IR connundrum

[Mark.W]

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

 

[Mark.W]

Just a thought but it could be the damp! I'm on a site in Poole and it's very moist where I am.

 

[Pete999]

Are you disconnecting ALL the circuit conductors from the CO Ls, Ns and cpcs??

 

[Pete999]

Just a thought but it could be the damp! I'm on a site in Poole and it's very moist where I am.

Well it would be damp in a poll wouldn't it? sorry my attempt at humour

 

[HandySparks]

Is ring continuity OK?

 

[Mark.W]

Yeah end to ends are good, as is r1+r2

R1 - 0.35
Rn - 0.39
R2 - 0.64
R1+R2 - 0.27

 

[HandySparks]

Yeah end to ends are good, as is r1+r2

R1 - 0.35
Rn - 0.39
R2 - 0.64
R1+R2 - 0.27

OK. Obviously, missing ring continuity could affect IR results when the ring is split.

BTW, I guess you mean r1, rn and r2.

 

[Mark.W]

Yeah it's auto correct lol

Start of
A new line
Auto capitalises
The first letter

 

[HandySparks]

Actually, looking at the figures again.
If you have about 500M IR for a complete ring, then splitting into two halves would give about 1000M for each half if the 'fault' is evenly distributed.

I don't really see a problem, especially as the figures are so high.

 

[tony mc]

Keep the test on for at least a minute and see how the reading change i would say that the reading would slowly go up slowly if it is a damp problem but I wouldnt lose any sleep over the readings posted!

 

[Pat H]

I'd agree the values look ok. The L-N us passing through two conductor insulations. L-E and N-E are only passing through the line conductor insulators as the CPC is bare.
A little moisture in the cable and you will see lower values.
Your tested proved the values where consistent even when split.

 

[westward10]

I don't see a problem here.

 

[telectrix]

the only problem as i see it is OP considering that 455Mohms is worthy of a second look. many MFTs only read up to 299Meg.

 

[Pete999]

the only problem as i see it is OP considering that 455Mohms is worthy of a second look. many MFTs only read up to 299Meg.

probably a strange thought, but any chance the OP could be misreading the MFT and stating OHMS instead.

 

[westward10]

the only problem as i see it is OP considering that 455Mohms is worthy of a second look. many MFTs only read up to 299Meg.

Mmm, second look then look somewhere else.