Altivar ATV12 Fault Codes: What Do OCF, ObF, OSF and nSt Mean?
What ATV12 codes OCF, ObF, OSF, OPF2, SCF and nSt mean, their likely cause, what to check and how to clear them, based on the official Schneider manual.
What do OCF, ObF, OSF and nSt mean on an ATV12 display? OCF is overcurrent, ObF is overbraking and OSF is mains overvoltage. nSt is not a fault but freewheel stop: the drive is waiting for permission to run. The tables below are written in our own words from the Schneider Electric ATV12 user manual (BBV28581, 02/2026, pages 111-116). They apply to the ATV12 series only.
Before touching the drive
- Disconnect all power, including external control power, lock the switches open and fit a "Do Not Turn On" label.
- Wait 15 minutes for the DC bus capacitors to discharge. The DC bus LED does not show that the bus is dead, and this voltage can exceed 800 Vdc.
- Measure across the DC bus terminals with a suitably rated meter. The reading must be below 42 Vdc.
- If the capacitors do not discharge, contact your Schneider Electric representative.
Work on the power circuit must be done by qualified electrical staff.
Codes cleared by a power cycle
Remove the cause first, then power the drive off and on. SOF and tnF can also be cleared remotely through a logic input assigned to RSF.
| Code | Meaning | Possible cause | What to check |
|---|---|---|---|
| OCF | Overcurrent | Wrong drC- settings, high inertia or load, mechanical locking | Parameters, motor/drive/load size, mechanism, ground connection and motor insulation. If needed add line chokes and reduce switching frequency SFr |
| SCF1 | Motor or ground short circuit | Short circuit or ground fault at the drive output | Drive-to-motor cable and motor insulation |
| SCF3 | Ground short circuit | Ground fault while running, switching motors while running, high leakage with parallel motors | Motor chokes |
| SCF4 | IGBT short circuit | Internal power component short detected at power-on | Schneider Electric representative |
| SOF | Overspeed | Instability or overspeed caused by application inertia | Motor, tFr setting (threshold is 10 % above it), braking resistor, sizing, speed loop gain |
| tnF | Auto-tuning fault | Motor not connected, one phase missing, special motor, or motor turned by the load | Motor/drive match, motor present; output contactor closed, motor fully stopped |
| CrF1 | Precharge | Charging relay control fault or damaged charging resistor | Power cycle, connections, supply stability, then your representative |
| InF1, InF2, InF3, InF4, InF9, InFb, InFE | Internal board, measurement, sensor or processor fault | Boards or data inside the drive | Schneider Electric representative |
| ---- | Application firmware problem | Invalid application firmware | Reflash it with the Multi-Loader tool |
Codes that automatic restart can clear
Once the cause is gone, these clear through automatic restart, a power cycle or an input assigned to RSF.
| Code | Meaning | Possible cause | What to check |
|---|---|---|---|
| ObF | Overbraking | Braking too sudden or driving load | Extend the deceleration time, add a braking resistor module if needed, measure the line voltage |
| OHF | Drive overheat | Drive temperature too high | Motor load, ventilation and ambient temperature; wait for it to cool |
| OLF | Motor overload | Excessive motor current | Thermal protection setting and motor load |
| OLC / ULF | Process overload / underload | Process out of step with the drive settings; for ULF, current below threshold LUL | Process and drive parameters, LUL and ULt |
| OPF1 | One output phase lost | One phase missing at the output | Drive-to-motor connections; output contactor if used |
| OPF2 | Three output phases lost | Motor not connected, motor under 6 % of drive current, output contactor open, unstable current | Connections; UFr, UnS, nCr and auto-tuning. OPL = nO can be used to test with a small motor |
| OSF | Mains overvoltage | Supply 10 % over the limit at power-on, 20 % over with no run order, or disturbed supply | Turn the drive off and measure the line; power on once it is back to normal |
| PHF | Input phase loss | Wrong supply, blown fuse, missing phase, three-phase ATV12 on single phase, unbalanced load | Power connection and fuses. Protection only works on load |
| SCF5 | Load short circuit | Short circuit at the drive output | Drive-to-motor cable and insulation |
| tJF | IGBT overheat | Temperature too high for ambient and load | Sizing, switching frequency SFr; let it cool |
| LFF1 | AI1 current signal lost | AI1 in current mode and input below 2 mA | Terminal connection |
| SLF1 / SLF2 / SLF3 | Modbus / SoMove / display communication | Connection interrupted | Bus, cable and time-out |
| SPIF | PI feedback fault | Feedback below the lower limit | Feedback, LPI and tPI |
| EPF1 | External fault | External device on a logic input | The triggering device |
Codes that clear when the cause is gone
| Code | Meaning | What to check |
|---|---|---|
| USF | Undervoltage | Line voltage and the USb- menu |
| CFF | Incorrect configuration | Factory settings or a valid backup; then your representative |
| CFI | Invalid configuration | Loaded configuration; the transfer may have stopped halfway |
| CFI2 | Download interrupted | Loader or SoMove connection; restart the transfer |
It shows nSt, so why won't the ATV12 run?
- Display dark: check the supply, including ground and input phases.
- nSt or FSt: if freewheel or fast stop is assigned to a logic input and that input is de-energised, the drive will not start. Acting at zero is normal, so a wire break stops the drive. Check the assignment under COnF / FULL / FUn- / Stt-.
- Run command: the input must suit the control mode set in tCC and tCt.
- Modbus: if the reference or command channel is on Modbus, the drive shows nSt until the network sends a command.
- RUN key: the RUN key is inactive at factory settings. Set Fr1 and Cd1 for local control.
Products this table applies to
The table covers the ATV12 family, for example ATV12H018M2, ATV12H037M2, ATV12H055M2, ATV12H075M2, ATV12HU15M2 and ATV12HU22M2. See variable frequency drives for replacements and the frequency inverter selection guide for sizing.
Frequently asked questions
How do you clear an OCF fault?
Remove the cause, then power the drive off and on. The ATV12 manual lists OCF among the codes that do not clear automatically.
What is the difference between OSF and ObF?
OSF means the line voltage is too high. ObF comes from braking that is too sudden or a driving load. Measure the line for OSF; for ObF extend the deceleration time first.
Why does OPF2 appear with a motor connected?
The manual also lists a motor under 6 % of the drive current, an open output contactor and unstable motor current. OPL = nO allows testing with a small motor, but it turns phase loss protection off in normal running.
Are ATV12 codes the same as ATV320 codes?
Many are, but the remedies can differ. See the ATV320 fault codes guide to compare.