The Merits of Ring Final Circuits

Found this whilst looking for something else...

Ring circuits: public discussion

A public meeting to discuss the issue of Ring circuits was held at the IET, Savoy Place, London on 31st October 2007.

The discussion was chaired by Eur Ing N C Friswell BSc(Eng) FIEE, chairman of the national wiring committee JPEL/64. There followed a presentation from Mr DWM Latimer MA(Cantab) CEng FIEE entitled, ?The history of the ring circuit? , Mr HR Lovegrove IEng FIET put the argument ?Disadvantages of the ring circuit? and Mr M White BSc CEng FIEE FCIBSE discussed the ?Advantages of the ring circuit?.

The papers from the speakers are available as a free download. Please see the 'Of Related Interest' section on the right-hand side of this page.

from:

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history paper (on the development of the ring final circuit and the

13A plug) is very interesting; I wasn't aware that there's a debate about the merits of ring final circuits, but the "advantages" and "disadvantages" papers seem immature and often spurious in their arguments; quite like a partisan pub-discussion fueled by much lager!
Reply to
Rumble
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Fascinating. I wonder what the Chairman's Summary was?

To my mind the advantages paper is well though out. The disadvantages paper seems to list a lot of theoretical problems thought up at a desk, but without any evidence of them occuring in practice and hence unsubstantiated -- anyone reading it with no prior knowledge of UK wriring would expect our systems are all bursting into flames, whereas we're actually one of the safest.

Reply to
Andrew Gabriel

it seems to me as an ameuteur that the arguments agains ring circuits in the kitchen are good.

washing machiines and dryers and dishwashers and microwaves are often near to each other, so the circuit isnt balanced so whats the point of having a ring?

and they say testing a ring circuit is often skimped, and if theres a break in a wire or 2 the circuit will still work.

is it just to make circuits baffling for non experts so we have to pay for experts?

but its the fact that if a live wire is broken that the ring circuit will still appear to work, all the sockets will work, but there could be 2 loose wires that makes me think ring circuits are bad....

Reply to
George

Good point, say if they're 1/4 the distance from one end of the ring, won't much more current (4x) go down that side of the ring than round the other side.

Seems to me rings were good for historical reasons, eg when wire and consumer units were relatively expensive in post war britain.

cheers, Pete.

Reply to
Pete C

Yup, saw that a while ago. For what is supposed to be a technical discussion, it seems to advance rather feeble arguments.

Reply to
John Rumm

Not convinced. You just need to plan carefully.

They frequently cope with real world scenarios more easily. The circuit does not need to be perfectly balanced either to remain safe and workable, you just need to avoid daft layouts with all the heavy loads concentrated at one end. Rings also tend to have a nifty natural ability to rebalance themselves in the event of abuse.

Test of all circuits may often be skimped - it not a problem restricted to rings. When you analyse the most common fault patterns that are typical found in circuits, many of them affect radials more seriously than rings.

Same goes for a broken earth on a radial.

Have a look at some of the scenarios discussed here:

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is it just to make circuits baffling for non experts

There are more complex things than basic topology that one needs understand before designing and implementing circuits.

Loose wires are far more common than broken ones IME. Where there is a broken wire, it is more likely to be an earth than a phase or neutral. Factoring the effects of these different potential events into the different circuit designs is not a clear cut "black and white" or "good and bad" analysis.

Reply to
John Rumm

Not for long....

The resistance of the cable is proportional to the conductor temperature, which is in turn proportional to the *square* of the current carried.

So the resistance of a wire in a typical circuit cable will rise from

7.4 miliohms/meter at 20 degrees C to around 18 miliohms/meter at 70 degrees (the maximum conductor temperature for a PVC cable). That means that at full conductor temperature, the shorter cables effective length increases by about 2.4 times.

If you do some sums, you will see it is actually quite hard to seriously overload one leg of the circuit when you take these factors into account. (unless you have cables already subject to heavy de-rating - in which case your design should have selected a different spec for the cable in the first place).

Oddly they have actually become more relevant with the passing of time. Today's electrical loads tend to be far more numerous and spread around than they ever were in the past (i.e. diverse loads spread over a big area). A situation that a ring circuit is ideally suited to.

Reply to
John Rumm

Then you need to up your amateur status via research. They have been around for a long long time.

Are you saying it's common to feed these things from sockets very close together? And that the CU is also close to these sockets for one leg, with a long run for the other? I'd say that a very rare occurrence.

