19.3 Electrical safety Safety devices Fuses and circuit breakers The current is larger than the wire is designed to carry The wire becomes very hot. Fire How to prevent too large a current from flowing through the circuit? Fuses and circuit breakers are used.

19.3 Electrical safety  Fuses are used in many electrical appliances, plugs, adaptors or extension units.  They are always connected to the live wire.  They are thin metal wires.  Circuit symbol: Video: How fuses work

19.3 Electrical safety How do fuses work? The current through the wire is larger than a certain value. The wire heats up and melts. The circuit breaks.  No, it must be replaced by a new one. Can a melted fuse be used again?

19.3 Electrical safety  Fuse rating indicates the current at which the fuse melts.  A fuse of fuse rating slightly higher than the operating current of the appliance should be used.

19.3 Electrical safety  They can be reset and used again.  They are used in consumer units. For example:  lighting circuit: 6 A circuit breaker  ring circuit: 30 A circuit breaker  Circuit symbol:  Circuit breakers break the circuit when the current is larger than a certain value. Simulation: How circuit breakers work

19.3 Electrical safety Earth wires The live wire touches the metal case. L N E heating element metal case of the oven The earth wire connects the metal casing to the Earth. The fuse melts and breaks the circuit. A large current flows from the live wire to the Earth.

19.3 Electrical safety  Even if the fuse fails to work, current flows through the earth wire instead of the person. L N E

19.3 Electrical safety Safety rules  Electrical appliance should be inspected by a qualified person.  Do not place the cord of an electrical appliance close to any hot object.  Avoid using more than one adaptor at one socket. Avoid using adaptors and extension units together.  Do not use portable electrical appliances in bathroom.  Do not touch any electrical appliances, sockets or switches if your hands are wet.

19.3 Electrical safety That’s the end of Section 19.3 Check Point Key Ideas Previous Page Exit