As we seem to be in the mood to endlessly debate this now-fixed case, lets move on to the issues with the case of (A) and why it would not be acceptable.
As for the OP's initial discovery there is nothing intrinsically wrong with (A) that presents an operational safety hazard here (assuming all cables are rated OK for ring final use, blah, blah) but it would be a problem for testing or future work as it is so unconventional and unexpected.
So how would it be coded any why?
The answer is probably heading towards the answer for (B), save for the "how many cables can my MCB take?" question.
Discuss
I would code situation (A) as a C2.
My reasoning...
(i) it's not a ring
(ii) it could be difficult (depending on cable lengths) to establish it exists
(iii) it could be difficult (depending on cable lengths) to establish there isn't a break in the interconnect
(iv) if we can't be certain it exists and we can't be certain it's continuous, we cannot be certain the cable won't be overloaded under normal use
(v) because we cannot be certain it's continuous it's feasible we may not test the entire circuit during IR testing
And that's the crux of it. It's mostly about our inability to properly test it and thus our inability to be certain it's safe.
My reasoning...
(i) it's not a ring
(ii) it could be difficult (depending on cable lengths) to establish it exists
(iii) it could be difficult (depending on cable lengths) to establish there isn't a break in the interconnect
(iv) if we can't be certain it exists and we can't be certain it's continuous, we cannot be certain the cable won't be overloaded under normal use
(v) because we cannot be certain it's continuous it's feasible we may not test the entire circuit during IR testing
And that's the crux of it. It's mostly about our inability to properly test it and thus our inability to be certain it's safe.
Excellent thread! Ordinarily by post #122 I'd have a long list in my mind of various points not yet addressed or imperfectly answered and still apparently worth tackling. Here, there's little I can add.
Although, one point that I can't recall being drawn attention to explicitly is to limit the scrutiny of the bow-tie circuit to the cable configuration. Consider a normal ring that is fully compliant in every way, that is rewired into a bow-tie. The only thing that has changed is the wiring layout; the number of points, total load, the area served and subdivision of the load into separate circuits have not changed. Comparing these two situations is the heart of the matter.
Clearly, if a situation requires two separate circuits or >32A, and yet is served by one 32A bow-tie circuit, it's inadequate, but a conventional single ring would be inadequate in the same way. This does potentially apply in the OP's scenario because there is evidence that the installation was originally two circuits totalling 64A OCPD, therefore it is likely that the present bow-tie is inadequate for reasons other than the way it's connected. Such problems could be equally important for both safety and compliance reasons, but they are not about bow-ties specifically.
The same is true for four conductors in a terminal - it could be a risk but it's not specific to bow-ties. One could imagine three conductors being securely clamped in a trefoil, and the fourth one not receiving its share of the force. Or, all four initially being clamped but not lying snugly side by side, so that thermal movement causes them to give into a slacker configuration. (I was pulled up by an NIC inspector for having put three cables into an MCB terminal!)
I agree that in operation, specifically, if the same points connected in a ring would be both safe and compliant, then the bow-tie will be equally safe or more so, due to the likely lower fault loop impedances at some points. However, during maintenance and testing I agree that it is a potential trap for the unwary that could reasonably be expected to result in confusion or incorrect methods being applied. It is a circuit layout that is not explicitly defined, cannot be simply tested by the method that is defined for RFCs, and does not compensate for these abnormalities by a significantly improved level of safety in some other way. That would make it a C3 IMHO.
Although, one point that I can't recall being drawn attention to explicitly is to limit the scrutiny of the bow-tie circuit to the cable configuration. Consider a normal ring that is fully compliant in every way, that is rewired into a bow-tie. The only thing that has changed is the wiring layout; the number of points, total load, the area served and subdivision of the load into separate circuits have not changed. Comparing these two situations is the heart of the matter.
Clearly, if a situation requires two separate circuits or >32A, and yet is served by one 32A bow-tie circuit, it's inadequate, but a conventional single ring would be inadequate in the same way. This does potentially apply in the OP's scenario because there is evidence that the installation was originally two circuits totalling 64A OCPD, therefore it is likely that the present bow-tie is inadequate for reasons other than the way it's connected. Such problems could be equally important for both safety and compliance reasons, but they are not about bow-ties specifically.