A 'break' in a radial circuit may also leave some sockets working, some still live and dangerous because of no earth or neutral. The answer is not to have a break. And testing should never be skimped. Or should poor workmanship be tolerated on rings, radials or any electrics. And as a DIYer it's up to you to make sure it isn't. It's not rocket science.

What's baffling about a ring?

The answer is simple - good workmanship. Otherwise don't touch electrics.

They are if anything even more appropriate these days than when first used due to the plethora of low current appliances we all now have.

Reply to
Dave Plowman (News)

How do you get that from the temperature coefficient of copper (0.00393)?

Maybe but how many other countries use them?

cheers, Pete.

Reply to
Pete C

Anyone?

John's figures look way wrong to me, giving a temp coefficient of copper as 4.8%/=B0C

This is over a factor of 10 out over 0.393%/=B0C!

cheers, Pete.

Reply to
Pete C

By using the round trip resistance from table 6E2 and the single conductor resistance from table 9A in the OSG... ;-)

Well spotted that man! (should teach me not to do sums at 4:30 in the morning)

Make that "rises from 7.4 to 9 mOhms/m. Which gives an increase in length of 1.2".

This ties in somewhat better with 7.41 ( 1 + 0.004( 70 - 20 ))

Very few... perhaps that is one of the contributing factors to why we have so many fewer accidents with fixed wiring?

Reply to
John Rumm

Perhaps not, as Holland have less accidents than we do.

I'd expect the main factors for fixed wiring are the age of the installation, how well the install was done, and the use of RCDs

Though with ring mains we're locked into using a plug top that needs correct fusing, carries less current and is different to the rest of Europe. And is bloody painful to step on in bare feet!

cheers, Pete.

Reply to
Pete C

On Tue, 8 Jan 2008 10:14:53 -0800 (PST) someone who may be Pete C wrote this:-

The current rating depends on the particular plug.

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lists the likely ones in a domestic setting.

I bet some of them get rather hot if operated at their rated current.

Reply to
David Hansen

Well if our plugs require correct fusing (which has a max of 13 amps) imagine the safety aspect of having a plug on a radial with only the protection offered by the device in the CU?

BTW all of Europe doesn't use the same outlets. Nor does it really matter anyway.

Reply to
Dave Plowman (News)

Don't think so -- none of the main continental European countries has less fatalities than us, only one of the Scandinavian countries (can't recall which one).

Holland has a nasty situation where they allow earthed appliances to be connected to unearthed supplies in what are supposed to be (but all too often aren't) earth-free zones. (They might not allow this anymore, don't know, but it was standard practice for a long time.) In the early days of trying to design an EU-wide plug (long since abandoned AFAIK), one of the requirements was that an earthed plug mustn't mate with the Dutch un-earthed sockets for this reason.

'Correct' fusing is rather a misnomer. All products which have been on the market for a decade or more have to work safely in any appropriate socket outlet in the EU. Many of these are protected at 16A, so you should actually be OK putting a 13A fuse in any appliance you bought in the last decade. I wouldn't necessarily advocate that, but the appliance must be safe when protected at up to 16A for use in other EU countries. (Extension leads are an exception, but it's pretty impossible to come up with workable rules which make extension leads safe. Some older appliances which predate the free market rules will have leads which are too long to safely use a 13A fuse, or run on a 16A circuit.)

Look on it as a safety feature -- "you better not step on me"! Most EU plugs you can step on with no consequences at all, until later when they fall to bits leaving you with a set of live contacts in your hand as you're plugging it in. A 13A plug generally inflicts enough pain before you get a chance to put your full weight on it to avoid you damaging it ;-)

Reply to
Andrew Gabriel

I bet they're much better than ours at rated current; have a look at the part insulated pins on the latter.

cheers, Pete.

Reply to
Pete C

Maybe in the 50s and 60s, these days a 16A MCB generally works much better than a 13 fuse.

cheers, Pete.

Reply to
Pete C

LOL! Nice logic there +)

Only pins up, the other way the L/N pins bend quite easily where they're part insulated.

A 2 pin euro plug is pretty hard to damage or get damaged by when being stepped on.

cheers, Pete.

Reply to
Pete C

You wouldn't be able to plug it in then...

They also have a nasty habit of falling out of the socket...

Owain

Reply to
Owain

What puzzles me is why so many standard plugs have the cord leading perpendicular from the outlet, rather than at right angles as in the UK plug. The UK plug means the cors are all neatly parallel with the wall, rather than getting in the way of whatever is in front of the outlet.

-- JGH

Reply to
jgharston

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