Ring main.

[JKMRK1]

Question I have is, is it ok to have x2 ring main circuits on one 32amp type B MCB??

If so does this meet the current regs.

TIA.

 

[pc1966]

Expats do it and Twin and Earth is illegal the main problem probably in Spain would be your insurance maybe an insurance company might not be happy with OPs arrangement again could they prove it is against any rules or unsafe.

In France where you have to follow local council rules you could get into quite a bit of trouble.

Outside of the UK you would not use a ring final circuit because you don't have fused plugs.

Without fused plugs your breaker has to be sized for the appliance cable, probably no more than 1mm so MCB no more than 10-16A. If you are limited to, say, 16A on the circuit, no more than a couple of sockets. If only a couple of sockets, then why a ring as a radial is perfectly suited for that case?

 

[radiohead]

It does not meat the regs BUT. if you exceed the loading I will be surprised but if you do the breaker will trip, ie doing its job.

Can you please give the regulation number(s) you are referring to?

 

[davesparks]

SC I have stated my point of view, and although an interesting post I really have nothing more to say on the subject, you questioned the dangerous statement, which is your prerogative, I just think sticking two separate systems on one OCPD forming one circuit out of two systems is inherently dangerous, I have no other arguments to continue, what next a lighting system added to a RFC circuit OCPD? or vice versa?

If you cannot make a reasonable technical argument to support your statement about it being dangerous then how can you expect anyone to take you seriously?

When people come on the forum saying that someone has told them their electrical installation is dangerous we always advise them to find out from that person exactly why it is dangerous and to get references to regulations.

Making a statement about something being dangerous without backing it up makes it appear that you have nothing to back it up and are condemning something as dangerous through a knee jerk reaction rather than any technical consideration.

 

[GBDamo]

All ifs and buts I know.

So if tested and it is two good rings and all sockets on both rings/floor area dont constitute an overload/regs breach then crimp up one leg from each and put the other in the OCPD.

one ring = resolved.

The OP has the smell of a short term fix that was never returned to with a shrug "well it's ugly but it aint going to kill anyone"

 

[Mike Johnson]

In France where you have to follow local council rules you could get into quite a bit of trouble.

Not so anything on the house owners side of the meter is the owners responsibility Consuel is not interested unless it's a new supply and then you have to apply to Enedis and Consuel will inspect, as long as you have one socket and one light fitted correctly they will instal and issue a certificate of conformity, only on re-sale or change of tenant is any type of inspection carried out on the whole installation and even then it's a tick box exercise.

 

[Pete999]

I don't think you can leave it there Pete, I respect your point of view but you have to state exactly what you believe the danger is here, simply saying it's dangerous without giving reasons is not very helpful to those who don't have your experience and are wanting to understand.
Your point about a lighting system added to a RFC circuit is illogical as Spock might say, a lighting circuit is normally wired in 1.0 or 1.5mm cable, and connecting that directly to a 32a OCPD would be a breach of regulations and potentially dangerous because the cable would not be adequately protected against overcurrent. There is a sound reason for not doing so.

OK I will try, we have several members saying it's not right but is it dangerous? well if qualified electricians are questioning " why do I say it is", reason: what signals are sending to trainees or naïve unqualified people? "that it's an it's not at all dangerous" I suppose many are saying the fuse or OCPD will trip if there is a problem so nothing wrong with it.
Testing, will be a problem, some may come to the conclusion that it's been OK all these years leave it alone, "I didn't do it so why bother saying anything"? harsh maybe but true in my book anyway, it's not compliant with BS7671, and to comply with 7671 we 1are trying to cut out dangerous installs aren't we? that's why in my opinion it's dangerous, I can remember when I was just starting out in the 60s, some of the Sparks would arrive to say install a new socket, no spare ways in the fuse board so cram the new cable into the nearest occupied fuse way, it'll be OK the fuse will blow if anything is wrong, dangerous then, dangerous now, in my opinion, you may not agree Radio head, but we aren't all blessed with being able to see into the future, no insult intended. That's why I consider it to be dangerous

 

[telectrix]

pete, i have to agree with you that it's bad practice, but can't really class it as dangerous, with the exception that nuisance tripping could cause failure of essential equipment e.g. life essential medical equipment where installed, simultaneous failure of both lighting and socket circuits leading to a possible fall in the dark, ( not to mention home brewing gear ), but i'm sitting on the proverbial fence on this. bad practice, yes, but on a EICR i'd be inclined to C3 it.