The same is true for four conductors in a terminal - it could be a risk but it's not specific to bow-ties. One could imagine three conductors being securely clamped in a trefoil, and the fourth one not receiving its share of the force. Or, all four initially being clamped but not lying snugly side by side, so that thermal movement causes them to give into a slacker configuration. (I was pulled up by an NIC inspector for having put three cables into an MCB terminal!)
I agree that in operation, specifically, if the same points connected in a ring would be both safe and compliant, then the bow-tie will be equally safe or more so, due to the likely lower fault loop impedances at some points. However, during maintenance and testing I agree that it is a potential trap for the unwary that could reasonably be expected to result in confusion or incorrect methods being applied. It is a circuit layout that is not explicitly defined, cannot be simply tested by the method that is defined for RFCs, and does not compensate for these abnormalities by a significantly improved level of safety in some other way. That would make it a C3 IMHO.
Glad to see I’m gaining some traction with the introduction of the new “bow-tie” circuits (oops, should say circuit as protected by one OCPD) Look out 20th edition !!!
There was another thread that brought up the "lollipop circuit" where something like an unused cooker feed has a kitchen ring final circuit added to it, and my issues with that were not the concept (as a garage CU with ring is much the same) but this issue of testability and documentation (or the likely lack of) to determine its existence and to have access to the ring ends for testing.
Now to me this is serious issue so I can understand @SparkyChick grading it as a C2 but equally it is not explicitly against any regulation that springs to mind (beyond good workmanship) and it is not "potentially dangerous" in the strict sense so it could easily be coded C3 as a result.
In software engineering there is something known as the "principle of least astonishment" which has it that anything behaving in an unexpected or unconventional manner is bad practice. We really need something equivalent in the wiring regulations:
Principle of least astonishment - Wikipedia
I think what this thread has thrown up is there really ought to be some regulation to cover issues of unconventional arrangements, inadequate documentation, or insufficienct access to cicuits junctions that present an issues for unexpected behaviour or inadequate fault coverage when testing.
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I can’t remember who said what now, but this is my opinion.
It is 2 circuits in one OCPD.
It has been designed, from the start, as 2 circuits in 2 separate OCPDs.... why they have ended up together is anyone’s guess... (although the spare way and a damaged mcb suggests it’s been a temp repair)
It should have been sorted properly soon after with a new breaker, but sometimes it’s difficult to get parts for older boards
Dangerous? No...
Against regs? Yes... for the reasons given in previous posts.
We are (mostly) all professionals here giving our take on a situation. We KNOW it shouldn’t be done like that, and it sets off alarm bells thinking what else could be wrong here.
Let’s agree to disagree in this situation and hope the OP takes the advice of getting someone to reinstate the missing breaker, and test the 2 circuits to prove there is indeed 2 rfc’s and no interconnection between the 2.
Apart from maybe the odd nuisance trip, I think this is not “emergency” work and can wait until after lockdown.
It is 2 circuits in one OCPD.
It has been designed, from the start, as 2 circuits in 2 separate OCPDs.... why they have ended up together is anyone’s guess... (although the spare way and a damaged mcb suggests it’s been a temp repair)
It should have been sorted properly soon after with a new breaker, but sometimes it’s difficult to get parts for older boards
Dangerous? No...
Against regs? Yes... for the reasons given in previous posts.
We are (mostly) all professionals here giving our take on a situation. We KNOW it shouldn’t be done like that, and it sets off alarm bells thinking what else could be wrong here.
Let’s agree to disagree in this situation and hope the OP takes the advice of getting someone to reinstate the missing breaker, and test the 2 circuits to prove there is indeed 2 rfc’s and no interconnection between the 2.
Apart from maybe the odd nuisance trip, I think this is not “emergency” work and can wait until after lockdown.
So called lollipop circuits were common in schools whereby a radial or to complicate matters a pair of 2.5s were taken to a 45A switch where the ring final to the socket outlets was connected from, teacher had overall control of having them on or off. This practice seems to have stopped probably due to increased use of additional rcd protection.
