Head scratching IR problem!!!!

[A-Non-eMouse]

Hi all

just wondering if anyone can explain my dilemma. I think I have the answer but need someone to hold my hand and tell me it's going to be alright :stooge_curly:

Rewired folks house a year ago and always kept it on the back burner to use as an assessment job if I wanted to join a part p scam. Anyway time has come to put it forward for an assessment job. He's the problem. When insulation resistance testing and before everything is terminated into mcbs and neutral and earth bars all readings on all circuits are getting the expected >299 mOhms across all conductors. So l/n l/e n/e all >299 mOhms on all 8 circuits. The problem comes when I connect everything up into board. My readings drop on a global test to -

100>mo n/e
100> mo e/l
245> mo l/n


Testing is not going through rcds at board, two mcb bus bars are linked and mcbs on and two neutral bars are linked together to.

And on a l/n to e reading out of interest I'm getting 70 mOhms rising to >100 mOhms

All loads disconnected.

Now I know these readings are a 'pass' by the book but I was expecting if all individual circuits test out at >299 mOhms. Same would be so for a global test, am I wrong?

I'm thinking parallel resistances here are at play, or long runs, or the rising mOhms scenario suggests some dampness but why would this not show itself on an individual circuit basis?

help I'm confused !:willy_nilly:

 

[Octopus]

As the "adequate" value is above 2 don't even think about it!

 

[telectrix]

for arguments sake, assume all 8 circuits each have an equal IR of 400meg. a global test is testing those 8 circuits in parallel, so you'd expect a reading of 50meg. simpless....

 

[Guest77]

Agree with Murdoch, put it out of your head, just let it go

 

[A-Non-eMouse]

Thanks Murdock for your speedy reply. Do you think a 'scary assessor' would question these readings or just look on them as the norm?

just trying to get my head round them.

 

[telectrix]

the only figures the scam will be interested in is your cheque > 299.

 

[Octopus]

I use a Metrel MFT and on the auto IR test it only shows upto and greater than 30 mohms so thats what most of my certs say!

It does do up to 1000 but that means changing settings and slowing down the testing process!

 

[A-Non-eMouse]

Thanks telectric. That's a good explaination. What I was thinking along the lines off. Do you think the rising on l+n to e is anything to worry about or would it be something like my tester is working its nuts off to push 500v down all the parallel paths? I had new batteries in to.

 

[A-Non-eMouse]

Haha to right the thieving munts.

 

[Darkwood]

Remember to use a capital M for Mega otherwise your expressing milliohms ...

 

[Risteard]

Remember to use a capital M for Mega otherwise your expressing milliohms ...

In fact it is for "Meg" rather than "Mega" in this instance, as the word is Megohms.

 

[Darkwood]

In fact it is for "Meg" rather than "Mega" in this instance, as the word is Megohms.

Mega is a recognised SI prefix as in ... mili, centy, decy, kilo, mega, giga, tera etc and relates to the number of zero's

 

[Darkwood]

As i can add or edit my last post Ill just add to it...

You are correct Risteard it has a variation in its spelling when its part of another word but when you are quoting the SI prefix to indicate the zero count its is spelled Mega.
You need to be better than that to get me even on a Sunday

 

[Risteard]

Mega is a recognised SI prefix as in ... mili, centy, decy, kilo, mega, giga, tera etc and relates to the number of zero's

LOL. I'm aware of that, which is why I said "in this instance".

I meant to put a smiley after it because it wasn't intended as a criticism.

But we can agree that there is a substantial difference between milliohms and Megohms!

 

[Silly Sausage]

But we can agree that there is a substantial difference between milliohms and Megohms!

About 12 orders of magnitude!

 

[PEG]

About 12 orders of magnitude!

...Which is a whole lot of cider to be drinking all on your own...:stooge_curly:

 

[A-Non-eMouse]

...Which is a whole lot of cider to be drinking all on your own...:stooge_curly:

First class