In an earlier contribution to this discussion,
Grant wrote:

Hi,

I want to extend the ring mains in my (1930's) house to add two double
sockets to a room. I've got the floorboards up and know where the new
cable needs to go. However, the thing that's stopping me going ahead
is the fact that the existing cable appears to be ever so slightly
thicker than the 2.5mm^2 that I was going to use. It is also
multi(6)-stranded instead of single-stranded. Is this to be expected
with older wiring (I believe a rewiring was done in the 70's)? There
is a 32A MCB at the fuse box so I thought that 2.5mm^2 would do the
job but having seen the existing wire I now have doubts. I don't want
to weaken the installation by using wire that is too thin.

After a bit of Googling it seems that 4mm^2 cable might be used in a
radial installation but I disconnected the wire between two sockets in
the room and they both still worked - does this allow me to conclude
that I have a ring mains? Also, 4mm^2 cable doesn't seem to be
available from B&Q, etc. - the next size up is 6mm^2.

Maybe the fact that I'm having to ask these questions suggests that I
should get in an electrician?!

Cheers,
Grant

2.5mm^2 is fine for a ring main as long as you *insert* it into the ring so
as to still have a continuous ring - rather than creating spurs. My house
has a mixture of older (stranded) cable and new solid stuff. Doesn't seem to
be a problem!

There is a limit (can't remember what it is!) to the permitted number of
outlets on a single ring - but you probably won't exceed that unless the
ring has already been extended.

My understanding is that any such work now comes under the provisions of
Part P of the Building Regs - and that, legally, the work needs to be
certified by a qualified electrician - or by Building Control if they are
capable! Many competent DIY-ers choose to ignore this - particularly if
there's no obvious evidence as to *when* the work was carried out.

But if you're not confident *and* competent, get an electrician.
--
Cheers,
Set Square
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