Fuses and circuit breakers
Fuses are used in 3-pin plugs and in the fixed wiring in a house.
- Fuses in plugs protect the flex of the appliance, and in doing so, the appliance itself.
- Fuses in the fixed wiring of a house protect the mains wiring.
- If a fault develops and the current in the wire becomes dangerously large, the fuse melts and breaks the circuit.
- Plug fuses come in different values. Although other values are available, the following rule is used to decide on the correct value of fuse to use:
- for an appliance with a power rating of up to 700 watts, use a 3 ampere fuse
- for an appliance with a power rating of 700 watts or greater, use a 13 ampere fuse
- Circuit breakers are automatic switches in the mains supply which do the same job as fuses. They break the live wire if a fault causes the current to become too large.
- (Credit) You should be able to say why fuses are in the live lead of an appliance. This is so that when a fuse blows it cuts off the live wire which is at a high voltage. The neutral wire is never at a high voltage.
- (Credit) You should be able to give a reason why a circuit breaker is better than a fuse. Some reasons are:
- they operate more quickly
- they only need to be reset, not replaced
- they cannot be replaced with the wrong size of wire
Video: How fuses and RCDs help protect us from electrocution