Ring Circuit R1+R2 readings

[Grant Naylor]

Still a relatively inexperienced so sorry if these seem obvious/dumb questions.

I wanted to spur a double socket next to an existing double socket in a bedroom in my own house on the first floor, sounded like a good idea!

EDIT: Isolated the circuit 1st!!

My first worry.

I loosen the socket face place and get my continuity tester. I place my continuity tester across live+neutral terminal screws and I get a voltage warning (no scale just a warning)? Plugged in my Metrel and it's reading 1V. Not really happy about this so I isolate the supply and everything seems OK back to 0V.

1st Question. Is this normal? I have isolated single circuits before and can't remember this happening. Continuity tester is proved to be working OK etc.

Anyway, all safe so I take off the socket face plate. The book Part P Dr (second Fix) suggests to check you have a ring before you begin. So I measure r1, rn and r2 at the socket.

r1 comes in at 0.36Ω
rn comes in at 0.36Ω

r2 comes in at 0.19Ω??? I was expecting 0.6Ω. The cpc is obviously not thicker than the live conductors nor is it the same size. It looks like 2.5/1.5mm T+E to me!

Re-took r1, rn and r2 and I got the same.

Put everything back and go to the consumer unit.

Find the ring circuit (cringe at finding the neutrals practically fall out of the terminal block!) and disconnect the ring to take r1, rn and r2.

r1 comes in at 0.35Ω
rn comes in at 0.36Ω

Hmm r2 comes in at 0.43Ω. Still lower than I what is expected.

Zs from the socket is 0.30Ω for a Type 2 32A MCB which is perfectly fine according to the OSG.

I noticed there is another socket a bit loose on the same ring and take that off to have another look. Find this has a spur already. No diagrams available etc (as normal).

With such a low r2 reading all I can assume is somewhere there is a parallel path? There is lot of suplementary bonding in my house. It was built around 20 years ago now. Anyone got any thoughts or things I should try to work out wth is going on?

Many thanks.

 

[telectrix]

it could possibly be your r1 and rn are a bit high due to a couple of poor connections in back of sockets. or could as you say be parallel paths.

 

[Grant Naylor]

it could possibly be your r1 and rn are a bit high due to a couple of poor connections in back of sockets. or could as you say be parallel paths.

Thanks, any thoughts on the warning I got after isolation? Should this making me nervous or is this normal?

 

[Blowcat]

getting a few volts is perfectly normal and nothing to worry about. It could be a simple back feed from the neutral or getting induced into the cable i would guess. Keep using your voltage tester and always remember to prove it before and after. I do a lot of testing and a good visual and checking of connections is essential.
r2 readings on ring circuits dont always add up to what you expect because of parallel earths and even the way they are connected in the socket especially if the T&E cpc are twisted together for a few inches.

 

[i=p/u]

r2 roughly 1.67 times the r1, rn and

 

[i=p/u]

how can you say high if you dont know length of circuit...just asking???? wise one.

it could possibly be your r1 and rn are a bit high due to a couple of poor connections in back of sockets. or could as you say be parallel paths.

 

[rob121]

how can you say high if you dont know length of circuit...just asking???? wise one.

I agree with Teletrix. If its not parrell paths and he has got the size of his conductors right, then I would be thinking the live conductors havent been terminated properly.

 

[Grant Naylor]

Thanks all for the replies.

I'm going to check all the sockets and map out a plan and see what I get. I was getting different readings across the sockets for Zs depending on which one I plugged it into. Always appears to be better on the right-hand side. They are Volex and again will be as old as the house.

Forgot to mention IR tests were 400+ MΩ across L/N and LN/E so at least that was OK.

 

[RexT]

Hi Grant,

I agree with telectrix. You could also check that your R2 is truely what you think it is. (I.E. a ring and nowhere else).
I have come across places where people have 'bonded' across circuits and to pipework. This would reduce the R2 reading and is a dodge used by some installers to reduce values or to path broken ring finals.
It could be worwhile you checking to see if you have got continuity from your CPCs tested off the main earthing terminal to that terminal.
This could show if there is a path to the MET which would normally not exist.
Dont forget you are dealing with low ohms values and as said above it could be down to poor terminations.
Best wishes
Rex

 

[Des 56]

If you have issues and concerns, then then do cross connections and measurement and not just these end to end readings

 

[Grant Naylor]

Yes see what you mean about the MET and the ring CPC's. Will certainly try that.

