What cable size?

[AndyDavis]

The Ring Upstairs and Ring Downstairs are each connected to a 32A MCB, typically using 2.5mm Twin & Earth cable. But the maximum current that a 2.5mm cable can handle is 20A, so how does it work with a 32A MCB?

Is it because a ring circuit has two wires in parallel, so in effect you have a (20+20) = 40A coverage. Wouldn't it be better just to use 6mm Twin & Earth cabling?

 

[fubar]

Is it because a ring circuit has two wires in parallel, so in effect you have a (20+20) = 40A coverage.

Not quite, becase not all the load will be at the furthest point on the circuit.
If you maths is strong, take a look at IEE Guidance Noate 1 or this article:
http://www.iee.org/Publish/WireRegs/Amd1andRC.pdf

Wouldn't it be better just to use 6mm Twin & Earth cabling?

You could use a radial circuit - indeed this is often considered for kitchens - but 6mm is harder to work with.

--
Michael

 

[ban-all-sheds]

The Ring Upstairs and Ring Downstairs are each connected to a 32A MCB, typically using 2.5mm Twin & Earth cable. But the maximum current that a 2.5mm cable can handle is 20A,

27A, actually

Wouldn't it be better just to use 6mm Twin & Earth cabling?

That would be a nightmare - trying to get 2 x 6mm² cables into the back of a socket....

 

[AndyDavis]

Does that mean its perfectly safe to use the 2.5mm cable?

Although the 6mm cable would be much harder to work with, would it be safer? Or is it that there's some physical limitation, other than blood and sweat!

 

[fubar]

Does that mean its perfectly safe to use the 2.5mm cable?

Yes

Although the 6mm cable would be much harder to work with, would it be safer? Or is it that there's some physical limitation, other than blood and sweat!

Under normal circumstances it would be no safer - as BAS pointed out, the maximum rating for 2.5mm is 27A (in cool free air - once you start burying cables in walls and take into account voltage ranges, it drops to 20A). The 32A circuit breaker (MCB) will trip well before any 2.5mm cable starts to get warm as long as the load is farily evenly distributed around the ring.

As I mentioned earlier, a designer may opt for a different design in a large kitchen (or in commercial or industrial spaces). If you a larger-than-average number of appliances in your kitchen, I'd suggest getting an electrician in to give some advise, otherwise a ring final will be fine.

--
Michael