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.

 

[Pete999]

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.

No not really, a circuit originate from 1 OCPD, secondly it's not a "Ring Main" it's a Ring Final Circuit RFC, pedantic but correct terminology counts these days.

 

[buzzlightyear]

Two rings of a circuit, got the regs?

 

[JKMRK1]

Two rings of a circuit, got the regs?

Yes I have the regs book, which states final circuits should be connected to a seperate way in the CU. But I've seen so many others argue this is OK??

 

[buzzlightyear]

No is the answer, you will overload the mcb
Are you adjusting a circuit or putting another one in and have no room in CU.

 

[DPG]

Yes I have the regs book, which states final circuits should be connected to a seperate way in the CU. But I've seen so many others argue this is OK??

I've never seen many people argue that two ring finals one one MCB is a good idea.

 

[JKMRK1]

No is the answer, you will overload the mcb
Are you adjusting a circuit or putting another one in and have no room in CU.

I've come across this in the house I've just purchased. There's a spare way in the board I'll add another MCB and seperate them.

 

[Pete999]

Yes I have the regs book, which states final circuits should be connected to a seperate way in the CU. But I've seen so many others argue this is OK??

I'll reiterate, a circuit originates from an individual OCPD if some dipstick has decided to combine 2 RFCs into 1 circuit incorrectly then He / She needs to hang up their screwdrivers, and take up another Trade.

 

[buzzlightyear]

I've never seen many people argue that two lring finals one one MCB is a good idea.

the chuckle brothers electrical. Lol

 

[JKMRK1]

I've never seen many people argue that two ring finals one one MCB is a good idea.

I'm not saying it's correct just saying what I've seen. That's why I've asked the question to make sure its correct.
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I'll reiterate, a circuit originates from an individual OCPD if some dipstick has decided to combine 2 RFCs into 1 circuit incorrectly then He / She needs to hang up their screwdrivers, and take up another Trade.

Thanks for the advice it is much appreciated?

 

[Pete999]

I'm not saying it's correct just saying what I've seen. That's why I've asked the question to make sure its correct.

Well no then it isn't
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I'm not saying it's correct just saying what I've seen. That's why I've asked the question to make sure its correct.
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Thanks for the advice it is much appreciated?

You are more than welcome Mate
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I'm not saying it's correct just saying what I've seen. That's why I've asked the question to make sure its correct.
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Thanks for the advice it is much appreciated?

See description of a circuit in OSG or BS 7671

 

[Mark Wright]

You could put more than one radial on a MCB but its not good practice.
2 Rings on 32mcb is dangerous are you sure it's not 2 radials?

2 rings would have four wires goinging into a MCB

Some people spur off a MCB maybe it was that - 3 wires?

 

[DPG]

If there is a spare way in the CU then I would question why someone has decided to combine the two circuits. I recommend doing full set of dead tests before connecting up.

 

[JKMRK1]

You could put more than one radial on a MCB but its not good practice.
2 Rings on 32mcb is dangerous are you sure it's not 2 radials?

2 rings would have four wires goinging into a MCB

Some people spur off a MCB maybe it was that - 3 wires?

Definitely two rings there are 4 cables in the MCB. I'm going to add another way and seperate them.

 

[Mark Wright]

Looking at this thread there is argument that it is safe but not common
_theiet.org/forums/forum/messageview.cfm?catid=205&threadid=32208

I suppose you could argue it's just extending the Ring??? - 2 large rings would surely cause constant tripping.

 

[James]

it could even be that originally it was 2 circuits.

failed mcb was removed and temporary supply taken from the one next to it.
late night tempory fix that never got finished off?

 

[DPG]

I suppose you could argue it's just extending the Ring??? - 2 large rings would surely cause constant tripping.
[/QUOTE]

It's not the same as extending the ring.

 

[SparkyChick]

I'm not saying I would do this because I wouldn't install like this, but I am going to play devils advocate.

Which regulations does such an arrangement breach?

And how would two ring final circuits installed in accordance with the regulations connected to the same 32A MCB be dangerous?

As I say I wouldn't do it, except as a temporary measure to restore supply, so I'm just curious about the thought process behind the statements.

 

[westward10]

Unless you have tested it a visual assessment that four conductors equate to two ring final circuits may or may not be correct. It could be four radials, one ring final and two spurs or just all four interconnecting with themselves.

