Insulation Reesistance results.

[SSE]

I installed a new ring for a utility room today, I tested the two legs before anything was connected and everything was all clear. Then once I connected all the fittings but never hitched anything in at the CU side my results seemed to change. Live-Neutral was fine >299 mega ohms, but Live-Earth was now giving me about >220-240 mega ohms & Neutral-Earth >250 megaohms. I then went and split the live, earth & neutral at a fitting, tested each leg and they were clear again, >299. Am I missing something glaringly obvious here or what??????

 

[Tuttle]

but it's not kilo ohms, is it? it's kilohms.

Depends how fast you say it and which part of the country you're from

 

[trev]

My Metrel goes to >1999M. Makes no odds really

 

[telectrix]

mcdonalds do a mega burger. is that where thew confusion arises?

 

[Brightspark2]

I wish my MFT wouldn't go up to 999M, what's the point? I would prefer it to stop at a more sensible value, like they used to.

Like infinite?...ha


Thats what the analogue robins used to read...

 

[SSE]

Yeah your testing the ring incorrectly.
Testing the ends without accessories on, you are not testing the entire circuit.

I tested both with and without the accessories on.

wheres the problem ? the min is 1M-ohm

I know it's ok by the book but it's the first time I've come across this with new cable.

Its a good result.. Stick on your cert get paid and go to the pub.. Ive tested rewires after the plaster and had lot less than that

Pub sounds good!

As has been said, 250 meg is a good measurement so don't worry about it.

However, I am concerned at your apparent lack of understanding of the test you are carrying out. If you test your two legs without your accessories connected then you are only testing between the distribution board and the point of first accessory. Unless you connected up your cabling to check the wiring at first fix, in which case the small drop in resistance obviously comes from either one or two of your accessories, or from where they have been finished. This is quite normal and shouldn't be worried about, but maybe you should think about reading up on what you are actually testing.

I only done it without the accessories on to try & rule out the lower reading being on the run from the consumer unit, this way with it being clear would have told me the dropin resistance was between the accessories. I'm more than capable of testing and don't need to read up on it, just hadn't come across this before. Any time I've done it it's been >299 on new wiring.

The other thing I noticed was if I held the lead on, very slowly the value started increasing sometimes going the full way to >299. This just my tester, leads or what?

 

[Tuttle]

Like infinite?...ha


Thats what the analogue robins used to read...

That's what they printed on the dial anyway. Surely it's impossible to measure something that's infinite.

 

[telectrix]

that's what infinite means. un-measureable. a bit like a good dump.

 

[Brightspark2]

That's what they printed on the dial anyway. Surely it's impossible to measure something that's infinite.

No it is possible...


You just have to keep moving the tape measure along every time it reaches the end...

 

[telectrix]

won't work. by the time you get to infinity, you'll be dead.

 

[PEG]

Even infinity is finite,you can double something infinitly and never reach a result but you can theoretically half it infinitly even with the knowledge of a finite result,zero. This is the theory used for payday loan structuring...

 

[GLENNSPARK]

spit on one of the sockets, you'll get a lot less than that. 240Meg. that's a result even God would be happy with... move on.

yeah....wingin n whinin caus it aint off scale.....
yet more that dont understand how damp from plasteres , parrallel paths & what is acceptable or for an older install etc....
about time this was all made clear it is.......

 

[Engineer54]

That's what they printed on the dial anyway. Surely it's impossible to measure something that's infinite.

The infinity symbol that is present on many of the analogue IR testers means a value beyond the measurement capabilities of the tester, not that the insulation resistance is infinite!! Test the same circuit with an IR tester that can measure in Tig ohms, and that will become clear. Most MFT's from what i can make of it, only have a top scale of 300 Meg ohms and standard dedicated IR testers anything from 500 Megohms and up.

 

[Knobhead]

TetraΏ is only on very few test sets. 1,000,000,000Ώ and normally only on 1000V and above.

Never tried shoving 5KV up a domestic circuit, could be fun to try!

 

[Engineer54]

There are plenty of 1KV IR testers out there that have a 1000 megohm range. No problem at all, shoving 1KV up a domestic circuit. ..lol!!

 

[Knobhead]

My 1000V Megger only goes to 999MΏ.

The Megger I had at work went in to 100’s of TΏ. Rotten sods wouldn’t let me take it with me when I retired. All the other test gear I was allowed to take but not that!

I wonder how many know the 1/10,000[SUP]th[/SUP] FLC calculations for IR readings. A must with old / large systems.