Insulation resistance issue!

[schoe]

Hi all posted this issue about a month ago and I'm still having problems.

I'm doing an insulation resistance test on a ring circuit,

L-n 500 mega ohms
N-e 500 mega ohms

But L-e is around the 150 mega ohms reading.

I no this is still well within the regulations but it's new cable so I don't no why I'm not getting 500 mega ohms as well.

The room was plastered and painted about a month ago so things should have dried out now so I'm pretty sure I can rule out damp as that was suggested before.

This is my issue, I've broken the circuit down and tested each leg individually and when I do this I get 500 mega ohms on each leg some of the results are more laboured than others but it does reach 500. It's only when I connect everything back up together do I get the lower reading.

I've been testing from the consumer unit with the wires disconnected from the breaker and bus bars so it can be parallel paths either.

If anyone could shed some light would really appreciate it. I don't understand why my live to neutral and neutral to earth are fine but the live to earth isn't.

Thanks very much,

Chris

 

[telectrix]

still damp, IMO.

 

[Octopus]

I experienced something similar once and tracked the issue down to a 2 gang socket!

i.e. as seperate legs the IR was great, when then socket was connected back in the IR value dropped!

 

[brucelee]

I had the same problem mate did exactly what you did splitting in half replacing some of the sockets etc
remaking ends off and then left it tested again and the readings have risen i was having probs with N-E and L-E bit now they have improved to over 200M/ohms
so think it as tel says still has some damp in the plaster
as if i do a extended test they all rise above >299

 

[schoe]

Brucelee I did an extended test it was a good five mins but the readings slowly Rose to 300m ohms. That was a few weeks ago though, re- tested last thing today and the reading started of low and started to rise, i stopped after a few mins though when it only rose to 150 mega ohms. I'm just not sure what to put on the scedule of test results as I'm hoping to use this job it's a complete rewire to show an assessor from elecsa.

 

[telectrix]

you just put down the readings as you get them. before we had these new fangled digital meters, it was common to enter >10Meg. can't see what the problem is as anything over 2Meg. is a pass. i can't wait till megger bring out a meter that reads up to 9999Meg, then we'll have queries on readings of 8000Meg.

 

[brucelee]

do as Tel says mate

if the reading is over 2M then it complies just write what ya tester says

 

[Deleted member 9648]

I admire the dedication here in chasing a 'poor' reading...(75 times the required minimum!).....but bl##dy hell mate,lifes too short.:mad2:

 

[malcolmsanford]

There are more things in heaven and earth, Horatio,than are dreamt of in your philosophy.
Hamlet

So as the Bard intended there are just little mysteries in life, and the electrical industry as it's full share, and your IR results is one of them.

​Agree with WP I think it is time to move on and put the 150MΩ on the cert.