ring main circuits

NickNickleby

Are ring mains still used?

To my thinking, a ring main was a way of providing lots of current carrying capacity without actually increasing the gauge of the cable - I'm obviously not an electrician, so that's just my thinking. I also think a ring main is a bad idea - risks might ensue if there's a break in the ring, ie all the current down a single leg.

I ask, because I recently looked inside a consumer unit and saw gazillions of MCB's and thinking to myself "is there one per socket?:eek::pac:" So I thought perhaps they're all radials.

Cheers

adrian92

I agree with you. Ring main system potentially dangerous.

A break on one of the two circuits, as you pointed out, will result in the remaing half talking up tye load.

Hopefully this approved system will be abolished

NickNickleby

Hi Adrian.

Ah, so it sounds like they're still 'legal'. But, would electricians nowadays still use this technique, or do they use radials (I hope that's the right term, my friends were electricians years ago, and I heard them using it to describe non-ring circuits).

In my own house, its a single ring main serving upstairs and downstairs, and this was never an issue till we knocked down a wall between the kitchen and dining room, to be left with a 2.5mm cable swinging from the ceiling :mad:. Unfortunately the shortcut remedy was to re-route the cable, rather than reconfigure as two separate circuits. I suspect the builder's, ahem, 'electrician' wasn't comfortable doing it the other way.

The good thing is that most things these days seem to demand less current than before, eg tv's and radios, and electric fires are a thing of the past - well in my house anyway. We bought more jumpers:pac::pac::pac:

Risteard81

A properly constructed and verified ring final circuit is entirely safe and has certain advantages. It could also be argued that a radial final circuit has increased risk with the cpc being broken but the socket-outlets still functioning, whereas with a ring final circuit there is redundancy with these. (Albeit obviously the protective conductor should also be in an intact ring.)

NeuralNetwork

They’re not an issue where used correctly and well designed.

One of the biggest problems with them is that the regulations in the U.K. tended to allow one per floor in domestic buildings with almost unlimited numbers of sockets. That’s only really acceptable in a very compact house.

That’s largely addressed in Irish regulations with specific circuit requirements for kitchens, where heavy loads are likely to occur and you should design systems to reflect real world use, not just barely comply with minimum technical requirements.

You’ve also an issue where the loads can be all at one side of the ring eg a cluster of kitchen appliance. If you’ve a very large/long ring that’s far from an ideal situation as the current carrying capacity is assuming flows in both directions. Again, modern Irish regs deal with that, but it’s not ideal if you’ve something like large numbers of plugged in heaters etc.

In a complex house layout or a more sprawling building they can have disadvantages too in the sense that a ring might not be very practical as a layout.

If someone breaks a ring in DIY work or a fault, you can end up with two radials on the same breaker without adequate protection and you’re also totally reliant on fused plugs being used universally to protect appliance cords.

Fault finding is also significantly messier in a house with say 2 rings instead of say a 20Amp radial going to each room. You can see a tripped breaker or if it’s an RCD trip you can isolate each circuit and localise the fault quite quickly by just flipping switches on the board.

I found in London when that happened you were left with a whole floor of the house tripped out. It was way way worse in old wiring with rewirable fuses, as were very common there.

As for the CPC (earth) breaking and being left disconnected, that’s a risk in either approach but there’s so much you can do in design to avoid every possibility of DIY hack jobs, the most likely cause of that.

NickNickleby

Thanks Risteard and NeuralNetwork,

Very well explained, cheers!

So, it sounds to me like rings are still very much a thing. In my house I can remember going round the : hall; living room; dining room; and three bedrooms trying to find the culprit when the ring fuse blew. (yep, it was that long ago - fuses. Anyway, my gripe at that time was that more individually protected circuits would lessen the impact of an outage. Perhaps, being fuses, there was less room to fit more fuse holders, limiting the number of circuits.

Gosh, rewireable fuses. We had them in a house in England when I was a kid. Also had round pin sockets and plugs and double adapters for the light socket. Handy if you needed light while ironing :eek::eek::eek:, yes, I remember seeing the iron plugged in to the light. But were going WAYYYYY back with that one.

My house wiring is a disaster, and some day I'm going to get it done, but I know the pain and expense it will involve. I'll probably ask for more circuits to reduce widespread impact of a mcb (very rarely) tripping. The kitchen has a red/black 2.5mm and a 4.0mm for the (now gas) cooker. Mrs Nick wants a new kitchen, all electric, so I know there's guaranteed pain there, probably lifting floors etc etc. AND the existing cables are just routed through the cavity blocks and out into the porch to the fuse box, where there's no earth rod connected - all the houses in the estate are like that, but many of them now have little green boxes sunk in the side passageway, where I presume a new earth rod has been installed.

