Bimetallic overload relays are components based on the principle of dilatation of thermoelectric parts, also called bimetallic. The operation of a relay is directly based on the different expansions that the metals present, in case they are exposed to a change of temperature. Overload relays are normally used to indirectly protect electrical devices from possible overheating, such as in motors and transformers, for example.
Overheating of an engine can be caused by a number of factors, such as mechanical overload at the tip of its axis, high start time, blocked rotor, lack of one or more phases and excessive deviations of network voltage and frequency, among others.
In case of any of these situations, the current or over-current increment in the motor must be controlled monitored in all phases by the overload relay. All terminals present in the main circuit of the overload relays shall be marked in the same way as the power terminals of the contactors with specific functions, according to the sequence number, and if there is a second sequence, it shall be identified with zero.