Fuses & Earthing

• One risk in electrical circuits is a surge in current

  Surge is a sudden increase in current

  This can damage an appliance, cause a fire, or give an electrical shock
• 4 safety mechanisms that can be used in electrical circuits

  Fuses

  Circuit breakers

  Earth wires

  Double insulation
• How does a fuse work

  Have a thin wire which melts and breaks the circuit when current is too high

  The rating of fuse is the current that will cause the fuse to break
• How do you decide which fuse rating to use for a given electrical circuit

  Generally you should use a fuse with a rating a few amps above the recommended current for the appliance.

  This means it won’t break under normal use. However, if there is a surge and the current rises significantly then it will surpass the rating and break the fuse
• Circuit breakers

  Act like a switch that will trip (open) when there is a surge in current

  They can be reset electrically, rather than having to be replaced
• How do earth wires protect us from electric shocks

  The earth wire is connected to the casing of the appliance. If the live wire touches the appliance casing the earth wire provides an alternating pathway for electricity to flow.

  This means we can’t get an electric shock
• Double insulation

  Where an appliance is covered in a layer of plastic. As plastic doesn’t conduct electricity, we can’t get an electric shock from touching it, even if the appliance is live