2+ faults on ring final? suggestions please

[GarethH]

Indeed, that would seem to fit with what you've described. To be sure, you ought to find that one of those latter sockets (the last one in the line) will have only one cable going to it. The 'radial type lashup' would normally be described as an (unfused) spur - perfectly acceptable, safe and and compliant with regs if it supplied only one socket (which clearly in not the case!)

I've checked the sockets in question and they have two wires going to them so I can't find the end of the unfused spur.

I'd hazard a guess that the builder thought he had extended the ring (hence he ran two new cables from the same room to the extension) but got it wrong. Maybe there's JB under the floor in bedroom 2 somewhere and the actual topology is two rings connected by a spur; dumbell shape if you like, who knows. That would at least explain why the affected sockets have two cables each though. I'll know for sure once I have physical access and will keep the circuit de-energised until then.

I don't want to fuse down and I agree that the easiest way would be to rectify the situation is as you said; establish the path of the cables though the affected sockets, break the existing ring, incorporate the affected sockets spur into the ring and then test for continuity, bridges, IR etc.

The radial circuit idea had crossed my mind too as for a few reasons -
o After this experience, I'm not a big fan of RF circuits
o I don't like the fact that the whole house except the kitchen is on one ring and the area total area served by the ring may well be approaching the limit.
o I'm in a pretty rare position to conduct improvement or remedial works with minimal disruption - some carpets already gone etc.
o There is sufficient access to cables to split the house ring into three radials of approximately equal size (# of sockets). The diagram doesn't show the whole story as all downstairs sockets are run via vertical drops from the upstairs ones.
o If the circuits were split into three radials in this manner then I don't think the 20A per-circuit limit would be a problem due to the likely nature of the loads on the circuits.

The CU would benefit from replacement (no RCD protection) and has no spare slots so I can't add a circuit - which I believe would be notifiable work anyway - without replacing the CU, which I'm sure would be notifiable(!). I'm considering having this done for the reasons stated - it seems to make sense and would probably be cheaper and be less hassle to do now.

Now I've found this issue, and having previously found and rectified another which was quite serious (no main equipotential bonding to the gas pipe), I think the whole installation could do with a check-up anyway.

I'm not sure if my electrician mate is a member of a self-certification scheme so, even if we conducted the CU replacement and testing together, I'm not sure that he could sign it off (not really sure how the legislation works in this regard). I'll have a chat with him about the options when he's here. I'd be nice to keep the costs down while still doing a proper job of course.

 

[JohnW2]

I've checked the sockets in question and they have two wires going to them so I can't find the end of the unfused spur. ... I'd hazard a guess that the builder thought he had extended the ring (hence he ran two new cables from the same room to the extension) but got it wrong. Maybe there's JB under the floor in bedroom 2 somewhere and the actual topology is two rings connected by a spur; dumbell shape if you like, who knows.

... even more fun to investigate, then! With a 'dumbbell', only if you interrupted the spur between the two rings (the middle bit of the dumbbell) would all the 'red' sockets stop working and would you find no continuity between the two cables at a 'red' socket'.If you interrupted the 'second ring' itself anywhere, you would get continuity (through the second ring) and all sockets would continue working. Does that correspond with what you experienced?

The radial circuit idea had crossed my mind too as for a few reasons -
o After this experience, I'm not a big fan of RF circuits
o I don't like the fact that the whole house except the kitchen is on one ring and the area total area served by the ring may well be approaching the limit.
o I'm in a pretty rare position to conduct improvement or remedial works with minimal disruption - some carpets already gone etc.
o There is sufficient access to cables to split the house ring into three radials of approximately equal size (# of sockets). The diagram doesn't show the whole story as all downstairs sockets are run via vertical drops from the upstairs ones.
o If the circuits were split into three radials in this manner then I don't think the 20A per-circuit limit would be a problem due to the likely nature of the loads on the circuits.

Ring finals are a strange concept, pretty unique to the UK and related countries, and an increasing number of people are favouring radials - which is what most countries have. It's certainly something to discuss with your electrician. Just one ring for the whole house (other than kitchen) is probably not ideal.

