Most modern socket circuits are ring circuits or ring mains as they are sometimes referred to. A cable leaves the consumer unit and travels to each socket on the main and when it reaches the last socket it then returns to the consumer unit, thus creating a ring. The advantage of this system is that power can reach the sockets in the circuit from both directions, which reduces the power load on the cables.
A ring circuit can serve an area up to 110 square metres (120 square yards), 2.5mm2 cable is used to wire the circuit and the circuit has a 30amp fuse or 32amp MCB on the consumer unit. It is usual for a house to have one ring circuit upstairs and one ring circuit downstairs.
Ring circuits can have extra sockets added to them by adding a ‘spur’ onto a ring circuit. A spur is a branch off the ring circuit, usually from an existing circuit, although a junction box could also be used. Theoretically as many spurs as sockets could be added, but the maximum load of the circuit (30/32amp) still exists).
See the following pages for more information,