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Topic Title: Discontinuous ring final - OR is it !?
Topic Summary: test results
Created On: 16 August 2012 04:07 PM
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 16 August 2012 04:07 PM
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psychicwarrior

Posts: 220
Joined: 18 October 2010

Hello everyone- any views on the test results in this scenario would be appreciated please. In relation to creating a 20A radial as a solution, briefly then:

Consider a Ring Final (32A 2.5/1.5 T&E) that has suffered abuse over time and appears to now be 'broken' at some point around it. Owner does not want carpets and flooring up, panels off etc if it can be helped.

Test 1 (end to end) at CU indicated >99.0 Ohms on all conductors indicating the ring was indeed discontinuous.
(my 17th meter posts its results this way)

However....

An IR test indicated a resistance of ~860 MOhms end to end on line conductor, ~760 MOhms Neutral and ~400 MOhms CPC.

Usually I would expect my meter to report >999 MOhms on a new circuit I had installed, so this had me puzzled as to the cause - made me think it wasn't discontinuous after all - but then again these are very high readings of course.

Then for interest, I released one leg from the the board, re-energised and tested for voltage across the released L-N. Meter showed 0.4v de-energised and 0.6v energised.

(Just as an aside, an IR test L-CPC on one leg gave a reading of only 2 MOhms, so the circuit isn't in the best shape to be fair - but still complies)

I am a bit of a worrier, but I conclude given best endeavours within the limits that the ring is effectively electrically discontinuous and therefore it is possible to make into a radial as such.

Do you concur, or am I jumping to conclusions - I think the end to end IR readings made me think as to why... I am puzzled or are these IR readings to be expected for one reason or another?

Minor works for a new de-rated prot.dev. and would you comment on the findings too for record should anything occur down the line?

Thanks for any help/comments on this one.
Chris

Edited: 16 August 2012 at 04:16 PM by psychicwarrior
 16 August 2012 04:36 PM
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AJJewsbury

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Sounds like you've done a pretty thorough job of showing that the two "legs" are independent of each other!

Were you thinking of creating one radial from them or two?

Things I'd check:

o Whether a 20A circuit will adequately supply the loads? (remember the regs require us to avoid small overloads of long duration as well as the more obvious tripping out nuisance).
o As the ring might not be broken in the dead centre (but could be 9/10th of the way round) - whether v.d. and Zs will still be adequate.

otherwise, sounds like a plan to me.
- Andy.
 16 August 2012 05:08 PM
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OMS

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o As the ring might not be broken in the dead centre (but could be 9/10th of the way round) - whether v.d. and Zs will still be adequate


You'll know that though, from finding the two sockets between which the break has occured. I guess the OP is actually going to disconnect the "outgoing" from those two sockets as otherwise you'll never know if there is just are live ends floating around under the floor - which gives rise to "can you run a new bit of cable between them"

regards

OMS

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Failure is always an option
 16 August 2012 05:42 PM
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Legh

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I've had this type of fault on a rfc where one leg ran through/across a chimney. needles to say that leg was disconnected and a new cable run between the sockets.

Start at one end of the ring and R1+R2 or Rn by adding each section as you go.

What you really want to find is that someone had either connected up the ring across a SFCU or DP switch leaving the cpcs disconnected or left one side disconnected at a socket outlet

What you don't want to find are multiple faults where it was left disconnected at a hidden JB, the cpcs disconnected elsewhere and some little rodent had cut it with a hammer and chisel in a past life.

Legh

-------------------------
Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 16 August 2012 06:11 PM
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daveparry1

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In a case like this I would power up one leg of the ring at a time and then go around doing a simple test, eg with the Martindale etc. to get an idea where the break is,

Dave.
 16 August 2012 09:08 PM
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psychicwarrior

Posts: 220
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thanks for the input - very much appreciated.

I have to be honest, i have traced some of the circuit to what i thought was the last socket on each leg and couldn't establish immediately any outgoing legs from these sockets that would be the continuation of the ring to the break as such - rather frustrated i was.

