Ring Final Circuits

[Pete10001]

Hi

I have been following sever forums, and on one I had a discussion about  RFCs I was adamant that the RFC could only be used for 13amp Socket outlets, it seems I could have incorrect, I read in Novembers PE that BS 7671 does not preclude it's use for other applications, has anyone got any thoughts on what sort of applications they mean. I don't practice our wonderful art any more retired now, can't get down to those awkward positions any more, I mean sockets and the like.

Pete TMIET

 

[steptoe]

Ive used rings for lighting circuits to keep Zs down where it wasnt practical to upsize the cable,

or perhaps as I was extending and it would have been prohibitive to replace all the existing cable.

 

[Pete10001]

Thanks Steptoe

 

[kerching]

I too have used a ring for lighting for the same reasons.

however incannot remember the last time i used a ring for sockets!

 

[Badger]

i use ring finals for sockets an awful lot i believe it is a much better wiring system due to the fact if a fault develops cutting into a cable on a ring gives a earth path either way round to fuseboard or outlets but on a radial if the earth is damaged half way from c/unit to end socket outlet the last few outlets from damage to end have no earth, plus the earth zs readings are lower in general. ill stick with ring finals for my whole of my days until im told im no longer allowed to install them.

 

[pewter]

On fire alarm circuits they are called loops

 

[SBS Dave]

Hi Badger,

If I follow your logic, you are saying that in the event of the continuity of the cpc being broken, with no damage or shorting to live or neutral, which would trigger circuit protection, then all outlets would function as normal. That means the fault could exist, but could stay undiscovered. In the meantime, the Zs of the outlets would increase substantially, due to radial cpc only, which could jeopardise disconnection times. Also, you would effectively have a 5mm cable ( 2 x 2.5mm), backed up by only a 1.5mm cpc, which probably doesn't meet the criteria for reduced cpc size allowances.

When you say it is a better wiring system, I assume you mean better than radials. Let's take a 32A kitchen ring circuit versus 2 x 20A radials. Ring capacity, 32A, total radial capacity, 40A. If a fault develops on the ring, the whole ring is off. If a fault develops on a radial, maybe half the kitchen would still be working. It could be argued that less cable is used with the two radials, because you don't have to complete the ring. This could offset the cost of the extra MCB / RCBO. With a 20A radial, there is no such thing as a spur off a spur, which means later extensions would be easy and still be safe. Testing of 2 radials is easier than testing a ring circuit, etc . 

Whilst I acknowledge there are good features of ring circuits, I cannot agree that it is a better wiring system. However, on your jobs, it is your opinion that counts, not mine.

Hi Pete 10001,

I too am a pensioner and a member of the IET. My memory is not as good as it once was, neither are my knees, but I still keep in touch with the Industry, via my SBS Trade Sales. I couldn't compete with these young guys, anyway, so I am happy for them to do all the installs, as long as they use my kit!!! 

David Stansfield MIET

 

[Badger]

so what happens then if a customer changes a socket as part of a radial and doesnt connect two earths together correctly thus parting the earth at that point the circuit there after will not be correctly earthed but there will still be a live and neutral thus working circuit but not protected, ill stick to ring finals as i feel that is the better wiring method. call me old fashioned,

 

[steptoe]

badger,

do you know or understand the one and only reason rings were ever allowed in this country?

and the ONLY reason for their continued use is pure and simply old habits, nothing else.

 

[steptoe]

^^^^

as above,

they are a bit like everything else,

outdated and living in the past,.

WTF do you think happened a lot of our motor industry?

couldnt move on into the future, so floundered.

 

[Sharpend]

Copper Shortage and WWII springs to mind  :innocent

I am not a fan of rings at all - Its ok if you understand them and ok if you know how to test them and alter them - sadly not many do.......

Strange that seeing as they are common to most domestic situations, perhaps a training issue?

 

[steptoe]

Strange that seeing as they are common to most domestic situations, perhaps a training issue?

same as most things domestic,

its 'always' been like that,,,,,,,,,,

 

[kme]

I`ve seen em used in a commercial environment - 4mm pyro ring, used as the submain feed to a floor of rooms in a hotel ( 100A HRC protection ]

 

[SBS Dave]

Hi Badger,

I think you have hit the nail on the head with regard to customers. Presumably the same nail that went through the cable in your first example, without damaging either the live or neutral. It is possible, but IMO, it would be quite rare, so most of the time, the protective devices would do their job

I don't think you can ever make any installation "customer" proof, which I take to mean DIYer. Not connecting the earths properly could be the least of your worries, since the DIYer will be messing with the browns and blues.

As I said above, I respect your opinion, but other than the "if the earth gets broken" scenario, what other features of the ring circuit do you think makes it a better wiring system??

SBS Dave

 

[Pete10001]

Hi Dave sbs

Nice to talk to another wrinkley, along with all the other good guys on this forum, good luck with sbs

Pete1001

 

[steptoe]

what I like about the ring is this,

if it gets broken you can still have 32amps flowing through a cable with a max capacity of 27amps,

saves having the heating on in the winter,  ]

 

[Manator]

Hi Badger,

I think you have hit the nail on the head with regard to customers. Presumably the same nail that went through the cable in your first example, without damaging either the live or neutral. It is possible, but IMO, it would be quite rare, so most of the time, the protective devices would do their job

I don't think you can ever make any installation "customer" proof, which I take to mean DIYer. Not connecting the earths properly could be the least of your worries, since the DIYer will be messing with the browns and blues.

As I said above, I respect your opinion, but other than the "if the earth gets broken" scenario, what other features of the ring circuit do you think makes it a better wiring system??

SBS Dave

I almost never wire in ring format any more. I can never understand why houses use rings, its probably because of the shortage of copper from the war years, and all the Chinese buying all the surplus.

I should imagine a mature seasoned well experienced electrician going into a house and ripping out half of the cable installed and still being able to satisfy regulations and requirements.

I have seen completed EIC's with a stated maximum demand well in excess of the main supply fuse. I must assume that they are just pretending to be electricians.

Rings are what people buy when they want to get married, not for a general wiring solution.

 

[batty]

Well I still install ring mains. I am interested as to what other people do on rewires? 

 Radials it seems to be the way people are wiring these days. So in say a four bedroom house would you put one 20 amp radial or  two on the bedrooms. What about kitchen/utility is that 20 amp radials also or a 32 amp on 4mm?

 On new builds do you use 2.5 or 4mm on a 20 amp circuit?

 

[steptoe]

i use a mixture tbh,

its mostly council refurbs i do, and they like to see a ring in the kitchen.

 

[Manator]

Well I still install ring mains. I am interested as to what other people do on rewires? 

 Radials it seems to be the way people are wiring these days. So in say a four bedroom house would you put one 20 amp radial or  two on the bedrooms. What about kitchen/utility is that 20 amp radials also or a 32 amp on 4mm?

 On new builds do you use 2.5 or 4mm on a 20 amp circuit?

Just look at what equipment will be used in a bedroom Batty. The best part would be under 6amps, however include the option (during winter) for a heater.

As for kitchens I have never liked the idea that a ring circuit could be easily balanced across all loads. The washing machine dryer and cooker is very often placed in a triangle very close together, and we have a habit of RCD ing freezers and fridges!

The next time your on a job, get a clamp meter and record the readings over a 24 hour period, you will be surprised at how low it is even with all your construction tools.

.