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Topic Title: Neutral -earth
Topic Summary: Testing
Created On: 15 October 2013 08:32 PM
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 15 October 2013 08:32 PM
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Ampman

Posts: 1016
Joined: 06 February 2006

Evening ,

Tested a residential home today & found a neutral earth fault .

20 kohms , seems a strange reading not a dead short , its on the lighting circuit ,

I had a look round , lights a wired in twin & earth .

IThe system is a mixture of 3 plate & joint box method as only one cable at some lights ,

Any ideas , There are em/lights on the circuit but downstairs lights which also have em/lights tested fine .

Cheers .
 15 October 2013 08:35 PM
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OMS

Posts: 19689
Joined: 23 March 2004

Like all these things, break it down into sections - you shold find it pretty quickly.

It'll be something "pinched" in an enclosure for sure.

Regards

OMS

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Failure is always an option
 15 October 2013 08:40 PM
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Ampman

Posts: 1016
Joined: 06 February 2006

oms ,

i looked in everything ,

care home is over 2 floors loft room as well , is it a major issue to leave ?

it will be coded on test sheet or at least mentioned that there is a fault
 15 October 2013 09:00 PM
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Zs

Posts: 2925
Joined: 20 July 2006

I agree with that OMS.

20 Kohms? Really, 20K? Doesn't freak me out I'm afraid. I assume that is insulation so what continuity reading do you have between the two?

Anyway, assuming that it is only one fault then this is a case for breaking the lighting circuit and I always guess at where the middle of it is. Then I can make encouraging noises to the client on the subject of definitely giving them back the good half and hopefully more.

I had one of these quite recently whilst changing a DB. I run continuity tests between conductors at the board. By 11 am I was already telling the client that their new RCD wasn't going to hold until I found something that I had identified. It got me musing as to why we get so many questions about the RCD not holding, only discovered at the moment of switch-on at the end of the job. Oh well, I digress.

This one turned out to be something new to me;

The light fittings had all been changed to the ones with a round silver base, about 3cm deep and in a circle form, which fits onto a bracket which we screw to the ceiling. The ones where the bracket is shaped like one of these ] only on its side. With the annoying little grub screws. This one was installed over an old ceiling rose and the installer had left the gizzards of the ceiling rose in place and very cleverly turned the bracket upside down and offered his screws through the ceiling rose holes. it had worked a treat except that there was no earth sleeving and the neutral was grinning some bare copper at the terminal. So, he'd made a dead short N-E with the metal of the bracket.

Simples. But it took five hours to find. I got to do my 'I fixed it' dance that day and everyone was happy. There is something magical about finding these so good luck and do let us know what it is.

Break it into large chunks first.

Zs
 15 October 2013 09:17 PM
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Ampman

Posts: 1016
Joined: 06 February 2006

Zs ,


This place has had addition after addition through the years ,

I will note the defect on the condition report ,

what code ?

Is it a dander or potential danger C2,

ive discovered it so must report it , its up to them then ,

I can price day rate to find re-wire as required .
 15 October 2013 10:13 PM
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Zs

Posts: 2925
Joined: 20 July 2006

ah, the what code question

Forgive me for not confirming or otherwise. I think coding, advising clients and design decisions are such personal aspects of our profession. The very core of who we are and how we are perceived.

With the exception of the clients of course, close friends, RocknRoll and OMS (thanks), anyone who has ever seen any of my reports has gone to town on what they think is wrong with them. Clearly I am not an authority. Hopefully someone else will stick their neck out for you, not that you need any help on coding if you get my drift?

Zs
 15 October 2013 10:28 PM
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kj scott

Posts: 2144
Joined: 02 April 2006

A number of Em luminaires on the same circuit will often give low N-E readings; but then should you be applying 500V to such circuits.
As for coding; how about 3 and requires further investigation.
Insulation testing as described by BS 7671 and GN3 doesn't work on most larger installations and has limited value; even in modern domestic installations.

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 15 October 2013 10:32 PM
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Zs

Posts: 2925
Joined: 20 July 2006

Originally posted by: kj scott


Insulation testing as described by BS 7671 and GN3 doesn't work on most larger installations and has limited value; even in modern domestic installations.


YO!
 15 October 2013 10:50 PM
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kj scott

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But true

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 24 October 2013 09:03 PM
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lyledunn

Posts: 624
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What a waste of time! The nature of modern installations and the practice of directing neutrals on to a common bar places ir testing in the garbage can. Low values of N E could indeed be a problem but it could equally result from legitimate connections in equipment. Are you really up for pulling the installation apart to trace something that might end up being a front end filter?
To be clear, I am referring to periodic tests as IR remains a key test in the initial verification process.
If the industry was really seriously concerned about IR, then circuits would be erected to facilitate testing in that regard.
Find something more productive to do during periodics and free yourself from blindly filling boxes on forms!.


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Regards,

Lyle Dunn
 24 October 2013 09:10 PM
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Thripster

Posts: 639
Joined: 22 August 2006

Sounds like a neon dropper resistance perhaps?

Regards
 24 October 2013 09:20 PM
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leckie

Posts: 1868
Joined: 21 November 2008

Why are you trying to find a "fault" while carrying out an EICR?
Just report what you find.

Why IR test N - E? If you are going to do an IR test, and not include the test as a pre-agreed limitation, just do line and neutral linked together, to earth. On anything bigger than a house it's usually pretty difficult to meaningfully carry out IR tests.

I think we should be able to carry out an "alternative" IR by using a clamp meter to measure earth leakage, on a milliamp range.

This is considered ok for petrol filling stations,so why not for general electrical installations?
 30 October 2013 10:54 PM
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HarryJMacdonald

Posts: 254
Joined: 15 May 2002

Agree over IR testing. And the worst one IMHO is the 12V MR16 type downlighters. Removing each and threading the little transformer out of the 2" hole is more likely to produce a fault that find one.
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