Insualtuion Resistance - individual circuits V bank of MCBs & RCD readings

[Pete999]

Yes that's that new approved test......Licking Of Conductors

Nice one

 

[Risteard]

That is incorrect. The insulation resistance values quoted are for individual circuits and that is why you record it as such.

I disagree. My understanding is that the reason for the box on the forms next to every circuit was simply to make the form look tidier.

However the Regulations require the minimum insulation resistance of 1 Megohm for the installation/part thereof and not for an individual circuit, therefore the effect of parallel resistances need be considered. In fact, Guidance Note 3 even suggests that insulation resistance should be tested with all circuits in parallel and not individually (except to find the cause of low readings of course).

 

[Hawkmoon]

I disagree. My understanding is that the reason for the box on the forms next to every circuit was simply to make the form look tidier.

However the Regulations require the minimum insulation resistance of 1 Megohm for the installation/part thereof and not for an individual circuit, therefore the effect of parallel resistances need be considered. In fact, Guidance Note 3 even suggests that insulation resistance should be tested with all circuits in parallel and not individually (except to find the cause of low readings of course).

If you get a lowish reading on one circuit, say 40 Meg (low but still acceptable) wouldn't it be appropriate to record it individually on the cert?

 

[Meggerman]

I do more than consider it, I test it!! I don't understand your post, you are saying you disagree but then also saying that GN3 suggests IR tests are done with all circuits in parallel.

 

[Meggerman]

I would not call 40M/Ohms low IR

 

[Hawkmoon]

I would not call 40M/Ohms low IR

It is if new install and all other circs are >200 - I was just making a point that if a circuit is unexpectedly low with no fault then it is right to record it - even if just for future monitoring of insulation deterioration.

 

[Octopus]

I use a Metrel and if I do all 3 cores automatically, I get >30

Low IR is less than 2!

 

[Hawkmoon]

I use a Metrel and if I do all 3 cores automatically, I get >30

Low IR is less than 2!

Yes but my point was mainly about individual circuit IR readings and the merits of separately recording them on a cert...

Your 'low' IR being < 2 Meg is ok but if you had a reading of say 4 Meg would you not consider that at least a code 3 to be investigated? At least record on the cert?

Or am I misunderstanding the point of your post?

 

[Octopus]

Yes but my point was mainly about individual circuit IR readings and the merits of separately recording them on a cert...

Your 'low' IR being < 2 Meg is ok but if you had a reading of say 4 Meg would you not consider that at least a code 3 to be investigated? At least record on the cert?

Or am I misunderstanding the point of your post?

Not a code 3, if I was testing as part of a board change I would comment on it and on an EICR I would recommend a retest in 3-5 years. The BIG issue with IR tests is that so many now seem to be done as L&N to E so the "real picture" isn't disclosed.

 

[Engineer54]

In fact, Guidance Note 3 even suggests that insulation resistance should be tested with all circuits in parallel and not individually (except to find the cause of low readings of course).

Are you sure you are reading correctly?? If that is actually what is being suggested in GN/3 then get a black marker and black it out because it's WRONG!!

Nothing wrong with conducting a global IR, but you DON'T record the global IR value, on official test record sheets, as the value for every circuit on a DB/CU, that is just plain bonkers!!

Do you know the reason for recording circuit IR values on official test reporting sheets??

 

[Risteard]

I don't understand your post, you are saying you disagree but then also saying that GN3 suggests IR tests are done with all circuits in parallel.

Seems like crossed wires then. I agree that circuits should be tested in parallel.

 

[davesparks]

Nonsense!

IR is tested per circuit, not just once over the whole installation.

On a large installation the parallel resistances of many perfectly healthy circuits could result in a fail on an overall test.

 

[Risteard]

IR is tested per circuit, not just once over the whole installation.

On a large installation the parallel resistances of many perfectly healthy circuits could result in a fail on an overall test.

I suggest you read Regulation 612.3.2

 

[davesparks]

1, that regulation says all distribution ccts with final circuits seperately, not the whole installation.

2, that regulation is nonsense!

 

[Risteard]

1, that regulation says all distribution ccts with final circuits seperately, not the whole installation.

As did I (I said the whole "installation or part thereof"). Simple installations with no distribution circuits should be tested as a whole.

And I don't agree that it is nonsense.