The ring final circuit was something of a kludge when it was devised, and it's remained a kludge ever since. So far as I'm aware, nowhere else in the world uses it outside of the U.K. and - to a much more limited extent - Ireland.
-
Looking for a smarter way to manage your heating this winter? We’ve been testing the new Aqara Radiator Thermostat W600 to see how quiet, accurate and easy it is to use around the home. Click here read our review.
Rewire questions
- Thread starter Mr M
- Start date
In view of what I've recently written, I suppose an 'ideal alternative' ('best of both worlds') would be to have radials with one of the variants of 'high integrity earthing' - i.e. L & N as a radial, but CPC as a ring.
I suppose that, if one is concerned about voltage drop, one of the advantages of a traditional ring final is the dramatic (up to 4-fold) difference it can make to the length of circuit one can have without exceeding guidance figures for VD.
I do have my reservations about the general use of 20A radials, the capacity of which can theoretically be exceeded by loads plugged in to just one or two double sockets, but they are OK is situations of 'known' lowish loading, and 32A radials are fine.
Kind Regards, John
That would certainly be an option, but is it really worth it? As soon as you reach whatever is plugged into the sockets or wired to an FCU you're back to relying upon a single earth connection for the appliance anyway. Realistically, how often does an earth on the fixed wiring go open compared to how often a missing earth might occur at the plug due to bad wiring, cords pulled and conductors damaged, and so on?
I'm not entirely convinced that any potential (no pun intended) reduction in voltage drop is really worth the extra issues that the ring, at least in its present form, brings with it. I'd rather just run a larger cable on a radial.
As we've descussed before, it's interesting that while the basic rule for what rings may serve hasn't really changed since their inception (aside from the change of 1000 sq. ft. to 100 sq. m. around 1970), the rules for radials seem to have undergone multiple changes on a fairly regular basis, as though it could never quite be decided.
But realistically, so long as separate provision is made for fixed, power-hungry appliances, and so long as a reasonable distribution of sockets on 20A radials is made, I don't think there is much of a problem, especially now that with central heating being so common people aren't tending to use portable heaters so much.
Remember that here in the U.S. we have general-purpose circuits which are rated at 15 or 20A, and obviously at 120V that's equivalent in power terms to if the U.K. were using 7.5 or 10A radials. Apart from occasional issues with things like multiple hair dryers being used simultaneously in bedrooms sharing a circuit, it really doesn't seem to cause any great problems.
True, but CPC faults in, or downstream of, the plug are probably more likley to be noticed than CPC ffaults in the fixed wiring. I agree that it's very unlikely, but I gather (but have no proof) that the CPC redundancy was one of the things which convinced the then IEE to allow the introduction of ring finals. One has to be careful about these "How often does ....?" arguments, since so many of the things we seek to protect against are extremely rare. How often, for example, would a metal accessory faceplate become 'live' if it were not earthed?
Speaking personally, I cannot ('within reason') get excited by VD considerations at all, particularly given that I've never seen my supply below 240V. I would therefore have to have a VD of at least 10% before the load even got down to the lowest permitted supply voltage.
No, in practice there is "not much of a problem, but it just seems a bit odd to have a multi-socket circuit which, at least in theory, could be 'fully loaded', or even 'overloaded' by what was plugged into just one double socket.
Kind Regards, John
I'm not sure I've ever seen anything to that effect. Where does that idea come from? To me, it would seem a little odd to accept the earthing redundancy as being sufficient reason to override the drawbacks of rings, given that the IEE then and right through to the IET today obviously has never had a problem accepting single earthing conductors on radial circuits.
In many parts of the world it's entirely possible to fully load a multi-socket circuit with a load connected to just one of those sockets: Our 15A receptacles on 15A circuits here in the States, 16A Schuko or similar sockets on 16A circuits in many parts of Europe, etc. Or to fully load a circuit with loads on two of the sockets: 15A receptacles on 20A circuits here, 16A receptacles on 20A circuits in Europe, etc.
stillp, IIRC.
Yes, but CPC redundancy would obviously only have been a 'secondary' reason. I think it is generally accepted that the primary reason was the belief (right or wrong) that it would require less copper, at a time of a serious post-war copper shortage.
Kind Regards, John
I imagine it is used everywhere that BS1363 sockets are used. Malta, Gibraltar, Malaysia, Singapore, Seychelles, Kenya, Cyprus, Hong Kong and others.
How, when and why?
And a labour shortage.
Take a 15A radial, find the "last" socket, run a length of 7/.029 back to the fuseboard - hey presto a 30A ring.
Certainly, that's the primary reason which I believe can be found in the post-war report, although it's been a good few years since I read through it.
That's the point, it's not. Even Ireland which uses BS1363 sockets (as IS401) doesn't use rings anything like so extensively. In many other British-influenced places BS1363 became the replacement for BS546 types, but still on radial circuits.
Or even just find two 15A radials with the sockets conveniently located and run a length of 7/.029 T&E between the sockets. I had that at one old place where the age of the cables made it obvious that's what had been done.
Was there an electrical reason for this reduction?
- Joined
- 28 Jul 2014
- Messages
- 1,969
- Reaction score
- 566
- Country
Bugger. 
Not only (as has already been pointed out) was that an increase (from 1000 ft² to ~1078 ft²), rather than a "reduction", but I presume that it was simply the result of minor 'rounding' after metrication, not a 'deliberate change'??
Kind Regards, John
Just as distances such as 6 ft. (for maximum distance between appliance and isolator, for example) became 2m in the metric revision.
Go back to the 13th edition and the rules permitted an unlimited number of number of BS1363 sockets (in domestic premises) on a 30A ring, but a maximum of only six on a 30A radial (a double socket counting as two). Where was there any logic in that?
The 20A radial rules then were much more restrictive, specifying a maximum of either (a) two sockets located anywhere, or (b) three sockets all in one room not exceeding 200 sq. ft. and not a kitchen (again, a double socket counting as two).
The 14th edition permitted a maximum of six sockets serving a single room not exceeding 300 sq. ft. and not a kitchen, otherwise limited to two as before.
Then was it the 15th edition which changed it to an unlimited number of sockets within a specified area, or was that later?
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
