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'R1+R2 (figure 8) reading' of a 'ring circuit double rings (figure 8) circuit'.
That's frightening for 'RFC supporters' even, and would really put some support in the 'pro radial camp'.....plenty of whom have problems testing a basic radial. They'd be totally scared out of their wits.
That's frightening for 'RFC supporters' even, and would really put some support in the 'pro radial camp'.....plenty of whom have problems testing a basic radial. They'd be totally scared out of their wits.
If the circuit complies with the actual regulations that specify what's acceptable (not appendix 15 which is a pictorial guide providing the most basic scenarios) then it complies and that's fine by me. Would I install like this? No. Have I implemented this? Yes, as a temporary measure to restore supply (had a callout last week where an MCB had failed following a fault - only issue was getting a good secure connection on the four conductors in the MCB).
As for the testing... test both separately as individual rings and then record the worst case values as required.
The figure 8 check is to establish that the topology of the ring is correct beyond the point of supply. In this case, you would as I've already said... test each ring separately to establish that neither is a figure 8 away from the origin.
I'll be honest, I don't know why people are losing their minds over this. We've pretty much all said we wouldn't install like it but as a temporary measure it's OK to restore supply. But I'm still waiting for someone to explain (a) why it's dangerous and (b) why it doesn't comply with the regulations.
And one final point... the regulations are a starting point. It's expected we have the mental agility to be able to use them to work out whether what we are planning on doing complies. To provide a list of everything that is allowed/not allowed, how could you... the number of possibilities is endless, we complain about the price of the book now... think about buying the encyclopedia britannica when the regs change because that's what you'd need if you want the regs to get anywhere close to being a hand holding guild of what to do in any given situation.
As for the testing... test both separately as individual rings and then record the worst case values as required.
The figure 8 check is to establish that the topology of the ring is correct beyond the point of supply. In this case, you would as I've already said... test each ring separately to establish that neither is a figure 8 away from the origin.
I'll be honest, I don't know why people are losing their minds over this. We've pretty much all said we wouldn't install like it but as a temporary measure it's OK to restore supply. But I'm still waiting for someone to explain (a) why it's dangerous and (b) why it doesn't comply with the regulations.
And one final point... the regulations are a starting point. It's expected we have the mental agility to be able to use them to work out whether what we are planning on doing complies. To provide a list of everything that is allowed/not allowed, how could you... the number of possibilities is endless, we complain about the price of the book now... think about buying the encyclopedia britannica when the regs change because that's what you'd need if you want the regs to get anywhere close to being a hand holding guild of what to do in any given situation.
D
davesparks
We all install circuits regularly which are of a design that isn't in BS7671.
There is no lighting circuit in BS7671.
There is no dedicated circuit for an appliance in BS7671.
There is no 3 phase circuit in BS7671.
There is no distribution circuit in BS7671.
Etc
Etc
There are rules and regulations to allow the safe and compliant design of any circuit, that part of the point of the regulations existing.
There are only standard circuits in BS7671 for final circuits supplying multiple socket outlets.
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The only circuits that are specifically 'discussed' in BS7671 are final circuits supplying sockets.
If we stuck to only ever installing circuits which are 'discussed' in BS7671 we would not be able to install a lighting circuit, cooker supply, any 3 phase circuit etc etc!
[/QUOT[/QUOTE]
there are only standard circuits in BS7671 for final circuits supplying multiple socket outlets.
We are indeed talking about a circuit serving sockets in this thread and not lighting or circuits serving appliances so I’m not sure why you brought these scenarios in to it? As you said,
there are only standard circuits in BS7671 for final circuits supplying multiple socket outlets.
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Great stuff marky the sparky. So, short answers please:[a ring final circuit should be continuous rings (as evidenced by the testing we are required to carry out). So, assuming in this situation the CPC is continuous, it's compliant.
