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Fuses and circuit breakers

Fuses and circuit breakers are both devices that 'break' if the current through them is too large.


A fuse is usually a thin piece of wire that will melt and break the circuit if too large a current flows through it. The thicker the wire the more current is needed to melt it and the higher the 'rating' of the fuse. The purpose of a fuse is to protect the wiring and the equipment. If the fuse was not there and something went wrong the wires themselves would get hot and maybe catch fire. In a plug the fuse is in a glass tube.

Fuses should also be connected in the live wire you should always switch off before changing a fuse.

The disadvantage a fuse wire is that it takes a finite length of time for the wire to heat up and break, and in that time damage may be done to the equipment.

Circuit breakers

A circuit breaker is an electronic circuit that will switch off the current if it is too great. Such a circuit is designed to operate much more quickly than a fuse and so the damage is less because the current is switched off in a much shorter time.

Circuit breakers are often used to protect the user if the casing of the equipment becomes live. They break the circuit before the person using the equipment gets a near fatal shock.

© Keith Gibbs 2011