How can the thermal overload unit be adjusted for different motor full-load currents?

The thermal overload unit is a crucial component in protecting electric motors from overheating due to excessive current. It functions by using a bimetallic strip that bends when heated, which opens a circuit if the temperature rises too high, indicating an overload situation.

To adjust the thermal overload unit for different motor full-load currents, changing the size of the heater is the correct approach. The heater inside the overload relay determines the threshold at which the unit will trip in response to overheating. Different motors have different full-load currents, and by selecting a heater that corresponds to the specific full-load current of the motor being protected, the overload unit can be effectively calibrated to offer the appropriate level of protection.

This adjustment is essential because a heater that is too small will trip too early, potentially interrupting normal operation, while one that is too large may not trip when needed, risking damage to the motor. Thus, selecting the proper heater size ensures that the thermal overload unit accurately responds to the motor’s full-load current requirements.