 

[radiohead]

In all honesty I cannot see anything in Bs7671 that this would contravene other than good workmanship. If it originates from one MCB it is a single circuit. Despite what has been said about it overloading there is no reason to assume it would be. A single ring with 10 double sockets could have 20 3kw heaters plugged into it.
Very poor practice though and it needs altering on that basis.
edit. Post crossed with Sparkychick who has reached the same conclusion.

 

[James]

@SparkyChick

I have been having similar thoughts,
I don't think its right, and its not something I would install as new.

however I have just been browsing the book, and nothing is jumping out to say I couldn't do it if I wanted to.

I think we can mostly all agree that it is certainly not best practice but if someone could point me to a reg number it would make me feel better.

 

[Pete999]

I'm not saying I would do this because I wouldn't install like this, but I am going to play devils advocate.

Which regulations does such an arrangement breach?

And how would two ring final circuits installed in accordance with the regulations connected to the same 32A MCB be dangerous?

As I say I wouldn't do it, except as a temporary measure to restore supply, so I'm just curious about the thought process behind the statements.

It may not disagree with any regulations, but SC you surely can see the apparent dangers of applying such a circuit.

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@SparkyChick

I have been having similar thoughts,
I don't think its right, and its not something I would install as new.

however I have just been browsing the book, and nothing is jumping out to say I couldn't do it if I wanted to.

I think we can mostly all agree that it is certainly not best practice but if someone could point me to a reg number it would make me feel better.

Don't think you need a reg number SC look up the description of a circuit.

 

[Mark Wright]

Yeah fairly interesting and I'm not saying I would do but considering Table H2.1 unlimited Sockets in 100m2 - probably could be considered as extending the ring without extra danger.

 

[davesparks]

It may not disagree with any regulations, but SC you surely can see the apparent dangers of applying such a circuit.

Don't think you need a reg number SC look up the description of a circuit.

I fully agree that this is incorrect and should not have been done.

But having said that what are the apparent dangers? I don't see any particular danger attributable to this.

The definition of a circuit is based around everything that is connected to a single way in a distribution board, so this would still count as one circuit, although it is nom-standard.
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You could put more than one radial on a MCB but its not good practice.

You can have two legs of a radial cir uit connected to an MCB, but that is not two circuits. Also it is not bad practice.

 

[DPG]

Bad design does not always have a reg number I guess.

 

[James]

CIRCUIT:
An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s).

I think the arrangement above matches the description

 

[Mark Wright]

I did wonder because the Design project limits you to circuits of 30m so I had several lighting circuit only rated about 2Amps I wondered in real life if I could in theory just put three of these say in to a single 6Amps MCB or maybe even more into a 10Amp MCB.
I think I'd be pushing my luck but couldn't find anything dangerous about it.

 

[radiohead]

The original question asks whether this is a breach of regulations. Nobody disputes it is poor practice, but the opinions of experienced people are not regulations and never have been.

 

[James]

@JKMRK1

wow, look what you have started here!!

I like the conversation thread,
you are listed as a trainee, when you get your qualifications you will be a qualified electrician. just look at the different ways the regs have been interpreted and peoples opinions on what is good, bad and indifferent practice.

as your time and experience in the trade expands, you will start to build an idea of what is a good installation and will also be more opinionated about what is not ok.

bottom line for me when I consider things that are not accurately defined, would I be happy if this was installed at my daughters house?
it normally guides my mind in the right direction.

 

[JKMRK1]

@JKMRK1

@JKMRK1

wow, look what you have started here!!

I like the conversation thread,
you are listed as a trainee, when you get your qualifications you will be a qualified electrician. just look at the different ways the regs have been interpreted and peoples opinions on what is good, bad and indifferent practice.

as your time and experience in the trade expands, you will start to build an idea of what is a good installation and will also be more opinionated about what is not ok.

bottom line for me when I consider things that are not accurately defined, would I be happy if this was installed at my daughters house?
it normally guides my mind in the right direction.

Tell me about it did think it would get so many mixed opinions!

Always tell myself it doesn't hurt to have a second opinion on things and as I wasnt certain about this that's what I done.

Thank you for the positive outlook and advice ?

wow, look what you have started here!!

I like the conversation thread,
you are listed as a trainee, when you get your qualifications you will be a qualified electrician. just look at the different ways the regs have been interpreted and peoples opinions on what is good, bad and indifferent practice.

as your time and experience in the trade expands, you will start to build an idea of what is a good installation and will also be more opinionated about what is not ok.

bottom line for me when I consider things that are not accurately defined, would I be happy if this was installed at my daughters house?
it normally guides my mind in the right direction.