I would expect schools or industrial places to have things documented though, with homes you really expect to find only the few "standard circuits" which is the issue!
What is interesting is pretty much everyone is unanimous these unconventional arrangements are a bad thing, but pinning it down to a specific test / regulation is proving harder. A bit like the "I know it when I see it" test from USA obscenity law
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Interestingly the Best Practice Guide #4 has this C2 coding example:
What is interesting is pretty much everyone is unanimous these unconventional arrangements are a bad thing, but pinning it down to a specific test / regulation is proving harder. A bit like the "I know it when I see it" test from USA obscenity law
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Interestingly the Best Practice Guide #4 has this C2 coding example:
- A ring final circuit cross-connected with another circuit (including live and circuit protective conductors)
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Testing this actually isn't as bad as it might first appear.... you can break into a ring for performing the continuity and fig8 checks at any point on the ring, so you can measure and record r1, rn and r2. Using the L-CPC cross link stage of the fig8 test you can establish an R1+R2 value for the ring portion of the circuit, and if you can find it, you can carry out an R1+R2 check on the feeder cable. If you can't find it, you can at least confirm R1+R2 from any point on the ring fed by the cable, sum those two and you have the R1+R2 for the circuit (you can also get someway to locating the feed into the ring - link L+CPC of the feedcable at the CU and then look for the lowest R1+R2 values on the ring), thus you can carry out the required continuity tests. IR is easy as is Zs. So, I don't particularly see testing a lollipop as the issue. I would say the documentation is the key, in particular making a note of where the transition point is so it can be accessed if required. Problems arise here if it's not a maintenance free junction box and it's say under the bathroom floor, so if I was going to do this, I might bring them up into a double box with a blank plate on and use some MF connectors like the Wago 221-613 lever connectors which can accept cables 2.5-6mm, then make a note of this on the certificate for the works, or even leave a sticker on the inside of the CU.
Just to be clear, I would code a ring final with any form of interconnect (either between the legs or different circuits) as a C2 and that scenario is against the regulations. The situation in the original post with two well formed rings connected to a single breaker, that would be a C3 for me, possibly an FI if I wasn't easily able to establish separation etc. In reality however, if I came across it on an EICR and I was able to prove they were both separate and safe and I had a breaker to hand, I'd probably just put a new breaker in the board and move one of the rings to the new MCB and record what I found and what I did on the certificate.
In software engineering there is something known as the "principle of least astonishment" which has it that anything behaving in an unexpected or unconventional manner is bad practice. We really need something equivalent in the wiring regulations:
Principle of least astonishment - Wikipedia
en.wikipedia.org
Having been a software engineer for over 20 years, I must admit that's a new one on me. The problem with trying to have the regs cover all eventualities is it would be a significantly larger volume and navigating it would be a nightmare.
The regs set out the basic rules and you have to use your experience and judgement to make an informed decision.
Technically, 433.1.204 is pretty much the entire definition of how a ring final circuit should be constructed (it goes without saying you must factor in other elements of the regulations). If your ring circuit meets that, it's hard to argue it's unsafe electrically. From a convenience perspective it's a different matter and it could result in an unsafe situation in the event of a power loss, but electrically as I say, I think it's hard to argue it's dangerous.
The regulations do cover all of these things, just not directly, so as above... it's down to your skill and judgement to determine whether what you're presented with is acceptable or not. We're all agreed we'd never install like this, not because it's electrically unsafe but because it could present a danger in other ways and because it is unconventional.
On the subject of documentation, I just look at it like this... if I got called out to one of my jobs, what information beyond the test results would help me and I generally stick whatever I think of on a generic continuation page and/or produce diagrams. I also try and think ahead a little during the install and maybe have designated areas for junction boxes (Typically Wagoboxes) and I record those.
Exactly!
If there is a blank cover over the former cooker switch and terminals behind it to gain access fine, but not if it has been tiled over.
A former colleague who is a software engineer told me about that one, I was astonished.