(btw it is marked up as a ring on a PIR issued for a rewire from not too long ago with associated test results that show it as ok - but no one seems to know whats happened in between to create this issue!)

I'm back there at some point as other work to do - other circuits are in a mess too - so i will have another look.

Its not easy this game some times - 1 2 3 ahhhhhh ;-)

Thanks again.
 16 August 2012 09:27 PM
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Phillron

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It seems to me as though the open circuits have not been located and that you are assuming that they will appear at the same position for each conductor
It would seem that the good legs of the ring need to be established to see where the continuity is lost for each,also to establish the points that have been made of how many on each leg ,Zs etc
 16 August 2012 09:29 PM
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Zs

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psychicwarrior, I use an easy adaptation of a continuity test for this kind of thing which might have some value on yours.

I have a plug with three little holes drilled through the top so that I can stick a probe in and touch against each of the terminals.

I disconnect one leg of the ring at the board, leave it off, and go round every socket plugging in the drilled plug to open it up, and with three flying leads connected (firmly) to the dangling leg at the board. It makes a reet mess of leads all around the customer's house and they get caught under doors and all sorts but what the hell. For SFCUs and the like, a touch of the CPC lead to both socket screws in turn helps with not having to unscrew, but you can't do the other two.

Effectively, I work dead and bell test each socket without having to unscrew it so it saves time.

That all sounds like plain sailing but sometimes a reading starts to go oingy boingy because of a diverted CPC or neutral usually, and I hope you haven't got one of those. You can actually do this with a bell but watch out bacause some of them like my steinel are too sensitive and can throw you off by ringing just because they can smell a connection. A proper meter will help you to map out the ring as you go.

Might help?

To answer your question; I'd be hesitant about just changing it to a radial without knowing where to disconnect the redundant leg just in case it is not broken in the same place. But IMO downgrading the breaker is a good call.

Zs
 16 August 2012 09:32 PM
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sparkingchip

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I have been know to use Dave's testing routine!

My next step would be to guess where the middle is and split it into two halves then test those as separate circuits, you may well find the breaks, if they are breaks, don't line up. But if there is a obvious disconnection of the circuit or it was never a ring in the first place then one end will be dead.

You could end up testing faults subsequently by halving each leg until you pin down the faults to locate them and resolve the issues.

Andy
 16 August 2012 09:47 PM
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Zs

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I used to do that Andy, then one rainy Sunday afternoon I went in the shed with the iPod, drilled three holes in a plug, messed around with it on the play-board and put it in a bag with three reels of singles and some lever type wago connectors..

Zs
 16 August 2012 10:14 PM
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sparkingchip

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I have the posh version of your kit:

http://www.screwfix.com/p/kewt...-socket-adaptor/31565

only mine has the NAPIT logo on it as I purchased it at the reception desk in NAPIT Towers (along with a NAPIT branded fleece, smart casual for the older man!)

Also:

http://www.screwfix.com/p/kewt...0mtl-test-leads/78937

And a Fluke voltage/ continuity tester, I like this set up because you can pull the probes off the Fluke and it all then plugs together, also being a voltage tester as well as a continuity tester it lights up to indicate there is a risk, unless of course both ends are connected to a voltage in which case it buzzes a continuity, so it is not fool proof.

Andy
 16 August 2012 10:16 PM
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psychicwarrior

Posts: 220
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@Phillron

I'm not assuming anything thank goodness :-) I didn't cover everything I have done in my OP. sorry.

@all

Thanks for the extra tips and testing mash-ups!
Its given me a few more ideas to consider.

It did occur to me that it might not have ever been a ring; that it was actually 2 radials incorrectly made into a ring perhaps - but the 'rewire PIR' i mentioned records a ring, so i best take it that it was originally.

Each of the separate legs I have to a socket point so far, tested out ok - but i will endeavour to persevere and take on the points mentioned to me.

