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.

 

[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.