The motor-breaker is a device that guarantees the control and the protection of the motor, it is fundamentally made of thermal and magnetic triggers that act in the starting of the electric motor against the burning by variation of voltage and current in the network, the elevation of temperature of the and overloads. The use of the circuit-breaker associated to the contactor allows the motor to be connected at a distance and in this circuit-breaker-contactor combination, both carry out the protection function.
The purpose of fuses is the protection of electrical systems against short circuit. In the protection of motor circuits, those of the functional class (gL), that is, with general protection function, are used. Its interruption is of delayed effect, because the motors, being inductive loads, promote current superior to the nominal one at the moment of departure. The most common delayed fuses are the NH and Delzed Diazed types. Bimetallic relays, also called overload relays, are used to protect electrical equipment from possible overload, obstructing the circuit above the rated current value. In these relays we can select any current value because its actuating current is adjustable in a range.