Insulation test results

[sparky40]

Hello All,
A recently wired ring main of mine has produced some results I wasn't expecting and wondered if anybody could advise me please.

Insulation Resistance Results were as follows;
P/N 54.5 M Ohms
P/E 48.9 M Ohms
N/E 59.1 M Ohms

Impedance Tests
r1 0.04 ohms
rn 0.06 ohms
r2 0.14 ohms

EFLI = 0.31


As this didn't please my test engineer can you imagine his anger when the other ring came out at;

Insulation Resistance
P/N 19.6 M Ohms
P/E 14.55 M Ohms
N/E 18.59 M Ohms

Impedance Test
r1 0.24
rn 0.24
r2 0.05

EFLI 0.31


Any ideas please on why the figures seem so poor on a newly installed circuit ????


Any help or advice would be appreciated as "Dunno, not my problem" was all the engineer could manage to say !!
Thanks in advance.

 

[industryspark]

the impedance tests look a little strange. what type of install is it and what cable type? swa's in factory? house?

is there any moisture from anywhere that could give low IR results, say from damp plaster maybe? any chance cables could be damaged when putting in (plasters trowel?)

a strange set of results indeed.

have you try'd the tests with a different meter. suppose the IR tests are above acceptable so ok, however there not what you would expect from a new install.

 

[sparky40]

Thanks for the reply,

It is a domestic install, cabled in T+E 2.5mm2. (a ring using around 35 metres)

The walls have been recently plastered so maybe some moisture there, all the sockets have been left off (un occupied at the moment) so I may test them myself tomorrow and see if the readings have changed as the heating was fired up today.
I can only use the meter he uses though. Fluke 1652. calibrated 6 months ago.

Thanks again.

 

[industryspark]

the plastering is a possible fault. id be a bit concerned about the impedance tests aswell. id be rechecking connections at all sockets if it was me.

then do the tests again. id also do the ring test aswell by cross connecting phase-neutral and phase-earth to prove that it is indeed wired as a ring.

you could always split the ring and test individual legs to see if you could trace a fault.

let us no what you find.

 

[RF Lighting]

Strange that both EFLI readings are the same.

 

[securespark]

The IR's are down: normally get higher than that. However, they are sufficiently high enough not to fret over.

The impedance readings are nuts.

Are these ring continuity end to end or what?

 

[sparky40]

Hello,
Yes they are end to end readings, after he went I did a P/N 'loop' and it came back as a ring main.
Going back there today and will let you know what happens.
Thank you for your help and views, I have been stumped by this as I cannot understand why the results are so erratic.
Thanks.

 

[supersparky]

ihave readings like that every now and again - though not with the insulation

what you have to do is null your meter again cos its lost the resistance of the leads and confused itself

 

[HDRW]

Strange that both EFLI readings are the same.

Not if they are taken at the CU - he's measuring the external wiring up to the CU, not that in the house. Would be interesting indeed if they were taken at the far side of the rings, though!

Cheers,

Howard