On 27 Jul 2004 10:15:46 -0700, (Fitz)
strung together this:

If I were to do the same downstairs I seem to have three options:
1) Stick with a radial circuit and use the perfectly good chunky wire
that's already there. This will require SWK to help with the maths so
I know how many sockets I can install.

No maths needed. A 20A radial, (probably what's already ther as that's
most common), can supply 50m^2 of floor area, a 32A ring main can
supply 100m^2

2) Ignore current radial and run new ring, travelling through the
ceiling void crossing the whole house, before coming down an exisiting
service duct into l/room then run as ring like normal. Downsides are
that this uses a lot more cable.

I'd do this, the extra cable isn't going to cost a fortune and won't
cause any problems.

3) Extended upstairs ring to include downstairs so that all sockets
are on one ring. Again this would need careful calculation to make
sure I'm not exceeding limits on potential load and cable length.

In a domestic installation load and cable lemgth calculations are
unneccesary unless you live in a huge mansion type property. Only
golden rule is one ring circuit shouldn't supply more than 100m^2 of
floor area.

4) Combined ring/radial. Does such a concept exist?

Not conventionally but if you could get a 6mm^2 cable through the
existing ducting, then you could place a junction box where the cable
enters the underfloor void and run a conventional ring with 2.5mm
cable. Might be worth running that one by whoever you're getting to
test the work after though as some people would be confused by an
unusual concept and just condemn it.

Is there any merit in attaching a junction box to
the old radial cable where it enters the under floor void in the
d/room and then running a ring of 2.5mm cable around downstairs?

No, you wouldn't be increasing any circuit capacity as the limiting
factor would be your run to the mains, so you may as well just rewire
the existing sockets, and add new ones, on a radial circuit.
--

SJW
A.C.S. Ltd