Radial Circuit using box installation method...

Sparkingchip:

Why not a 16 amp radial with 1.5 mm twin and earth?

No specific reason other than I have 300+ meters of 2.5mm NYM and only a fraction of 1.5mm, suppose I could just order up some more. 

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

Timeserved:

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 ?. 

Or you have your row of sockets above the kitchen counter. From there you take a length of 2.5 mm² via a switch to a single unswitched socket underneath for the dishwasher, washing machine, or WHY. One appliance, max 13 A. (Not forgetting of course that a double 13 A socket-outlet is still rated at 13 A for the pair.)

Timeserved:

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 ?. 

 

Apart from 2-way extension cubes, which - for a reason I've never been able to fathom - aren't required to be fused. And you can stack them!

AJJewsbury:

That diagram looks distinctly German - black for line and two-pin with scraping earth arrangement for the sockets,


There is a lot of variety of styles between countries - often one convention re-inforcing another over time - with little more than historical accident at the start of the divergence. European style sockets for example traditionally had a screw terminals where the wire was wrapped around under the screw head against a flat plate (a bit like on BS 951 clamps) rather than there being a "tunnel" - hence it was difficult to reliably terminate more than a single conductor in a socket terninal so junction boxes became the automatic way of doing things - even when using singles in conduit which looks bizzare to UK eyes. Once everyone was using joint boxes there was little need to "improve" the sockets to take multiple conductors, so the situation stuck. The UK on the other hand seemed to like tunnel terminals from an early date - which made shoving multiple wires into the same terminal easy and reliable - so as soon as the cost of the extra cable needed for 'looping in' dropped below the cost of a JB and the extra labour in installing it, looping-in caught on and joint boxes were mostly relegated to alterations and additions. The American had a similar problem to the Europeans, but they had more space in their back boxes - so ended up joining multiple conductors using "wire nuts" (screwits in old English) in the back of the box and just taking a single fly lead to the accessory - so a bit of a half-way house.


   - Andy.

That rings true, and is very interesting.  The image is indeed from a German section as the French and Italian ones were even more strange and that was the closest I could obtain an image to reflect what I was trying to ask. 


Those boxes still come with screw terminals in some but are very very rare, they are push connectors now.  I have seen the US system you refer to and indeed you are correct they seem to terminate in the box with all the cables behind and then take another cable into the socket/switch.