Household electricity

In a nutshell

There are two types of electricity supply - alternating current (a.c.) and direct current (d.c.). In a plug, the live wire is brown, the neutral wire is blue, and the earth wire is green and yellow.

Mains supply

In alternating current supplies the charges are constantly changing direction. Alternating currents are produced by alternating voltages.

The UK mains supply is an a.c. supply at around $230 \space V$ . The frequency of the a.c. mains supply is $50 \space Hz$ .

Mains electricity is produced by generators that rotate, which causes the direction of the current to continuously keep changing. The voltage then also varies with a sinusoidal patten: there is a peak positive voltage which reduces down to zero, and then a peak negative voltage. This pattern repeats continuously.

Battery supply

Cells and batteries supply direct current. In a direct current the charges always move in the same direction. Direct current is created by a direct voltage.

The image below on the left shows an a.c. waveform. The image below on the right shows a d.c. waveform.

Physics; Electricity and circuits; KS4 Year 10; Household electricity

Physics; Electricity and circuits; KS4 Year 10; Household electricity

Plug cables

Most electrical appliances are connected to the main supply via three-core cables. These have three wires inside them, each with a copper core surrounded by a coloured plastic insulation.

The colour of the insulation on each cable is used to identify its purpose. The three types of cable are shown in the table below.

Type of wire	Colour	Description
Live wire	Brown	The live wire carries the voltage. It alternates between a high positive and negative voltage of around $230 \space V$
Neutral wire	Blue	The neutral wire completes the circuit. When the appliance is working normally, current flows through the live and neutral wires. The voltage of the neutral wire is around $0 \space V$
Earth wire	Green and yellow	The earth wire is for safety. It diverts the current if there is a fault with the circuit, and prevents the casing from becoming live. The voltage of the earth wire is also around $0 \space V$

Fuses are also a part of the plug design. A fuse is a safety device designed to melt if the current is too high. This breaks the circuit and protects the high current from damaging the appliance.

The diagram below illustrates the positions of the components within a plug:

Physics; Electricity and circuits; KS4 Year 10; Household electricity

1	Earth wire
2	Neutral wire
3	Live wire
4	Fuse
5	Cable grip
6	Three-core appliance cable

Note: Plug sockets have switches which are connected in the live wire of the circuit. This is so the circuit can be broken - the appliance becomes isolated and the risk of an electric shock is minimised.