Anyway, I appreciate all the comments. As usual here on the professional forums, ask and you you shall receive.

Cheers!

NeuralNetwork

Rings are still a thing, but they're probably used less in Ireland than they are in the UK.

That may well be because of the history of having used more continental-inspired wiring historically here, so practices may have been more conservative around use of rings, even if the regulations allow them.

If you go back to houses built in the 1950s and into the 60s here there were 16 amp 'Schuko' plugs commonly used for example - the same as modern CEE 7 sockets found in most of Europe today.

It very much just depends on the choices made by whoever designed the system though, but 20amp radials are far more commonly found in Irish wiring than they would be in the UK.

The older fuses here are Siemens derived, DIN-standard 'bottle' shaped 'Diazed' and 'Neozed' cartridges. They're still used in quite a lot of applications where a fuse is required, including in industrial settings. The UK rewirable type wasn't used here, nor were UK cartridge fuses for domestic circuit boards.

I'm not sure if the UK ever used Diazed in homes, but it was definitely used in industry.

You could sort of describe the Irish approach to wiring as having influences from Britain but also from continental European standards, mostly in line with German and some Scandinavian approaches driven by influence of Siemens, ASEA, AEG etc in the earlier days.

Older UK regulations were also a bit of a free for all. When you consider that before the 1970s there were competing types of plug/socket design, the old BS546 (round pin) system was a total mess of different plug sizes and mutually incompatible sockets and you even had different power boards in the UK using different voltages at one stage.

So, from an Irish point of view standardising on 220V 50Hz and (at least initially) using a single plug type made sense, although British standards got added to the mix.

The present-day UK regs and fittings are a pretty logical system though. I'm just wondering exactly what's going to happen as Brexit causes further divergence if the UK stops using CE marking for example, it will be very problematic for a lot of devices and I would suspect we'll have to move more towards European standards again.

adrian92

The op pointed out the risk with ring main, no way of knowing if there is an open circuit. (A separate point is the use of fused plug especially 13 amp which provide no protection. Hopefully Ireland will use the EU standards)

NeuralNetwork

NeuralNetwork wrote: »

That’s largely addressed in Irish regulations with specific circuit requirements for kitchens, where heavy loads are likely to occur and you should design systems to reflect real world use, not just barely comply with minimum technical requirements.

It does say in 101 that ring circuits should not be used in kitchens.
(page 311 ring final in domestic & similar) But should not isn't don't !
Haven't looked in 10101 .

maxamillius

Came across two rings in a friends house the other day. Upstairs & downstairs sockets on one and the kitchen on the other.
Upstairs and downstairs ring has 13 sockets on it.
Kitchen has 5.
Both on 20amp breakers.

User3.

maxamillius wrote: »

Came across two rings in a friends house the other day. Upstairs & downstairs sockets on one and the kitchen on the other.
Upstairs and downstairs ring has 13 sockets on it.
Kitchen has 5.
Both on 20amp breakers.

Not the greatest

There isn't a lot of use for them now in domestic work

Ring main circuits and Ring final circuits still have a lot of uses outside of that

Risteard81

User3. wrote: »

Not the greatest

There isn't a lot of use for them now in domestic work

Ring main circuits and Ring final circuits still have a lot of uses outside of that

I still install ring final circuits from time to time. But it always annoys me when I come across a ring final circuit protected by a 20A device. I mean why? What is the point? Pretty much the main benefit is that it can be protected by a 32A device (or 35A fuse for older jobs), so why install one and then remove the actual benefit? It's just idiotic.

User3.

I worked on large commercial jobs where the boards were all 4sq ring finals and C20 mcbs

maxamillius

Risteard81 wrote: »

I still install ring final circuits from time to time. But it always annoys me when I come across a ring final circuit protected by a 20A device. I mean why? What is the point? Pretty much the main benefit is that it can be protected by a 32A device (or 35A fuse for older jobs), so why install one and then remove the actual benefit? It's just idiotic.

Seems very odd alright, always assumed they were on 32a breakers, first time I’ve seen them on 20s. House was built in the 90s

User3.

maxamillius wrote: »

Seems very odd alright, always assumed they were on 32a breakers, first time I’ve seen them on 20s. House was built in the 90s

A lot do put them on 20s , I'd say they're gone now for new domestic work

They still have uses in industry and power distribution

Risteard81

User3. wrote: »

I worked on large commercial jobs where the boards were all 4sq ring finals and C20 mcbs

A commercial job is a bit different because that might be snaking around trunking and perhaps has been done that way for volt drop reasons. But in a domestic dwelling, why go to the trouble of installing a ring final circuit and then derating it to a 20A protective device?

gctest50

So if the ring breaks the cable will be way below its' capacity ?

