Low Resistance on IR Testing

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.

I here you, not sure how building inspection will like the Cert with them figures on.
 
Sponsored Links
This is for myself, thank god
Oh, that makes it rather different from what I was envisaging. In that case, I'm with Harry ... if it were me I would accept the situation and 'live with it' (with periodic testing along the way). As Harry has also said, as far as bureaucracy is concerned, "if it passes, it passes", so I don't really think that the BC people could really (successfully!) make an issue of it.

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
I realise that we are all frantically trying to think of 'other explanations', but give that essentially the same IR results have been obtained on several installed circuits and on various unused bits of the (same) cable, I think that it really defies credibility that any explanation such as you suggest could apply similarly in all those cases, doesn't it?

Kind Regards, John
 
Sponsored Links
Whilst the megger may be 'happy' to read >999 on an open end, there is the possibility that it has a problem providing an accurate reading under 'load'. Have I missed reading the response stating it has had it's calibration checked.
 
Have I missed reading the response stating it has had it's calibration checked.
We were told that it was 'last checked' about 2 years ago.
Whilst the megger may be 'happy' to read >999 on an open end, there is the possibility that it has a problem providing an accurate reading under 'load'.
It should, of course, not be significantly 'loaded' by a cable that is connected to nothing. Perhaps more to the point, my understanding is that the same meter gives a >999 MΩ reading on at least one in-situ circuit that was wired with different cable.

Kind Regards, John
 
I agree but there must be 'some load' to develop resistance measurement, even if only a few μA (100MΩ at 250V = 2.5μA)
If there's the possibility of damp being the problem, the cables could be 'dried out' by passing a suitable 'high' current at low voltage through to a L-N shortened far end
 
I agree but there must be 'some load' to develop resistance measurement, even if only a few μA (100MΩ at 250V = 2.5μA)
True, but isn't that a circular argument? If there were "a few μA flowing" (anything more than, say, 0.25 μA at 250 - i.e. 1000 MΩ), and having some effect, that would surely mean that there was something wrong with the cable.
If there's the possibility of damp being the problem, the cables could be 'dried out' by passing a suitable 'high' current at low voltage through to a L-N shortened far end
IF dampness was having any effect on the insulation of the cores, there would have to be something fundamentally wrong with that insulation - remember the reference to my ongoing experiment in which T+E (and, I forgot to mention, also removed L&N cores of T+E, as well as 'alarm cable) have been permanently submerged in brine for 6-7 years and still show an IR >1000 MΩ at 1000 V.

As I said before, the only real way in which dampness/moisture could affect 'OK cable' would be at the ends, where the conductors had been exposed - hence my mention of hair dryers. However, it's all but inconceivable that the same 'dampness issue' would similarly affect several different lengths of cable - some installed and others still on drums, isn't it?

Kind Regards, John
 
Hmmmm - this again! What's the problem this time, I wonder? I think this software probably needs some taming! ...

upload_2019-2-15_23-31-50.png
 
Have I missed your answer to the "what was the IR of your sample?" question?
 
Have I missed your answer to the "what was the IR of your sample?" question?
No, you haven't missed it - and I would certainly be interested to know the answer to that question of mine.

Hopefully it was low enough for TLC/manufacturers to accept that there is a problem!

Kind Regards, John
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top