IR connundrum

[Andy_G]

Th

Hey Guys

I've got a bit of a head scratcher that I was hoping someone could help with.

I have a ring main feeding 7 points. When testing IR btw L&N I get 967Mohm but when testing N-E & L-E I get 455Mohm. I split the ring and tested as 2 radials and the results suddenly come back all clear at >1000Mohm L-N L-E and N-E??? When I reconnect the ring it's back down to 455Mohm??

I've checked all connections at the sockets and all good.

Any ideas??

Cheers
Mark

this is the kind of 'conundrum' I like to get on jobs, I.e the type you can just come back to think about when you are bored with nothing to do for an hour..455 Meg ..I want some of those conundrums in 2017

 

[Andy_G]

I t

Thanks for all the replies guys. I agree the results are good but I wasn't worried about them I was just curious as to why I was getting a lower reading when testing to earth. I was hoping to see them all around the same value.

otally understand why you wanted to know the actual reason as it is always helpful to know why things happen as opposed to just knowing that they happen,electrical theory is fascinating and the more you learn,the more you realise how little you know...hence why most avoid asking 'why'....

 

[1Justin]

Hey Guys

I've got a bit of a head scratcher that I was hoping someone could help with.

I have a ring main feeding 7 points. When testing IR btw L&N I get 967Mohm but when testing N-E & L-E I get 455Mohm. I split the ring and tested as 2 radials and the results suddenly come back all clear at >1000Mohm L-N L-E and N-E??? When I reconnect the ring it's back down to 455Mohm??

I've checked all connections at the sockets and all good.

Any ideas??

Cheers
Mark

Disregarding, for the moment that with figures that high you shouldn't hesitate to move on. However it still can make sense.
The structure of T&E cable means there is about twice as much insulation between L-N as between LE or NE. So any leakage will be expected to be larger in the latter case. When you split the ring, assuming you broke it near the middle, each half L-E + N-E would be approximately doubled. Hence all 1000Mohm.
Wait till you get a damp installation 1000 times worse than you have there, and have to make a judgement..