6.3.3 - The radial circuit
Two types of radial circuit are permitted
for socket outlets. In neither case is the number of sockets
to be supplied specified, so the number will be subject
to the constraints of load and diversity. The two standard
1. - 20 A fuse or miniature circuit
breaker protection with 2.5 mm² live and 1.5mm² protective
conductors (or 1.5 mm² if m.i. cable) feeding a floor area
of not more than 50 m². If the circuit feeds a kitchen or
utility room, it must be remembered that a 3 kW device such
as a washing machine or a tumble dryer takes 12.5 A at 240
V and that this leaves little capacity for the rest of the
2. - 32 A cartridge fuse to B888
or miniature circuit breaker feeding through 4 mm² live
and 2.5 mm² protective conductors (or 2.5 mm² and 1.5 mm²
if m.i. Cable) to supply a floor area no greater than 75m².
The arrangement of the circuits is shown
in (Fig 6.6). 4mm² may seem to be a large cable size in
a circuit feeding 13 A sockets. It must be remembered, however,
that the 2.5 mm² ring circuit allows current to be fed both
ways round the ring, so that two conductors are effectively
in parallel, whereas the 4 mm² cable in a radial circuit
must carry all the current.
Fig 6.6 - Radial circuits
Radial circuits can be especially economic
in a long building where the completion of a ring to the
far end could effectively double the length of cable used.
As for ring circuits, danger can occur if flexible cords
are too small in cross-section, or are too long, or if 3
A fuses are not used where appropriate.
The minimum cross-sectional area for flexible
cords should be:
0.5mm² where the radial circuit is protected
by a 16 A fuse,
0.75mm² for a 20 A fuse,
or 1.0mm² for a 30 A or 32 A fuse.