2011

Risteard81 wrote: »

A commercial job is a bit different because that might be snaking around trunking and perhaps has been done that way for volt drop reasons. But in a domestic dwelling, why go to the trouble of installing a ring final circuit and then derating it to a 20A protective device?

To push up standards.

You could ask why should the CPC be increased to the same size as the phase conductor even when maximum permissible disconnection times are already being exceeded.

You could also ask why the casings of motors have equipotential bonding cables connected to them even when it has been proved that it makes no measurable difference to the resistance between it and all simultaneously accessible conductive parts.

In industrial installations we normally wire lighting circuits in 2.5 mm sq. cable regardless or length of run and have no more than 6 luminaries per circuit.

I know from direct experience that many of the offices in the IFSC have socket circuits wired in ring using 4mm sq. cable in ring fed from 16A C type RCBO’s. When I questioned this (I was an apprentice at the time) I was told that it provided a more reliable circuit that remained safe in the event that the ring was broken. Even though they were wired in class 4 steel conduit and steel trunking and all cable runs were short CPC’s were 4 mm sq. This meant that even when a CPC was broken / not properly connected earth fault loop impedance tended to be sufficient. So again under various fault conditions the circuit remains safe.

NeuralNetwork

I’d agree there’s nothing wrong with a ring, what always concerned me about them was the practice of allowing 32amps on inappropriately smaller conductors and also the reliance on local fusing to protect flexes.

From the point of view of providing a robust, safe power supply a ring on 20A or 16A MCB makes sense to me.

The use of rings in houses in the U.K. came down to a post war copper shortage apparently and a desire to save materials while providing more sockets.

The U.K. systems always had a bit of an extreme approach to fusing and ludicrously complicated arrangements.

If you look at the old BS546 round pin system, it had at least 3 different types of plug and socket - 2amp, 5amp and 15amp, all of which were mutually incompatible. Then you’d a further set of incompatible 2 pin plugs (the current British shaver plug, which looks like a Europlug with shorter, fatter pins is derived from one of them.)

The logic was that you had different ratings of circuit for different devices, but the reality was everything was plugged in with messy adapters and plugs with adjustable pins and so on.

The U.K. then adopted the current rectangular pin system, with over-fused ring circuits local fusing and continued a similar and quite weird focus on fusing everything at very low ratings. So you ended up with table lamps with enormous, fused plugs.

Elsewhere in the world you normally have one socket type rated at 15 or 16 amps (Schuko, NEMA etc) sitting on a 16-20Amp circuit and it will accept grounded or non grounded plugs, or compact plugs like Europlug, suitable for different appliances and an assumption that appliances and plugs can survive a fault current for long enough to trip the MCB or fuse, without needing local fusing.

We’ve ended up with very large 13 amp grounded plugs on everything from a tumble dryer to a laptop, to a phone charger and they are enormous & impractical and we’re back to weird folding pins & so on again on some devices.

It’s one of those systems that seems over engineered and often to be a solution in search of a problem.

Also in the modern era we are increasingly in a world of many, small and portable electronic appliances. So having an ability to have plenty of sockets makes sense. However, you don’t need a system that seems to imagine we would all be carrying multiple 4 bar electric fires, kettles and tumble dryers around from room to room.

Instead, the systems that have an ability to use compact plugs like Europlug & NEMA now have big advantages from a practical point of view.

Also things like safety shutters have been adopted in other systems and RCD usage is far more universal in most continental countries (and Ireland) than the U.K., where it became mandatory much later.

I think the system we use tends to be over hyped by rather nationalistic U.K. commentary online. In reality it’s safe but it’s bulky and impractical.

2011

NeuralNetwork wrote: »

I’d agree there’s nothing wrong with a ring, what always concerned me about them was the practice of allowing 32amps on inappropriately smaller conductors and also the reliance on local fusing to protect flexes.

+ 1

From the point of view of providing a robust, safe power supply a ring on 20A or 16A MCB makes sense to me.

You wouldn't be alone.

The U.K. systems always had a bit of an extreme approach to fusing and ludicrously complicated arrangements.

I can't say I have seen their "extreme approach to fusing".
Have you any examples?
All I can think of was how they permitted rewardable fuses long after we had banned this madness.

NeuralNetwork

I mean that in all other systems there’s an assumption that an appliance plugged into a socket is generally very safe and the flex isn’t going to burst into flames at any moment because it has been designed with the assumption that it should be able to withstand a fault on a typical socket circuit, long enough not to need the addition of local fusing.

