Fuses and earth wires

• Entry Level Certificate
• Earth wire


  A safety wire to stop the appliance becoming live, preventing electrocution
• Live wire


  • Carries alternating current from the mains electricity supply
• Neutral wire


  • Completes the circuit
• If the live wire touches the metal casing

  The whole kettle could become live
• The earth wire stops the kettle from becoming dangerous to touch
• What happens when the live wire touches the metal case of the kettle

  1. Large current flows through the earth wire

  2. Large current flows through the fuse

  3. Fuse melts and breaks the circuit

  4. Kettle switches off at once
• Fuse


  Designed to melt and break at a specific current
• Different fuse values


  • 3 A
  • 5 A
  • 13 A
• A lamp has a maximum current of 0.25 A. The correct fuse value is 3 A
• A kettle has a maximum current of 10 A. The correct fuse value is 13 A
• The fuse value has to be higher than the maximum current but not too high
• Using the right fuse prevents fires
• Double insulation


  Some double-insulated appliances do not need an earth wire
• Double-insulated appliances


  • May have an insulating lining that stops the live wire from touching the metal casing
  • May have a plastic casing
• The earth wire is the safety wire
• The fuse contains a thin piece of wire which melts if the current is too high
• Using a 13 A fuse in a lamp with a maximum current of 3 A could lead to overheating and fire
• Appliances and their maximum current in A

  • Kettle: 11.0 A
  • TV: 0.5 A
  • Microwave: 5.0 A
  • 3 A lamp with a 15 A fuse
  • 3 A lamp with a 5 A fuse