If everyone was as competent and conscientious as you would not be debating this now! Thanks again for your detailed inputs.
No us lot are not working at all, but practicing our keyboard skills.
The short answer is electrically, if the rings comply in their own right with the regulations, they should be safe, but there are possibly implications with the installation not being split to minimise inconvenience and possibly danger from other factors (such as a loss of power to say life supporting equipment). It's unconventional and I don't think any of us would install like it, but certainly I would do it at a pinch to restore supply as a temporary measure.
As someone who is not registered with a scheme, I try to look for ways to carry out my work without needing to get my 3rd party certifier involved (extra hassle and expense). It's possible that whoever put the 2nd ring on the same breaker as the 1st may have done it simply to avoid building control notification.
Depending on the area (in square metres) extend the ring. Failing that then use a spare way and create another ring circuit.
Probably don't have a spare way, that's why there are 2 RFCs crammed into one OCPD maybe?
Good answer SparkyChick.
Folk often get hung up on OSG which is just a conventional way of doing things for safety and compliance.
Lets consider two examples:-
House 1/
A ring final circuit on ground floor with 40 points.
Floor area served 70 sq m
Ring length end to end 40m
Majority of cable under floorboards
TN supply with Ze 0.23.
Consumer unit in middle of the house.
To be used by an "average" family.
Everybody happy so far?
House 2/
Same spec but the floors are solid so the points are drop fed which increases cable end to end length to 120m.
We then worry a bit about R1 + R2 and volt drop.
By doing as 2 rings we could make them 65m & 55m.
Oh that sounds better.
We might make them different ring final circuits on two different circuits so adding a bit more resliance to the installation. I think most of us would choose this remedy.
However, for instance, no spare fuseway. So we put all 4 ends on one fuseway.
All the considerations are the same as for house 1/ and we`ve improved R1 + R2 and volt drop considerations.
Providing that all the terminals in the consumer unit can hold all the conductors electrically and mechanically sound and we label conductors accordingly then ok.
A ring final circuit can have any topology just in the same way that a radial can.
This circuit might be described as a "butterfly" circuit.
A 3 or 4 ring circuit you might call a "clover" circuit.
By definition all of these circuits are just one circuit being connected to the fuse/breaker on one fuseway.
The circuit in 2/ could be argued as better than in 1/ because it`s improved the Zeds and volt drops.
I did have one person insist that if they found this scenario thay would remove one end of each ring and join them to create just one ring on that circuit. That does seem a bit silly but it is something many of us would initially consider I think.
I think we've already establish a standard naming convention for this as per @David Prosser 's proposition in this post:-
Ring main. - in - UK Electrical Forum
, Ring main., UK Electrical Forum, ElectriciansForums.net Est.2006 | Free Electrical Advice Forum and page_number.
www.electriciansforums.net
I think the standard is BS DP1 - Naming conventions for unconventional/unorthodox ring final circuits (1st Edition - 2020).
I've just heard ammendment 1 is due in a couple of weeks, C&G are working on a qualification so we can prove our competence... the standard is £75 a copy, the exam is £150 and I believe a corrigendum will follow for the single page document in a matter of days. Got to keep up with the IET in terms of quality control
Then settle for it being a final circuit which isn't a ring final circuit. Let's call it a double ring final circuit if you prefer. (Or call it a crap final circuit if you like - few will disagree.)
Well I called it a butterfly circuit, anybody can call it what they want, no problem. Just like the age old cooker circuit, modified cos cooker not needed so a ring produced from that point, some call that a "lolipop" circuit or a "lassoo" circuit (not implying a cowboy job I hope!). The butterfly or whatever you call it just like the lolipop can be a decent circuit designed using sound engineering judgement and be ok. The fact that they are not easily recognised as standard circuits does nothing to detract from that. It might confuse the unwary a little but you could ask "should they really be adding/modifying these circuits if they do not fully understand what they are doing?". Answer No, they could ask someone who does know though and there is no shame in that. There is no person who knows everything about everything.
I disagree about calling them crap circuits though.
