IR test

[jonthesparks]

Some advice please .
when doing IR test , generally i test the lighting circuit with the load shorted (L-N) and test across earth and live or neutral as removing all lamps and disconnecting fluorscents is time consuming .
now and again i will test the whole CU in this way .

Firstly , why is it that on some occasions a perfect reading (on a megger <999) is obtained , while sometimes anything between 10-800 Mohms is found .

secondly , when recording these results on the report is it correct to include the L-N column or not ?

lastly , how is it possible that when doing IR test normally (load not shorted ) a lower reading is sometimes found on N-E even though this is dead test and main switch is isolated

cheers

 

[telectrix]

firstly. damp, dirt, dead spiders, etc.
secondly, if you don't measure L-N, then on the test sheet you should enter N/V.
for the last bit... parallel paths? bonding?

 

[PEG]

Consider that question dealt with :stooge_curly:

 

[D Skelton]

Firstly, why is it that on some occasions a perfect reading (on a megger <999) is obtained

Can I ask why you are testing circuits operating at less than 500V on the 1000V setting?

 

[telectrix]

he's not. he means > 999 Ω , which is the megger's upper reading limit.

 

[D Skelton]

he's not. he means > 999 Ω , which is the megger's upper reading limit.

At 1000V.

At 500V the upper reading limit is >299.

Hence why I ask why he's carrying out IR tests on the 1000V setting.

 

[shanky887614]

At 1000V.

At 500V the upper reading limit is >299.

Hence why I ask why he's carrying out IR tests on the 1000V setting.

skelton flukes only go upto 299 same as some other brands.

at least the couple flukes ive used in the past

 

[D Skelton]

skelton flukes only go upto 299 same as some other brands.

at least the couple flukes ive used in the past

I wouldn't know about Flukes, I use Meggers.

 

[telectrix]

my mistake. was thinking of my megger BM401. that reads >999 on 500V test. the 1553 , as you say, is >299 on 500V.

 

[HappyHippyDad]

Hello Jon,

I think the first question has been answered.. here is a link that gives a thorough explanation View attachment insulation resistance explained.pdf

As for the second question I was concerned about not filling in the L-N IR column but from other threads it seems this does not always get filled in (and like Mr DS said enter a N/V). However if I found any unsatisfactory L/N - E IR results on a circuit I would then do a L-N also just to do a thorough check.

I think the third question means why can N-E be lower than L/N-E with regards IR testing. I suppose if the Insulation on the L was pretty poor then the results would be better with a N-E test. But if you haven't unplugged everything or left the lights in then I would have thought they would be the same!

 

[Geordie Spark]

Can I ask why you are testing circuits operating at less than 500V on the 1000V setting?

Load ....... Aim .........and ........

 

[ian.settle1]

he's not. he means > 999 Ω , which is the megger's upper reading limit.

Still be worried at that reading must mean >999MΩ

 

[telectrix]

hah. my typo. missed the M.

 

[Englishman]

At 1000V.

At 500V the upper reading limit is >299.

Hence why I ask why he's carrying out IR tests on the 1000V setting.

My 1720 goes to 999M at 500v....

 

[Geordie Spark]

My MFT is bigger than your MFT ......Nernerner :biggrinjester:

 

[davesparks]

My IR tester goes to infinity!!!!

 

[Geordie Spark]

My IR tester goes to infinity!!!!

Shhhhh! ...... you're making them all jealous.

 

[davesparks]

Shhhhh! ...... you're making them all jealous.

Dammit you were supposed to say 'mine goes to infinity and beyond'!

Didn't you read the script?

 

[Geordie Spark]

Dammit you were supposed to say 'mine goes to infinity and beyond'!

Didn't you read the script?

I didn't get the chance to .... the bloody dog ate it.

 

[davesparks]

I didn't get the chance to .... the bloody dog ate it.

Haha, any excuse! It'll be detention for you where you can write out 100 lines of 'I must not feed my homework to the dog'