 

[radiohead]

OK I will try, we have several members saying it's not right but is it dangerous? well if qualified electricians are questioning " why do I say it is", reason: what signals are sending to trainees or naïve unqualified people? "that it's an it's not at all dangerous" I suppose many are saying the fuse or OCPD will trip if there is a problem so nothing wrong with it.
Testing, will be a problem, some may come to the conclusion that it's been OK all these years leave it alone, "I didn't do it so why bother saying anything"? harsh maybe but true in my book anyway, it's not compliant with BS7671, and to comply with 7671 we 1are trying to cut out dangerous installs aren't we? that's why in my opinion it's dangerous, I can remember when I was just starting out in the 60s, some of the Sparks would arrive to say install a new socket, no spare ways in the fuse board so cram the new cable into the nearest occupied fuse way, it'll be OK the fuse will blow if anything is wrong, dangerous then, dangerous now, in my opinion, you may not agree Radio head, but we aren't all blessed with being able to see into the future, no insult intended. That's why I consider it to be dangerous

Thanks Pete, however you and several others have stated it is not compliant with Bs7671, but as yet nobody has backed that up with a regulation number. In order to be non compliant there MUST be an applicable regulation number.
The only one I can think of with no knowledge of the load and area covered is 'good workmanship', and that is subjective. Other regulations may apply if the circuit has an excessive loading or covers an excessive area, but that would apply to any circuit and could not be applied to this circuit alone.
The point on testing is not really valid, such a circuit remains testable in exactly the same way as any other circuit, any competent electrician should be able to ascertain the nature of the circuit and adapt the test accordingly.
I still do not think you have given a single valid reason as to why this is dangerous or non compliant.
And to clarify again, I would not do it except as a temporary fix as suggested by others, because I think it would be unprofessional and poor practice, but if considered dangerous, then even as a temporary fix it would be a non starter. I'll state now, I would have no problem at all with using this as a band-aid in the event of a failed device on a friday afternoon.

 

[Pete999]

Thanks Pete, however you and several others have stated it is not compliant with Bs7671, but as yet nobody has backed that up with a regulation number. In order to be non compliant there MUST be an applicable regulation number.
The only one I can think of with no knowledge of the load and area covered is 'good workmanship', and that is subjective. Other regulations may apply if the circuit has an excessive loading or covers an excessive area, but that would apply to any circuit and could not be applied to this circuit alone.
The point on testing is not really valid, such a circuit remains testable in exactly the same way as any other circuit, any competent electrician should be able to ascertain the nature of the circuit and adapt the test accordingly.
I still do not think you have given a single valid reason as to why this is dangerous or non compliant.
And to clarify again, I would not do it except as a temporary fix as suggested by others, because I think it would be unprofessional and poor practice, but if considered dangerous, then even as a temporary fix it would be a non starter. I'll state now, I would have no problem at all with using this as a band-aid in the event of a failed device on a friday afternoon.

Amendment 3 134.1.1
" Good workmanship by skilled (electrically) or instructed (electrically) persons and proper materials shall be used in the selection and erection of the electrical installation. The installation of electrical equipment shall take account of the manufacturers' instructions"!

 

[Mike Johnson]

Different people have different standards, if there is not a regulation that covers a particular situation then, it is up to the individuals integrity/knowledge/experience to assess if something is acceptable.

 

[radiohead]

Pete just out of interest regarding the temporary fix scenario. Lets say you had a failed mcb and there was no possibility of a replacement until Monday and no other fix, vulnerable elderly client, would you leave that person without power to an essential circuit or double up a ring just for the weekend?

 

[Vortigern]

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 for isolation 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.
I rest my case m'lud!

 

[SparkyChick]

So I figured I'd go through the regulations and look at things that specifically talk about ring final circuits and give my thoughts on them in regards to the current situation and then give some thoughts about possible breaches.

Discussions like these are, in my humble opinion, vital learning tools. They also serve to reinforce the importance of being able to think beyond the regs and your own past experience and to that ends, the regs include this statement...

"While the publisher and contributors believe that the information and guidance given in this work is correct, all parties must rely upon their skill and judgement when making use of it."

This case is a good example I feel where skill and judgement come into play. The regulations aren't the be all and end all, they are the starting point.

"2 Definitions - Ring final circuit. A final circuit arranged in the form of a ring and connected to a single point of supply."

So by definition, the circuit in the OP is organised as two rings. Unorthodox? Yes. Unsafe? Assuming that in all other ways it complies, then probably not.

