insulation resistance test

[lukesparky123]

just a quick one when doing an insulation resistance test at 500v why is it if it passes on the meter it says >500mo ??

 

[brizospark]

Depends on what meter u r using

i.e. on a megger it will show >299Mohms (note the capital M)

 

[DaveyD]

You are sending out 500v (on a typical 230v) but reading the resistance value of the insulation. ie how much is leaking across. In this setting over >1 MOhm is the minimum.
Regards
Dave

 

[lukesparky123]

iv got a fluke what says >500mohms but my mates robin says >999mohms why is this what do you put on your test form ?

 

[DaveyD]

yes mate, it's what ever your meter says so long as >1 MOhm

 

[pmac10]

as mentioned, guess it depends on the meter, on the megger in our gaff we get >1000Mohms (testing 3 phase motors)

 

[Rappid]

iv got a fluke what says >500mohms but my mates robin says >999mohms why is this what do you put on your test form ?

I have a Fluke, I always put 500+ on my test forms.

 

[J@mes]

I put the maximum my meter shows. That's what you should put, don't put >1Mohm as that doesn't really give an indication if the installation is starting to degrade compared to previous results

For example

You test and get 30Mohm, but put >1Mohm on the sheet, then test a year later and get 2Mohm, but put >1Mohm on the sheet as these results are a clear indictation that the installation is beginning to degrade.

 

[brucelee]

Its the maximum reading on your meter so u put that but as others have said 1M/ohm min anything under 2M investigate

 

[WDMDL]

In situations where BS7671 applies, the minimum being 1Meg in most cases, it's no point going to the n'th degree.
The maximum displayed reading is two orders of magnitude (100 times) greater than the acceptable value.

Another industry I used to work in had minimum values of 2Meg for existing circuits and 50Meg for new circuits.
We mainly used to use Megger BM82/2 instruments which read up to 200Gig on the 1000V test.
Then it was a case of how long do you hold your finger on the button?

Edit: And in the earlier days when we used the analogue Meggers, we always wrote >2G on the certs (because 2G was the last scale marking), never infinity!

Simon.