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Science

Mains electricity

The UK mains electricity supply is about 230V and can kill if not used safely. Electrical circuits, cables, plugs and appliances are designed to reduce the chances of receiving an electric shock. The more electrical energy used, the greater the cost. Electrical supplies can be direct current (d.c.) or alternating current (a.c.).

Wiring a plug

You should know the features of a correctly wired three-pin mains electricity plug and be able to recognise errors in the wiring of a plug.

The cable

A mains electricity cable contains two or three inner wires. Each has a core of copper, because copper is a good conductor of electricity. The outer layers are flexible plastic, because plastic is a good electrical insulatorinsulator: Material that is a poor conductor of electricity or heat.. The inner wires are colour coded:

Colours of inner wires within a cable

colourwire
blueneutral
brownlive
green and yellow stripesearth

The plug

The features of a plug are:

  • The case is made from tough plastic or rubber, because these materials are good electrical insulators.
  • The three pins are made from brass, which is a good conductor of electricity.
  • There is a fusefuse: An electrical component that protects circuits and electrical devices from overload by melting when the current becomes too high. between the live terminal and the live pin.
  • The fuse breaks the circuit if too much current flows.
  • The cable is secured in the plug by a cable grip. This should grip the cable itself, and not the individual wires inside it.
The blue neutral wire goes to the left, the brown live wire to the right and the green and yellow striped earth wire is on top. The fuse fits next to the live wire.

The inside of a plug

The diagram shows the key features of a correctly wired three-pin mains plug.

Where does each wire go?

There is an easy way to remember where to connect each wire. Take the second letters of the words blue, brown and striped. This reminds you that when you look into a plug from above:

blue goes left, brown goes right and striped goes to the top.

Back to Electricity index

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