Electricity power is measured in watts. The electricity flow is referred to as the electric current and this is measured in amps. The driving force behind this current is measure in volts. In the UK the public electric supply is set at 230 volts. This supply is referred to as the alternating current, where as the supply from batteries is referred to as direct current. The mains supply is known as alternating current because the current can be transformed from one voltage to another depending on the application.
The lighting circuit runs from the consumer unit, linking a series of lighting ports. Cables are then laid from these electrical ports to the electric switches. This circuit requires a 6 amp fuse be used to protect it from faulting. This circuit can supply up to a maximum of 1200 watts but it is good practice to have it supplying much less than this. If working at near capacity the circuit may become over loaded, especially if high wattage bulbs are used.
The ring main circuit is wired as a ring that begins at the consumer unit before looping back to it, providing electric flow to the socket in both directions. This circuit can supply a floor area up to 100 m2. This circuit requires a 32 amp fuse to protect it from electrical fault. You can fit an array of sockets on this circuit but the total wattage can not exceed 7000 watts. If a larger electrical flow is required, then additional ring circuits must be installed.
An alternative to adding additional ring circuits, is to use a spur on a ring circuit. Extra sockets can be added to a ring circuit through spur branching from the main ring circuit or the junction box. There is a theoretical output, which will allow for an additional single or double socket. This circuit can not serve rooms of more than 100 m2 and its maximum load is still 7000 watts. Any larger than this and the circuit would most certainly malfunction causing a total outage.
The socket outlets can have a maximum load of 3000 watts, serving a 13 amp plug. The plug itself is fitted with a 3 amp or 13 amp fuse, in accordance with the wattage rating of the appliance connected to it. Finally, an appliance that is a large consumer of electricity and in constant use eg electric stove, an electric shower or an electric chest freezer, will have its own circuit which is extended from the consumer unit. If this type of appliance was connected to the shared circuit, it would take a too large a share of the throughput and the circuit would fail. Now you have a better understanding of the circuitry in your home, you can undertake electric work in a safe manner.