"543.7.2 Socket-outlet final circuits
543.7.2.201 For a final circuit with a number of socket-outlets or connection units intended to supply two or more items of equipment, where it is known or reasonably to be expected that the total protective conductor current in normal service will exceed 10 mA, the circuit shall be provided with a high integrity protective conductor connection complying with the requirements of Regulation 543.7.1. The following arrangements of the final circuit are acceptable:
(i) A ring final circuit with a ring protective conductor. Spurs, if provided, require high integrity protective conductor connections complying with the requirements of Regulation 543.7.1
(ii) A radial final circuit with a single protective conductor:
(a) the protective conductor being connected as a ring, or
(b) a separate protective conductor being provided at the final socket-outlet by connection to the metal conduit or ducting, or
(c) where two or more similar radial circuits supply socket-outlets in adjacent areas and are fed from the same distribution board, have identical means of short-circuit and overcurrent protection and circuit protective conductors of the same cross-sectional area, then a second protective conductor may be provided at the final socket-outlet on one circuit by connection to the protective conductor of the adjacent circuit
(iii) Other circuits complying with the requirements of Regulation 543.7.1."
Since this is about the implementation of high integrity earthing, we once again have to make an assumption. In a domestic situation it's unlikely high integrity earthing will have been installed.
"643.2 Continuity of conductors
643.2.1 The continuity of conductors and connections to exposed-conductive-parts and extraneousconductive-parts, if any, shall be verified by a measurement of resistance on:
(i) protective conductors, including protective bonding conductors, and
(ii) in the case of ring final circuits, live conductors."
Testing... we are required to conduct specific tests on ring final circuits. These can easily be done but the results sheets are not designed to record multiple ring result sets for a single 'circuit'. I would perhaps use two lines of the schedule of results to ensure I captured all the relevant information, with clear labelling applied to the circuits within the consumer unit to allow easy identification later (and thus allow easy cross referencing of results).
So, now lets look at some possible areas this installation could breach the regulations.
@Pete999 has already provided one in the form of 134.1.1. This is however somewhat subjective. If we assume the cable is sized correctly, it's properly supported along it's run, it's properly installed (protected against mechanical damage for example, all conductors are properly identified etc.) and the connected accessories are compliant with the required standards, the only possible reason we may be in breach is if the manufacturers instructions provide guidance on the number of conductors in a particular termination at the consumer unit. With a 3036 rewireable board this could be a problem, with early MCBs it could be a problem, with 60898 compliant MCBs it's not likely to be an issue (4 x 2.5mm sq. conductors) but with 61009 compliant RCBOs it may be a problem due to the reduced size of the terminals. So, an assessment of the overall installation and the terminations should be made to determine if there are any issues (this is no different to any other circuit).
"314 DIVISION OF INSTALLATION
314.1 Every installation shall be divided into circuits, as necessary, to:
(i) avoid danger and minimize inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Chapter 46 and Section 537)
(iii) take account of hazards that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor (PE) currents not due to a fault
(v) mitigate the effects of electromagnetic disturbances (see also Chapter 44)
(vi) prevent the indirect energizing of a circuit intended to be isolated.
314.2 Separate circuits shall be provided for parts of the installation which need to be separately controlled, in such a way that those circuits are not affected by the failure of other circuits, and due account shall be taken of the consequences of the operation of any single protective device.
314.3 The number of final circuits required, and the number of points supplied by any final circuit, shall be such as to facilitate compliance with the requirements of Chapter 43 for overcurrent protection, Chapter 46 and Section 537 forisolation and switching and Chapter 52 as regards current-carrying capacities of conductors.
314.4 Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board. The wiring of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent the indirect energizing of a final circuit intended to be isolated."
This is the section I think we are most likely to be in breach of when considering this arrangement.
314.1 (i) as this arrangement has the potential to take out all the sockets in the event of a fault, (ii) arguably this is a case of inconvenience for the installation user whilst we are working because whilst we can facilitate safe inspection, testing and maintenance, we have to shut off all sockets which may result in incovenience for the user, (iv) nuisance RCD tripping could be a problem, but no more than two ring circuits connected to different breakers on the same RCD (a situation that occurs quite frequently with split load boards).
314.2 ordinarily this may not be a problem, sure it's inconvenient but what happens if say someone has a new requirement for some medical equipment? Having all the sockets on a single circuit wouldn't be a good plan in this case as a fault could take out the supply to life support equipment. Arguably this should be considered and addressed when the equipment is installed, but it may not be and thus we could have a dangerous situation.
