Rings vs Radials

[sparkwright]

I don't think this gets discussed enough on the forum.

Personally I think a 30 amp ring circuit in 2.5 mm2 is better than one or more 20 amp radials in 2.5 mm2.

The ring obviously has more capacity than one 20 amp radial.

It can serve a larger floor area.

One ring will take up fewer fuseways at the board than say two or more 20 amp radials needed to match capacity.

If a cable in a ring somehow gets damaged, the circuit could be converted into one or two 20 amp radials with minimal damage and disruption.

One unnoticed fault in the cpc will still mean each socket has an earth connection.

***

What about 30 amp radials in 4 mm2?

They are ok, but no one wants to spend extra money on 4 mm2, then struggle getting three or four wires into a terminal.

 

[stillp]

I don't think this gets discussed enough on the forum.

 

[EFLImpudence]

I don't think this gets discussed enough on the forum.

I agree.

Personally I think a 30 amp ring circuit in 2.5 mm2 is better than one or more 20 amp radials in 2.5 mm2.

Don't be personal.

The ring obviously has more capacity than one 20 amp radial.

That depends how big your ring is.

It can serve a larger floor area.

I only have several small floors.

One ring will take up fewer fuseways at the board than say two or more 20 amp radials needed to match capacity.

That is true numerically speaking.

If a cable in a ring somehow gets damaged, the circuit could be converted into one or two 20 amp radials with minimal damage and disruption.

I didn't think you liked 20A radials.

One unnoticed fault in the cpc will still mean each socket has an earth connection.

Oh, that bit is true.

What about 30 amp radials in 4 mm2?

If 30A BS3036 then not compliant.
If 32A MCB then BRILLIANT.

They are ok, but no one wants to spend extra money on 4 mm2,

Don't tell them how much the cable is.

then struggle getting three or four wires into a terminal.

It not a struggle. It's bendier.

 

[sparkwright]

Forgive me for using the 30 amp terminology for 4 mm2 radials, and for reminding me about 3036 fuses, I can remember using 30 amp cartridge fuses for these.

By converting a damaged ring into one or two radials is of course (as you know perfectly well! ) more a matter of convenience than preference.

 

[JohnW2]

Personally I think a 30 amp ring circuit in 2.5 mm2 is better than one or more 20 amp radials in 2.5 mm2.

Except in very low demand areas, I personally think that 30/32A sockets circuits are always preferable to 20A ones, regardless of the ring/radial issue. A 20A circuit is not adequate for 2 x 13A loads - indeed, not even adequate for one 3kW load and one 2kW load.

What about 30 amp radials in 4 mm2?

As I recently wrote, that would probably be 'the best of all worlds' since the usual debate is not actually a ring/radial one, but is about the dispensation in BS7671 to have 2.5mm² cable 'under-protected' in a ring final. A 4mm² (Method C) ring would do away with that issue, but would afford the (albeit small) benefits of CPC redundancy and lower EFLI (as compared with a 4mm² 32A radial). However, as you go on to say ...

They are ok, but no one wants to spend extra money on 4 mm2, then struggle getting three or four wires into a terminal.

(although 3 x 4mm² into may terminals {e.g. MK ones} is not much of a problem)

Kind Regards, John

 

[PrenticeBoyofDerry]

Don't be personal........

That depends how big your ring is.

Not getting personal then?

 

[PrenticeBoyofDerry]

Both ring and radial circuits play a part when I consider the best option for a particular circuit.
If think they both have pros/con and can lend themselves favourably in certain situations.

But there is nothing worse to find a ring final circuit, that has had the DIY arse ripped out of it!

 

[JohnW2]

Both ring and radial circuits play a part when I consider the best option for a particular circuit. ... If think they both have pros/con and can lend themselves favourably in certain situations.

It would be interesting if you could give some examples of situations in which you would favour a ring, and of other situations in which you would favour radial(s). [we are, of course, talking only about sockets circuits]

Kind Regards, John

 

[ericmark]

One radial for each socket from their own RCBO a modern equivalent of the old 15A system would clearly remove many problems associated with one device causing a disruption of supply to many but the cost and size of consumer unit means in real terms it is impracticable.