IThe CU would benefit from replacement (no RCD protection) and has no spare slots so I can't add a circuit - which I believe would be notifiable work anyway - without replacing the CU, which I'm sure would be notifiable(!). I'm considering having this done for the reasons stated - it seems to make sense and would probably be cheaper and be less hassle to do now.

I think you should seriously consider that. As you say, 'new circuits' (as well as CU changes!) are notifiable. Also bear in mind that any 'new sockets', or any new cables buried <50mm deep (i.e. virtually all of them!) in walls must have RCD protection. A new CU, with two RCDs and enough capacity for as many circuits as you would like may well be the most sensible way to go now.

I'm not sure if my electrician mate is a member of a self-certification scheme so, even if we conducted the CU replacement and testing together, I'm not sure that he could sign it off (not really sure how the legislation works in this regard). I'll have a chat with him about the options when he's here. I'd be nice to keep the costs down while still doing a proper job of course.

Even if he's not a member of the self-certification scheme, he can undertake all the testing and (if he has been involved with all the work) issue an Electrical Installation Certificate. If, as seems likely, notifiable work is involved, if he cannot self-certify, then you will obviously have to notify in the usual way, but the LABC will probably accept his test results and may well decide that little/no inspection is called for. With some LAs, that results in appreciably lower notification fees. If you are going to have to notify, it is certainly worthwhile getting all the notifiable work done 'in one go' - since the notification fees are 'per go'!!

Kind Regards, John

 

[GarethH]

... even more fun to investigate, then! With a 'dumbbell', only if you interrupted the spur between the two rings (the middle bit of the dumbbell) would all the 'red' sockets stop working and would you find no continuity between the two cables at a 'red' socket'.If you interrupted the 'second ring' itself anywhere, you would get continuity (through the second ring) and all sockets would continue working. Does that correspond with what you experienced?

A minor breakthrough perhaps. I've found a 'red' socket that has a single cable to it. So, it seems this may be the end of the unfused spur.

The dumbbell idea seems unlikely now and was only a theory - an attempt to explain where the end of the unfused spur might be to in a manner that fitted all of my observations at the time. This socket is downstairs and is fed from the problem room which is directly above. So obvious in hindsight!

I can't get a second cable back to this socket easily so it would make sense to have it as a single-socket unfused spur off the ring if indeed I do retain the ring. This would certainly involve lifting the carpet and floorboards in the room above.

If I was to get the CU replaced and the ring replaced with several radials, I think there may already be sufficient access to cables without having to lift any additional carpets and floorboards. That would be quite a bonus.

In either case, sufficient testing in order to ascertain the actual topology and confirm this socket is the end of the unfused spur seems to be the next step.

 

[JohnW2]

A minor breakthrough perhaps. I've found a 'red' socket that has a single cable to it. So, it seems this may be the end of the unfused spur.

Aha! There really aren't many other possibilities. With only one cable, it must be 'the end' of something - either a true radial (clearly not in your case) or a spur from a ring.

I can't get a second cable back to this socket easily so it would make sense to have it as a single-socket unfused spur off the ring if indeed I do retain the ring.

Yes, maybe.

If I was to get the CU replaced and the ring replaced with several radials, I think there may already be sufficient access to cables without having to lift any additional carpets and floorboards. That would be quite a bonus.

Indeed.

In either case, sufficient testing in order to ascertain the actual topology and confirm this socket is the end of the unfused spur seems to be the next step.

Indeed. As I'm sure I've said several times, fully ascertaining that topology has got to be the starting point, no matter what approach you end up taking! Let us know what emerges!

Kind Regards, John

 

[GarethH]

Indeed. As I'm sure I've said several times, fully ascertaining that topology has got to be the starting point, no matter what approach you end up taking! Let us know what emerges!

What I should have said is that I had some more work to do - I'm in absolute agreement with you on the need for a systematic approach and I'm grateful for your help!

Over the last couple of days:

I've re-checked all other sockets in the house and this is the only socket which could be the end of that spur.

I've looked at all the FCUs and none of these could be another end as none of them are "on" the spur. I can't find any other accessories that may be attached to the circuit.

