On Fri, 30 Apr 2004 11:07:27 +0000 (UTC), in uk.d-i-y "Charles
Middleton" strung together this:

I was expanding some plug sockets from singles to doubles in my house the
other day and noticed the following. I powered off what I though was the
upstairs sockets and set about testing them to make sure that they were not
live before I comenced work.

It was at this point that I noticed that my downstairs sockets where off as
well. To cut a long story short it seems that the house is wired up
basically with two MCB's - one for the kitchen and one for the rest of the
house. Not sure at this stage of the rating. So all of the sockets in the
house less the kitchen are wired onto one ring circuit.

Quite common, most new houses that I wire are done similarly, 1 ring
for the front and 1 for the back. It makesx wiring easier.

As 2.5 twin and earth is rated at 25 amps and I only have one circuit for
all of the sockets, this means a maximum load of 25 amps and I make that a
maximum of 5.5kw. Is that correct?

Depends, if they are ring circuits then there are 2 cables to each
socket in effect, the MCB\ fuse size for this is 32A so that's your
maximum. This is more likely to be what you have.
The other way of doing things would be a radial, with 2.5mm cable you
will only be able to have 16A.
The cable ratings are maximum - in ideal situations. In practice they
need derating because of the way the length\resistance and thermal
effects lower the current carrying capacity of the cable.

Im just hoping that this will be enough for all of the stuff Im planning to
run.

- 2 x PC's probably running most of the time including permanently switched
on router.
- Home cinema system running intermittently
- Various other appliances, vacuum cleaner, phone chargers etc.

What do people think? For info the house is a two bed semi so perhaps the
developers didn't think that two ring circuits (upstairs and downstairs)
would be required.

2 rings will be fine for what you want, 2 PCs, home cinema and phone
chargers will probably struggle to peak at 10A if all switched on
together.
--

SJW
A.C.S. Ltd.