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.

 

[buzzlightyear]

buy a megger does exactly what it says on the tin. not bells and whistles on some

 

[Wilko]

A couple of late night thoughts
Looking at manual, it seems to say current is limited to 2mA during IR measurement. This perhaps means that by 15V the circuit is passing 2mA and the mft stops the measurement. This would imply about 7.5k Ohms resistance N-E. You could try to measure the resistance directly using mft continuity function to confirm, for what it's worth.
Perhaps there is still an appliance connected, a polarity issue?

 

[Soulsurfer]

A couple of late night thoughts
Looking at manual, it seems to say current is limited to 2mA during IR measurement. This perhaps means that by 15V the circuit is passing 2mA and the mft stops the measurement. This would imply about 7.5k Ohms resistance N-E. You could try to measure the resistance directly using mft continuity function to confirm, for what it's worth.
Perhaps there is still an appliance connected, a polarity issue?

Thanks Wilko, I've been running around disconnecting odd items, any switches with neons etc, tv boosters, anything & everything but not sure what else it could be. I'll try the cont test across N-E Monday cheers

 

[Richard Burns]

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?

 

[seltechpc]

@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.

 

[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.