The point I want to get to is to account for all the socket points etc and to verify they are all electrically sound as such - and to ensure at the 'last one(s)' there is no outgoing floating wire.

Thank you

Edited: 16 August 2012 at 10:25 PM by psychicwarrior
 17 August 2012 06:33 AM
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ebee

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That`s the thing about rings - such problems can sometimes produce a bit more head scratching than radials do.
But we are British and proud of our rings - they keep us ahead of Europe.

A complete clean 3 conductor break is easy to find either by separating the legs and powering up individually whilst testing each socket with a "three light thingy" or the dead test using Zs plug or one of the bought ones or the battery & bell/buzzer test.

Multiple breaks or breaks of different conductors at different locations can add to this joyous approach though.

All good clean fun and gives a sense of achievement once you solve/correct it.

Radials are for whimps - you never get such a sense of satisfaction

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 17 August 2012 09:45 AM
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psychicwarrior

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What doesn't help is when work is done to an installation that is not up to standard. Installations are usually fine (inc ring finals) if built and maintained by competent persons.

In this case, a supposed rewire was undertaken ~5 years ago and the owner maintains they thought they were getting a full rewire. A new consumer unit was definitely provided and yet the only paper work supplied for it all according to the owner was a PIR !

On the PIR it identifies this circuit as a ring, but what if it wasn't. I cant see why it would be recorded as one if it wasnt, but then why issue a PIR and leave some of the other circuits in a mess. It all leads to doubts etc.

Any way just supposing one ends up doing all these tests and end up with two apparently electrically sound legs that do not appear to be connected (by a broken piece of cable) but are terminated in a 32A breaker as a ring ? maybe something curious/obvious has been missed - maybe not - maybe someone left it like that but didnt mark it as a radial from when it stopped being a ring. maybe... arrghhh :-)

I can see why it is so frustrating to competent folks on here who come across shoddy work carried out on installations left at the expense of what I dont know in the long run.
 17 August 2012 10:38 AM
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OMS

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It may have been designed as a ring, but believe me thare a bloody thousands of them out there that aren't - the classic i guess you've yet to discover is the ring and the radial immersion circuit mixed up so you have the immersion and one leg of the ring in a 32A MCB and the other leg of the ring in the 20A MCB - then you hve the ends of GF and FF rings mixed up - the permutations are endless.

add to that the occasional landing socket that was disconnected when the bathroom and WC were knocked into one room - it goes on and one.

My advice - get a battery and an old freidland door bell - drill out a plug top, Zs stylee - split the circuit and start doing continuity tests - it's not difficult, it won't take long, it will give you some definite answers and I suspect you'll learn a lot from it.

we've all been there - the confusion kicks in because you can't actually see the bits of cable and that causes some sort of mental block - experience overcomes that.

Decide if you want to resolve the problem or not and then just go for it - the best advice I can give you is to stop thinking and start doing - stop focusing on the numbers coming out of your super duper test kit - start listening for the dulcet sound of a friedland screwed to the lid of a plastic lunch box with a battery inside it and sketch out what you are doing as you go along - you'll crack it in no time - from there you'll know if making whats left of the circuit into two radials is practicable (in terms of approx equal loads etc and limiting Zs) or is it easier just to sort ot the break(s)

Don't take the above the wrong way - I work in an industry where people like me can talk for bloody hours about theoretical problems in circuits and installations and never break into sweat or get the knees of the tweeds dusty. But I trained as a spark, and i still have just a trace of site dust under my nails - and believe me there is a time for talking, but when that's done you just have to crack on and solve it - and that needs a bit of simple application of the knowledge you have and needs you to open things up and look, see, smell and then do basic tests.

I went to help out a young lad starting out as a self employed spark recently (called in by his client actually, a friend of a friend of mine) - great woes, wailing and gnashing of teeth because there was a broken RFC - third socket in, and lo and behold the neutral on one leg was winking at me inside the socket box - installed by one of the god awful core twisters - overdone it as usual and it had snapped - ditto with the hot wire about 4 sockets further along - probable cause was the bloody paper hanger loosening and twisting around the sockets.