The old U.K. approach was that a lamp, for example, was connected to a 2amp plug which went into a 2 amp socket and that was protected by a low rated fuse on the fuse board (in theory anyway).

They carried that approach over to BS1363 by placing a fuse in every plug. So you’d have a table lamp plugged in via a 3amp fuse in the plug itself.

Everywhere else just uses 15 - 16 amp rates socket circuits (or 20 amps) protected by an MCB and that’s all they seem to need.

France, for example, at one stage used local fusing with fuse carriers in every socket and light switch and abandoned it in modern wiring as unnecessarily complicated and subject to possible risks like people bypassing fuses.

It just seems to be a solution for a problem that nobody else seems to have and a very bulky solution!

Risteard81

2011 wrote: »

To push up standards.

You could ask why should the CPC be increased to the same size as the phase conductor even when maximum permissible disconnection times are already being exceeded.

You could also ask why the casings of motors have equipotential bonding cables connected to them even when it has been proved that it makes no measurable difference to the resistance between it and all simultaneously accessible conductive parts.

In industrial installations we normally wire lighting circuits in 2.5 mm sq. cable regardless or length of run and have no more than 6 luminaries per circuit.

I know from direct experience that many of the offices in the IFSC have socket circuits wired in ring using 4mm sq. cable in ring fed from 16A C type RCBO’s. When I questioned this (I was an apprentice at the time) I was told that it provided a more reliable circuit that remained safe in the event that the ring was broken. Even though they were wired in class 4 steel conduit and steel trunking and all cable runs were short CPC’s were 4 mm sq. This meant that even when a CPC was broken / not properly connected earth fault loop impedance tended to be sufficient. So again under various fault conditions the circuit remains safe.

I fear you've missed my point. I acknowledged that there may be legitimate reasons with a commercial installation. My question was why in a domestic environment someone would go to the trouble of installing a ring final circuit and then derating it to 20A - taking away pretty much the main advantage of it being a ring final circuit.

I believe that ring final circuits have their place, and I still install them. That said, it's far less usual for me to install them than it was in the past, when pretty much all domestic socket final circuits would have been ring final circuits - and also in non-domestic premises in trunking and conduit. I probably tend towards radials nowadays, but where a ring is advantageous I'll use it.

It's not "pushing up standards" installing a domestic ring final circuit on a 20A device - it's fundamentally misunderstanding the nature of a ring final circuit, Kirchoff's law etc.

Risteard81

2011 wrote: »

All I can think of was how they permitted rewardable fuses long after we had banned this madness.

Rewirable fuses (BS 3036) are still permitted under BS 7671 (subject to a 0.725 derating factor), however since the 17th Edition (2008) there was a note that fuses should preferably be of the cartridge type.

adrian92

We differ, a bit, on ring main.

What about the use of 13A fuses on each plug?

Risteard81

Risteard81 wrote: »

I fear you've missed my point. I acknowledged that there may be legitimate reasons with a commercial installation. My question was why in a domestic environment someone would go to the trouble of installing a ring final circuit and then derating it to 20A - taking away pretty much the main advantage of it being a ring final circuit.

Perhaps to make it responsibly failsafe and they're being paid by the hour?

2011

Risteard81 wrote: »

My question was why in a domestic environment someone would go to the trouble of installing a ring final circuit and then derating it to 20A

So that in the event of a break in the ring the cables in the circuit remain protected by the overcurrent device. This would not be the case if a 32A MCB was used.

NeuralNetwork wrote: »

I’d agree there’s nothing wrong with a ring, what always concerned me about them was the practice of allowing 32amps on inappropriately smaller conductors and also the reliance on local fusing to protect flexes.

+1
Point well made.

Although the standards in industrial / commercial installations tend to be higher, the fact that the same laws of physics apply can be forgotten at times

Emptur.

If you have a longer run on final circuits they're handy for that even fused at 20A , keep the voltage drop to regulation

kramer1

My main experience with ring mains has been when some one changes the board, doesn't bother verifying anything and you end up with a ring main fed from both ends through a 20 amp breaker. I know none of this should happen as nobody but a rec should be near a fuse board and a rec should have enough sense to test while changing one bit I've seen it a few times

Emptur.

kramer1 wrote: »

My main experience with ring mains has been when some one changes the board, doesn't bother verifying anything and you end up with a ring main fed from both ends through a 20 amp breaker. I know none of this should happen as nobody but a rec should be near a fuse board and a rec should have enough sense to test while changing one bit I've seen it a few times

Switch off each MCB individually and check for dead

Should be part of a board upgrade

kramer1

Emptur. wrote: »

Switch off each MCB individually and check for dead

Should be part of a board upgrade

Should be, but come across some real cowboy stuff out there