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Fuses
Fuses are included in circuits to stop excessive currents from flowing. if the current gets too high, cables can burn out and fire can start. A fuse contains a thin section of wire, designed to melt and break if the current gets above a certain value. Usually, fuses are contained in catridges, which make it easy to replace them.
Some fuses use fuse wire, the thicker the wire the higher teh current that is needed to make it ‘blow’.
A fuse represents a week link in the electricty supply chain.
Replacing a fuse is preferable to having to rewire a whole house.
It is important to choose a fuse of the correct value in order to protect an appliance.
The current rating of the fuse should be just above the value of the current that flows when the appliance is operating normally.
Circuit breakers
A circuit breaker is an automatic switch which cuts off the current in a circuit if this rises above a specified value. It has the same effect as a fuse but, unlike a fuse, can be reset (turned ON again) after it has tripped (turned OFF).
In the type shown above, the current flows through two contacts and aslo through an electromagnet. If the current gets too high, the pull of the electromagnet becomes strong enough to release the iron catch, so the contacts open and stop the current.
Pressing the reset button closes the contact again.