Fuses and earthing

• Surges

  Sudden increase in current which can..

  ~ Damage appliance

  ~ Cause a fire

  ~ Electric shock
• Used to protect against surges in a current?

  ~ Fuses

  ~ Circuit breakers
• Fuses have a thin wire which melts and breaks circuit when the current is too high.
• Generally, you should use a fuse with a rating a few amps above the recommended current for the appliance.
• Which fuse rating would be appropriate for a kettle designed to operate at 5 A of current?

  8 A
• Circuit breakers are like a fuse that can be reset after they break the circuit.
• Fuses

  Good..

  ~ Simple / cheap
• Fuses

  Bad..

  ~ Permanently broken
• Circuit breakers

  Good..

  Tripped -> Turn of circuit

  ~ Replaceable
• Circuit breakers

  Bad..

  ~ More expensive
• How earth wires protect us from electric shocks..

  1 ~ The earth wire is connected to the casing of the appliance.

  2 ~ If live wire touches the appliance casing, earth wire provides alternative pathway for electricity to flow.

  3 ~ No electric shocks from touching the casing.
• An appliance has ‘double insulation’

  Therefore it most likely..

  Has a plastic casing but no earth wire.