Old ring circuit, high readings at cross-over tests steps 2 & 3

[Technician]

Following on from PK's high r1 but r1+r2 low thread,

http://www.talk.electricianforum.co.uk/question-answer-board/18307-electrical-installation-condition-report-r1-very-high-but-r1-r2-low.html#post245793

I was looking at a ring final circuit over the holiday week that has been in service

some 35 years. It is one of those where about half the sockets are spurs

and no tests were done when the board was changed in 2005. Some of the

reads are high at steps 2 and 3 in the sequence and Ze is no more than 0.2 Ohm.

When looking at it I found that there are no kitchen loads. That has its own ring.

In conclusion I thought the best thing to do was change the breaker from a B32

to a B20 or a B16 to give a higher allowable value of Zs. It only supplies light loads.

Do you guys have any other ideas? The thought of direct intervention to place

the sockets on spurs into the ring fills the householder with dread.

All else is OK with it.

 

[Zeespark]

Tech, what is your earthing arrangement at this place that you were at?

AndyGuinness

 

[Technician]

TN-S. Zee. Ze in this area is between 0.15 and 0.2 ohm.

 

[Zeespark]

TN-S is a max of 0.8ohms Tech, so I don't see an issue, I could be wrong though.

AndyGuinness

 

[steptoe]

what Zs are you getting that requires a downsize of the OCPD

 

[Theorysparky]

or is it the multiple sockets on a spur that is causing the issue ????

 

[Technician]

There are no multiple sockets so far as I can tell, but the

next stage is a visual. There was one defective socket

which I picked up on step 3 but the circuit reads plus Ze

when compared with the values of Zs max gave me cause

for concern. Could be that I am worrying over nothing, but

I do like to have my ducks in a row.

I left my record book behind so I cannot get to the reads yet.

I take your point though, Zee, about the maximum value.

 

[Sidewinder]

Post the measurements you got as you worked through each stage of the testing would help us give you a better idea?

 

[batty]

35 year old sockets may be a bit worn are they original.

 

[Electroglow]

The ir reading sometimes are a lot lower because of old and warm sockets. What were the ir reading?

 

[SPECIAL LOCATION]

Post the measurements you got as you worked through each stage of the testing would help us give you a better idea?

Agreed..

though he did say...

I left my record book behind so I cannot get to the reads yet

. :Salute :^O

 

[Technician]

Yes; will do; they are instructive.

 

[Doc Hudson]

This group of posts have been moved from PKBristol's r1 high / r1+r2 low thread. http://www.talk.electricianforum.co.uk/question-answer-board/18307-electrical-installation-condition-report-r1-very-high-but-r1-r2-low.html#post245793 As they appear to becoming a topic in their own right that could get quite a bit more in depth and PK was still due to post further results back on his own thread later. On post #27 31/12/11 he did say "i'll post results. Should be interesting. Thanks. Paul." It could get a bit messy if we have two lots of further results coming back on the same thread.

Doc H.

 

[Technician]

Old ring main, possibly 1970

 

[ProDave]

and I suspect That these will have to be spurs from spurs and therefore single sockets,

again, dependent upon results of test to be completed.

You can't just spur on spur and get away with it by only using single sockets.

If you MUST spur on spur, then the spur needs protecting at it's origin by say a FCU with a 13A fuse in it.

 

[Technician]

:SaluteThat is accepted Pro Dave, I ommitted to state that.

 

[Technician]

Just finished yesterday doing the live Zs reads for this

ring final;

I had a highest read of 1.15ohm at one socket and after

visuals and checks I screwed down the terminations at

the backs of the sockets. On one I had two clear turns

on one screw. No surprises there.

This had the effect of briging down live Zs at furthest

point to less than half of 1.15ohm, in fact a lot less.

I have done a few of these up to now but I had not seen

quite as bad on first tests.

Full test results to follow with PFC's and all, plus have

confirmed where the spurs are and that the worst suspect

sockets were actually on the ring, so if he wants to have

extra sockets that will not be a problem.

The other side of the same coin is that I can leave the

existing circuit breaker in without changing it.

I think, in concluding, it supports the argument for a 10

year recommended periodic in non-rented domestics.

 

[Electroglow]

What were your continuity results after u tightened the terminals up?

When ever I have a high reading I always take the skt of and 9 time out of ten its a loose connection

 

[Technician]

Electroglow, I had two reads that concerned me, one at 1.15ohm

which is the max according to the OSG for that circuit breaker.

I had 0.43ohm after doing the terminals up, as I said, on that socket

one was a two turn move and I had similar results on the others.

Hardly surprising after 35 years.