No one died, boyo was a bit red faced, but he learnt a good lesson and the client, being a reasonable sort of chap accepted that it was his problem anyway, regardless of the quote and paid for the lads extra half day on site - I got a good brew and half coated digestive biscuits - result all round

Good luck

Regards

OMS

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 17 August 2012 10:51 AM
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davezawadi

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There is a common assumption that two 2.5 cables into one CPD is a ring circuit! I have seen this on a number of duff PIRs and of course its a stupid mistake to make, and proves that no actual measurements were ever made. Just last week I was sent an EICR to examine which had another "mistake". Some bright spark had replaced a CU, but it was difficult (and too slow) for him to get under the floor to check the existing circuit. He wired two 2.5s to a SFSU, called it a ring, connected the existing wiring to the output and recorded the value for the "ring" bit on an EIC. Now this is really a radial circuit with parallel cables, but a subsequent EICR failed to test the circuit properly either, but it should have been obvious that something was not quite right when testing the EFLI at each of the alleged "ring" sockets, as none of the readings would have matched!

Now to the actual question. Measure the EFLI at each socket, and you will find the circuit topology quite quickly. You will have to do this as a dead test if the installation is TT, but one of the Socket&See test plugs on the ohm meter makes it quite quick. It is not a ring so must have two radial chains, and when you have all the readings and the physical locations of the sockets it is very likely that the closest two may have had an interconnection. A quick look in the back, and all may be revealed. As there could have been spurs on the original ring, the lack of other wires is not definitive but is a good guide. Also the readings at the end of the chains (the highest figures) will show if the radials are satisfactory as they stand.

-------------------------
David
CEng etc, don't ask, its a result not a question!
 17 August 2012 01:21 PM
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psychicwarrior

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thanks guys - the way i have written my [reply] posts does seem like i was dwelling on it rather than doing.
actually, i did, in my own way, do most of that mentioned here in the half day i was there initially but as i admitted to being a worrier (and i admit i do over think things - character flaw perhaps), i was wanting to review the scenario with you, some test results, alternative possibilities, mistakes in approach and perhaps sanity check myself in the face of the circumstances.

one never stops learning

thanks again for the input.

i am acutely aware now why some call for the discontinuation of using ring finals as when someone works on them that doesnt understand fully perhaps, it can end up in a pickle. RFC's do not phase me as an option to use and test, but once they get hacked over time the end results can be a bit tricky to suss on occasion.

regards
Chris

Edited: 17 August 2012 at 01:28 PM by psychicwarrior
 17 August 2012 09:00 PM
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Zs

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Originally posted by: psychicwarrior

(and i admit i do over think things - character flaw perhaps), regards

Chris


Never, ever a character flaw Chris.

If we all knew things but never thought about them then the world would be a boring place and it wouldn't move on. The questioning person is better to be around than he/she who just accepts everything as given.

'What if?' Perfect little words, on so many levels.

BTW....Did you get it sorted?

Good weekend Chaps, I'm logging off in favour of some hard work and well-earned play while the weather holds.

Zs
 18 August 2012 07:05 PM
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Dave69

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cant you just ask the customer if they have any sockets that are not working, they prob wont have as the ring is being fed both ways, so take one leg of the ring out of the CU and power the other leg up and check which sockets work, hopefully you should be able to work out what sort of order the sockets are wired in, so go to the last socket (turn the power off first unless you're brave and mad) disconnect the cables and then with the power on check which cable is live and which is dead, reconnect the live cable and then repeat the complete thing for the other leg. Hopefully when finished you will be left with 2 dead cables and it should be obvious where the those cables run.

it does seem strange that L-N and cpc are all broken and no ones knows anything about it, if a lovely little mouse or rat had had their teeth into it you may get one broken conductor or possibly two
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