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.

 

[LastManOnline]

I was going to edit that post, but figured you get that I was referring to the use of boards with significant capacity and not 3 phase installations.
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I'm very much in favour of breaking with convention, when doing so fulfills a need or improves upon convention - whether that be a one off circumstance or in a more widespread manner.

What I struggle with here are the potential limitations placed upon homeowners as that house could have new occupants 2 or 3 years from now, with very different requirements to the current occupant. It may be that you have got this installation bang on the money for the style of property, but I can only consider the issue from my own perspective and limited experiences. Your ideas may not meet with universal approval, but I like that they challenge convention and give me something to think about.

The more you mull it over, the less unconventional it will seem. Believe me, by nature I, m very cautious and "doing things once and doing it right" is my natural way. In the electrical Industry we are taught to follow the regs rigidly. Correct. However, breaking with convention in order to improve matters is in my experience not really encouraged. It tends to be a case of "that's, how we have always done things". However, it's clear that someone somewhere is doing this, otherwise we would never have new regs and new improvements. I never challenge convention for the sake of it. There must be a very definate practical goal.

 

[Cbuk2k2]

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?

Is that any worse than a multi stranded 6mm or 10mm cable?

Always seems strange to me sparks dont bootlace these.

 

[davesparks]

Is that any worse than a multi stranded 6mm or 10mm cable?

Always seems strange to me sparks dont bootlace these.

Yes it is different to a coarse stranded cable. Coarse stranded cables have the strands compacted tigether at manufacture and they are further compacted together by the termination. Multiple seperate conductors terminated together can, if not done properly, result in one conductor not being clamped at all.

Ferrules are only required for fine stranded cables as screw terminals can cut through the strands or spread them out so that good contact is not made.
Coarse stranded conductors don't suffer from these same issues if correctly terminated.

 

[Cbuk2k2]

Yes it is different to a coarse stranded cable. Coarse stranded cables have the strands compacted tigether at manufacture and they are further compacted together by the termination. Multiple seperate conductors terminated together can, if not done properly, result in one conductor not being clamped at all.

Ferrules are only required for fine stranded cables as screw terminals can cut through the strands or spread them out so that good contact is not made.
Coarse stranded conductors don't suffer from these same issues if correctly terminated.

Just looks strange to me where I’d almost always see some sort of crimp even on corse stranded cables.

 

[davesparks]

Just looks strange to me where I’d almost always see some sort of crimp even on corse stranded cables.

When/where would you always see some sort of crimp on coarse stranded?

 

[Cbuk2k2]

When/where would you always see some sort of crimp on coarse stranded?

Offshore oil and gas/petrochemical is where I work mainly.

Seems to be fairly standard practiceon the sites I’ve worked on.

 

[davesparks]

Offshore oil and gas/petrochemical is where I work mainly.

Seems to be fairly standard practiceon the sites I’ve worked on.

OK, so that's a specialised industry with its own rules and regulations, not really something you can compare to general installation work.

What type of crimps are used on coarse stranded cables? Are you talking about ferrules or something else?

 

[Cbuk2k2]

OK, so that's a specialised industry with its own rules and regulations, not really something you can compare to general installation work.

What type of crimps are used on coarse stranded cables? Are you talking about ferrules or something else?

We work to the same BS7671 rules as everyone else, I’m not aware it’s driven by any of the ATEX regulations etc. It’s just how I’ve always known it be done. Could be an American thing or a marine thing as there is a lot of crossover there.

Depends on the application but non insulated lugs and bootlace crimps are probably the most common.

 

[stevethesparks]

Will also be seen on all BMS panels

 

[davesparks]

It just seems weird to me that bootlace ferrules are being used on coarse stranded cables.
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Will also be seen on all BMS panels

Any idea why?

 

[David Prosser]

Not seen it on gas production systems so not ATEX as far as I can see.

Also on all the lighting and power distribution panels for our BMS non of the SWA has ferrules on. The control cables obviously are.

 

[stevethesparks]

It just seems weird to me that bootlace ferrules are being used on coarse stranded cables.
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Any idea why?

Not sure, at the time (approx 11-9 years ago) we were undertaking work for around 3 BMS firms, and all their panels had it, even the panels internal 13amp socket outlet.

 

[Ian1981]

It just seems weird to me that bootlace ferrules are being used on coarse stranded cables.
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Any idea why?

Bootlace Ferrules on say 6 mm conductors seams to be the new YouTube electricians fad, one does it they all do it, spacing rcbo’s when the circuits are likely to be lightly loaded is another, monkey see monkey do.

 

[stevethesparks]

Not such a bad idea on screw terminals that are not quiet big enough for a folded 6mm, but not in cage clamp type terminals.

 

[Mike Johnson]

They do make the installation look neat, but I wished they had harmonised colours in the different sizes.

 

[Ian1981]

I don’t think it makes it look any neater, a bit of coloured plastic showing on the conductor, they are a necessity on fine stranded conductors but make no impression on me when used on standard coarse conductors, I just think why when connected to a circuit breaker inside a CU?

 

[Mike Johnson]

If the circuit breaker has a cage connector I agree, but not when putting a multi strand cable into a standard screw connector, can't guarantee the whole of the cable is connected securely the strands that are not under the screw are a potential ark point.

