Ring Continuity Readings

[ukants]

Does anybody know when 2.5mm flat pvc/pvc t&e started to have 1.5mm cpc rather than 1.00mm? Just checking continuity on the circuits of my house and noticed that the cpc for the socket rings seems to be 1.00mm. The very small upstairs ring is 25m at most with 3 sockets, but with spur (via 13a FCU) going into attic/bedroom with another 3 sockets (another 10-15m).
The readings are:
r1: 0.14
rn: 0.14
r2: 0.50

Even if the cpc is 1.00mm csa, the reading seems way too big at about 3.5 times the phase readings.
I'm now going to check the connections at each outlet, re-test, and if no improvement, start splitting the ring to detect any fault.
Is this the right way to go about it?

Your thoughts would be appreciated.

 

[Adam_151]

~ '81

 

[ukants]

Thanks Adam,
any thoughts on the readings?

 

[Adam_151]

I think you're right, there is a bad connection somewhere

(sorry, was on the phone trying to get through to a supplier who didn't think it was worth answering it when I was posting)

 

[ukants]

Thanks for that Adam

Wasn't meaning to be pushy. I know what you mean about suppliers !!

 

[ukants]

Just found a very dodgy junction box I need to investigate, so I'll just have to turn everything off for a while. Will let u know the outcome.

 

[securespark]

What are the loops?

 

[sparkybird]

Just as a point of interest how many other people would investigate this as a fault?

You have proved continuity and it's a low reading so doubt the loops will be too high and I would say that you could end up causing more problems by disturbing connections than you end up solving. Not to mention damage to walls etc. Or am I a lazy b****er??

SB

 

[plugwash]

Or am I a lazy b****er??

the readings are suggestive of a fault somewhere. Doesn't that mean that they should be investigated?

 

[ukants]

Hiya folks,

The highest Zs from all the sockets is 0.48 ohms (which is, quite rightly, the last socket on the spur in the attic). By my calculations max loop for a B32 mcb protected circuit, taking into account the three-quarter rule, is approx 1.12 ohm, so I’m happy with that. Have I missed something?

Update: just re-tested the R2 without the b****y croc clips and got a much less worrying 0.36 ohms !!

As an aside, all the upstairs sockets (first floor, not attic) only have two cables coming into them. I expected one of them to have three, to account for the spur leading to the attic. I can think of two scenarios:
1. One of the first floor sockets is actually already a spur with the other cable being the attic spur…or
2. There is a joint box somewhere which I cannot find yet, which accounts for the spur, and the first floor sockets are a true ring.
The R1+Rn reads seems about right:
R1=0.14
Rn=0.14
R1+R2=0.28
Sockets ranged between 0.05 - 0.07 (appox ¼ of R1+Rn), so that seems ok.
And …
R1+R2 (0.14+0.36)= 0.5
Sockets ranged between 0.12-0.13 (approx ¼ of R1+R2), so all good there as well.

So….I’m thinking I’ve got 1.00mm cpcs and probably a hidden joint box somewhere!!

 

[securespark]

1. One of the first floor sockets is actually already a spur with the other cable being the attic spur…

But then wouldn't one of the FF sockets still have 3 cables in?

 

[sparkybird]

Plug - well, maybe? But continuity has been proved, so what we have is a slightly loose connection as the circuit is old or, as the OP subsequently found out - dodgy croc clips.

If this was a new circuit I'd just run, I would be more concerned, but I guess if I found this in PIR, I'd note it to keep an eye on, not suggest the whole circuit be dismantled to find it.

Any other views?

 

[ukants]

But then wouldn't one of the FF sockets still have 3 cables in?

Of course it would. Just testing . It's been a long day!!