543.6.1 the protective conductor shall be incorporated in the same wiring system as live conductors (re: overcurrent protection)

The conductors are all in the same joined-up containment system as a whole, but might not be all together in the same segment at various points.

I'd always assumed - and now you mention it, it is just an assumption - that 'in the same multicore cable or wiring system, or immediate proximity' phrase was meant to mean that all the relevant conductors would be present at the same point. So you couldn't for instance have a complete loop of conduit or trunking running around the perimeter of a room with everything running say 'clockwise' around it  so one leg of conduit might contain just contained L (or SL) and another just N. The fact that all the bits of conduit are joined up somewhere wouldn't seem to make much difference to me (although I admit the words of the regs could be read that way).

It's like the old "spider wiring" you used to see in houses for lighting circuits from the 1960s-1980s - done in single core sheathed wiring. L would find the shortest route between switches and N the shortest route between lights and SL the shortest route between switch and light. It all worked but the large areas of "loops" can cause havoc interference-wise, especially to things like hearing-aid loops and audio equipment. I presumed that it was that sort of practice that these regs were meant to prohibit.

   -  Andy.

Thank you AJJ ,  I agree with wiring to remove as many issues as possible.

The 'loop-in' (3-plate) is the best approach to avoid all these issue, but it does come with a 'penalty' of more cables running to the grid switch (in the virtual example I gave earlier)  epecially in all pvc containment.  It seems how twin and earth might mandates the wiring routing approach is what is 'best' to follow where possible ... even if wiring in singles  .

Good lighting wiring design experience in complex lighting settings would seem to be a good skill  ;-).

I think 'spider wiring' (the right way) can be very useful and efficient if from a central [to the installation] junction panel enclosure  and where all the conductors radiate out from that to the points of use.

I will rest on this one as Im now fed up of it too. :-)   Cheers everyone.

Thank you AJJ ,  I agree with wiring to remove as many issues as possible.

The 'loop-in' (3-plate) is the best approach to avoid all these issue, but it does come with a 'penalty' of more cables running to the grid switch (in the virtual example I gave earlier)  epecially in all pvc containment.  It seems how twin and earth might mandates the wiring routing approach is what is 'best' to follow where possible ... even if wiring in singles  .

Good lighting wiring design experience in complex lighting settings would seem to be a good skill  ;-).

I think 'spider wiring' (the right way) can be very useful and efficient if from a central [to the installation] junction panel enclosure  and where all the conductors radiate out from that to the points of use.

I will rest on this one as Im now fed up of it too. :-)   Cheers everyone.