Tell me about it did think it would get so many mixed opinions! Always tell myself it doesn't hurt to have a second opinion on things and as I wasnt certain about this that's what I done. Thank you for the positive outlook and advice ?

 

[Mark Wright]

Going the other way round and this is from a European web site

"The rules for ring wiring say that the rated current of the cable must be at least two-thirds of the rating of the protective device. This means that the risk of prolonged cable overload can be considered minimal. However, in practice it is very rare to find a ring with a different protective device than a 30 A fuse, a 30 A circuit breaker or a 32 A circuit breaker and a cable with a cross-section different from the one mentioned above."

right or wrong what's the common response to finding a Ring on a 20A MCB or wired in 4mm??

 

[ipf]

Just a point.
Two rings or not, in general, what are FIRST thoughts on four (or more) cables in a circuit breaker terminal, whilst carrying out an EICR?
How long is a piece of string, maybe?

 

[radiohead]

Just a point.
Two rings or not, in general, what are FIRST thoughts on four (or more) cables in a circuit breaker terminal, whilst carrying out an EICR?
How long is a piece of string, maybe?

It would depend on an informed engineering judgement as to whether the conductors were securely terminated for me.

 

[James]

Just a point.
Two rings or not, in general, what are FIRST thoughts on four (or more) cables in a circuit breaker terminal, whilst carrying out an EICR?
How long is a piece of string, maybe?

It says to me that things have probably been done on a tight budget, i.e. the consumer unit has not got enough ways for what they want to supply.

look out for other things that may have been overlooked!

 

[DPG]

It says to me that things have probably been done on a tight budget, i.e. the consumer unit has not got enough ways for what they want to supply.

look out for other things that may have been overlooked!

But there's a spare way in this particular CU.

 

[radiohead]

Tell me about it did think it would get so many mixed opinions! Always tell myself it doesn't hurt to have a second opinion on things and as I wasnt certain about this that's what I done. Thank you for the positive outlook and advice ?

I dont think you have got mixed opinions, nobody has said this is anything other than bad practice. But the question concerns regulations, and as yet nobody has given an actual regulation that this breaches, and throwing hands up in horror does not count as a regulation.

 

[David Prosser]

For all we know it could only be two double socket outlets in the circuit.
I propose we call these bow-tie final circuits from now on!

 

[James]

But there's a spare way in this particular CU.

Still, tight budget could also mean tight on time, not got another breaker in the box?
never mind, its Friday the pub is open, just stick it in the other breaker and we are out of here!!
when you see an obvious short cut like that it makes me look for others.

 

[Risteard]

You could put more than one radial on a MCB but its not good practice.

You couldn't, because by definition it would be one radial.

2 Rings on 32mcb is dangerous are you sure it's not 2 radials?

How is it dangerous, apart from the potential issue with the four conductors in the terminals/cage clamp (which although crap is unlikely to be an issue in real terms)?

 

[DPG]

Still, tight budget could also mean tight on time, not got another breaker in the box?
never mind, its Friday the pub is open, just stick it in the other breaker and we are out of here!!
when you see an obvious short cut like that it makes me look for others.

Yep, fair point.

 

[SparkyChick]

I fully agree that this is incorrect and should not have been done.

But having said that what are the apparent dangers? I don't see any particular danger attributable to this.

The definition of a circuit is based around everything that is connected to a single way in a distribution board, so this would still count as one circuit, although it is nom-standard.

@Pete999 , Dave has summed up my own personal view to a T.

If both of the rings are correctly installed and the cables sized correctly, then I'm struggling to see how this arrangement would be any more dangerous than each of them connected to their own MCB, sure from an isolation point of view it's less than ideal, but from a safety perspective I don't see how it's any less safe than a ring final running from it's own 32A MCB. If you were talking two ring circuits supplied by two MCBs with one leg of each ring in each MCB, that's another matter (have seen this and nearly got bit by it, thankfully my chicky sense started tingling and I did another check at the socket I was working on).

And I'll reiterate what I said... I personally wouldn't do it, except as maybe a temporary solution to restore supply in the event of say an MCB or RCBO failure. But I think it's an interesting thought exercise because I'm not sure what regulations it would be breaching. The closest I can come to is largely dependent on how you define circuit.

