The ring is 2.5mm fed by 32A MCB. I know that I can run a single fitting (e.g. 2-gang socket) off a ring as a spur. Alternatively, I believe I can run a fused radial off the ring as the fuse stops excessive current doing down the radial. However, can I run a 4.0mm radial (unfused) off the ring as a 4.0mm radial is rated to carry 32A (single phase)? It feels logical as you can have a 32A 4.0mm radial on its own and the ring supports 32A. I appreciate logic doesn't always apply though.
Why wouldn’t extending the ring be as easy?
Generally the ring only needs to go the the first double socket, as the last one can be a spur.
The permissible length of a spur depends on its position on the ring, not that that is often taken into account.
However, can I run a 4.0mm radial (unfused) off the ring as a 4.0mm radial is rated to carry 32A (single phase)?
Not by simply connecting into a double socket-outlet as you have shown, because the terminal capacity in BS 1363 doesn't support sufficient cross-sectional area. Some manufacturers' terminals might be up to it. but definitely not a "standard approach" because of that.
The standard terminal capacity for BS 1363 series accessories on the fixed wiring side is that the terminal must be capable of terminating each of the following combinations: 3 no. 2.5 sq mm conductors, 2 no. 4.0 sq mm conductors, or 1 no. 6 sq mm conductor.
2 no. 2.5 sq mm conductors with a spur of 1 no. 4 sq mm conductor exceeds this terminal capacity.
But you could of course achieve the same effective topology using a joint box, or even a few wagos in the back of the socket. (In some parts of the world, accessories often accept a single conductor per terminal and wire-nuts or similar in the back box for looping or spurring is the normal approach.)
- Andy.
The standard terminal capacity for BS 1363 series accessories on the fixed wiring side is that the terminal must be capable of terminating each of the following combinations: 3 no. 2.5 sq mm conductors, 2 no. 4.0 sq mm conductors, or 1 no. 6 sq mm conductor.
Which is a bit of a shame really - as often we need to terminate 4 c.p.c.s into a socket - two for the ring, one for a spur and another for the back box. Often of course the c.p.c.s. are just 1.5mm² and we can 'get away with it' but it would be better if it was really compliant. It'll probably become more of an issue as manufacturers move to lever terminals that only take one conductor per hole.
- Andy.
Are you saying that the 32A / 4sq.mm. radial circuit with branches is a myth and not possible to install?
not at all - just BS 1363 doesn't necessarily accommodate that approach - so you may well have problems even with entirely compliant accessories. Sometimes we don't have a choice (e.g. customers have picked some pretty polished metal ones or some such).
I'm just suggesting that it would be better if BS 1363 recognised what actually (and entirely reasonably) happens in the real world.
- Andy.
may I suggest using others which are fit for purpose.
You may ... but even if you select ones that the manufacturer says today are suitable for the terminal capacity you require, I'm sure there's a little clause that says specs subject to change without notice, so the only thing you can rely on in this case is the terminal capacity as indicated by the standard (that is often said to be the "minimum requirement", but of course care is required because if the terminal is too big, it will not safely accommodate and terminate the required combinations).
There would be nothing wrong with "splicing" stuff together as Andy says, but this is either extra enclosures, or deeper backboxes.
It feels logical as you can have a 32A 4.0mm radial on its own and the ring supports 32A.
Can you? If T&E or multicore not armoured), only clipped direct (ref method C) ... or where overload protection is not required ... i.e. not for socket-outlets. Have a look at Table 4D5 for example. Insulated and sheathed singles would be OK clipped direct, also insulated singles in a surface-mounted conduit or trunking with no derating factors at all.
So in reality, looks like it's doubtful for many applications for socket-outlets generally.
Surely the terminal capacity is just the physical measurement and nothing to do with any regulation or requirement.
The manufacturer is unlikely to stipulate 3 x 2.5sq.mm. for example if the terminals will happily take 3 x 4sq.mm.
Are you seriously saying that you have come across sockets, the terminals of which will not accommodate 2 x 2.5 with the ends doubled over; i.e. 10sq.mm.
Then if the socket will take 3 x 4sq.mm. you would not use it for just 1 x 2.5 because it is too big?
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