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Electricity in the Home

Mains supply is ac, Battery supply is dc

  • There are two types of electricity supplies- alternating current(ac) and direct current(dc)
  • In ac supplies the current is constantly changing direction. Alternating currents are produced by alternating voltages in which the positive and negative ends keep alternating
  • The UK mains supply is an ac supply at around 50Hz
  • By contrast, cells and batteries supply direct current
  • Direct current is a current that is always flowing in the same direction. It’s created by a direct voltage.

Most cables have Three Separate Wires

  • Most electrical appliances are connected to the mains supply by three-core cables. This means that they have three wires inside them, each with a core of copper and a coloured plastic coating.
  • The colour of the insulation on each cable shows its purpose
  • The colours are always the same for every appliance. This is so that it is easy to tell the different wires apart.
  • You need to know the colour of each wire, what each of them is for and what their pd is:
  • LIVE WIRE=brown. The live wire provides the alternating potential difference(about 230V) from the mains supply
  • NEUTRAL WIRE=blue. The neutral wire completes the circuit-when the appliance is operating normally, current flows through the live and neutral wires, at 0V
  • EARTH WIRE=green and yellow. It is for protecting the wiring, and for safety-it stops the appliance casing from becoming live. It doesn’t usually carry a current-only when there’s a fault. It’s also at 0V

The Live Wire can give you an Electric Shock

  • You body is at 0V. This means that if you touch the live wire-a large potential difference is produced across your body and a current flows through you.
  • This causes a large electric shock which could injure or even kill you
  • Even if a plug socket or a light switch is turned off there is still a danger of an electric shock. A current isn’t flowing but there’s still a pd in the live wire. If you made contact with the live wire, your body would provide a link between the supply and the earth, so a current would flow through your body
  • Any connection between live and earth can be dangerous. If the link creates a low resistance path to earth, a huge current will flow, which could result in a fire.