The provision for earthing terminals is similar to the live ones, except that they need to be able to clamp as little as one 1.5 mm² conductor.

It says this about screwless terminals:

"12.10.4 Screwless terminals which are intended to be used for the interconnection of two or more conductors shall be so designed that: …

b) each conductor is introduced in a separate clamping unit (not necessarily in separate holes)."

So only 3 x 3 levers.

You have a good point about 4 cables: I suppose that your spur would have to be earthed at the backbox terminal.

Does anyone know what the OP's diagram has to do with 'simplifying'?

I imagine the red lines represent low resistance current paths that are in fact  made of insulated metal wire and are much longer , and far more convoluted, than on the diagram, and A denotes current in amps flowing in a line adjacent to the letter. There is the complication that if that is true it depicts a centre fed radial, not a ring, and the  layout and choice of letters is unusual, but not impenetrable.

I'd be the first to agree it is not a standard schematic  diagram to BS3939 nor the ISO standard for that matter.

Mike

mapj1 said:

it may be possible to slightly overload the short path as that gets the lions share of the current.

Many years experience suggests this never happens in any normal household

Off at at compete tangent, but that made me think...do we know what the typical loading of a domestic ring these days actually is compared to when the  "2.5mm ring" first come in? With no evidence at all I'd imagine that the overall loading is typically lower, although the number of actual loads plugged in is higher...loads of smart things but not so common to have 2kW bar heaters around as it was! But I may be totally wrong.

Given of course the other thread on here about there being no such thing as a "standard home"!

Ah, this time of year takes me back to the annual hunt for the two way adapter so we could plug the Christmas tree lights and the television in at the same time into the only socket in the living room...we 'ad it tough...tell that ter young folk today and they won't believe you...

I think that Andy is spot on. When I rewired Daughter's home, I put in 4 double sockets for each desk. Lots of appliances, but no high loads. Frankly, there was no penalty for putting in too many.

Yes, in those days we had adaptors, but not those 4-way sockets on the end of an extension lead.

Ahh well thinking of modern youth and all that, but our Christmas lights (12 20volt lamps in series on cotton covered flex ) had an adapter to plug into a bayonet lampholder.  Later we made a lead with a 13A plug, some twisted twin flex and a lampholder on the end so they could be plugged in and not disturb the lighting. Only about 2 or 3 years ago I visited my parents to hear that they had been thrown away, at about the time when they were probably becoming museum worthy

Mike