Low Resistance on IR Testing

[Harry Bloomfield]

No, the new reel was on my living room floor, lol. Nothing close, no power lines etc...

If I hold the test button down for a long time, the reading steady goes up and up...... Not seen this before. I mean like 10 sec or so....

Yep, cannot wait for the results - I am intrigued.

I wonder if the 10 seconds you mention above, might be due the batteries resistance increasing, the longer the button is held in? Meggers draw quite a bit of current, to generate the voltage. Straw clutching time...

 

[wcavanagh]

Im all for the straw clutching also

 

[Jackrae]

Out of idle interest, during your testing have you tried reversing the megger connections to see what effect, if any that has.
And have you tested individual cores to the CPC wire.

 

[flameport]

If I hold the test button down for a long time, the reading steady goes up and up.

That's normal with long cables, it's due to the cable acting as a capacitor - 2 long conductors with insulation between them.
However the effect should only last for a few seconds at most, and the reading should increase quickly to a steady maximum.

 

[wcavanagh]

Same result with different meter as expected. New reel is coming in army 100Meg

 

[wcavanagh]

Live to cpc 10meg
Natural to cpc 9.9meg

 

[333rocky333]

Yes, I think we're all very surprised, and most of us probably still find it 'hard (or 'impossible'?) to believe'.

The thing which I personally find most 'hard to believe' is that essentially the same 'problem' seems to exist in relation to several separate lengths of the cable (different circuits). That would imply that, if it is due to something 'wrong' with the cable, it must be 'something wrong' throughout the entire length of the (n fact, more than one) drum of the cable - which really does seem incredibly improbable.

As you say, the fact that the finished item is, or should be, tested prior to release by the manufacturer should prevent faulty products getting to market, we all know that, for whatever reason, that process is not totally foolproof. Even aircraft and spacecraft have suffered from this 'imperfection'.

I wait with bated breath for the results of testing with a different meter!

Kind regards, John

One common factor is they have all been stripped, could the problem be caused by the method of stripping, ive seen a few cables ruined due to overzealous knife stripping

 

[wcavanagh]

I don’t strip with knife use my cable shears

 

[Harry Bloomfield]

You sound as if you know what you are doing, so I don't suppose there is plaster or paint on the cable ends? Really running out of ideas now.

Regarding the suggestion about cables charging up due to capacitance. Yes, that can and does happen on extremely long cables, but this is unlikely on short domestic cable runs. If the reading is gradually improving over seconds, it is because the insulation drying out, being expelled by the tiny amount of heat generated by the current leakage.

 

[JohnW2]

Same result with different meter as expected. New reel is coming in army 100Meg

Although I realise that, in subsequent posts, people are desperately trying to find other possible explanations, I really don't see that, no matter how 'extraordinary' it may be, the finger can now be pointing in any direction other than the one is which you're praying it doesn't point, can it? Sorry!

What's really odd is that, if this is a 'cable batch problem', that TLC have not received any other reports - are there perhaps a lot of people out there who don't IR test their new circuits, I wonder?!

How many reels of this stuff did you buy, and over what period of time? How much have you used, and how much is left?

Kind Regards, John

 

[wcavanagh]

Indeed, nothing like that, I’ve even tested a left over reel just now. Same poor results, 50 meg

The house is plastered and painted, it’s going to be a massive job to remove and replace

 

[wcavanagh]

Used about 5 reels in total, I have one and three quarters left over. Was a self build project so was bought over a year ago, maybe 1.5 and first fix was about 1 year ago. I will have to dig receipt out but I did not buy all reels at once I remember. But they are all same make they seem to have same labels etc.

TLC have been sent a sample as they requested for testing.

All this dont help me decide if I should strip all out. Tech above 1 meg should be fine so, do I pull it all out, rip walls replaster delay move in etc...... oh I don’t know.

I know if I was to test an existing install it would be a pass.

 

[JohnW2]

TLC have been sent a sample as they requested for testing.

Good. What length did you send them, and what was the IR of it when you measured?

All this dont help me decide if I should strip all out. Tech above 1 meg should be fine so, do I pull it all out, rip walls replaster delay move in etc...... oh I don’t know.

Do I take it that is work for a customer, rather than for yourself (that's what I've been assuming - but maybe I'm wrong?)? If so, and if you haven't done so already, should you not start discussing the situation with the customer?

Kind Regards, John

 

[Harry Bloomfield]

Used about 5 reels in total, I have one and three quarters left over. Was a self build project so was bought over a year ago, maybe 1.5 and first fix was about 1 year ago. I will have to dig receipt out but I did not buy all reels at once I remember. But they are all same make they seem to have same labels etc.

TLC have been sent a sample as they requested for testing.

All this dont help me decide if I should strip all out. Tech above 1 meg should be fine so, do I pull it all out, rip walls replaster delay move in etc...... oh I don’t know.

I know if I was to test an existing install it would be a pass.

As you have confirmed the IR does rise when a voltage is applied from the Megger and it more than meets the regulations, then I would leave it in, power it up and hope. You could maybe do a retest further down the line, to see if the IR has settled or improved.

 

[wcavanagh]

This is for myself, thank god