IR Test ? Weird issue N-E only

[Soulsurfer]

Hey all, just doing some tests on a small extension and have a weird issue with IR on lighting circuit, all switches left open as nightmare to strip all lamps, fittings etc.. L&N to CPC not ramping up over 7-15V DC then resetting test !

L-N on 250V or 500V 31-32 Meg
L-E 32.6 Meg
N-E won't go ! Tried all obvious things to remove out of circuit plus new mains smoke detector etc.. but still no good, any ideas ?
Only fed at moment on a B MCB 6A no RCBO etc.. head scratching or feeding something hidden maybe or a fault ?
Thanks.

 

[Soulsurfer]

@Soulsurfer, My wife is coming over to Jersey on Sunday visiting family for a week. I have a Martindale IR tester (nearly said Megger). I am happy to lend it to you for the week if you think it would help. She said she is happy to take it for you. PM me if you would like it and we can swap details.
I have a Megger 1721 and sometimes use the old IR tester if peculiar things happen, MFT's do speed up the job but they can waste a lot of time also.

Wow that's so cool of you mate, have you seen IR issues with your 1721 then ?
& you say Sunday, as in tomorrow or next week? As am off on holiday a week today with the wife & kids so won't be here. If so thanks for the offer that's very kind.

 

[seltechpc]

Nothing really a problem sometimes I pick up a stray voltage and it stops ramping up, it is a lot quicker to shove the old IR tester on, at least you know what you are getting.
Wife is arriving Jersey this Sunday 6th and flies back Sunday 13th so it sounds just right. I'll probably take out the 6 AA cells to save weight in the hold luggage. If you are happy with this PM me with contact details and we can set it up. I am just sorry I am not going this time, I would enjoy giving you a hand with the fault.
Best of luck next week.
Paul

 

[Soulsurfer]

Nothing really a problem sometimes I pick up a stray voltage and it stops ramping up, it is a lot quicker to shove the old IR tester on, at least you know what you are getting.
Wife is arriving Jersey this Sunday 6th and flies back Sunday 13th so it sounds just right. I'll probably take out the 6 AA cells to save weight in the hold luggage. If you are happy with this PM me with contact details and we can set it up. I am just sorry I am not going this time, I would enjoy giving you a hand with the fault.
Best of luck next week.
Paul

You're an absolute star Paul, cheers and when you're next over ( if you are ) let's get you out for a beer & thank you ! Thanks again, I'll pm in a few mins mate, Matt

 

[seltechpc]

Love to go for a beer Matt, probably be over next May. Cheers.

 

[Soulsurfer]

Perhaps see what resistance result you get with an autoranging multimeter to give you an idea of what may be happening, but do check that there is no voltage present first.
The manual does say capacitative loads would cause the voltage to rise slower than expected but I cannot see that there would be a capacitor (or enough capacitance in a circuit) across N-E.
Does the MFT not show any error graphic on failed testing?

Hey Richard, I don't think there was any error symbols or anything bad on meter at all, just wouldn't fire up anything to do with N & E.

 

[Octopus]

^^ what happens when you test a bit of random cable?

 

[Soulsurfer]

^^ what happens when you test a bit of random cable?

Just works perfectly straight to full test V at around 550V dc on the 500 range and >999Meg on screen.

 

[Octopus]

^^ in which case the installation must have a fault ...............

Got any downstream RCD's - they can give off very odd results?

 

[Soulsurfer]

So with playing last thing yesterday I had killed power and all breakers closed except the 3 x rcbo's which obviously stopped the ramp up to IR test due to internals I'm guessing.

With set on 500V and one lead croc clipped to bus bar and other to earth bar the tests ramp up to 349V max but when certain mcb's are opened the test runs to the full 500V and >999 Meg value, the breakers for heating controls (Boiler) and cooker make the test drop out again to 349V approx and 0.27Meg, Same seems to happen with those mcb's closed Bus bar to Neutral bar and the test button is locked on / continuous 500V applied etc.. If I close mcb to radial that supplies ( I found out ) a washing machine and dryer and outdoor shed ! it drops from 500/ >999Meg to around 500Meg and 300V approx then I take it the motor start capacitor or other internals get charged up and the reading steadily rises to 800+ Meg again, if breaker opened it just ramps to 500V instantly and >999Meg.

