Tim W wrote:
Bill Payer
wibbled on Monday 19 October 2009 12:07

Our house was built around the early to mid 60s (so has "modern" PVC
twin & earth cabling) and has just one ring main feeding the whole
house. We want to add in some extra sockets but obviously I don't
want to overload the one circuit so I've had an idea that I want to
run past you peeps here.

Most family/friends houses seem to be wired with an upstairs ring
and a downstairs ring. My idea is to go to all the sockets in the
upstairs rooms and basically pull the cables out of the sockets,
back down to under the floorboards and joint them there (either with
"traditional" junction boxes or with crimps/heatshrink sleeve), so
that the continuity of the ring is preserved but it is now just
serving the downstairs sockets, then run a new ring for the upstairs
sockets, and adding new sockets to each ring where needed.

Is this OK?

TIA,
Bill

In principle it sounds fine. Crimps would be an excellent way to
joint the cable provided that you have a proper crimping tool and are
happy with how it's enclosed. Another way, if you are concerned about
the accessibility of the joints is one of the new Hager Ashley
maintenance free junction boxes:

http://www.tlc-direct.co.uk/Products/ASJ803.html

Those have spring contacts and good cable clamps and IME (of the
smaller lighting ones) *very* well made.

The only 3 flies in the ointment AFAICS (other may see more):

a) Is your cable in good condition after 40 years? Even PVC has a
finite life.

Thanks for the quick reply Tim! )

You make good points there. I've taken some of the sockets off and all
connections look to be clean and tight with no signs of
burning/brittleness/overloading and I've had a couple of the floorboards up
and can see no signs of any damage. Visually, everything looks OK.

b) Depending on how well you can see the cables being run, you have
to watch out for the possibility of creating an incorrect ring by
mistake (eg 2 radials or a figure of 8 ring). it would be worth
testing as you go to ensure that the cable you are about to joint is
going where you think.

Noted

c) Part P - whatever... But for something like this, it would be worth
borrowing a Megger or similar and actually testing the resultant ring
for peace of mind at every socket outlet. Then you can prove there
are no insideous wiring errors (perhaps resulting from the original
circuit, like a broken or loose conductor somewhere you can't see)
and that the insulation is still good.

Will do. I'll also test the existing cabling before starting any work to
supplement the visual as in your (a) above.

Another approach could be to break the original ring deliberately
into 2 or more 20A radials - this might be simpler if it leaves you
with a reasonable distribution, though your kitchen/utility room
might scupper this with a large presence of high loads in one
place?... There're no real restrictions on radial topology if you can
be sure that 20A is enough for each circuit.

Hmm, that's a thought. Thanks Tim.

Bill