #3
Welsh Anorak
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Default Re: Neon tester vs dodgy wiring

I totally agree - that's why I'm not putting myself forward. I have carried out full house wiring to the 17th edition and had it signed off for rental by a suitably qualified electrician, but this sort of remedial work is something I don't want to get involved with.
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Old 19th Nov 2018, 7:05 pm   #4
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Default Re: Neon tester vs dodgy wiring

Rubber cable is still in the mix!? It could of course have gone mushy and semi-conductive if it's anywhere that is subject to overheating or rodent pee for example..

I hate it when people are put in this position. You've done your bit by notifying the owner and not ignoring it. You earthed one and the others are still live..something is very wrong! I wonder if the house has ever had water damage and not been re-wired after..

(Hang on- it's not being induced by a nearby radio transmission antenna is it?)

I would say put it in writing in a friendly way and get the hell out!

Dave

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Old 19th Nov 2018, 7:25 pm   #5
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Default Re: Neon tester vs dodgy wiring

I believe the fact the house is being rented out necessitates a current NICEIC inspection certificate, so all earth loop impedances etc will be logged in the inspection. In its present state it won't pass and for good reason.
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Old 19th Nov 2018, 7:42 pm   #6
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Default Re: Neon tester vs dodgy wiring

If the "electrics given a clean bill of health a year ago" means a formal NICEIC in service test and inspection there should be a sticker on the consumer unit with the date of test and the date of the next recommended test/inspection.
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Old 19th Nov 2018, 7:45 pm   #7
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Default Re: Neon tester vs dodgy wiring

Sounds dodgy! The metal faceplates should be earthed.

The Philpott does have a good point though - is it RF that's getting in (though it would have to be in a strong field). The neon screwdriver and your meter would respond to either; your partner may not be familiar enough to tell the difference between a 50Hz shock and an RF one, but probably would be unwilling to learn the difference in feels and re-sample the faceplate. It's getting well beyond what you were expecting to be doing - but 'scoping the faceplate relative to a stake-in-the-ground would reveal if it's 50Hz leakage or something else.
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Old 19th Nov 2018, 8:08 pm   #8
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Default Re: Neon tester vs dodgy wiring

What device measured the voltage of the faceplate?

If it has a high impedance it may be measuring the current leakage through the capacitance between the live and earth conductors. This can happen if there is a break in the earth connection (even if the insulation is OK). X2 capacitors from live to earth in some equipment might be adding to the problem.

However 10mA is a significant current.

The wiring should be considered unsafe until proven otherwise.
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Old 19th Nov 2018, 8:12 pm   #9
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Default Re: Neon tester vs dodgy wiring

Just to clarify:

A formal inspection and test of the system is called an EICR - Electrical Installation Condition Report. This is what is needed, and any competent electrician can carry one out. (Formerly known as a PIR - Periodic Inspection Report)

The NICEIC - National Inspection Council for Electrical Installation Contracting is one of a number of organisations who provide oversight and monitoring of Competent Person Schemes. Electricians and electrical businesses can sign up for membership, in which case the NICEIC provide a quality assurance service over the contractor.

There is no need for whoever carries out the EICR to be a member of the NICEIC; they could equally well be members of NAPIT for example, but NICEIC is probably the best known. Note that some work in dwellings is subject to building regulations Part P, which imposes further requirements on the contractor if they are to certify it themselves.

Unearthed lighting points are still commonly found. 10mA leakage from one point is abnormal and, earthing or no earthing, requires investigation. A proper EICR will pick it up, although it is no secret that many EICRs are very sloppily done. My experience of rubber cable (VIR or TRS) is that the mechanical soundness of the insulation varies from absolutely fine to non-existent, but rarely does it lose its otherwise excellent insulation resistance.
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Old 19th Nov 2018, 8:21 pm   #10
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Default Re: Neon tester vs dodgy wiring

RCCB? They should surely have been replaced by RCDs in the previous millennium??

30mA RCDs are the basic game-play this century.