Either of upstairs or downstairs lights mcb's do the same thing but to a lesser effect, drop the test voltage and the resistance readings.
If I try one croc on N bar to E bar I get 0V and 0.04Meg as max reading on display !

Take the L and N out mcb or N bar and test individually and I get 31.6Meg L - E
& 33Meg L-N at 500V test voltage but N-E is no use goes mostly to 7V then as far as 15V then stops and goes to zero on display and won't ramp again if test button pushed again.

This is the rubbish I'm dealing with and I only extended a few lights and sockets into an apparently recently partly rewired main house areas ! No certs or test results when that was all done of course !

 

[Soulsurfer]

^^ in which case the installation must have a fault ...............

Got any downstream RCD's - they can give off very odd results?

Not found any yet but anything is a possibility in this place, found a random old square junction box from old wiring stashed under floor upstairs too and is all over the place cables old and new in a spaghetti mess ! Thanks.

 

[Octopus]

Not found any yet but anything is a possibility in this place, found a random old square junction box from old wiring stashed under floor upstairs too and is all over the place cables old and new in a spaghetti mess ! Thanks.

Hum ......... I thought the problem was in your "new" extension wiring...........

Basic knowledge, a decent tester and patience will locate the issue - so which circuit have you narrowed it down to?

 

[Soulsurfer]

Hum ......... I thought the problem was in your "new" extension wiring...........

Basic knowledge, a decent tester and patience will locate the issue - so which circuit have you narrowed it down to?

I thought it was on the lighting circuit that has been extended into the extension and it is seemingly, but also caused by other circuits doing same thing to the meter. I was wondering if on the old wiring they had mixed up neutrals or borrowed one to have caused a weird fault !

 

[Richard Burns]

Test each circuit that is possibly causing a problem from Neutral to cpc without any connection to the board, this will just test the circuit and not any anomalous earth connection but at least may narrow down the fault.
If each circuit is still causing problems then you have some crossovers somewhere probably via supplementary bonding and earthing of water systems.
If not and a specific circuit is identified then you can break up the circuit to close down on the fault, if the fault is clear then you can test the circuit once the cpc is connected to the earth bar and see if there is a further fault.

 

[Ian1981]

Is there any metal stud work in the new extension with cables passing through it?

 

[Soulsurfer]

Is there any metal stud work in the new extension with cables passing through it?

No nothing like that, only original garage roof joists then a stud frame on concrete pad at rear of garage which is an ensuite bathroom. Unless builder has been slinging screws in all over the place !

 

[Octopus]

Out of interest did you do ALL the electrics in this extension?

 

[Soulsurfer]

Out of interest did you do ALL the electrics in this extension?

Yes bud, there was an existing cable left coiled in there builder has said customer had asked previous spark to leave ready for future use and second two legs for sockets, so I'd traced them back to upstairs ring removed old jb they'd used under floor and checked all cables and used to feed a few sockets and lights in the garage conversion that the cables were apparently left ready for.

 

[Simon1979]

Agree with Richard, avoid the lump test and retest individual circuits. I have come across supplementary bonding connected to lights upstairs and sockets downstairs which was fun.

If you still have access to the jb which you have gone from perhaps disconnect and test your work to rule this out. Same could be said with the ring circuits.

 

[Soulsurfer]

Hey all, just spent best part of today final fixing the last kit at the wonky house !
So going over all seperately through the circuits I have so far concluded that the problem is definitely not on any of my new wiring, but is on the leg from the mcb to the rest of the downstairs lighting circuit !