Just a point.
Two rings or not, in general, what are FIRST thoughts on four (or more) cables in a circuit breaker terminal, whilst carrying out an EICR?
How long is a piece of string, maybe?

Absolutely, it's not good, and it would be a C3 from me, unless there were clear signs of bad connections (loose cables, heat damage etc.) in which case it would be a C2. My reasoning... does it present a danger now or would it present a danger if something else happened? Potentially it might, but so would any ring final circuit and I'm thinking broken or poor end to end continuity or some other error in installation.

But like I said, I'm just curious about peoples thought processes and reasoning. We can't remember everything and we certainly can't know everything so it's an interesting topic for debate
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right or wrong what's the common response to finding a Ring on a 20A MCB or wired in 4mm??

Could be a long cable run, the 20A MCB could be a left over from a broken ring when someone downgraded it to be safe, the 4mm could be there because the Zdb at the source of the circuit was too high for 2.5mm to cut it from a Maximum Zs perspective, or in extreme cases even a maximum NL loop impedence perspective.

But if it was safe and compliant, I'd just be asking myself why?

I did a rewire job last year and ran a ring in 4mm. It was a mistake on my part... I picked up the wrong reel and just cracked on. Was a costly mistake, but hey ho

 

[pc1966]

Ugly but not dangerous. This circuit, not me (but close enough)

In terms of overload you can overstress the 32A MCB on a ring with only 4 items plugged in, so unless this was conjoining two rings that had been chosen to separate high-demand loads it is not really any worse than a bigger single ring.

What is curious is why was this done? The OP says there is one slot free so probably this was a temporary fix for a failed MCB that has become permanent.

 

[ipf]

It would depend on an informed engineering judgement as to whether the conductors were securely terminated for me.

You could probably make sure on that if reconnecting after testing. Available breaker? Terminal and c/b condition? Circuit condition? General install condition?
Like I say, how long's a piece of string?
Definitely needs improvement though, probably C3, dependant upon what it leads to.

 

[DPG]

Ugly but not dangerous. This circuit, not me (but close enough)

In terms of overload you can overstress the 32A MCB on a ring with only 4 items plugged in, so unless this was conjoining two rings that had been chosen to separate high-demand loads it is not really any worse than a bigger single ring.

What is curious is why was this done? The OP says there is one slot free so probably this was a temporary fix for a failed MCB that has become permanent.

Exactly. I would be doing some testing before going any further.

 

[ipf]

Ugly but not dangerous.

Hey, be careful! You don't know who's lurking.

 

[pc1966]

right or wrong what's the common response to finding a Ring on a 20A MCB or wired in 4mm??

Both are rare but not in any way dangerous.

4mm is needed if the end-to-end length is over about 106m, but on a multi-floor building you could have a fair amount of that used up in the CU-to-floor run up and down so it need not be a ridiculously large area covered.

I have seen 20A BS3036 rewireable fuses used for the ring before so there may be some historic reason for that, and it is quite possible that a CU upgrade just copied the existing fuses with the nearest MCB.

 

[7029 dave]

Its still only one circuit , the only danger I could see if you lost a couple of legs off this multi RFC.

 

[Mark Wright]

Both are rare but not in any way dangerous.

4mm is needed if the end-to-end length is over about 106m, but on a multi-floor building you could have a fair amount of that used up in the CU-to-floor run up and down so it need not be a ridiculously large area covered.

I have seen 20A BS3036 rewireable fuses used for the ring before so there may be some historic reason for that, and it is quite possible that a CU upgrade just copied the existing fuses with the nearest MCB.

Yeah my first Response to OP questions was NO! this is Dangerous but thinking about it can't really find how although A break in 2 rings would be very bad.

But then looking at it the other way round 20A or 4mm that's actually safer but not considered standard - so what response would this cause.

 

[pc1966]

But then looking at it the other way round 20A or 4mm that's actually safer but not considered standard - so what response would this cause.

The Best Practice Guide #4 has various things mentioned that are departures or non-compliance with the standard that are not unsafe so don't merit a code.

Probably you would add it as a comment, more so the 20A MCB as it might be prone to nuisance trips if it serves several power hungry things (washing machine, tumble dryer, dishwasher, etc).

 

[Pete999]

Are we not going off piste Lads and Lasses? the original scenario was 2 separately wired RFCs connected to a single OCPD, this constitutes a single circuit, no matter how you twist and turn with it which is not only bad practice but in my opinion a dangerous situation, Discuss.