Radial Circuit using box installation method...

mapj1:

Given that UK socket back boxes are much bigger than their continental counterparts, we do not need the joint box, and can tee off at any convenient double socket.

As others have noted, junction  boxes are not something you normally design in from the outset on socket circuits, but rather are a sign of later additions or changes during building works, Perfectly acceptable though, so long as done properly.


Unfused spurs from a 32A radial need to be in 4mm (*), and not all sockets will take 3 lots of 4mm cable comfortably - I'd want a deeper box than the minimum 25mm for that.


(*) though I agree, given that a single twin socket is OK on 2,5mm2 from a 32A ring, then it will be perfectly OK on a 32A  radial too, and then in the  book of perfectly good but confusing circuits there is the lassoo - with a ring of 2.5mm on the end/side of a 4mm feeder.

No such book exists, but I often think it should.

You can have a single socket cabled in 2.5mm from a 4mm cabled socket has long as the 2.5mm cable is clip direct which gives it a 27A rating given that a single socket will only ever be loaded to 26A max limited by the 13A fuses in the plugs. So the deciding factor is the installation method and cable derating factors as far has I'm aware ?. 

regards ts

mapj1:

Given that UK socket back boxes are much bigger than their continental counterparts, we do not need the joint box, and can tee off at any convenient double socket.

As others have noted, junction  boxes are not something you normally design in from the outset on socket circuits, but rather are a sign of later additions or changes during building works, Perfectly acceptable though, so long as done properly.


Unfused spurs from a 32A radial need to be in 4mm (*), and not all sockets will take 3 lots of 4mm cable comfortably - I'd want a deeper box than the minimum 25mm for that.


(*) though I agree, given that a single twin socket is OK on 2,5mm2 from a 32A ring, then it will be perfectly OK on a 32A  radial too, and then in the  book of perfectly good but confusing circuits there is the lassoo - with a ring of 2.5mm on the end/side of a 4mm feeder.

No such book exists, but I often think it should.

You can have a single socket cabled in 2.5mm from a 4mm cabled socket has long as the 2.5mm cable is clip direct which gives it a 27A rating given that a single socket will only ever be loaded to 26A max limited by the 13A fuses in the plugs. So the deciding factor is the installation method and cable derating factors as far has I'm aware ?. 

regards ts