The readings with a fed rcd fused spur out of circuit (very old underfloor heating)
were with my Megger 1731
L+N -E = 0.5 Meg
N-E = 0.5 Meg
L-N = 0.03 Meg
L-E = 4.34 Meg.

but tested from point where leg feeds the new works is every test >999 Meg.

Old cable from the lights circuit back to board was stopping at 41V max dc and read 0.07 Meg so 70k Ohms on L-N / L-E & there was no voltage or any error/alerts on display, also tested with a very kindly lent dedicated IR tester from a UK member who had sent one over ;-) and had exactly the same readings on that tester too.
N-E test sat at 0V and 0.00Meg Ohms !

As also recommended by a couple of you gents I also tested the resistance N-E and it was on >999 Ohms.

I swapped the mcb feeding the circuit out to the extension lights for a new rcbo too.
Also upon testing other circuits I had some varied results on IR tests too;

Kitchen ring final : L+N-E = 2.33 Meg
L-E 2.30 Meg
N-E 2.3 Meg
L-N 2.30 Meg
all stayed the same whether cps's in earth bar in cu or loose.
also checked end-end
r1 0.36
rn 0.35
r2 0.58 so all o.k. there too.

lots of hidden sockets, appliances and defective plinth heater disconnected too.
( turns on but element switches shorts the pd ! )

Another small lighting circuit was far lower L-E at 447 Meg
whereas L-N, N-E were both >999 Meg

Lights again
L-N and also L-E >999 Meg
N-E 414 Meg

and finally radial feeding appliances was >999 Meg
with again N-E at lower 326 Meg !

Always N-E playing up the most.

Trying to get customer to allow checking further into the old j.b. wiring where the lighting circuit issue is but he isn't keen on getting it done.

Thanks again everyone, highly valued advice.

 

[Octopus]

Good feedback.

Re the readings from the old RCD spur.... Suggest you replace the RCD spur with a non RCD spur and retest, then see the ir results shoot up ....

 

[Soulsurfer]

Good feedback.

Re the readings from the old RCD spur.... Suggest you replace the RCD spur with a non RCD spur and retest, then see the ir results shoot up ....

Thanks chief, all I ended up doing was tripping it and pulling the fuse carrier out to see if that would work. I'll maybe run by on the way to next nice clean rewire tomorrow and check that. Adjusting old wiring is a pain ! & the green goo in there today plus midget scruits ....no wonder the insulation isn't great !

 

[seltechpc]

Well done Matt, pleased you got it sorted mate. Very good report on what you found, you will be glad to put that lot behind you.

 

[Soulsurfer]

Well done Matt, pleased you got it sorted mate. Very good report on what you found, you will be glad to put that lot behind you.

Thanks Paul, and thanks again for the special delivery from your lovely wife with your tester yesterday evening. Very helpful, and lovely family you all are. I'll see you in a little while for that beer in the sun

 

[Richard Burns]

Thanks chief, all I ended up doing was tripping it and pulling the fuse carrier out to see if that would work. I'll maybe run by on the way to next nice clean rewire tomorrow and check that. Adjusting old wiring is a pain ! & the green goo in there today plus midget scruits ....no wonder the insulation isn't great !

Nice to hear back on progress.
Certainly sounds like it is the RCD FCU causing the odd readings as neutral and earth were still connected at the time of test on that part.
The cable back to the board, hmm not sure, if the cable was still connected at the board and RCD protected with the main switch on and lighting MCB off then that would be normal, other than that something electronic tagged in between board and your test point or the cable is damaged and wet.

 

[Soulsurfer]

Nice to hear back on progress.
Certainly sounds like it is the RCD FCU causing the odd readings as neutral and earth were still connected at the time of test on that part.
The cable back to the board, hmm not sure, if the cable was still connected at the board and RCD protected with the main switch on and lighting MCB off then that would be normal, other than that something electronic tagged in between board and your test point or the cable is damaged and wet.

Thanks Richard, I'll do a quick swap over with the fcu prob tomorrow then see if they want anything further checked out. Thanks again.