Chapter 6—Motor Protection112 Power Xpert C445 Global Motor Management Relay MN042003EN—January 2019 www.eaton.comTable 23. Parameters That Control the Transition ProfileFigure 109. Start Cycle and Transition TimingMotor Thermal OverloadThe Overload function models the thermal characteristics ofa motor and generates a Fault Trip event that de-energizesthe motor before motor damage will occur. This is intendedto protect the motor and power wiring from excessivecurrent. Trip curves are defined by applicable agencystandards. The trip class for any particular Overload class isuser adjustable. When the FLA is entered for the motor, thethermal capacity value will be calculated to model the motortemperature during motor operation. Thermal capacity can becharacterized by the calculated value representing therelative position with regard to the Trip Class curve. Forexample; a motor running at a thermal capacity value of 85%is much closer to an Overload Fault Trip than the same motorrunning at a thermal capacity value of 25%.The following items are associated with the electronicOverload function of the C445.● An Overload Fault Trip will occur when the calculatedthermal capacity reaches 100%.● An Overload Fault Trip cannot be cleared by power cyclingthe device – the thermal capacity calculated value is storedin non-volatile memory.● Two thermal capacity models are used. One model isenabled while the coil is energized (motor is running) and asecond model is enabled while the coil is de-energized(motor stopped). The second model has a longer timeconstant.● A RESET button is located on the Base Control Moduleand the User Interface. Depressing this button will clearany Overload fault that has been latched, but is no longerpresent (thermal capacity must be less than 100%).Resets can also be initiated through the communicationport.● An auto-reset option is available. This provision enables theunit to automatically reset when the fault has cleared.CAUTIONIn the Auto Reset mode, caution must be exercised to assurethat any restart occurs in a safe manner. Auto Reset modeshould not be used in environments where excessive restartattempts may cause component damage and/or createunsafe conditions.Parameter Units Increment Minimum Maximum Default NotesMotor Transition Threshold Percent % 1% 25 200 115% Modbus Register = 1086Motor Start Threshold Percent % 1% 1 100 30% Modbus Register = 1084Motor Stop Threshold Percent % 1% 1 50 5% Modbus Register = 1085Start Cycle Time s 1% 2 360 10% Modbus Register = 1078