Money is a consideration and 2 ring finals will cost less than 4 radials specially if each has it's own RCBO.

Also the size of the consumer unit 12 way is about the maximum standard unit and one has to consider this as well.

So first consider the number of circuits 1-Hob, 2-Oven, 3-Shower, 4-Imersion heater, 5-Garage, 6-down-stairs lights, 7-upstais lights the list goes on and will change house to house but 3 ring finals will need likely 8 radials to replace them. So look at with 20A radials what is required.

Washing Machine dedicated
Tumble Drier dedicated
Dish washer dedicated
Immersion heater dedicated
Oven dedicated
Kitchen radial
Rest of down stairs radial
Upstairs radial

To be fair many of those listed should be dedicated radials as the appliance is over 2kW and not classed as portable but in the real world we don't.

There is really no argument radials are better but rings are cheaper assuming RCBO's on every circuit.

So now look at saving costs and using two RCD instead. You have lost the advantage of circuits straight away it really does not matter radial or ring one fault takes out half of the house.

So look at the compromise by using rings you need less protective devices so with a ring system you can likely use 6 RCBO's where with radial 10 MCB's and two RCD's.

Now this is the problem in the real world it's not just looking at radial v ring in isolation but as a whole and what we can afford.

So looking at what is wrong with the ring.
1) Sockets close to either end can cause an overload although rare.
2) Poor workmanship and maintenance can cause an over load.

The second seems to be main reason against the ring final. Poor workmanship can cause the ring to be broken and so can poor maintenance. In the main down to poor records. If on installing a ring a mid way socket is selected and the loop impedance recorded both line - neutral and line - earth it takes seconds to test once a year to highlight any faults.

I have two sockets which are marked up and I know they were tested and then the ring was confirmed then re-tested so simply plugging in once a year and without testing ring continuity as such I know it's OK as if there was a break the impedance would shoot up.

If we are saying after doing work it's not tested then the radial is more dangerous as only a single earth connection so more likely to lose an earth. If it is being tested then no problems with a ring.

Clearly there is a case for both. I have two non dedicated radials and two non dedicated rings. The radials were originally dedicated and are only there because of history.

I have discussed many times the case for a dedicated supply to fridge/freezer. Now mine have nice blue lights so with a power failure I would notice but before there is an LCD display but I rarely looked at it. So if the supply failed while at home how long before you would notice? But with the ring far more is lost so you notice the loss earlier. However there is more chance of losing the ring than radial. But main concern is when on holiday and when on holiday likely only the fridge and freezer running anyway so same chance of tripping.

So where would you use a non dedicated radial. Only time is where there is a likely hood of high earth leakage for example a row of computers. But it would have to be RCBO and likely not true domestic.

So to me in spite of saying radials all on their own RCBO's are best I simply could not afford it so would go for two rings on RCBO's rather than 5 radials on MCB's sharing a RCD every time.

As to splitting rings into two radials well maximum cables for ring is 106 meters and maximum cables for 20 amp radial is 32 meters so it is very dependent on how close the ring was to the limit. With 16A that increases to 42 meters next MCB down is 10A and that will allow 71 meters.

So it's not so simple just splitting a ring when there is a fault one may need a 10A MCB on one leg at 20A on the other if not split in the centre. Also to my mind if there is a fault you want to find it.

 

[bernardgreen]

If a cable in a ring somehow gets damaged, the circuit could be converted into one or two 20 amp radials with minimal damage and disruption.

Conversely if one needs an extra MCB in a fully populated CU with a bit of cable one can convert two radials into a ring and create a space in the CU

 

[ericmark]

Having separate radial for each bed room does give parental control of the TV. In real terms only in the kitchen do we ever draw full 13A on any socket so 16A radial to every room would not be a problem except when one looks at the consumer unit.

