Make sure you have isolated any circuit you are working on
A radial circuit is a mains power circuit found in some homes to feed sockets
and lighting points. It is simply a length of appropriately rated cable feeding
one power point then going on to the next. The circuit terminates with the last
point on it. It does not return to the consumer unit or fuse box as does the
more popular circuit, the ring main. To see the wiring at the back of the
socket please go to the ring main project.
The descriptions below apply only to a circuit for power sockets. Lighting circuits are dealt
with in a separate project.
There is no limit to the number of sockets used on a radial circuit and, just like
a ring main, spurs, or extra sockets, can be added. The number of spurs
must not exceed the number of existing sockets. The images below are all
rated for use with a radial circuit and can be bought by clicking on them.
Two types of radial circuit are permitted for socket outlets.
20 Amp fuse or miniature circuit breaker protection with 2.5 mm² cable can feed a
floor area of not more than 50 m². The maximum length of cable is 33m
30 Amp cartridge fuse to B888 or miniature circuit breaker of 20amp with a 4 mm²
cable can supply a floor area no greater than 75m². The maximum length of cable to
be used is cable is 38m when used with a cartridge fuse and only 33m when used
with an MCB
Radial circuits are generally used in larger buildings where, to return the cable back to
the consumer unit can effectively double the cost of the installation.
As with a ring main, units and appliances which draw large amounts of current such
as showers and electric cookers nut be installed on their own circuit.
Additional wiring can be added to a radial circuit to turn it into a ring main
Please also check the rules very carefully for ring mains and radial circuits. You are
limited in the length of cable you are allowed to use in both circuits and long spurs
could make you exceed the limit. If this is the case you are asking the circuit to use
much more energy than the circuit is designed for. More energy = more heat and
cables can catch fire. Part P of the new building regulations could involve a check on
any additional circuitry by qualified electricians when you sell your home. This can
affect your sale, you could be breaking the law and your house insurance may not be
valid. Please be absolutely sure you know what you are doing and get all of your work
checked by a qualified electrician.