Key takeaways
A drive that trips and takes a line down costs the same production minutes whether the code is F0001 or OC. This reference explains the fault families common to every variable frequency drive, the first checks for each, and where to go for the exact codes on the brands most plants run.
It is written for maintenance technicians, electricians and plant engineers who need the line running again without swapping a drive on a guess. For CNC control alarms rather than drive faults, see our machine troubleshooting guides.
Manufacturers use different numbering, different abbreviations and different display conventions, but the protection circuits inside a drive are broadly the same. Learning the families transfers across every brand on your site, which is more useful than memorising one vendor list.
| Fault family | Typical labels | What it means | First checks |
|---|---|---|---|
| Overcurrent | OC, OCA, F0001 class | Current exceeded an instantaneous limit, so the drive tripped to protect itself and the motor | Turn the shaft by hand, look for a jam, tight belt or failed bearing. Then check acceleration time and current limit |
| Overload | OL, OLT, motor overload | Sustained current above rating, integrated over time. Thermal rather than instantaneous | Compare actual load current against motor nameplate. Check for undersized motor, worn mechanics or blocked flow |
| Overvoltage | OV, OU, bus overvoltage | DC bus voltage rose above limit, usually while decelerating a high inertia load | Lengthen deceleration, check whether a brake resistor is fitted and healthy, measure incoming supply voltage |
| Undervoltage | UV, LU, bus undervoltage | DC bus fell below limit, from supply sag, a lost input phase or a loose connection | Measure all three input phases under load. Check terminal tightness and upstream fusing |
| Overtemperature | OH, OHT, heatsink over temp | Heatsink or internal air exceeded limit | Clean filters and heatsink fins, confirm cooling fans spin, check cabinet ambient and door seals |
| Ground fault | GF, EF, earth fault | Current is returning through earth instead of the motor circuit | Isolate and megger the motor and the full cable run. Long or damaged cables are the usual culprit |
| Short circuit | SC, SCF | A phase to phase short was detected on the output | Disconnect the motor and test the drive output alone, then test motor windings phase to phase |
| Input phase loss | LF, PF, input phase | One incoming phase is missing or badly unbalanced | Check fuses, contactor contacts and incoming terminals. Measure phase to phase at the drive terminals |
| Output phase loss | OPL, output phase | The drive sees no current on one output phase | Check motor terminal box, cable joints and any downstream contactor or isolator |
| Feedback loss | PGO, encoder fault | Encoder or tachometer feedback was lost in a closed loop configuration | Inspect the feedback cable, connector and shield grounding before replacing the encoder |
| Communication loss | CE, bus timeout, network fault | The drive stopped receiving commands from PLC or fieldbus | Check the network cable and termination, then whether the PLC was reset or the scan stopped |
| External fault | EF, ETR | An external contact told the drive to trip | Trace the wired input. It is often a motor thermistor, a vibration switch or a safety interlock |
Once you know the family, the vendor list gives you the exact code and the parameter that governs it.
Three families account for most of the drive trips maintenance teams actually chase, and each has enough depth to deserve its own guide.
A reset clears the code, not the cause. The trips that return week after week almost always trace to one of four things: a mechanical load that has changed, a cable or termination that is degrading, cooling that is no longer adequate for the season or the dust level, or a supply problem that only appears when a large load elsewhere in the plant starts.
That last one is easy to misdiagnose, because the drive faults and the drive gets blamed. If several unrelated drives trip on undervoltage at similar times of day, the investigation belongs at the transformer and the incoming supply, not at any single drive.
Escalate to the drive vendor or a specialist when a ground fault persists after the motor and cable have been cleared, when a short circuit fault repeats on a drive whose output tests clean, when firmware or parameter recovery is needed without a verified backup, or when the fault sits inside a safety function. Those are not places to experiment on a running line.
Most plants can name their worst machine but not their worst fault code. If every drive trip is logged as a coded downtime event, you can rank faults by frequency and by minutes lost, and the chronic ones get an engineering fix rather than another reset. Without that record, the same fault gets rediscovered by a different technician every few weeks.
Fabrico reads production signals from the control or from an IoT gateway on older equipment, so a stop is captured with its true start and end time instead of being written down later from memory. A drive trip can then be attributed and turned into a work order with the asset, its history and its parts already attached.
The trips that stay invisible are the short ones. A drive that faults, gets reset and runs again inside a minute rarely reaches any log, yet across a shift those minutes outweigh the long breakdowns. Fabrico can also use cameras pointed at the process to explain stops nothing else recorded.
Is there a universal VFD fault code list? No. Codes are vendor specific and often model specific. Fault families are universal, which is why identifying the family first is faster than searching a code you may be reading from the wrong manual.
My drive trips on overcurrent but the motor seems fine. What now? Check the mechanics under load rather than at rest, then the acceleration time and current limit parameters. An acceleration ramp that is too aggressive for the inertia produces genuine overcurrent on a healthy motor.
Why does the same drive trip on overvoltage only when stopping? Because deceleration turns the motor into a generator and pushes energy back into the DC bus. Either the ramp is too short for the inertia or the braking resistor is missing, undersized or failed.
How often should a drive fault be acceptable? A drive that trips repeatedly is telling you something is wrong outside the drive. Treat any fault that recurs more than once on the same asset as an engineering problem rather than an operating inconvenience.
Can I reset a fault remotely? Technically many drives allow it, but resetting without eyes on the machine risks restarting into a jam or a genuine fault condition. Confirm the cause is gone before the drive is allowed to run.
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