The Ring Main (WJEC GCSE Science (Double Award)): Revision Note

The Ring Main

• All electrical appliances are connected to the mains supply

• In the UK, a three-core cable is used consisting of:

  • A live wire

  • A neutral wire

  • An earth wire

• The insulation covering each wire is colour-coded for easy identification:

  • Live wire – brown

  • Neutral wire – blue

  • Earth wire – green and yellow stripes

Live, Neutral & Earth Wires

A mains-powered appliance in the UK contains live, neutral and earth wires

• Every country has a slightly different configuration, with many using two-pin plugs and plug sockets such as in the USA and mainland Europe

  • The earth wire is still present in the two-pin plugs, just more hidden

• The three wires have distinct purposes

The Live Wire

• The purpose of the live wire is to carry the alternating current from the mains supply to a circuit

• It is the most dangerous of the three wires

• If it touches the appliance without the earth wire, it can cause electrocution

The Neutral Wire

• The purpose of the neutral wire is to form the opposite end of the circuit to the live wire to complete the circuit

• Because of its lower voltage, it is much less dangerous than the live wire

The Earth Wire

• The purpose of the earth wire is to act as a safety wire to stop the appliance from becoming live

• This prevents electric shocks from occurring if the appliance malfunctions or the live wire breaks off and touches the case of the plug

The Ring Main Circuit

• Electrical circuits in houses are always connected in parallel for two main reasons

  • Each appliance will have the same voltage across it (this means, for example, all lamps will have the same brightness)

  • Each appliance can be switched on independently, and if one breaks, the others still work

• The looped parallel circuit that connects the electrical appliances in a household is called a ring main circuit

• The ring main is connected to the consumer unit so it can be controlled from centrally

The Ring Main Circuit

Simplified diagram of the main ring in a domestic circuit. Each socket is placed in parallel on its own loop

• The advantages of a ring main circuit are:

  • The cables can be made thinner because there are two paths for the current

  • Each part of the cable carries less current because the current flows two ways

  • It is more convenient since sockets can be placed anywhere on the ring

  • Each socket has a voltage of 230 V (in the UK) which can be added anywhere on the ring and operated separately