The Merits of Ring Final Circuits

[David Hansen]

On Thu, 10 Jan 2008 02:33:54 +0000 someone who may be John Rumm wrote this:-

I could pull the plug out of the socket with mine, which can be done without moving anything.

[Dave Plowman (News)]

Well yes, but hobs weren't the issue. Of course these need a suitable isolator switch. Especially since non I've seen have a built in one - unlike many other appliances. Things like washing machines and dishwashers are what I'm on about.

As regards needing an isolator switch I'm not sure the power of the device matters to the principle.

I'm clear on the arguments about having a separate circuit for things like a freezer to prevent faults elsewhere removing the supply to these and causing unnecessary expense through wasted food etc. But what I take issue with is the blind statements from prats like dribble who seem to think the loads from a washing machine etc are in some way special requiring its own radial. Or that it requires a separate isolator.

[Doctor Drivel]

Chav, if there are sockets under the sinks then none needed over worktop.

Read the links, they go into it. They say:

The disadvantages of Ring circuits are numerous:

?? Compliance with Regulation 433-02-04 ?? Not understood - lack of training of electricians from other countries ?? Susceptible to fault conditions ?? Testing and fault finding is very time consuming and costly ?? Fault conditions are not apparent when in use ?? Use more cable and take longer to install - waste of resources ?? Generally not cost effective

Advantages of Radial circuits

Greater flexibility

?? Less cable would be needed, means ?? Less time to install, means ?? Lower installation cost ?? Also means, less drain on the world's resources of copper ?? The problems created by Regulation 433-02-04 - distributing load evenly in a ring circuit (that nobody takes any notice of) would disappear thus reducing the exposure of the contractor to a breach of regulation claim. ?? Considerably less time required for inspection and testing. ?? Less likelihood of installation faults ?? Any breaks or loose connections will be readily identified when testing. Disadvantage of Radial circuits ?? More circuits required means: ?? Larger distribution boards ?? More circuit breakers required

Chav, you must get to know the difference between an radial and ring.

Chav, you must get to know the difference between an radial and ring.

[Dave Plowman (News)]

If you're going to the bother at the design stage of fitting an isolator switch, why not simply provide a socket outlet for the appliance which isn't behind it and therefore reasonably accessible? They all come with mains leads long enough to allow this.

[Dave Plowman (News)]

Same here - a deliberate design feature in my case. As regards having an isolator switch I doubt any repair man would rely on it but would want to unplug the appliance before servicing.

[Dave Plowman (News)]

Prat, if an electrician 'from another country' doesn't 'understand' a final ring circuit he/she simply shouldn't be touching anything electrical in this country as he's not qualified to do so.

Please keep your future dribbling about how not to cut plastic pipe. It's what you're best at. Leave electrics to those who provide sensible information.

[Roger]

The message from "Dave Plowman (News)" contains these words:

Unsightly trailing leads (that may or may not be a trip hazard depending on how clever your layout is) may be sufficient impetus to some people to hide the socket away behind the device. Such a socket doesn't have to have its own isolator, it could be on a spur, but if there is not a convenient socket to spur off putting in either a new socket or a FCU to spur off takes much the same effort and gives much the same end result visually. The FCU may never get used in an emergency but it is there in the no doubt remote possibility that it would be useful.

[Doctor Drivel]

Please eff off as you are a plantpot.

[Doctor Drivel]

There is a distinct move away from rings and being compatible with the rest of the wrold.

[Dave Plowman (News)]

Any hard evidence for this wild statement? Not that I'd expect you to bother with the facts in this matter anymore than any other you spout your dribble about.

Perhaps you regularly take your home to other countries where compatibility might matter. But most in this country don't live in trailers.

[Andrew Gabriel]

There's no move away from rings whatsoever, even where it might make some sense.

[Doctor Drivel]

Please eff off as you are a plantpot.

[John Rumm]

Then yours does not need separate isolation.

