Thermal compensation control for a motor starter

A motor starter thermal-compensation control (10) is disclosed in which an ambient temperature sensor (36) is positioned to sense ambient temperature and provide an ambient temperature signal in a motor starter (12). Additional temperature sensors (30,32,34) are mounted in thermal communication with each bus bar (22,24,26) in a motor starter (12) and to monitor the temperature of each pole. A microprocessor (28) is connected to each of the temperature sensors (30,32,34,36) and periodically receives the temperature signals to monitor change in operating temperature of the motor starter (12). The control (10) adjusts the output of the motor starter (12) based on the change in the operating temperature (200) so as to maintain a constant output as the ambient temperature increases, or the internal resistance of the device increases with temperature increase. In order to adjust the output, the system increases the FLA ampacity (96) to compensate for the temperature increase. If the ampacity reaches the device's limits (98,108), the starter (12) is prevented from engaging the motor (14) with the power supply until it has sufficiently cooled down (106). The control (10) calculates an estimated cool down time and displays the cool down time (112) to prevent unnecessary start attempts during cool down.