Schneider Altivar ATV312 / ATV12 Fault Codes Quick Reference

SOF: Overspeed

SOF indicates that the estimated motor speed has exceeded the permitted level. Schneider associates it with instability or a load that drives the motor faster than commanded.

On the ATV12, the manual defines the overspeed point in relation to maximum frequency tFr, so an incorrectly low tFr setting can contribute to the trip. Check the commanded frequency, tFr, motor parameters, and speed-loop stability settings before increasing any limit.

If SOF appears during deceleration, the load may be regenerating into the drive. High-inertia fans, centrifuges, unwinders, and descending loads can continue to drive the motor as the VFD reduces its output frequency. A longer deceleration time or correctly selected braking hardware may be required.

ObF and OSF: Do Not Confuse Braking With Supply Overvoltage

ObF is an overbraking fault. It usually appears while the motor is decelerating and returning energy to the DC bus. Increase the deceleration time first. Check whether the load is overhauling, whether the line voltage is already high, and whether the application requires an approved braking module or resistor.

OSF is a mains overvoltage fault. Check the actual input voltage at the drive, compare it with the rating on the nameplate, and look for supply disturbances or incorrect transformer taps.

The timing is useful evidence. An overvoltage code while stopped or at power-up points more strongly toward the supply. A trip during rapid deceleration points more strongly toward regenerated braking energy.

OHF and OLF: Drive Heat Versus Motor Heat

OHF means the drive temperature is too high. Check the cabinet ambient temperature, ventilation openings, heatsink contamination, fan operation where fitted, mounting clearance, switching frequency, and load. Wait for the drive to cool before restarting.

OLF is a calculated motor overload fault. It is normally associated with motor current remaining above the thermal protection setting for long enough to reach the trip threshold. Confirm that ItH matches the motor nameplate current and that the actual current is balanced and appropriate for the load.

Resetting OLF without correcting the load or thermal setting does not solve the problem. Also remember that external motor thermal protection may be required for multiple motors, very small motors, motor switching, or applications where the drive’s model does not retain thermal state after power loss.

OPF, OPF1, OPF2, and PHF: Phase-Loss Faults

OPF on the ATV312 and OPF1/OPF2 on the ATV12 concern the drive-to-motor side. Check all three motor leads, output terminals, cable continuity, motor windings, and any downstream contactor. An output contactor must not open while the drive is supplying the motor unless the control system and drive configuration are designed for it.

PHF concerns the incoming supply on applicable three-phase models. Check all input fuses, phase-to-phase voltages, terminal tightness, contactor condition, and phase balance. The protection is load-dependent, so a weak phase can appear normal with the drive idle and collapse when current rises.

Do not disable phase-loss detection simply to keep a machine running. Schneider provides configuration options for specific test or supply arrangements, but those settings should only be changed after confirming that the exact drive and application permit it.

USF: Undervoltage

USF means the line supply or DC bus has fallen below the drive’s threshold. Measure the input voltage while the fault is occurring, not only when the machine is idle.

Common causes include a weak supply, undersized wiring, a failing upstream contactor, loose terminals, blown or high-resistance fuses, generator instability, and voltage sag when another large load starts. If the voltage at the drive remains correct during the event, the internal precharge or measurement circuit may require further investigation.

LFF, LFF1, EPF, and EPF1: External Signal Faults

The ATV312 uses LFF for loss of the 4-20 mA reference on AI3. The ATV12 uses LFF1 for an AI1 current-loss condition when AI1 is configured for current and the scaling conditions in the manual are met.

Measure the loop current, verify transmitter power, check polarity and common connections, and confirm the analog input assignment. Do not bypass the loss-of-signal response until you have considered what the machine should do when the sensor cable breaks.

EPF on the ATV312 and EPF1 on the ATV12 are user-defined external faults. The VFD is reporting an event from an assigned logic input or control function. Trace the external circuit: safety relay status, pressure switch, thermal contact, PLC output, permissive relay, or other interlock.

This is a common point where unnecessary drive replacement happens. If the external input is active, replacing the VFD will not remove the real cause.