The electric wiring in a house consists of several circuits.
The immersion heater and cooker require large amounts of current and have their own circuits.
Lights have their own circuit. This means that if one fuse blows, other devices on other circuits will still work and thinner wire can be used.
The ring main circuit is the one that powers all the plug sockets. Having the ring mian circuit separately makes it easy to add an move plug sockets.
Electricity enters the house through a mains supply cable. A meter measures the amount of electricity supplied, and the cables are then fed into a consumer unit – a safety device containing a main switch so the electricity supply can be switched off in an instant, should there be a fire or flood for example, along with all the fuses or circuit breakers for each circuit.
There are only two cables into your house – live and neutral. The earth cable inside your house is separate from the boards supply.