Household electricity
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Explainer Video
Summary
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 . The frequency of the a.c. mains supply is .
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.
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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 |
| 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 |
| 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 |
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:
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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.
FAQs - Frequently Asked Questions
What is the voltage of the UK a.c. mains supply?
The voltage of the the UK a.c. mains supply is around 230 V.
What is direct current?
Direct current is a type of electrical supply where the the charges always move in the same direction.
What is alternating current?
Alternating current is a type of electrical supply where the charges are constantly changing direction.