The performance of the fuses in the electric motors is due to the fusion of an element by the Joule effect, generated by the sudden increase of current in a given circuit. The fuse element has physical properties, that its melting point is less than the melting point of the copper.
Essentially, fuses are applied elements with the main objective of limiting the current of an existing circuit, thus harmonizing its interruption in cases of short circuits or long overloads, for example. The short circuit is nothing more than a connection, almost without resistance, between conductors under voltage, or it is also an intentional or accidental connection between two points of the same system or of some electrical equipment, or of a component, by means of of an impedance considered low.
Under these conditions, by a negligible transient resistance, the current may have a value many times higher than the operating current, so that the equipment and part of the plant may undergo a thermal stress, a bearable current of short duration, or even an electrodynamic, a nominal current of excessive impulse.