What is the earthing-scheme? Round here everything [with power supplied by two-wire overhead lines] is TT. You may find older "PME" schemes which are deeply frightening if you're supplied with overhead lines where loss-of-neutral could be an issue [neutral / earth can rise towards line if the neutral-circuit is opened]
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Old 19th Nov 2018, 8:32 pm   #11
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Default Re: Neon tester vs dodgy wiring

Quote:
RCCB? They should surely have been replaced by RCDs
RCCB (Residual Current Circuit Breaker) is an older term that is more or less synonymous with RCD (Residual Current Device) and is still widely used to refer to RCDs. I think you may be referring to the distinction between RCDs and the older ELCBs (Earth Leakage Circuit Breakers), specifically VOELCBs (Voltage-Operated...) that sense the difference in voltage between a rod and the system MET. These provide minimal protection against electric shock and are mostly legacy devices that may be well past their use-by date. They were widely installed to meet disconnection times for fault protection on systems with High Ra (typically TT systems) before the general requirement for additional protection using RCDs.
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Old 19th Nov 2018, 9:28 pm   #12
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Default Re: Neon tester vs dodgy wiring

I think I read that CPCs (earths) on lighting circuits didn't become mandentary until 1966.
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Old 19th Nov 2018, 9:52 pm   #13
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Default Re: Neon tester vs dodgy wiring

Glyn, are these switches perhaps some cheap brand that don't comply with UK regs ? Or are they the type with a metal switch?
I can't see otherwise how a metal faceplate could be leaking 10mA.
If that was really the case then three of them would trip an RCD.
You could just change the switches to normal types with no metal front plates.
This would get you out of trouble.

David.
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Old 19th Nov 2018, 9:55 pm   #14
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Default Re: Neon tester vs dodgy wiring

Quote:
Originally Posted by Welsh Anorak View Post
I'm not Part P
No one is. It's a building regulation and nothing more.
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Old 19th Nov 2018, 9:57 pm   #15
Sinewave
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Default Re: Neon tester vs dodgy wiring

Quote:
Originally Posted by McMurdo View Post
I believe the fact the house is being rented out necessitates a current NICEIC inspection certificate,
Can be done by anyone qualified. Doesn't have to be anything to do with the NICIEC.
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Old 19th Nov 2018, 9:58 pm   #16
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Default Re: Neon tester vs dodgy wiring

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Originally Posted by G6Tanuki View Post
RCCB? They should surely have been replaced by RCDs in the previous millennium??
Regulations aren't retrospective, so there wouldn't have been a need to replace it unless faulty.
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Old 19th Nov 2018, 9:58 pm   #17
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Default Re: Neon tester vs dodgy wiring

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Originally Posted by Rubberfingers View Post
If the "electrics given a clean bill of health a year ago" means a formal NICEIC in service test and inspection there should be a sticker on the consumer unit with the date of test and the date of the next recommended test/inspection.
Does it?
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Old 19th Nov 2018, 10:24 pm   #18
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Default Re: Neon tester vs dodgy wiring

Quote:
Originally Posted by teetoon View Post
Glyn, are these switches perhaps some cheap brand that don't comply with UK regs ? Or are they the type with a metal switch ?
I cant see otherwise how a metal faceplate could be leaking 10ma.
If that was really the case then 3 of them would trip an RCD.
You could just change the switches to normal types with no metal front plates.
This would get you out of trouble.

David.
They'll only leak 10mA if they're actually connected to earth, not just sitting there, so they won't trip an RCD.

But as you ask, where is the leak to the faceplate coming from? If it's still there with the switch hanging from its wires then it's just the switch and the plastic replacement will sort it. If it's not, it must be coming from the backbox which is an altogether dodgier state of affairs.
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Old 19th Nov 2018, 10:54 pm   #19
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Default Re: Neon tester vs dodgy wiring

Quote:
Originally Posted by G6Tanuki View Post

What is the earthing-schema? Round here everything [with power supplied by two-wire overhead lines] is TT. You may find older "PME" schemas which are deeply frightening if you're supplied with overhead lines where loss-of-neutral could be an issue [neutral / earth can rise towards line if the neutral-circuit is opened]
Hi G6,
In fact, almost all new connections from supply companies are PME (with a few exceptions)! It's their preferred distribution method and has several advantages. Very low earth loop impedance being the main one.
Older, overhead, 2 wire supplies were often TT, but it's very unusual these days. PME is king!!

There are several special scenarios where PME will not be offered, ie- to all metal buildings, petrol stations, marinas etc, but most new domestic installations will be PME.

Cheers
Nick
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Old 19th Nov 2018, 10:56 pm   #20
teetoon
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Default Re: Neon tester vs dodgy wiring

Chris, Glyn said he earthed the switch via a milliameter and 10ma was drawn and all was well except the other switches still showed leakage. Hence my saying that if 3 of the switch plates were connected to earth and leaking 10ma each then that would be the trip current of a domestic RCD.

Very difficult to diagnose without seeing the switches and the situation though but whatever, if they are giving a nip then it needs to be resolved.

David.
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