I identified a socket which I believe to be immediately before the end socket and separated the wires there. Continuity testing showed that all of the other spur sockets retained continuity with each other but there was no continuity between the spur and the last socket. The physical locations of these sockets also suggests they could be immediate neighbours.

One thing bothers me now: while it seems certain that these sockets are directly-connected, all the tests I've done are negative tests - i.e. they would tell me if this wasn't the case but don't tell me for certain that those sockets are directly connected.

Without physical inspection, is there a more positive test or is the absence of any contradictory evidence after an exhaustive search sufficient?

 

[JohnW2]

I identified a socket which I believe to be immediately before the end socket and separated the wires there. Continuity testing showed that all of the other spur sockets retained continuity with each other but there was no continuity between the spur and the last socket. ... One thing bothers me now: while it seems certain that these sockets are directly-connected, all the tests I've done are negative tests - i.e. they would tell me if this wasn't the case but don't tell me for certain that those sockets are directly connected.

I'm not sure I completely understand. If you have established that all the sockets have continuity with one another, in what sense are you concerned that you are not certain that they are directly connected? Are you simply saying that you do not get know which socket is connected to which? If that's your concern, I suppose you could disconnect all the sockets and cables, and spend a happy hour with a long wire doing continuity tests to work out which are the two ends of each cable!

Kind Regards, John

 

[GarethH]

I don't think I explained myself very well. By directly-connected, I meant sockets which are immediately next to each other on the spur (i.e. there are no other sockets in-between).

To incorporate the end socket into the ring on a guaranteed single-socket spur I'd need to identify the socket / accessory that feeds it and be sure there's nothing else in-between.

I believe I have located the piece of cable that feeds the end socket from the penultimate one and have disconnected this cable from the spur during testing. Continuity testing confirms this; after disconnection, there is no continuity between this cable and every other accessory I can find on the circuit - all looks good.

However, there is still the possibility that there is some accessory I cannot find - despite checking thoroughly - could be connected to this cable with a hidden joint. I know that there are quite a few JBs under the floorboards for example which could feed a hidden accessory and this is my only remaining doubt.

I can't think of a testing method (besides maybe resistance?) that proves there are no junctions present on the last stretch of cable so it seems that I can only infer the cable is contiguous rather than absolutely proving it.

Unless such a test exists, it seems I must make assumption and I wanted a "sanity check" that this is a reasonable assumption.

 

[JohnW2]

I can't think of a testing method (besides maybe resistance?) that proves there are no junctions present on the last stretch of cable so it seems that I can only infer the cable is contiguous rather than absolutely proving it. ... Unless such a test exists, it seems I must make assumption and I wanted a "sanity check" that this is a reasonable assumption.

No, I don't think there is any electrical test which could tell you if there were a JB or accessory in the course of a path you had identified - unless, of course, there was some load connected to the JB/accessory (in which case there would be a measurable L-N resistance). Short of ripping up all the floors and walls until you can see every inch of every cable, you're probably just going to 'make that reasonable assumption'!

Kind Regards, John

 

[plugwash]

I can't think of a testing method (besides maybe resistance?) that proves there are no junctions present on the last stretch of cable so it seems that I can only infer the cable is contiguous rather than absolutely proving it. ... Unless such a test exists, it seems I must make assumption and I wanted a "sanity check" that this is a reasonable assumption.

No, I don't think there is any electrical test which could tell you if there were a JB or accessory in the course of a path you had identified

Certainly nothing you could do with an ordinary electricians toolkit.

For academic interest:

TDR might work but it would depend on how the size of the discontinunities compared to the frequency range of the cable. You could probablly spot a branch cable that way but an accessory would be much harder to spot.

 

[GarethH]

Thanks guys - I suspected as much but you never know what tricks other people may have thought of.

I have some interesting electronic test kit but no TDR unfortunately,

 

[JohnW2]

For academic interest: TDR might work but it would depend on how the size of the discontinunities compared to the frequency range of the cable. You could probablly spot a branch cable that way but an accessory would be much harder to spot.

I have to say that the last two or three times I've had BT guys out to deal with telephone wiring/network faults, they have been totally misled by their technology into time-consuming wild goose chases for faults in locations far from where the faults actually turned out be.

Kind Regards, John