A ring circuit is a multi-outlet power circuit which may supply an unlimited number of 13-amp plugs, socket outlets and fixed appliances but is limited to supplying an area not exceeding 1000 sq ft (100 sq. m). Where the floor area exceeds this, more than one ring circuit is necessary. It is wise to install two ring circuits in homes of under 1000 sq. ft (100 sq m) so as to have the advantage of double the load capacity for portable appliances. In a two-storey house this would mean a ring circuit on each floor.
The circuit consists of a 2.5 sq mm twin and earth PVC sheathed cable starting from fuseway terminals in the consumer unit, passing through the various rooms and areas and returning to the same fuseway terminals. Thereby completing a loop or ring. Switched socket-outlets and fused connection units, the latter for fixed appliances, are connected to this cable anywhere along its route. In addition spurs of the same size and type cable can branch off the ring cable and may supply a maximum of either two socket-outlets (two singles or one double) or one fixed appliance. Such socket-outlets are usually situated off the main route of the ring cable.
The number of spur cables is limited to the number of outlets connected to the actual ring cable.
Socket outlets should always be of the switched type and be mounted at a height of not less than 6 in. (15 cm) above floor level or a work-top, as in a kitchen. The recommended height is 12 in. (30 cm) above floor level. The 13A switched socket outlet is available in a wide range, in various colours and finishes, in single and double assemblies and also with neon indicators. Double socket outlets are advisable wherever possible.
Fused connection units for supplying fixed appliances are also available in a variety of types and finishes. Shaver sockets may be connected to a ring circuit.
A radial circuit is a multi-outlet power circuit which supplies a limited number of 13 A socket-outlets and fixed appliances. There are two principal types. One is a 30 A circuit supplying up to a maximum of six 13A outlets. The other is of 20A current rating and may supply up to two 13A outlets which may be increased to a maximum of six if all are in one room with a floor area not more than 100 sq ft (9 sq m), provided the room is not a kitchen and none of the appliances is a fixed water heater. Thus, while the 30A radial may serve the kitchen, the 20A is suitable for the living room or bedroom.
Cooker circuit. A cooker circuit is a radial circuit but supplies only the cooker For small and medium-size free-standing or built-in cookers it can be of 30A current rating. For the larger family-size cooker, including split-level versions, a 45A circuit is needed.