 

[sparkwright]

If a cable in a ring somehow gets damaged, the circuit could be converted into one or two 20 amp radials with minimal damage and disruption.

Conversely if one needs an extra MCB in a fully populated CU with a bit of cable one can convert two radials into a ring and create a space in the CU

Not necessarily.

With a radial circuit you can spur and branch wherever you like, to save cable perhaps, so there could be many spurs in a 'tree' formation.

One wouldn't want to spend too much time sorting out how a large radial could be wired.

 

[sparkwright]

Having separate radial for each bed room does give parental control of the TV.

So does a good old fashioned bo11ocking.

 

[JohnW2]

It's probably worth repeating here what I wrote in the other thread, namely:

It is perhaps worth remembering that the 'debate' is not actually about 'radials vs rings', per se, but, rather, about rings in which (per the 'dispensation' in BS7671) the In of the OPD exceeds the Iz of the cable.

If we were comparing a 32A (OPD) 4mm² (Method C) radial with a 32A (OPD) 4mm² (Method C) ring, then the ring would surely 'win', without argument. I can think of no sense in which the radial would 'be safer', but the 'CPC redundancy', and perhaps the lower EFLI, would confer some theoretical safety benefits to the ring.

Kind Regards, John

 

[ericmark]

I think all too often we say there is a problem with a system when really the problem is the use of the system not the system its self.

The ring system is very good. The problem is when people destroy the ring be it a wire come off a socket terminal when stuffed in to a back box which is too small or wire cut too short or any other action which causes the ring to be broken. If the rules are followed this will be highlighted during testing but so often testing is omitted.

But also of course errors can be made with radials and if this is with the earth terminal it can also be dangerous.

Education seems fail the ring system where we hear people talking about a lighting ring or fitting a ring in a garden shed. Even people who should know better seem not to understand the ring final system. I found one electrician had fitted twenty 110 volt BS EN 60309 sockets without build in MCB protection as a ring around a workshop using a 10 kVA transformer and a 32A MCB on the output.

I had the job when I pointed out the error of fitting sockets with MCB's in the socket.

I am sure we can all list the errors found due to even electricians making mistakes with rings.

However there is also plus side. I was sent to second fix an house when the normal electrician doing the work was ill. I fitted all sockets then tested the ring which was not a ring there was a break. I visited the next door house and realised it had an extra socket to what I had fitted. Use of hammer did locate the socket box which had been plastered over. Had it been a radial circuit this fault could have been missed and there would have been live wires behind the plaster with no indication as to where.

So here the situation which could have resulted without testing in two radials on a 32A MCB with testing resulted in correction.

The jumping to conclusions without testing also causes problems I have seen a 7/036 cable feed sockets with a 2.5mm link between them where some one clearly thinking it was a ring extended the circuit. It was however a radial circuit.

But one can't condemn either 4mm radial or the ring final because some people don't understand the system.

I will admit I often when talking about a ring final do miss out the word final. With a ring system with is not a ring final then the cable is capable of taking the full load. The idea is any part of the ring can be isolated in order to do work on the cable without switching off the whole supply ring. This is very different to the ring final system.

The word final means it's at the point of use. Even if another circuit is taken from the ring final some places there will be direct access.

I once worked on a warehouse where sockets were required for cleaning equipment some was fitted with a BS EN 60309 plug and some with a BS 1363 plug so both outlets were required. The warehouse walls were 25 foot high and there was loft space access it was also quite big so volt drop was likely a problem. We used SWA and glands so walls could be washed without ingress to sockets. In the loft space the ring (4mm) had a series of FCU's and each FCU feed a radial to the pair of sockets.

When it came to making out paperwork an argument started. Was this a ring final? I said no as there were no sockets fed direct from the ring all were fed from a FCU. Next were the drops radials or spurs? I said a radial as fused independent a spur to my mind was not fused. However BS7671 does call them spurs even when fused from a ring final but if not a ring final but just a ring then are they spurs or radials.

I still think calling it a fused spur is wrong it's a radial to me a spur is not fused.

Lets see the comments?