On Wed, 16 Jun 2010 13:52:32 +0100, "TheScullster"
wibbled:


Thanks for comprehensive response!
Can you clarify a couple of points please? For 2.5mm cable, each leg of
the ring should only be pulling 16A presumably to cover the 32A total
breaker capacity. ISTR that 2.5mm is nominally rated at 20A as a spur.
So in both/all cases, the 23A rating will not be an issue - right?

Right and wrong ;-

The regulations require each leg of the ring to be capable of handling
20A continuously. It's an arbitrary, round, made up number that has some
leeway for current imbalance between the 2 legs. Meet 20A for any+every
section of cable and you're OK.

Might I suggest procuring a copy of:

http://www.amazon.co.uk/IEE-site-Gui...dp/0863418546/
ref=sr_1_1?ie=UTF8&s=books&qid=1276703557&sr=8-1

It's a condensed domestic summary of the regs with lots of diagrams, and
the more pertinent tables (though they forgot to mention reference method
B so you have to be a bit creative). You can do stuff that's not in there
that is still regs compliant, but if you do what the OnSite says, you're
guaranteed to be OK. Good section on bonding with minimum wire sizes too.

That is totally worth the 16 quid even if all you do is put in one
circuit.


The cooker cable is run in 6mm, currently serving a hob and double oven
and run in clip-top trunking, so that should serve the future purpose.

Yes. 32A is a pretty standard circuit. I'm running one, even though I
will have a gas cooker. You are allowed to have a 32A radial socket
circuit and that's what I will do - 13A socket on the bit behind the
cooker. Right place and the isolator switch next to the cooker still does
what is expected. If anyone wants an electric cooker, all they have to do
is switch the socket for a cooker terminal plate.

Some time ago, another poster gave links to images of his first fix
work. Can't remember the culprit, but he showed conduit being used
between boxes, with the conduit passing through grommets into each box.

That'll be me:

http://photos.dionic.net/v/public/bu..._0019.jpg.html

I did it to stop the conduit sliding out.

From your suggestions above, it appears that as long as the conduit
protrudes into the box to protect the cable from the sharp box hole
edge, a grommet is not required - is this correct?

One or the other is perfectly acceptable - as long as the cable is
protected from the sharp edge of the hole. You could even use a conduit
through-hole adaptor.

One other question - is your run of cable massively long? The other thing
that can go wrong is too high a cable impedance (Live-Earth loop) and/or
too much voltage drop.

"Normal" runs are Ok, but it's worth asking if you live in a 10 bedroom
mansion and the main CU is in the garage beyond the stables(!!) You get
the idea...


Phil





--
Tim Watts

Managers, politicians and environmentalists: Nature's carbon buffer.