(putting sockets for under counter appliances in adjacent cupboards can work well here)

[John Rumm]

That is fine when possible. In some cases however it won't be - i.e. appliances either side, or narrow kitchen etc.

[John Rumm]

It is good design to provide a means of isolation for the appliance should it be required in the case of an emergency. If there were black smoke pouring out of a tumble drier, most would prefer to throw a switch in preference to having to grab the whole machine and pull it out.

Obviously if the socket is accessible without moving it then this is fine as an isolation method. If it is not however, and the only way to get at it is to move the appliance, then a separate switch capable of isolation should be used. Dribble's suggestion of using the circuit MCB is not acceptable.

[John Rumm]

Now what are you prattling on about?

In a battle of wits, this is like fighting with an unarmed man...

(by the way, if you are going to parrot a document you found on the web, it might be a good idea to chose one that is not as feeble and easily demolished as this one, or heaven forbid, you could even try applying some reasoning of your own)

This actually quite simple unless parts of the ring are subject to high derating factors. A little thought as to layout of the circuit is all that is required.

This is not a fault of the circuit design.

Less susceptible than a radial when looking at the effects of the two most common real world faults (high resistance connections, and broken earth connections)

This is nonsense really. Many of the tests are actually easier to perform on a ring circuit. The only time ring testing becomes difficult is when one is attempting to reverse engineer a circuit that has been bodged and the true topology is unknown.

Some are some are not. Same as with a radial. However the potential for truly dangerous faults like a completely disconnected earth are much greater on a radial.

This is again nonsense in most cases. Layout of socket positions should be taken into account obviously, and there is no requirement to use a ring topology where a circuit is linear in layout and wiring access is from one end. However in many cases a ring will be appropriate, and a radial would frequently need wiring in 4mm^2 cable to meet an acceptable design standard. Working with 4mm^ cable is significantly slower and more expensive than 2.5mm^2. The alternative is multiple radials which negates any arguments of reduced cable use etc.

Again no supporting evidence for this, and plenty of evidence to the contrary. A ring circuit may nee replacing with three or four radials to maintain the same flexibility. This will in most cases use more cable, and certainly more CU space and MCBs

No true. Lower area of coverage, lower maximum power capacity, poorer performance in most fault scenarios.

These are also predicated on a false assumption, and hence can be ignored.

This is more thought experiment stuff. Compliance with the regulation is not difficult. In cases where it would be then additional radials should be used to factor out large fixed loads.

covered above

This is not logical.

Straw man argument. They would be equally readily identified regardless of circuit type.

More cable, less power availability, smaller area of coverage, poorper fault performance etc... covered above.

[Pete Verdon]

Where would you put such a thing? With a washing machine under a worktop, and with units either side, what piece of wall that isn't behind the appliance can be reached in any sensible manner? The only solution I've seen that technically qualifies is the god-awful "drill a hole in the worktop and thread the mains lead" option, but I know you're not suggesting that.

A socket behind the machine isolated by a switch above the worktop seems like the obvious answer to me.

Pete

[Pete Verdon]

That's nice. I can't.

Fair enough. But if he's going to be servicing it then he's probably pulling it out from under the worktop anyway, so that's not a problem.

Pete

[Andrew Gabriel]

Mine is in the rear of the adjacent cupboard (on the wall), with a hole cut between the units large enough to feed the plug though. (These are IKEA units and back right on to the wall.) Actually I put a socket every 600mm along the wall behind the cupboards so there's one behind the machine too, but this was just for future flexibility with appliances and cupboards and appliances were always intended to plug-in in the next cupboard.

[Dave Plowman (News)]

Indeed. Separate isolating switches will have to be installed as they are not the norm so will involve a deal of disruption and making good. So you might as well just add some sockets in a better place access wise and save the clutter of unneeded switches. Unless you like the look of switches on your walls. Which are just something else to go wrong in the chain.