Rings, chains spurs - electrical :-)

Hi,
just pondering on rings and spurs (for 13A).
Now to my simple mind a ring supports more load (or whatever the correct term is) because the electrons can go either way round the ring and don't bump shoulders as much.
A spur off a ring carries less load because there is only a single route for the electrons.
Now if you (for the want of a better description) add a ring as a spur, do you have a chain or just an unusual ring?
i.e. if you break into a ring (assume chopping into a straight run of cable, leaving two ends, 'ring in' and 'ring out'), and instead of taking 'ring in' and connecting it to the start of your new ring, and in a seperate junction box take 'ring out' and connecting it to the end of your new ring, you just connect all four cable ends in a single junction box.
You then have a physical 'figure of eight' configuration.
Is this a logical ring?
Or is this just a fancy spur because of the loading on the connections in the junction box reduce or undo the benefits of having a ring?
In some ways a trivial query, but it does save on one junction box :-)
TIA
Dave R
--




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Sound's about right, in a funny sort of way.

You can't add a ring as a spur from a ring.

No, it's a contravention of BS7671:The Wiring Regulations.

You can't do it so it doesn't matter.

If you use two you can do it properly. ..
SJW A.C.S. Ltd.
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Out of interest, where?
I'd have thought that provided you could prove adequete voltage drop characteristics, disconnection time and cable loading, then it would be fine. If the ring spur is taken near to the mid point of the circuit, I'd have thought that this would apply. If taken near the end, the ring would be unbalanced, possibly leading to cable loading issues.
Obviously, I wouldn't particularly recommend a "chain" circuit, but can't see why it would be specifically banned. You'd have to do the calculations from first principles, though, as you couldn't use the precalculated tables for standard final circuit types.
Christian.
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On Wed, 11 Feb 2004 14:00:35 -0000, "Christian McArdle"

I'll come back to you on that one. It is definitely not within the regs to run a figure of eight type circuit. I remember this from being an apprentice! I know there are various references that can be interpreted as not running a figure of eight circuit but you know how the regs are worded! ..
SJW A.C.S. Ltd.
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I would have thought they are allowed, but the calculations required to prove so in a particular case would be too involved!
Christian.
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From my mental picture, which may be faulty, I can't see a major problem, apart from the ability of the connectors in the junction box to handle the load - this is the only point where a chain (figure of 8) and a ring differ. Visualise taking a standard ring circuit, and then adding a junction box in the middle to convert a 0 to an 8.
If you move the two sets of wires (ring in and ring out, or ring left and ring right) from common connectors to two seperate connectors, then the rest of the topography is the same.
It does make things more complex though - it seems akin to runing two small rings off a single fuse/circuit breaker. The total loading is the same as one large ring; the maximim distance between a socket and the consumer unit is reduced; the only increase is in having four wires (both ends of two rings) into one set of connectors instead of two.
If you are having space problems around your consumer unit you could run e.g. 4mm (or whatever is the electrical equivalent of 2*2.5mm) from the CU to a junction box, then run your 2.5mm ring from that junction box. Makes possible sense to run a single wire (spur) of heavier wire (4mm+) to the upstairs, then run the ring (2.5mm) from there.
My untutored view of this (based on simplistic electricals from 'A' level physics tw**bum**ple years ago) is that the electrical characteristics would probably not cause a problem, but checking and enforcing the regulations might be that much harder.
Cheers
Dave R
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Not quite, because the load from the second ring is borne by the first ring. This will be seen by the first ring as a heavy point load, possibly well in excess of 20A, applied at a particular point. If this point load was near one end, it could easily overload the shorter path through the ring.
Attaching two small rings to one MCB is very different and actually increases electrical safety, as each ring will be capable of taking the whole MCB current without problems, but is probably not expected to.
Christian.
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ring.
in
<snip>
This is where my head doesn't grasp the difference.
If the small additional ring, making the combined circuits well within spec for a complete ring circuit when added to the existing ring, is added as a 'point' which can then pass load the long or short way round the ring, how is this different from a heavy load point when each end of the new ring is added to a point on the old ring, which is split?
Is the strength of a proper ring circuit that it will force the load to go both ways round the ring, whereas the 'point' connection will allow all the load to try and go down the shorter side of the ring?
For those fretting about me implementing non-standard wiring this is at the moment a philosophical question, and should I extend a ring circuit I will as usual follow the good advice of this NG :-).
Cheers
Dave R
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It isn't*. Even on a conventional ring circuit, you should ensure that likely loads are spread around. It is not permitted to install a ring so that all the expected heavy loads, such as washing machines, tumble dryers etc are all at one end.
Christian.
*Actually it is slightly different. The point load could be well in excess of 20A, unlike a double socket.
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As has been mentioned before on this group by me, and probably many others, is that although you or me cannot see why technically a particular configuration cannot be used the regs err on the side of caution and have to cover their own backs. A lot of the regs is open to different interpretations depending which way you read it. The regs isn't neccesarily a good read for a diy'er, more likely sensible option is a guide to the regs and\or the on site guide which explains the regs rather than just stating them.

Although you can do this it is totally a different arrangement to what you originally said. If you were to run two 2.5 cables _directly_ to a single junction box then take the ring from there is acceptable. Adding anything into this first leg is not ok.

Got it in one. I'm not sure whether you're thinking of actually putting this into practice against regulations and the advice of the group or purely theoretical. If the former, don't do diy. ..
SJW A.C.S. Ltd.
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When I asked some (IMO reasonably competent) sparks about this they said No. When I said Why? (as one does :-) they said because of the difficulty of testing it.
Discuss ;-)
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On Wed, 11 Feb 2004 15:10:14 +0000, John Stumbles wrote:

Look at the procedure outlined in the On Site Guide if you have a ring on a ring you will get strange results. And won't be able to use that method. In particular you wont be able to tell if the subsidiary ring has full ring continuity.
In operation once installed correctly I can't see any way the arrangement would be less safe than the same 'normal' ring circuit with the same amount of wire and the same number of sockets.
The set of installations passable by a NICEIC inspector is less than ... the set of installations that comply with the wiring regs which is less than ... the set of installations that are safe enough to use which is less than ... those which work.
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Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
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being
No.
less
less
I suspect a variation of the KISS principle at work here: Keep It Simple == Safe
Certainly for domestic work where the installation is unlikely to be documented (and if it were the documentation would be likely to get lost during the lifetime of the installation) and may be worked on by all sorts of people I can see an argument for restricting the range of acceptable installations to those less likely to cause surprises which could potentially be disastrous.
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I agree that it probably should be against regs for that reason. However, I haven't seen anything in them to suggest it is.
Christian.
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I
I haven't got my copy of the regs yet so I'll defer to you on that, but I did notice that Scaddan specifically mentions it as a configuration which might arise as a result of DIY work (implied deprecation :-) and talks about how to detect such a (mis-)configuration by testing.
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