VFD faults and warnings — diagnostics
How a fault differs from an alarm/warning, acknowledgement, common drive fault groups and a procedure for finding the cause.
Fault vs warning
| Fault (trip) | Alarm / warning | |
|---|---|---|
| Motor | switched off (coast or ramp stop) | keeps running |
| Reset | after removing the cause — by acknowledgement | usually clears itself when the condition disappears |
| Example | Siemens F07011 — motor overtemperature (trip) | Siemens A07910 — motor overtemperature (warning) |
Terminology differs: Siemens uses F… for faults and A… for alarms (warnings); ABB uses fault and warning; Danfoss uses alarm (with trip) and warning; Rockwell uses fault and alarm. That is why each record in the diagnostic database states its type in the manufacturer's classification.
Some faults require a power cycle or are flagged as trip lock — they cannot be acknowledged from the keypad or the network.
Acknowledgement
A fault is reset with the keypad Reset button, a digital input, a control-word bit (bit 7 of STW1 on a rising edge for PROFIdrive) or automatically (auto-reset with a limited number of attempts). Do not enable auto-reset carelessly: the motor may start unexpectedly.
Common fault groups
| Group | Typical causes | What to check |
|---|---|---|
| Overcurrent | short acceleration, jammed machine, short circuit in cable or motor, wrong motor data | acceleration time, cable and motor insulation, mechanics |
| DC link overvoltage | short deceleration, regeneration from the load, high mains voltage | deceleration time, Vdc_max controller, braking resistor |
| Undervoltage | mains dip, lost phase, blown fuse | supply, contactors, fuses |
| Drive overtemperature | dirty heatsinks, failed fan, hot cabinet | cabinet ventilation, drive fan, switching frequency |
| Motor overload (I²t, thermistor) | mechanical overload, low-speed operation without forced cooling | load current, thermal model parameters, PTC/KTY sensor |
| Ground (earth) fault | insulation damage, moisture, long cable with high capacitance | insulation tester (with the drive disconnected!), cable, output reactor |
| Communication loss | broken cable, wrong address, network timeout | see Modbus troubleshooting |
Finding the cause
- Record the fault code and time and the preceding events from the drive's log.
- Look up the code in the manual for the same model and firmware version — the same numbers mean different things in different series.
- Check the values at the time of the fault (many drives store current, DC voltage and frequency).
- Check the most likely causes first: mechanics, cable, ramp parameters.
- Do not reset repeatedly without analysis: a recurring overtemperature or ground fault will destroy the drive.
Tools
- Diagnostic Database — fault and warning codes with causes and links to the official manuals.
Connections
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Sources
Updated 2026-10-01