low IR

[terry1969]

hi did a IR on a shed board L-N was 0.11Mohms so took out the radial circiut and light circuit did them separately and was fine 299Mohms so why low when they are connected to the shed board????? dont do much testing so help be nice cheers

 

[snowhead]

What was the result when you connected them back into the board?

 

[terry1969]

yes mate

 

[Pete999]

yes mate

Eh??

 

[terry1969]

Eh??

when i connect the circuits back to the board still get that low reading when do L-N at the board

 

[telectrix]

IR tests should be carried out with L and N dissed from the board, so that low reading is irrelevant.

 

[terry1969]

IR tests should be carried out with L and N dissed from the board, so that low reading is irrelevant.

really ok just didnt understand why as testing whole board was taught was fine

 

[Risteard]

really ok just didnt understand why as testing whole board was taught was fine

It is, but presumably you have lamps /loads/Neons in circuit?

 

[Pete999]

IR tests should be carried out with L and N dissed from the board, so that low reading is irrelevant.

Hi Tel don't normally question your replies, but looking at table 10.3.3 in the OSG it says.
"For an installation operating at 400/230V , although the IR value of 1Mohm complies with BS7671, where the IR reading is less than 2Mohm the possibility of a latent defect exists. in these circumstances each circuit should be tested separately" The original test was obviously a global test at the board.

 

[Octopus]

hi did a IR on a shed board L-N was 0.11Mohms so took out the radial circiut and light circuit did them separately and was fine 299Mohms so why low when they are connected to the shed board????? dont do much testing so help be nice cheers

Why were you testing the shed?

 

[terry1969]

Why were you testing the shed?

new install

 

[Octopus]

That should be easy peasy to split down and find the issue then

 

[terry1969]

That should be easy peasy to split down and find the issue then

did break it down the radial and lights was fine

 

[Octopus]

Surely you must have seen a difference at some point!

Does the shed have a cu and if so what type? What is at the house end of the circuit? How many circuits in the shed?

 

[terry1969]

Surely you must have seen a difference at some point!

Does the shed have a cu and if so what type? What is at the house end of the circuit? How many circuits in the shed?

2 circuts on own cu and off a 40a breaker in house

 

[westward10]

did break it down the radial and lights was fine

When you say it was fine, what was fine each radial between L/N or the supply to the shed board.

 

[terry1969]

When you say it was fine, what was fine each radial between L/N or the supply to the shed board.

did the l-n to each circuit after removing from the board, just low when connected to the board, when testing the whole board l-n

 

[westward10]

Well it shouldn't be, have you got the switch off at the board.

 

[terry1969]

Well it shouldn't be, have you got the switch off at the board.

yes mate trust me completely confused

 

[westward10]

I take it the board has a rcd main switch it could be reading across that. Switch off the MCBs and take the supply neutral from the neutral bar.