Line -CPC Insulation resistance

[endecotp]

It’s strange that you’re seeing essentially the same thing on multiple circuits. Are the readings all very similar, as if you’re actually observing exactly the same fault, or do they differ a bit?

It would be odd for the sort of thing securespark describes to affect more than one or two.

I suggest you choose the simplest affected circuit (e.g. a cooker or shower) and disconnect at both ends, so you’ve just got the cable itself, and measure that.

Frankly I suspect you’ll look at it on Monday and you’ll have a “d’oh” moment as you spot an obvious mistake!!!

 

[bernardgreen]

It’s strange that you’re seeing essentially the same thing on multiple circuits.

One common factor is the meter, have you tested it on known resistances to verify it is working properly ?

 

[JohnW2]

One common factor is the meter, have you tested it on known resistances to verify it is working properly ?

Yes - but the meter is common to both the 'good' and the 'bad' IR measurements ...

....as I understand it, the OP is getting (presumably all with the same meter) readings of ~200MΩ for all circuits originating 'on one side' of the CU and ~0.2MΩ on all the circuits originating on 'the other side' of the CU.

Kind Regards, John

 

[securespark]

What do you mean by 'dead short', and do I take it that the pinhole penetrated the insulation of one of the conductors?

0.0X.

Yes, there was a short between NE.

 

[studentspark]

Frankly I suspect you’ll look at it on Monday and you’ll have a “d’oh” moment as you spot an obvious mistake!!!

I would be very pleased if it was a "d'oh'" moment, hence this post. Am I being stupid!!

But I don't think I am

 

[studentspark]

One common factor is the meter, have you tested it on known resistances to verify it is working properly ?

Yes on a socket and see calibration tester,

 

[JohnW2]

0.0X. ... Yes, there was a short between NE.

I 'm a bit lost. I really can't see how a 'pinhole' could result in a true 'dead short' between L and N in T+E (which I assume is what it was). Even if there were pinholes in absolutely identical places in the insulation of the N and E, that, in itself, would not enable the conductors to come into contact and, in T+E, any short between L and N has almost inevitably also got to involve the CPC. I'm rather puzzled

Kind Regards, John

 

[securespark]

It surprised me too. I Meggered the cable intact, then stripped it back to three individual conductors. There was a small breach of the insulation on the N. When I retested, the figure was clear.

 

[333rocky333]

Are the lives still in the breakers and your testing with them still in the on position

 

[JohnW2]

It surprised me too. I Meggered the cable intact, then stripped it back to three individual conductors. There was a small breach of the insulation on the N. When I retested, the figure was clear.

I can but assume that the cable must have got quite severely 'twisted' since, when the conductors are in their 'normal' relative positions, small deficiencies in insulation will not result in any of them coming into copper-to-copper contact. As one might expect, this rodent-attacked cable (which I suspect is probably far worse than your 'small breach of the insulation on the N') IRd fine, but had I 'severely twisted it', then two (or all three) of the conductors could well have come into copper-to-copper contact ...

Kind Regards, John

 

[John D v2.0]

Looks like fried mouse for dinner there!

I assume if the pin is still in the pin hole then it could give a decent short, although I'm not sure how many pinholes are actually made by pins nowadays.

 

[JohnW2]

Looks like fried mouse for dinner there!

One might think so, but there were no nearby corpses, even skeletal ones!

I assume if the pin is still in the pin hole then it could give a decent short, although I'm not sure how many pinholes are actually made by pins nowadays.

I'm sure you're right - but I also doubt that there was still a 'pin' in the 'pinhole' that secure reported!

Kind Regards, John