314.4 this point has resulted in a lengthy discussion in the past in relation to a similar topic (is it ok to combine radial circuits on one MCB). It could be argued that each ring is a final circuit in it's own right and thus should be supplied by a separate way but as the definition of circuit is somewhat wishy washy, it can be argued that 'a circuit' is defined as whatever is connected to a particular way in the distribution board.
"411 Protective Measure: Automatic Disconnection of Supply"
If both rings are installed correctly and are capable individually of meeting the requirements for this, when connected to the same protective device they should continue to meet these requirements. We would of course need to check the earth fault loop impedance and as good practice check the line-neutral loop impedance to ensure it doesn't exceed the maximum EFLI for the circuit breaker (to ensure we can meet our disconnection time for LN faults). Clearly we need to conduct more testing, but essentially this is no different to any other circuit.
These are my thoughts about it. I don't believe there are any clear contraventions of the regulations with such an arrangement. Much of it is down to one's interpretation/views. From a safety perspective, assuming the circuit is permitting no option; not to be disregarded or modifiedconnected to it's own MCB.
Discuss
We are indeed talking about a circuit serving sockets in this thread and not lighting or circuits serving appliances so I’m not sure why you brought these scenarios in to it?
What is the danger?
What reg(s) does it break?
Why wouldn’t you?
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I’m sorry, I didn’t write that! That was a post from SC. I accidentally quoted it and spent the next 20mins and two bottles of beer trying to delete it in the edit option!
Sure thing fella. I'm still interested in your answers though.
I don’t see any real danger having taken into account loads on both circuits.
As for the regs that it contravenes, it would depend on how you interpret the regs. I have had this arguement with SC and others before now and it all came down to how we interpreted the regs. Most of the her post makes sense but I disagree in what I think the spirit of what the regs mean about the definition of a circuit. I have brought this up with NICEIC tech, NICEIC assessor, IET, and a well known You Tuber and all have the same opinion as I do. It comes down to making the installation simple. Bunching circuits together in OCPD complicates so it goes against what the regs are trying to achieve. This is why BS7671 is constantly being updated, not just because of the advent of new tech but to take grey areas away. I’m not big headed enough to claim that I’m correct as the way the regs are written about the definition of a circuit leaves a lot still in the grey area but until they re write it we will be having this argument at Ad infinitum.
Fun though isn’t it!
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But to pin it down a bit more, davesparks said earlier that the only circuits that are specifically ‘discussed’ in BS7671 are those supplying multiple sockets outlets. These are in appendix 15 and as they are in BS7671 they are a ‘requirement’. Please see my previous post about the definition of ‘requirement’. Requirements are not to be adjusted, tinkered with, or adapted.
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Because whilst I think in the broadest sense it complies with the regulations... it just doesn't feel right. I can't explain why it feels wrong, it just does, seems like an over complication with regards to testing and it may not break the installation up nicely with respect to minimising inconvenience in the event of a fault/isolation for work.
Plus having done it a couple of times in emergencies to restore supply, I've found I've always had problems with the 4 conductors in the one MCB.
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Whilst we disagree on the definition of circuit, we both agree that part of that is the somewhat vague wording in the regs. And in the grand scheme of things, I think we both agree we wouldn't install it from scratch.
As for appendix 15, we can agree to disagree and yes, debating some of this can be fun and educational
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ebee
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Yes a double/triple/quadruple ring in one circuit would be more difficult to test than a single ring in one fuseway. Similarly a tree circuit for say lighting for instance would be more difficult than a simple radial that goes from no1 to no2 to no3 etc etc until the last point. But all are correct, compliant and safe if done properly. Just because it`s not listed in appendix 15 (informative) or the On Site Guide, does not make it wrong. So long as you follow the Regulations (Normative themselves) then you have complied with BS7671.
BS 7671 is not a statutory document, it does not have the force of law (If however you have agreed in contract to work to BS7671, then it is covered by contract law) . Having said that, it would be a very brave (or foolish) man than does not follow BS7671 because that would mean that one day you might have to prove your alternative to be equally as safe before a bloke in a wig whilst you are gripping the rail.
BS 7671 tells is what is to be achieved, not how to achieve it, some examples are shown in the appendix but you are not compelled to use them.
