'Insulation Resistance'

[1john]

So I've been told too, aparantly if you look on really old stained slass windows in churches and the like it can be seen that is has "run".

http://en.wikipedia.org/wiki/Glass#Behavior_of_antique_glass

Please ignore my quoted statment

 

[EFLImpudence]

An amorphous (or synonymously, non-crystalline) material can be defined as one which is topologically disordered and which does not exhibit either the long-range translational order (periodicity) characteristic of single crystals, or the long-range orientational order characteristic of quasicrystals. Within this definition, such materials could be either solid or liquid, and this distinction is essentially simply one of timescale. A material is a solid when there is no observable long-range translational diffusive motion during the duration of the experiment; in other words, dynamic disorder is absent.

Oh well, shall have to wait and see.

 

[JohnW2]

Given the very high proportion of off-topic messages in this thread, do I take it that ChrisRogers is the only person reading this thread who has seen a fall in insulation resistance that could not be explained by anything other than (assumed) natural deterioration of PV insulation?

Kind Regards, John.

 

[scousespark]

I doubt many of us will live long enough to come across PVC which has deteriorated, due to age, to the extent it fails an IR test. I have removed cable which has broken down to to external factors (favourite being sun damage to outdoor cables). We do come across peridhed VIR, but that's not really what you are asking about.

I haven't come across duff cable, but that doesn't mean it isn't out there.

Do you really IR test every drum? I suppose you could do that if you buy a couple each year.

What exactly are you trying to prove with your experiment with your submerged cable?

 

[JohnW2]

I doubt many of us will live long enough to come across PVC which has deteriorated, due to age, to the extent it fails an IR test. I have removed cable which has broken down to to external factors (favourite being sun damage to outdoor cables). We do come across peridhed VIR, but that's not really what you are asking about.

That's exactly what I would have expected, but was interested in getting confirmation. I suppose what stimulated this is a fascination about the way that terminolgy has developed in the world of electricians - e.g. 'IR' testing will very rarely relate to 'insulation resistance' in the normal sense, whilst 'continuity testing' is a pretty ill-defined phrase ('continuity', in the literal sense, can exist in the presence of a resistance which is unacceptably high for the situation concerned).

I haven't come across duff cable, but that doesn't mean it isn't out there. Do you really IR test every drum? I suppose you could do that if you buy a couple each year.

As I said, it's just paranoia, but I usually do - and started because a friend of mine claimed that he had come across some duff cable. As you say, it is really not much of a burden to me - 30 seconds work, very occasionally.

What exactly are you trying to prove with your experiment with your submerged cable?

It started, 3 or 4 years ago, as a very short-term experiment to settle an argument with a friend who seemed to believe that PVC T&E was not safe if it got wet. As time went by, it seemed a shame not to let the experiment 'go on for ever', just outvof interest, although I don't have much expectation of being able to measure an insulation resistance at any point in my lifetime!

Kind Regards, John.

 

[ban-all-sheds]

In my round tuit box I've got a length of T/E which had been on a catenary to the garage for donkey's years.

Nice and dry by now - one day I'll zap it, and then put it in a container of water for a good long soak and zap it again.

 

[JohnW2]

In my round tuit box I've got a length of T/E which had been on a catenary to the garage for donkey's years. Nice and dry by now - one day I'll zap it, and then put it in a container of water for a good long soak and zap it again.

I'd be interested to hear the results and, if I were a betting man, would probably bet on it being OK.

I would suspect that the greatest risk is if it were exposed to UV for many years and then handled (e.g. to get it down and into your box!). I'm actually not convinced that UV damage, per se, necessarily affects PVC insulation resistance, but it can make the PVC brittle, so subsequent handling can result in cracking etc.

When I first moved into this house, nearly 25 years ago, I dug up some (totally unprotected, and not very deep!) buried Imperial PVC T&E that had been supplying an outside light for goodness knows how many years, and that cable IRd fine.

Kind Regards, John.

 

[RMS]

In my time I have never come across a cable that has naturally degraded enough to result in a low insulation resistance.

The causes are commonly damage caused by third party. I do recall a friend having to rip out a newly installed cable that was faulty. He explained that on further investigation there was a fault within the cable that he put down to a fault in the manufacturing process. Maybe it is a good idea to test all new cabling prior to installation.

I use to work with an electrician that was convinced the reason one would not necessarily install twin and earth outside was due to the rain.

 

[JohnW2]

In my time I have never come across a cable that has naturally degraded enough to result in a low insulation resistance.

Thanks. As I expected.

The causes are commonly damage caused by third party. I do recall a friend having to rip out a newly installed cable that was faulty. He explained that on further investigation there was a fault within the cable that he put down to a fault in the manufacturing process. Maybe it is a good idea to test all new cabling prior to installation.

It's obvioulsy the case that no manufacturing process (or even the pre-release testing they should undertake) is infallable, so I guess there will always be some rogue cable being sold - but it seems to be incredibly rare. However, for someone who buys as little cable as I do, to test it all 'on arrival' is a trivial business, and therefore not a burden.

I use to work with an electrician that was convinced the reason one would not necessarily install twin and earth outside was due to the rain.

That's more-or-less the 'argument' which caused me to commence my ongoing experiment 3 or 4 years ago!

Kind Regards, John.

 

[17thman]

pvc surrounded by those polystyrene balls goes horribly sticky and can break down fairly rapidly.