The Ring Main (WJEC GCSE Physics)

• 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