 

[Ian1981]

If the circuit breaker has a cage connector I agree, but not when putting a multi strand cable into a standard screw connector, can't guarantee the whole of the cable is connected securely the strands that are not under the screw are a potential ark point.

Yeah true but like I say , I mostly see this at CB terminals

 

[Mike Johnson]

I'v been retired for over ten years so I don't see it at all, except for any work I do for myself, so if I see it it's my fault. I have just put in a set of Aico multi detectors and the 1.5mm cable I used was multi strand so both ends have bootlaces, and I thought it looked good even if I do say so myself.

 

[ackbarthestar]

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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.

May I be the devil's advocate?
2 small ring final circuits could be connected in series to provide one rfc and thus could be connected to one OCPD. Quote Reply Report Edit
Source URL: Ring main. - https://www.electriciansforums.net/threads/ring-main.185730/

 

[nicebutdim]

May I be the devil's advocate?
2 small ring final circuits could be connected in series to provide one rfc and thus could be connected to one OCPD. Quote Reply Report Edit
Source URL: Ring main. - https://www.electriciansforums.net/threads/ring-main.185730/

Surely two ring finals connected in series would no longer constitute two circuits and, as such, would only be once circuit connected to the MCB?


To be clear; I'm asking a question, rather than telling you that you're wrong

 

[DPG]

Trying to get my head around how you wire 2 RFCs in series.

 

[nicebutdim]

Trying to get my head around how you wire 2 RFCs in series.

That's what made me ask the question.

The original installer would know that they were originally two circuits, as would the person who connected them together, but anyone making a subsequent inspection would only see one circuit.

 

[ipf]

May I be the devil's advocate?
2 small ring final circuits could be connected in series to provide one rfc and thus could be connected to one OCPD. Quote Reply Report Edit
Source URL: Ring main. - https://www.electriciansforums.net/threads/ring-main.185730/

Aye, 3 through crimps and you're away, no probs......and if Zs a touch high you could leave the cpc's as they are.
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Trying to get my head around how you wire 2 RFCs in series.

Think we know what ackbar means though, don't we?

 

[DPG]

Aye, 3 through crimps and you're away, no probs......and if Zs a touch high you could leave the cpc's as they are.
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Think we know what ackbar means though, don't we?

Probably me being dense.

 

[Andrew Hunter]

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.

Absolutely no chance should there be 2 RFC in a 32A MCB. Neither should there be a 2.5mm2 radial let alone 2,3 or 4. It is covered in the regs and is further legislated against in test and inspection.
Firstly assuming it is 2 RFC then it is in-fact an interconnected ring main which is the whole purpose of the ring final test to avoid. The reason for avoiding is simple should either of the two rings of an interconnection become open circuit then the circuit becomes two or even four radials.
Which also answers all other scenarios the 2.5mm2 Cables of a radial circuit on 32amp supply will become over loaded and be a potential fire hazard.
Also it becomes problematic when conducting test or fault finding.

 

[Pete999]

Surely two ring finals connected in series would no longer constitute two circuits and, as such, would only be once circuit connected to the MCB?


To be clear; I'm asking a question, rather than telling you that you're wrong

You're right, 2 RFCs in 1 OCPD = 1 circuit

 

[Wilko]

Hi - apologies if I’m just restating something already said as I’m late to the thread.

Early on @SparkyChick asked for the “Reg That Says No” to putting 2 RFC into one OCPD. My thought is Chapter 43, protection against overload. RFCs are a bit of a load management exercise and now we have possibly offended Reg 433.1.1(i) where the rated current of the protective device ( In ) is less than the design current ( Ib ).

 

[radiohead]

Absolutely no chance should there be 2 RFC in a 32A MCB. Neither should there be a 2.5mm2 radial let alone 2,3 or 4. It is covered in the regs and is further legislated against in test and inspection.
Firstly assuming it is 2 RFC then it is in-fact an interconnected ring main which is the whole purpose of the ring final test to avoid. The reason for avoiding is simple should either of the two rings of an interconnection become open circuit then the circuit becomes two or even four radials.
Which also answers all other scenarios the 2.5mm2 Cables of a radial circuit on 32amp supply will become over loaded and be a potential fire hazard.
Also it becomes problematic when conducting test or fault finding.

Great contribution....I have been thinking for a while now that 325 posts in what this thread really needs is someone to re-say what has already been said several dozen times. Genius.

 

[davesparks]

Absolutely no chance should there be 2 RFC in a 32A MCB. Neither should there be a 2.5mm2 radial let alone 2,3 or 4. It is covered in the regs and is further legislated against in test and inspection.

Legislated against? Please do expand on this and tell us which piece of legislation you are referring to?

You can find and view all current UK legislation documents for free here: Legislation.gov.uk - https://www.legislation.gov.uk/

 

[JBW175]

As it’s Easter and this thread isn’t long enough already, I thought I’d resurrect it.

found this on an EICR today. Old Wylex board, with 2 RFC’s into one 30A BS3036 rewireable OCPD.

Trust me, there is a forth wire, just can’t see it on the phot.