Low Resistance on IR Testing

[Harry Bloomfield]

I was wondering, they were stored in a garage for over a year, wonder if that caused an issue?

Moisture should not be able to penetrate PVC insulation, most of my spare cable is kept in my garage and no issues at all. Pyro/MI cable and armoured cables could suffer, so were supposed to be sealed at the ends, when cut.

 

[wcavanagh]

This is why im so confused about the whole thing.

 

[Nozzle]

When was your megger last calibrated?

Nozzle

 

[wcavanagh]

Just checked 2 years, will borrow another meter tomorrow to compare, that’s a good call. Options are running out.

 

[securespark]

I have just tested the remains (about half) of a roll of old colour 3C&E I bought in 2004 and put in the shed in 2005.
I tested the MFT and it showed open circuit with the crocs apart and dead short with them together. Tested the cable on 250 and 500V and it showed >1000 meg.

 

[wcavanagh]

Maybe a meter issue, I HOPE, we shall see, no reply from supplier yet.

 

[JohnW2]

Moisture should not be able to penetrate PVC insulation, most of my spare cable is kept in my garage and no issues at all.

Indeed, and that is, if anything a major understatement. As I wrote back on page 1 ....

Other than where the cores are exposed (i.e. at terminations), no amount of moisture should make any difference to PVC cables. I am now a good few years (6-7 years, I think) into my long-term experiment of T+E (and also '50V alarm cable') submerged in concentrated brine, and, at the last check, all were still 'off the scale' of IR testing at 1000V (Edit: see post #9 of this thread )

Kind Regards, John

 

[wcavanagh]

My mate will bring his fluke over tomorrow and we will test again.

 

[JohnW2]

I have just tested the remains (about half) of a roll of old colour 3C&E I bought in 2004 and put in the shed in 2005. I tested the MFT and it showed open circuit with the crocs apart and dead short with them together. Tested the cable on 250 and 500V and it showed >1000 meg.

Indeed, and I can 'better that'. I've just tested the (small) remains of some old-colours T+E which was already pretty old when I moved to my present house in 1987, and which has literally been continuously in my (detached) garage since then. Again, >1000 MΩ at all voltages, including 1000V - and that probably dates back to 1980 or thereabouts.

Kind Regards, John

 

[JohnW2]

Maybe a meter issue, I HOPE, we shall see, no reply from supplier yet.

I certainly hope, for your sake, that your 'hope' proves to be justified - but, as you know, almost everything you have discovered and reported to us seems to go against that explanation.

Kind Regards, John

 

[wcavanagh]

Oh I know......

Clutching at Straws here, if I have to replace all, it means re-plastering, decorating, etc.....

 

[JohnW2]

Oh I know...... Clutching at Straws here, if I have to replace all, it means re-plastering, decorating, etc.....

I imagine that it would achieve nothing but, if it were looking to be heading in that direction, if it were me I think that I might be included to speak to a lawyer about the issue of 'liability'.

Kind Regards, John

 

[wcavanagh]

TLC have responded, and they have not had any reports at all. Have requested samples back etc...

So that don't help for now.

 

[JohnW2]

TLC have responded, and they have not had any reports at all. Have requested samples back etc...

Fair enough.

You presumably need to make sure that any samples you do send to them are ones which do IR 'unsatisfactorily' - otherwise they will simply not believe you!

Have you yet tried IR-ing short lengths of the suspect cable?

Kind Regards, John

 

[Harry Bloomfield]

Fair enough.

You presumably need to make sure that any samples you do send to them are ones which do IR 'unsatisfactorily' - otherwise they will simply not believe you!

Have you yet tried IR-ing short lengths of the suspect cable?

Kind Regards, John

I would also suggest removing the accessories during your installed cable tests, just to confirm it is the cables with low IR.

When I carried out IR tests, I would usually test the whole installation combined as a first step, I was so confident there would be no IR issues.