What causes low IR readings?
I’m currently at the second fix stage of a rewire and before all the flooring goes down I’ve decided to do r1+r2 readings to make sure everything is continuous and polarity is correct. I also decided to do insulation resistance tests and have got lower than expected readings.
On the downstairs lighting circuit I got a reading of around 200-300Mohm. After breaking the lighting circuit down I found the reading was caused by the switch cable in the utility room however I can’t get to the entire length to inspect it. I might replace this one as it is a quick run.
I went to test a few radials circuits and they were perfect >1049Mohm. Went to do the upstairs ring and I was getting about 400Mohm Between neutral and earth.
Downstairs ring between live and earth I was getting around 600Mohm then it will climb to about 1000Mohm.
I know these readings are satisfactory as I’ve looked in the guidance note and it says minimum insulation resistance is 1Mohm but on a new install anything less than 20Mohm needs investigating.
I’ve read moisture is the main culprit and can be caused by damp from plastering, but it’s been plastered about 2 months ago.
There are no loads or sensitive equipment on the lighting circuits. On both rings there is a fused spur with no neon however I did forget to take the fuse out but that couldn’t cause these readings could it?
What else can cause readings to be lowered to these numbers?
I know guidance note 3 says less than 20Mohm is needs investigating but would you investigate if you got these readings or is it just over the top and a waste of time?
What causes low IR readings? for more information
You may reply to this message here.
I’m currently at the second fix stage of a rewire and before all the flooring goes down I’ve decided to do r1+r2 readings to make sure everything is continuous and polarity is correct. I also decided to do insulation resistance tests and have got lower than expected readings.
On the downstairs lighting circuit I got a reading of around 200-300Mohm. After breaking the lighting circuit down I found the reading was caused by the switch cable in the utility room however I can’t get to the entire length to inspect it. I might replace this one as it is a quick run.
I went to test a few radials circuits and they were perfect >1049Mohm. Went to do the upstairs ring and I was getting about 400Mohm Between neutral and earth.
Downstairs ring between live and earth I was getting around 600Mohm then it will climb to about 1000Mohm.
I know these readings are satisfactory as I’ve looked in the guidance note and it says minimum insulation resistance is 1Mohm but on a new install anything less than 20Mohm needs investigating.
I’ve read moisture is the main culprit and can be caused by damp from plastering, but it’s been plastered about 2 months ago.
There are no loads or sensitive equipment on the lighting circuits. On both rings there is a fused spur with no neon however I did forget to take the fuse out but that couldn’t cause these readings could it?
What else can cause readings to be lowered to these numbers?
I know guidance note 3 says less than 20Mohm is needs investigating but would you investigate if you got these readings or is it just over the top and a waste of time?
What causes low IR readings? for more information
You may reply to this message here.