 

[Grant Naylor]

I measured

R1+RN = between 0.21Ω to 0.24Ω
R1+R2 = between 0.25Ω to 0.29Ω

However, this is all but 1 room which happens to be above the kitchen.

I remembered there are some sockets at almost ceiling height (I still need to check if they are on first floor ring ). I got higher than any other room in the bedroom above the kitchen with R1+R2 up to 0.65Ω at one of the sockets.

The Zs elsewhere were a MAX of 0.31Ω again all but in this room which were 0.51Ω. I also noticed the readings would change and the sockets seem very slack.

Getting there! Will investigate the sockets in the kitchen ceiling and look at replacing the sockets in this bedroom.

 

[laws]

sorry could you explain what you mean by parallel paths? thanks

 

[SirKit Breaker]

Still a relatively inexperienced so sorry if these seem obvious/dumb questions.

When will people with little or no experience get the message. THERE ARE NO OBVIOUS, DUMB, SILLY OR STUPID QUESTIONS, so stop apologising!
We all learn't, we all asked. If you dont ask you wont find out. Just because some of us have been doing this all our lives doesn't mean we assume everyone else has. Your questions are certainly not dumb, they are relevant to what you are doing and learning. The answers to me are fairly obvious, thats because i have more than 30 years experience, you haven't, so to you the answers will not be obvious. NEVER BE AFRAID TO ASK, AND NEVER APOLOGISE FOR DOING SO.

Cheers............Howard

 

[RexT]

Hi SirKit Breaker,

Yes its great to see someone say it and I think you are correct.
When I was in college it was 'the dumb question' that was asked but the person who had the courage to ask it was thanked as there were probably three or four others in the class who thought it but did not ask it.

Best wishes

Rex

 

[kenny james]

i was always the one that use to ask the dumb question!, everybody would laugh when we left college i would be thanked by those who laughed who would say thats what they wanted to ask but was too afraid of asking!!.

 

[Grant Naylor]

@laws

This is an additional path to earth that has been introduced into the circuit. This maybe due to bonding of extraneous-conductive parts; or another example I suppose would be SWA that introduces parallel paths due to the earthing of the steel wire in addition to the CPC within the wire.

Essentially with parallel paths the CSA of the CPC is increased so the resistance would be lower that expected.

 

[SPARTYKUS]

Still a relatively inexperienced so sorry if these seem obvious/dumb questions.

When will people with little or no experience get the message. THERE ARE NO OBVIOUS, DUMB, SILLY OR STUPID QUESTIONS, so stop apologising!
We all learn't, we all asked. If you dont ask you wont find out. Just because some of us have been doing this all our lives doesn't mean we assume everyone else has. Your questions are certainly not dumb, they are relevant to what you are doing and learning. The answers to me are fairly obvious, thats because i have more than 30 years experience, you haven't, so to you the answers will not be obvious. NEVER BE AFRAID TO ASK, AND NEVER APOLOGISE FOR DOING SO.

Cheers............Howard

Howard

best post I have read for weeks.

Fine fellow.

 

[Rivo]

Whilst we are on the subject of R1+R2 readings, if I set my Megger multifunction tester on to Loop test, and plug it in to a socket, this reading will be my Zs.

Do I still have to mess around removing CPCs and Lines at the DB to get the R1+R2 readings or can I just N/A it on the PIR?

 

[malcolmsanford]

Whilst we are on the subject of R1+R2 readings, if I set my Megger multifunction tester on to Loop test, and plug it in to a socket, this reading will be my Zs.

Do I still have to mess around removing CPCs and Lines at the DB to get the R1+R2 readings or can I just N/A it on the PIR?

You don't have to mark not doing the R1 + R2 as anything, as you can easily do a R2 test on a PIR, as really on a PIR confirming continuity of protective conductors and your Zs is fine.