Yes, a ring per floor is a very common arrangement, although I'd prefer to see the upper and lower floors each served by both rings as it will give a better load distribution.
The actual area served by each circuit is another aspect of the way rings are implemented here that I don't like.
Many references these days make mention of the heavier kitchen loads than in times past, but then suggest that a separate ring be installed to feed the kitchen. It still results in one ring carrying the bulk of the heavy loads while the others carry minimal loads.
Unfused spurs can be wired in the same size cable as the ring itself, i.e. usually 2.5 sq. mm. Such a spur is allowed to feed only one socket outlet or one fixed appliance. (A twin, or duplex, socket counts as one for this purpose). The original ring specifications allowed two sockets to be fed on a spur.
A fused spur can be wired in smaller cable. The ring spur units take the BS1362 fuse, the same type as used in 13A plugs.
Such fused spur lines are sometimes used where a ring is the most convenient circuit to tap, e.g. adding a wall light where it would be hard to run cables back to a lighting circuit. You could tap the ring with a fused spur, fit a 3 or 5A and fuse and run the light spur with 1 sq. mm cable.
[This message has been edited by pauluk (edited 11-17-2002).]
