Installation test results

[JohnW2]

When i wrote L-E & N-E those were the series measurements of L&N with CPC. I linked them out using a Wago221 in the backbox of the immersion isolator & measured at the ends in the CU.

That's what I assumed - thanks for confirming.

@JohnW2 - the end to end measurement of 1.65 Ohms i mentioned by way of reference on my final ring is the CPC vs ~ 0.45 Ohms for the live conductors. Again, i need to verify cable diameters, but if 2.5mm for line, and 1mm for CPC that's not too far out.

I'm not so sure about "not too far out". If your estimate of 20m is even remotely correct, the 2.5mm² live conductors should be about 0.18Ω and the CPC about 0.29Ω if 1.5mm² and about 0.44Ω if 1.0mm².

I've just ordered myself a R2 wander lead (they're expensive! had to resort to ebay to find one at a reasonable price) so i'll try your suggestion of measuring the end to end continuity of the cpc when that arrives.

As I said, that's obviously the definitive test. As for the cost of the 'long leads', I have one if these, which enables me to use a standard mains extension cable/drum on the rare occasions I need a long lead ...

I still need to do my Ze / Zs measurements, but from memory, I think Ze is about 0.35 Ohm - which would give a Zs of ~ 2 Ohmm and a PFC of ~ 115A. By my reckoning, a 16A MCB / RCBO with Type B curve should still trip instantly (Zs @ 2 Ohm < Max permissible Zs @ (230*.95)/(5*16) = 2.43 Ohm). It's not ideal and I'd still like to know why the reading is so high. One for the next time i power down.

As you say, the Zs is going to be 'low enough' for a B6. The concern would obviously be that if the resistance of the CPC is so much higher than it should be, this could indicate iffy connection(s) which might progressively (or, even, 'suddenly') become 'much worse.

Kind Regards, John

 

[Licklieder]

Well, I finally managed to carve out some more time when i can switch everything off and had a go at working out what was happening with my flying lead.
Long story short - i was testing the wrong CPC. Not quite sure how i was getting continuity before, but with the help of the flying lead i worked out that the CPC I thought i was testing as part of the immersion circuit was actually one leg of the ring main. I guess i was getting continuity via the earth bonding to my plumbing. Thought i had disconnected the bonding previously, but i guess i must have been wrong.

The continuity values this time make much more sense. IR values were as before :

L-N 0.13 Ohm
N-CPC 0.19 Ohm
L-CPC 0.20 Ohm.

One problem resolved. And on to the next...

 

[JohnW2]

... Long story short - i was testing the wrong CPC. Not quite sure how i was getting continuity before, but with the help of the flying lead i worked out that the CPC I thought i was testing as part of the immersion circuit was actually one leg of the ring main. I guess i was getting continuity via the earth bonding to my plumbing. Thought i had disconnected the bonding previously, but i guess i must have been wrong.

Fair enough - that all makes sense (and explains why your previous results were not 'as expected').

The continuity values this time make much more sense. IR values were as before :
L-N 0.13 Ohm .... N-CPC 0.19 Ohm ... L-CPC 0.20 Ohm. ..... One problem resolved. And on to the next...

As you say, much closer to 'expected' - and I'm glad you have now got it 'sorted' as they would say!

Kind Regards, John

 

[Licklieder]

And the next problem was my final ring.

Initial testing indicated a difference in L-L and N-N continuity (0.45Ohm vs 0.38 Ohm) that i wasn't happy with, and CPC continuity that again seemed way to high - though having resolved the earlier issue, i surmised this would change. I've managed to get the live conductor continuity to match - don't know which socket it was i took off, but they now match at 0.38 Ohm. CPC continuity has improved - last time i measured 1.65, this time it's 0.96 Ohm. Better but it still seems high, So I used my flying lead and measured continuity to CPC at each socket in turn :

Hall : 0.07
Lounge 1 : 0.12
Lounge 2 : 0.20
Lounge 3 : 0.29
Kitchen 1 : 0.36
Kitchen 2 : 0,48
Kitchen 3 : 0.51
Bed1 1 : 0.70
Bed2 2 : 0.72
Bed2 3 : 0.72
Bed2 4 : 0.85
Bed1 1 : 0.86
Bed1 2 : 0.94

Most of the progressions seem to make sense to me with the exception of kitchen3 to Bed 1 #1. I double checked a junction i had inserted in the ring when i split it, but that didnt' change the readings. I have a suspicion there's another inaccesible junction in my bathroom wall - there was a shaver point removed when i had it redone a few years back, but i have no chance of getting to that as all the walls have been tiled.

So it looks like it is what it is. I'll need to double check the wire size when i next power down, but the CPC is quite a bit smaller than the live conductors. if it's 1mm csa, then the figures actually look right - 0.94 is 2.5 times 0.38. Was it typical to use a 1mm cpc on a ring back in the late 60's if wiring in singles ?