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.

 

[Risteard]

Just pulled related L,N,E from terminals at Cu to test

The 17th Edition requires the cpc to be connected to the Earthing arrangement before conducting insulation resistance tests - therefore the cpc should NOT be removed from the Earth bar. Otherwise a fault to Earth that isn't a fault to the cpc won't be detected.

 

[westward10]

I suggest you retest with the cpc connected to the earth bar, close all switches and retest, use 250v if you are concerned.

 

[Soulsurfer]

The 17th Edition requires the cpc to be connected to the Earthing arrangement before conducting insulation resistance tests - therefore the cpc should NOT be removed from the Earth bar. Otherwise a fault to Earth that isn't a fault to the cpc won't be detected.

Thanks

 

[Soulsurfer]

I suggest you retest with the cpc connected to the earth bar, close all switches and retest, use 250v if you are concerned.

Will do & with main switch open too !
& if readings good I'll bang the 500 on, thank you, was thinking it was maybe N-E fault or something!

 

[westward10]

If the neutral is disconnected you don't need the main switch off but with your tester backing off with the L/N to earth test maybe you have a fault. I don't use an mft to understand their quirks, life is too short

 

[buzzlightyear]

Bit of a hitler the wife

not another one!
.

 

[Soulsurfer]

Tried again today, still at job now searching for any issues ! 32 Meg L-N & L-E but N-E won't test nor will L+N -E with switches closed, open, ufh Rcd spur found and isolated, lamps out & in, dimmers swapped for standard switches, main switch off at cu and only L&N out N bar /
mcb ! Anyone seen this before ? Fault somewhere ? I'm cracking up here

 

[Des 56]

Ditch your multi function tester and get yourself a proper dedicated insulation resistance tester
I prefer that its me who decides when a test can proceed, not some all singing and dancing modern playtool that is all things to all situations

 

[Soulsurfer]

Ditch your multi function tester and get yourself a proper dedicated insulation resistance tester
I prefer that its me who decides when a test can proceed, not some all singing and dancing modern playtool that is all things to all situations

Just ditched my Fluke and bought a shiny new Megger 1731 on NIC assessors advice ! So would it be likely a stand alone IR tester would do something? As I ditched my seperates for the Fluke !

 

[Octopus]

Tried again today, still at job now searching for any issues ! 32 Meg L-N & L-E but N-E won't test nor will L+N -E with switches closed, open, ufh Rcd spur found and isolated, lamps out & in, dimmers swapped for standard switches, main switch off at cu and only L&N out N bar /
mcb ! Anyone seen this before ? Fault somewhere ? I'm cracking up here

Sounds like fun.

How many separate circuits are you talking about?

 

[HandySparks]

Tried again today, still at job now searching for any issues ! 32 Meg L-N & L-E but N-E won't test nor will L+N -E with switches closed, open, ufh Rcd spur found and isolated, lamps out & in, dimmers swapped for standard switches, main switch off at cu and only L&N out N bar /
mcb ! Anyone seen this before ? Fault somewhere ? I'm cracking up here

So, just break the circuit into sections and home in on the fault.

 

[Soulsurfer]

So, just break the circuit into sections and home in on the fault.

Love to but some of the fault is on a few circuits as whole board / global IR test was sitting at >999Meg until around 5 seperate circuits were brought online via breakers and then any one of them caused bonkers readings !!

 

[Octopus]

DO NOT fault find using global IR ............ it won't work ( well it might eventually) but its not the way to approach this...

You need patience, a note book and a pen ............. then test each circuit (cpc's connected to CU) one by one then it will be easy............................ and if you find yourself going round in circles, then walk away and go back afresh another day.

 

[westward10]

Worse thing you ever did was to ditch your perfectly good separates for some temperamental mft, I won't give one van space. What does it do when you try to test N/E.

 

[Soulsurfer]

Worse thing you ever did was to ditch your perfectly good separates for some temperamental mft, I won't give one van space. What does it do when you try to test N/E.

Goes to ramp up the volts but stops mostly max 15V and reverses back down again, locks out, whereas L-N L-E ramps straight to 550V approx

 

[westward10]

Have you read the instructions to see what this indicates.

 

[Soulsurfer]

Have you read the instructions to see what this indicates.

Yes, a few times but only issue it lists is if voltage present, and that at 50V it will inhibit the test.

 

[buzzlightyear]

Just ditched my Fluke and bought a shiny new Megger 1731 on NIC assessors advice

good man, meggers have been going of years and the pretenders are only catching up.

 

[Soulsurfer]

To be fair I wanted one since company I worked for had 1553 years ago and it was fantastic and this one is a work of art and technologically another universe but this blinking job is driving me bonkers cause it won't let me get a reading L&N to earth or N-E as is refusing to allow 500V or even 100 V test ! Can't see any reason why

 

[buzzlightyear]

had my assessment to day .asked the test engineer what test gear have you got
guess a megger.

 

[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.