F078 fault in WEG CFW900 Drive indicates a Motor Overtemperature. This means the motor’s external PTC thermistor detected excessive heat, triggering a hardware-level thermal protection trip.
Cause:
Fault related to the PTC temperature sensor installed on the motor.
- Load on the motor shaft is too high.
- Load cycle is too short (high number of starts and stops per minute).
- High ambient temperature around the motor.
- Poor contact or short circuit (resistance < 100 Ω) on the wiring connected to the motor thermistor.
- Motor thermistor not installed.
- Motor shaft locked.
Note: The fault can be disabled by setting C7.5.2 = 2 or 3. It is necessary to program Slot X analog input and output for PTC function.
Remedy:
Check mechanical load on the motor shaft and optimize start/stop duty cycles. Ensure proper motor cooling. Measure thermistor wire resistance to verify it is > 100 Ω. Confirm correct installation and parameters on Slot X and parameter C7.5.2.
