On 19/02/2013 00:41, Stephen H wrote:
On 18/02/2013 21:21, John Rumm wrote:
On 18/02/2013 21:14, John Rumm wrote:

Some will argue that you can get even more load on it since a 13A BS1361
fuse

Sorry typo, BS1362 - 1361 are mains incomer fuses!




Incidentally. There has been a thought about ring mains that has
bothered me for some time.

in a perfect world, you have a continuous live loop and a continuous
neutral loop on a 32A MCB ring main, from teh CU to all the sockets and
then back to the CU.

What if you had a break in the cable between the CU and the last socket?
This converts the ring main to a radial circuit.

Indeed it does...

In reality you could have a break anywhere - and would then get a pair
of radials.

However each circuit topology has strengths and weaknesses. There are
several types of faults (high resistance connections being the most
common, followed by disconnected conductors, and finally disconnected
cables). Each will have different effects.

The options are covered in some detail he

http://wiki.diyfaq.org.uk/index.php?...rload_currents

Lets assume the ring main is then loaded to its full capacity of 32A.

This would mean that *ALL* the current would be flowing along one route
between the CU and the first socket (assuming multiple appliances
plugged in a various points around the radial.

Can a single 2.5mm2 T&E really sustain a 32A continuous load?

Depends on the circumstances and how quick it can shed heat. It also
very much depends on how long you can keep that load on for. Rings
typically serve general purpose use sockets, which form a diverse load.

Also as I understand it, you should only have a 20A mcb on a radial
circuit wired in 2.5mm T&E.

Yup

if you complete the radial into a ring, then
the MCB can be changed to a 32A MCB.

Obviously.

--
Cheers,

John.

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