"433.1.204 Accessories to BS 1363 may be supplied through a ring final circuit, with or without unfused spurs, protected by a 30 A or 32 A protective device complying with BS 88 series, BS 3036, BS EN 60898, BS EN 60947-2 or BS EN 61009-1 (RCBO). The circuit shall be wired with copper conductors having line and neutral conductors with a minimum cross-sectional area of 2.5 mm2 except for two-core mineral insulated cables complying with BS EN 60702-1, for which the minimum cross-sectional area is 1.5 mm2. Such circuits are deemed to meet the requirements of Regulation 433.1.1 if the current-carrying capacity (Iz) of the cable is not less than 20 A and if, under the intended conditions of use, the load current in any part of the circuit is unlikely to exceed for long periods the current-carrying capacity (Iz) of the cable."

That regulation is the only real technical specification for a ring final circuit and you'll no doubt notice it's focused for the most part on the current carrying capacity of the cable.

Since we don't have access to the circuit in question we have to make some assumptions, so if we assume each individual ring is designed and installed correctly and is compliant with this regulation in it's own right, by extension if they are both connected to the same OCPD they will still be compliant.

"433.4 Overload protection of conductors in parallel
Where a single protective device protects two or more conductors in parallel there shall be no branch circuits or devices for isolation or switching in the parallel conductors.
This regulation does not preclude the use of ring final circuits with or without spur connections."

"433.4.1 Equal current sharing between parallel conductors
Except for a ring final circuit, where spurs are permitted, where a single device protects conductors in parallel and the conductors are sharing currents equally, the value of Iz to be used in Regulation 433.1.1 is the sum of the current carrying capacities of the parallel conductors. It is deemed that current sharing is equal if the requirements of the first indent of Regulation 523.7(i) are satisfied."

These two excerpts are really about conductors in parallel and the mention of ring final circuits is to exclude them from the provisions of 433 clauses.

"523.7 Conductors in parallel
Where two or more live conductors or PEN conductors are connected in parallel in a system, either:
(i) measures shall be taken to achieve equal load current sharing between them
This requirement is considered to be fulfilled if the conductors are of the same material, have the same cross sectional area, are approximately the same length and have no branch circuits along their length, and either:
(a) the conductors in parallel are multicore cables or twisted single-core cables or non-sheathed cables, or
(b) the conductors in parallel are non-twisted single-core cables or non-sheathed cables in trefoil or flat formation and where the cross-sectional area is greater than 50 mm2 in copper or 70 mm2 in aluminium, the special configuration necessary for such formations is adopted. These configurations consist of suitable groupings and spacings of the different lines or poles or
(ii) special consideration shall be given to the load current sharing to meet the requirements of Regulation 523.1.

This regulation does not preclude the use of ring final circuits with or without spur connections.

Where adequate current sharing is not possible or where four or more conductors have to be connected in parallel consideration shall be given to the use of busbar trunking."

As with 433, this section is excluding ring finals from the erection guidelines around conductors in parallel.

"543.2.9 Except where the circuit protective conductor is formed by a metal covering or enclosure containing all of the conductors of the ring, the circuit protective conductor of every ring final circuit shall also be run in the form of a ring having both ends connected to the earthing terminal at the origin of the circuit."

As this is domestic, it's likely to be wired in twin and earth (another assumption), but this is just clarifying the installation requirements of the CPC. We all know the conductors of 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 for isolation 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 compliant in every other way, there should no increased risk of danger from this arrangement as the conductors will be adequately protected (they would be if they were installed on their own MCB).

Would I install this way? No because I don't believe it adequately splits the installation to minimise inconvenience. I would however do this to restore supply in the event of a fault. I agree we should be doing our utmost to ensure people don't believe this is acceptable, but from a regs perspective as stated, I don't believe it breaches them but I am happy to be proven wrong. From a danger perspective I don't believe it is any more dangerous than a ring final connected to it's own MCB.

Discuss

 

[DPG]

Good post SC. I agree, not dangerous, but I still think it falls foul of the 'Good workmanship' reg. Borderline case admittedly.

 

[pc1966]

Of all the regulations it seems 314.4 is the most relevant point, but again it is more about following good practice than creating any actual danger by contravening it.

The cable clamp size is a point that could cause actual danger if somehow the cables were not adequately connected as a result. But in this case it was a MCB and generally they would take the size of 4 * 2.5mm CSA (maybe struggling if ends bent-back of course).

Still it gave us something to do for a while!