Another example to consider is a radial circuit, be it lighting or power points. You might branch out at some point for instance 1 begats 2 begats 4 begats 8 etc etc, it is still a radial circuit, again with different topology but nonetheless sound (some call them "trees"), in fact you could start it off with two conductors (or more) at the CU and it`s still ok - might be a beggar to test though! - you`d have several ends for Zs. It is up to the designer if they want to create one circuit,
In my example No 2/ is actually better in terms of volt drop and R1 + R2 than example No1 is.
I would prefer to call them "Bow Tie" circuits sounds more sophisticated don't you know, can't get on with "lollipop" circuits sounds very childish, "Dragon fly" or a "Damselfly" at least they have four wings, can't think of a "Butterfly" with four wings.
I prefer to call them an abortion, work of the Devil.
hate to correct you there, but like bees, butterflies do have 4 wings.
A butterfly has four wings, two forewings and two hindwings. They are attached to the second and third thoracic segments (the meso- and meta-thorax). Strong muscles in the thorax move the wings up and down in a figure-eight pattern during flight. ... It must then wait for the wings to dry before it can fly.
they also have 6 legs, so that could be 3 rings on a circuit.
But the hind wings are much smaller and not considered a lifting wing, they are there to counter balance the movement of the front wings hence the erratic flight, but a Dragonfly can hover.
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The Work of the Devil is Clingfilm or is that the Devil spawn.
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The Work of the Devil is Clingfilm or is that the Devil spawn.
The rear set of butterfly wings are not always smaller the orange sulphur for example have slightly larger rear wings.
I wasn't referring to all non-standard circuits as crap. I'm not hygely in favour of four conductors in a circuit breaker etc. though. So it was this particular arrangement which I was suggesting that many might consider to be crap.
A ring supplied by a suitably sized radial feeder is something which I have absolutely no difficulty with, even though it is non-standard.
Whatever you label them does not really matter, they are not crap circuits, they may be decent reliable circuits if undertaken properly. The only problem is they are not commonly listed. BS 7671 tells you what to comply with it does not tell you how to comply. So long as you use sound electrical design it complies and is safe. No less so than if you use a bog standard ring or radial.
I can give one example of a circuit that probably does not comply but is nonetheless safe :-
a bog standard ring final circuit B32A MCB with a spur of one twin socket at the origin of the ring i.e from the fuseway. Compliant Yes. Now disconnect the ring but leave the spur in place, so now its a twin socket on a 32a mcb. we would not like the look of it but removal of the ring has not rendered it unsafe has it?
Easy, just the ring of that particular fault. Same as any circuit connected in your consumer unit.
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The test would give the most onerous as the answer which should be the 65m ring part of the circuit
I never suggested that any of them were unsafe. In fact I specifically stated that the circuit in question was not unsafe unless there was an issue with the connections to the four conductors at the origin.
Going round in circles indeed... or going round in rings...
earlier in the thread.... much much earlier... it has been established by the OP that there is two rings from one OCPD. Tested, and not found to be one ring and two radials.
It has also been established that there is a spare way in the board, and a suspect damaged breaker, possibly removed from the board.
it is highly likely, Your Honour, that these two rings have been put together as a stop gap, Friday afternoon, temporary fix until Monday.... and was never returned to.
Discussing whether it is safe or not is a mute subject... because the OP, I believe has mentioned previously that he (or his electrical representative) will seperate the two rings into seperate ocpd’s as soon as he can.
I surmise from this that the case is now closed, and no further discussion is required.
earlier in the thread.... much much earlier... it has been established by the OP that there is two rings from one OCPD. Tested, and not found to be one ring and two radials.
It has also been established that there is a spare way in the board, and a suspect damaged breaker, possibly removed from the board.
it is highly likely, Your Honour, that these two rings have been put together as a stop gap, Friday afternoon, temporary fix until Monday.... and was never returned to.
Discussing whether it is safe or not is a mute subject... because the OP, I believe has mentioned previously that he (or his electrical representative) will seperate the two rings into seperate ocpd’s as soon as he can.
I surmise from this that the case is now closed, and no further discussion is required.
Can you expand on that please your closing evidence is not clear 
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