I`ve been thinking

I suppose that limiting the number of unfused spurs from a ring protects cables from overloading. Having just one single OR one double 13 Amp socket connected to an unfused spur aids fault finding and prevents overloading. It would not be good to have ten double sockets connected on an unfused spur from a ring wired in 2.5mm2 T&E, as the cable could become overloaded if many appliances were plugged in and used at the same time. an unfused spur can run from the origin of the ring (consumer unit) OR from other places on the ring such as existing socket outlets or between  sockets via a junction box. We must remember that the spurs are protected by a 30 or 32 Amp protective device at the consumer unit. Historically the floor area serviced by a ring circuit was limited to 100m2. 


433.1.204 requires that the current carrying capacity of the cable should be not less than 20 Amps., and if  under the intended conditions of use, the load current in any part of the circuit is unlikely to exceed the current carrying capacity of the cable (Iz) for long periods 433.1.1. is complied with.


Z.

Not sure I follow your overloading reason Zoom,

• One point i.e. one single or one twin at any spur position on a ring would not encourage overloading of any spur and the ring as a whole would offer the same load protection of the ring via the OPD whether points are on ring or on spurs . It`s the same current in the same instances

Reg. A.38 of the 14th Edition of Regulations for the Electrical Equipment of Buildings 1966 (I.E.E.) said: For ring final sub-circuits complying with Regs A.30-33, the total number of spurs shall not exceed the total number of socket-outlets and stationery appliances connected directly to the ring.  Reg. A.31 said: Each socket-outlet of a twin or multiple socket-outlet unit shall be counted as one socket-outlet for the purpose of Reg. A.30 and Table A.3.M. So the intention was to maintain a proper ring rather than having an "artificial" ring supplying too many spurs.


Z.

Agreed Zoom but what is the benefit. Other than to not produce a very untidy circuit. A ring final with no points on ring just say 20 junction boxes on ring. Each junction serves one point at the end of each spur. 5 points spurred directly at the OPD "fuseway".


Or


25 points on the ring, not a spur in sight.


The only benefit with the second circuit is no horrible junction boxes but if these junction boxes were changed to points then no problem.

So what is the (practical) difference? Just good housekeeping?


The little Devil in me is making me consider installing such a ring as in the first example and sitting back seeing what comments are made during an inspection and tes.

That would be interesting! ?

Benefit of having many sockets on a real ring final. Versatility. New sockets can be added if needed onto a real ring final circuit. This may not be possible from an existing unfused spur if already fully "occupied". 


Z.

Yep agreed on that. I always advise that any socket I install on a ring can have one each added at a later date if required but that is the only benefit I can envisage really

O.K. Years ago I have seen bungalows being built. Sometimes a large metal or plastic water tank would be installed in the loft before the roof was fully fitted in place, as the loft hatch would not allow access for the large water tank from inside the completed bungalow. But with electrics we would not install junction boxes in a loft space when rain could enter them. So, on outside walls of a bungalow we would be fart arsin' about with junction boxes in a loft space in the dark with limited head room to cut into the ring final to drop spurs. I don't fancy that at all. Plus, look at the additional labour and materials time involved. I much prefer to terminate the ring cables at sockets where I can sit down to do the job.


Z.

I suspect some of it is the history. Prior to the ring, at least domestically, all sockets of significant load were on single point radials, one fuse, one cable one socket.

Light loads, like the wireless perhaps connected to a lighting circuit, either by 2 pin socket or bayonet adapter.

Which is fine for a house requiring up to about 3 sockets at 15A each.... then the complexity of the fuseboard starts to limit you and a lot of wire converges on it.

The ring was intended to allow a socket in each room and the ability to carry you (max 3 bars) electric fire from one room to another, as required, while eliminating extension cables under doors and yet not requiring one fused branch per room, and a requirement to sell the idea of being able to use apparently undersized cable, is that most sockets are fed from both sides, and an assumption that only one or two sockets at a time are fully loaded. Electrically speaking of course, so long as you can do good joints, there  is no issue with mixed radials rings, rings with all sockets as spurs, lollipops etc,  but you can see from the way they are not popular, that collectively electricians are by nature very wary of anything unusual.

It was necessary to get people away from the 'comfort zone' of wiring like previous practice which we would now recognize as a single point radial. Indeed to force people to think like this, for a brief period it was also recommended that the cores of the ring be unbroken. I suggest this is so impractical that it must have fallen shortly after the first attempt to actually thread one up.

To sell the idea of the ring without too much opposition it needed to be simple to understand, with simple rules, and underwritten in a sense by some authority. 

(Look at the number of folk who see a centre fed radial and imagine it is not permitted because there is not one shown in the OSG, or call it two circuits sharing a breaker to see how this happens.)


Once established as reliable, one can then relax the requirements a bit.

I have worked in houses where the ring circuit has been wired through the floor void with the ring supplying the first floor sockets in the bedrooms and every ground floor socket being wired as a spur from a first floor socket above it.


That absolutely minimises the cable used, but it means there is not a socket in the house you can connect another spur to and the number of spurs equals the number of points on the ring.


So to add another socket or spur you have to cut and joint the ring to extend it from upstairs, wherever the new point will be located.


Andy Betteridge

I just wonder these days if full 32A capability is actually needed in a domestic setting?

Looking at the drive for energy efficiency from appliance manufacturers, is there really a need for a ring circuit in today's houses?

Washing machine water heater? Say 2KW/10A max. Same with spin/tumble dryer and dish washer.

Lounge/sitting room/bedrooms? Isn't 16A/20A enough?

Rings suffer from an inordinate amount of abuse by the uninitiated adder-ons who get going even before the ink is dry on a perfectly installed and pristine Ring Final.

I've seen it where a superficially small number of sockets has been requested to keep the price down, then as soon as you've driven away in your van, they get busy themselves with a trip to B&Q and all of your hard work is in vain.

Far better to drop in a few radials and let them hack at those - less room for mistakes then.