Quiggles wrote:

All the ring mains can be integrated nicely, but I was wondering
whether the original lighting radial circuit can be added as a spur off
of the new lighting radial circuit, without contravening any electrical
regs.

Yes, since there is no such thing as a spur on a radial - connections
are allowed to branch any which way they like, and from any location
(the term radial is in effect a slight misnomer). Hence you could common
both circuits at the CU if you wanted.

However you need to look at firstly the total load, and secondly what
makes most sense and what is going to be most useful in practice.

For loading you should work on a principle of 100W per lighting position
or actual load (whichever is higher) no diversity is allowed.

From a practical point of view, it can work better if you arrange that
there is still enough light to move about the place safely and get to
the CU when any one circuit trips - so the traditional upstairs /
downstairs split is not always the best - but you need to be mindful of
doing unexpected things that could leave for example just one lighting
position live when you turn off the rest of that floor. Sometimes a non
maintained emergency light is a better solution for this problem.

--
Cheers,

John.

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