Insulation Resistance

Jamieblade1 · Sep 7, 2014

Hi guys,

I've recently just completed a rewire of a small 2 bed bungalow consisting of 4 circuits. I have tested the kitchen ring and it has tested fine, the same with the lighting circuit. On testing the heating circuit and general ring main, the insulation resistance between L-N on both circuits is 0.3 Mohms. Between L-E and N-E they test fine at over 200Mohms. I have looked for the obvious i.e nails through cable in capping etc twists and kinks in cable. The cables move freely in the capping when pulled. The 1.5mm supplying the fused spur in loft for the heating is no longer than 6 meters in length. The general sockets however, I have split the ring down to find the leg which is causing the low reading and it seems to be the supply from the consumer unit to the first socket. But as I've said there are no nails, plaster, clips or anything on the cables. Really frustrating now, especially as the bungalow has just been skimmed!

Any chance it could be faulty cable?

Any help will be greatly appreciated.

Cheers

Jamieblade1 · Sep 7, 2014

No the heating is directly from CU on its own circuit. The leg in question is the ring main to the rest of the bungalow. From the CU to the first socket, it's a reading of 0.3mohms L-N. From the first socket to the rest of the bungalow, it tests completely fine.

Plonker 3 · Sep 7, 2014

Jamieblade1 said:
Hi guys,

I've recently just completed a rewire of a small 2 bed bungalow consisting of 4 circuits. I have tested the kitchen ring and it has tested fine, the same with the lighting circuit. On testing the heating circuit and general ring main, the insulation resistance between L-N on both circuits is 0.3 Mohms. Between L-E and N-E they test fine at over 200Mohms. I have looked for the obvious i.e nails through cable in capping etc twists and kinks in cable. The cables move freely in the capping when pulled. The 1.5mm supplying the fused spur in loft for the heating is no longer than 6 meters in length. The general sockets however, I have split the ring down to find the leg which is causing the low reading and it seems to be the supply from the consumer unit to the first socket. But as I've said there are no nails, plaster, clips or anything on the cables. Really frustrating now, especially as the bungalow has just been skimmed!

Any chance it could be faulty cable?

Any help will be greatly appreciated.

Cheers

How have you done this of the job has been plastered?

Jamieblade1 · Sep 7, 2014

Because the cables move freely in the capping, I have also managed to pull the leg out from CU to first socket and there's is no physical damage at all.

Plonker 3 · Sep 7, 2014

So when you pulled the leg out why didn't you change it? Or even carry out a IR test on it?

Jamieblade1 · Sep 7, 2014

Yeah I will when I go back tomorrow, I'd just had enough after trying to get my head round why both cables would show the exact same fault L-N when they're not even from the same drum and different size.

dazza1981 · Sep 7, 2014

Something ain't adding up here mate, as dill said if you have identified what leg it is then what's the problem or am i missing something ????
Surely as you did the wiring you know all routing of cables you would be in a good position to sort it.
Im not sure i can add anymore to the advice already given tbh.

Jamieblade1 · Sep 7, 2014

Yeah I have identified the leg and will sort it but as I said, I just thought it was slightly weird how the heating supply and first leg had identical issues that's all, that's why it was confusing me and wanted a second opinion.

Brightspark2 · Sep 7, 2014

Dillb said:
Have you disconnected the cables from the DB then carried out the IR test?

This....

7029 dave · Sep 7, 2014

As mentioned, strip it down on the said section,ir test direct on the cable in question, both ends(I would) to prove cable.

Octopus · Sep 7, 2014

Jamieblade1 said:
Yeah I have identified the leg and will sort it but as I said, I just thought it was slightly weird how the heating supply and first leg had identical issues that's all, that's why it was confusing me and wanted a second opinion.

Hum, that does sound a bit of a head scratcher. Have you tested for continuity between both sections of cable?

Please do update the thread with what you find.