John Rumm wrote:
Jim wrote:
We've got a similar problem in that we have solid floors downstairs so
all of the ring mains will need to run in the suspended ceilings. The
trouble being that there is a 50m cable length limit on the ring main,

Where did you get that figure from?

There is a maximum 100m^2 floor area that should be served by a single
ring.

The actual cable limits will depend on the voltage drop or earth fault
loop impedance of the circuit and the selected cable type (which limit
kicks in first depends on the actual details).

Your typical 2.5mm^2 T&E with 1.5mm^2 CPC with Type B 32A MCB would
allow 106m of cable (table 7.1 OSG 17th edition). Note this is longer
than the 84m previously allowed in the 16th edition due to the extra
voltage drop now permitted for general purpose power circuits.

Thanks, that's very helpful. The 50 metre number came from:

http://diydata.com/planning/ring_main/ring_main.php

"The length of cable used in a ring circuit is limited
to 50 metres for circuits protected by an MCB."

If that number is wrong then that means we have plenty to play with and
there's no sense in coming up with ad-hoc solutions.