How Do Fuses Work?

Fuses have been in operation for a longtime, and their job is to prevent circuits from overloading. When exposed to a current above permitted levels, the fuse will "blow" and break the circuit. The central part of the fuse is the delicate melt wire, which is in line with the live circuit and which carries the current, yet burns up if the flow exceeds a certain level, thus breaking the circuit.

Fuses are very sensitive to rapid increases in current as occurs with a short circuit. With smaller increase in the current such as occurs in circuits attached to too many appliances, e.g.,  an air conditioner and appliances in the summer or a heater and appliances in the winter, the increase of current is smaller and it doesn't rapidly blow the fuse. To detect these current changes modern circuits have circuit breakers, overload relays and MCBs. These devices respond rapidly to changes in current and quickly break the circuit. 

Read About Parallel Circuits in the Home