When the first homes were wired for electricity, at the very end of the 19th century, very little had been invented in the way of electrical appliances and thus lighting was the main use for electricity. With the domestic availability of the electric motor, which by 1910 was to power domestic fans, vacuum cleaners, food mixers etc. came the need for power circuits, with socket outlets around the house.
Eventually houses were fitted with both 15 Amp and 5 Amp sockets, each socket outlet being wired from a seperate circuit. The plugs and sockets came in two pin or three pin varieties, both having round pins. Unlike modern day 13 Amp plugs, the old 15 Amp and 5 Amp types were not usually fused.
The modern way of wiring a power circuit is to use a system called a ring circuit, or ring main. This involves wiring the live, neutral and earth cables from the consumer unit, to each socket outlet and back to the consumer unit (the ends of both of the live wires are connected into the same fuse). This enables the current to flow in either direction around the circuit to supply the sockets, and means that smaller diameter cable can be used than with the old radial system.
In a normal house, two ring circuits are used, one for upstairs and one for downstairs, although more can be used if required. Each country has a governing body to lay down regulations concerning electricity both in the home and at work. It is these bodies who determine the maximum number of socket outlets to one circuit, and the maximum load for each circuit.
