Insulation Testing Conundrum

Piratepete · Apr 12, 2012

Hi Guys

Domestic - Old Hager Box 14 MCBs RCD Main Switch. Totally stuffed with wiring - not keen to disturb

Tested the Full L+N busbars to E. IR = 1.8 Meg b****r! So close to 2 Meg!

Tried L busbar to E -all trips off. 1.8 Meg!!!!!!!!! - had to disconnect RCD!

Tried each cct in turn L to E. Five of them reduce IR to about 1.8 Meg. Obviously a nonsence!

I'm theorising that one cct has a low IR Earth to Neutral and I'm seeing feedback through these other ccts which may have something connected/switched on.

Is the only way that I'm going to solve this problem going to be to disconnect the Neutrals one at a time to try and find a cct with low IR?

Cheers
Pete

MarkieSparkie · Apr 13, 2012

Sorry mate if this is not what you wanted to hear, but you need to IR test each circuit separately. Remove or isolate all loads. Initially, test each isolated circuit one at a time with the neutrals commoned. Only if your results still suggest a common fault to several circuits would you need to separate the neutrals and retest.

SirKit Breaker · Apr 14, 2012

Your 1.8meg, on the whole installation, is due to resistances in parallel. You will have to disconnect each circuit as stated earlier, and see what effect that has. With 14 circuits, my best guess is that if you do them individually your readings will come back into spec at 2 meg plus. If one circuit is low and pulling down your resistance total value, then you will find it fairly easily.

Cheers............Howard