F0078 fault in WEG CFW701 Drive indicates Motor Overtemperature. This means the motor’s external PTC thermistor detected excessive heat, triggering a hardware-level thermal protection trip.
Cause:
- Excessive load at the motor shaft.
- Severe duty cycle (too many starts / stops per minute).
- Too high surrounding air temperature.
- Loose connection or short-circuit (resistance < 100 Ω) in the wiring connected to the motor thermistors.
- Not installed motor thermistors.
- Blocked motor shaft.
Note: It can be disabled by setting parameter P0351 = 0 or 3. An analog input and an analog output must be set for the PTC function.
Remedy:
Check the mechanical load on the motor shaft and resolve any blockages. Reduce high start/stop duty cycles if possible. Measure thermistor wire resistance to ensure it is > 100 Ω. Verify proper installation and wiring.