The multiple ring as one circuit scenario is not wrong, most of use would not use it (me included). To state something is wrong when in reallity it is not can occasionally lead to trouble. i.e. if you are a pro and someone states that your proper works is improper to a customer, that might affect your reputation or livelyhood, you`d be a bit miffed and might consider court action (or "industrial training" using your steel toe capped boots!).
I`m old enough to have seen missinterpretation giving rise to trouble. A customer told me that a previous installer used the "wrong cable" on a ring final. I saw the cable and asked why he thought it was wrong. The Local Authority Grants Officer had told him it was wrong. Actually when I questioned a little further it became apparent that the grants officer had said no such thing. What the grants officer had actually stated was that the ring was wired in 4.0 T & E and it need only be 2.5 T & E, he was probably actually praising it as being over the minmum size required ( unless he was thinking of price difference or saving a few polar bears). I gently pointed this out to the customer that his previous bod had done a good job, I would not feel easy seeing this poor fellows reputation tarnished by the ill informed.
BS 7671 is not a statutory document, it does not have the force of law (If however you have agreed in contract to work to BS7671, then it is covered by contract law) . Having said that, it would be a very brave (or foolish) man than does not follow BS7671 because that would mean that one day you might have to prove your alternative to be equally as safe before a bloke in a wig whilst you are gripping the rail.
BS 7671 tells is what is to be achieved, not how to achieve it, some examples are shown in the appendix but you are not compelled to use them.
The multiple ring as one circuit scenario is not wrong, most of use would not use it (me included). To state something is wrong when in reallity it is not can occasionally lead to trouble. i.e. if you are a pro and someone states that your proper works is improper to a customer, that might affect your reputation or livelyhood, you`d be a bit miffed and might consider court action (or "industrial training" using your steel toe capped boots!).
I`m old enough to have seen missinterpretation giving rise to trouble. A customer told me that a previous installer used the "wrong cable" on a ring final. I saw the cable and asked why he thought it was wrong. The Local Authority Grants Officer had told him it was wrong. Actually when I questioned a little further it became apparent that the grants officer had said no such thing. What the grants officer had actually stated was that the ring was wired in 4.0 T & E and it need only be 2.5 T & E, he was probably actually praising it as being over the minmum size required ( unless he was thinking of price difference or saving a few polar bears). I gently pointed this out to the customer that his previous bod had done a good job, I would not feel easy seeing this poor fellows reputation tarnished by the ill informed.
Although radials and not ring finals you are allowed to put multiple 'circuits' in one MCB in some foreign regs, France, Norway and Germany being amongst them i believe. I don't think it's inherently unsafe just because it's against the regs, just poor practice when done in the UK.
ebee
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Do not be offended if I ammend that a bit but a circuit is defined by the Overcurrent Protective Device (Fuse/MCB) therefore several radials (or rings) connected at one fuseway is one circuit. Whether it`s bow tie or trees or whatever it`s just one circuit.
Here`s one though, a ring final or a radial is a "final circuit" however if you fuse down, say with a 3A fuse via a fused connection unitto form say a local lighting circuit for instance then from the 3A fuse is a circuit in its own right too and the circuit feeding it (the ring "final"!) is its distribution circuit too . Good innit?
Just to make it clear in France, Germany and Norway it is against the Regulations to have more than one circuit to a MCB, if we are talking Radials, 12 sockets to a 2.5mm circuit and 8 to a 1.5mm circuit, there are quite a few specific appliances that have to be on their own circuit.
I don't know if the regs have changed since i was last there (in like 2011) but i'm fairly sure you could have more than one radial 'circuit' going into a disjoncteur in France. I remember seeing a picture taken from a book showing three separate lighting radials going into the same MCB and no mention of a limit. Obv they wouldn't do real circuits there because they don't use them, it's all radial.
Don't know if you could for sockets but as far as i see it if you can have 12 sockets on one MCB i don't see how two lots of 6 and 6 would suddenly make it dangerous from a power perspective even if two ring finals, just poor practice. The only thing i can think of is it being a tighter squeeze for the wiring at the MCB but again you can have multiple wires going in anyway as per the French regs so don't see the issue there.
Either way, personally i would just have them all on their own MCB. There's literally no reason not to unless as Chick says it was a temporary emergency thing.
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