Insulation resistance - low reading

[sideshowbob]

Hi,

I've tested all the circuits seperately and all reading have come back fine (>500 MOhms) except the test between Neutral and Earth of one of the lighting circuits which is 9 MOhms.

Does anyone know why this might be

Thanks

 

[industryspark]

what kind of installation is it?

new? just been plastered? give some more info.

but hey look on the bright side-at least it complies!

 

[sideshowbob]

Its a mixture of fairly old instalation, probably 15 - 20 year, and new modifications some of which are in newish plaster

 

[fattony]

You could split the circuit in half and test from the board to the halfway point to try and identify exactly which part of the circuit is causing the low reading, if that proves to be ok the split the the last part of the circuit in half and test again, as has already been said it needs to be above 0.5M ohm to comply and I believe its good practice to rectify anything under 2M ohm

 

[sideshowbob]

thanks for the replys,

what i'm trying to figure out though is the possible/probable cause ie

nail through cable, damp, ghosts

Cheers