On Mar 11, 5:13*pm, "ARWadsworth"
wrote:
John Rumm wrote:
On 10/03/2012 10:53, Lieutenant Scott wrote:
On Sat, 10 Mar 2012 07:54:28 -0000, ARWadsworth
wrote:

Lieutenant Scott wrote:

I see. Why are lighting circuits never rings, and why does the
lighting wire sold in DIY stores always seem to be rated at 16
amps ish, while I've never seen a lighting circuit have a
fuse/breaker of anything other than 5/6A.

The point of the ring is to allow 20A cable to form a circuit
that safely uses a 32A MCB.

There would be no point in doing that is you were using 16A cable
with a 6A
MCB

I suppose you could use even thinner wire.

10A is probably the largest size MCB you will see in a house for
the lights.
You might see 16A used in factories etc. BTW it's not 16A
lighting cable, look at

http://wiki.diyfaq.org.uk/index.php?...es#Cable_Sizes

Ah so 16A becomes 8A in insulation. Doesn't that mean we should be
using huge cables for ring mains?

You need each leg to be good for 21A when used in that configuration,
which 2.5mm^2 is usually comfortably inside, but it does depend on the
exact details of the installation. If the cable is installed in
insulation and this can't be avoided, then you will need to uprate to
a larger cable, or change your circuit design etc. With modern
insulation practices, it is something the designer needs to pay more
attention to.

That should read 20A per leg:-)

--
Adam- Hide quoted text -

- Show quoted text -

Talking of safety, you should see the wirenuts the Yanks use.
http://en.wikipedia.org/wiki/Wire_nut