Safety first
- Follow site lockout/tagout rules before opening a drive enclosure, lifting motor leads, or testing output wiring.
- Do not repeatedly clear a fault until you understand the cause. Repeated resets can hide evidence and can restart equipment unexpectedly if permissives are still true.
- Wait for the drive DC bus discharge time required by the exact drive manual and verify absence of hazardous voltage before touching conductors.
- Do not megger a motor while it is still connected to the drive output. Isolate the motor leads from the drive first and follow the drive and motor test procedures.
- Do not bypass safety inputs to prove a point. If a safety circuit is involved, prove the safety chain using the approved machine safety procedure.
Common symptoms
- Drive is faulted and will not run after a stop/start command.
- Fault returns immediately after reset.
- Drive runs unloaded but faults when coupled to the machine.
- Drive trips during acceleration, deceleration, or high load.
- HMI reports drive communication loss or stale drive data.
- Analog speed reference disappears or jumps to an unexpected value.
Quick checks
- Record the exact fault code, drive catalog number, firmware, network path, motor nameplate data, and whether the fault was active or in history.
- Capture output current, DC bus voltage, commanded frequency, output frequency, start source, speed reference source, and last known load condition.
- Ask what changed first: motor replacement, belt tension, mechanical work, parameter download, network change, line power event, or enclosure service.
- Check whether the drive faults with the motor uncoupled or unloaded. That quickly separates many mechanical/load issues from wiring or drive setup issues.
- Compare motor nameplate data to drive parameters, especially motor FLA, base voltage, base frequency, overload current, acceleration time, deceleration time, and boost settings.
- For networked drives, check the physical Ethernet link, IP address, subnet, adapter status, and whether the controller still owns the I/O connection.
Field procedure
Follow the sequence before changing parameters, replacing hardware, or cycling power.
1. Preserve evidence before clearing
- 1Take a photo or screenshot of the fault display and the HMI alarm banner.
- 2Save the current drive parameter file if software is available.
- 3Record recent drive history, uptime, commanded speed, load state, and whether the process was starting, stopping, jogging, or running steady.
- 4If the drive is controlled by a PLC, capture the command bits, reference value, feedback value, ready/running/fault bits, and any explicit message status.
2. Classify the fault by energy path
- 1Line side: incoming power, input fuses, supply sag, phase loss, surge, and regenerated bus overvoltage.
- 2Motor side: ground fault, shorted output phase, output phase loss, motor overload, stalled motor, and overcurrent.
- 3Thermal: blocked heat sink, failed fan, high enclosure temperature, dirty filter, or insufficient drive spacing.
- 4Control: auxiliary input, safety input, analog signal loss, start source mismatch, speed reference mismatch, or parameter defaulting.
- 5Network: embedded EtherNet/IP, option card, DSI, Modbus, or controller ownership loss.
3. Prove the easy external causes first
- 1Verify line voltage phase-to-phase and compare it to the drive rating and site history.
- 2Inspect input fuses, disconnect, contactor, line reactor, terminal torque evidence, and any recent heat discoloration.
- 3Inspect motor cable routing, shield termination, output reactor/load filter, motor junction box, and moisture or coolant exposure.
- 4Check enclosure airflow, fan operation, filter condition, heat sink contamination, and ambient temperature.
- 5If the fault is communication-related, verify link LEDs, managed switch port status, duplicate IP evidence, and controller I/O module fault text before power cycling devices.
Diagnostic groups
Use these buckets to separate evidence and avoid chasing unrelated symptoms.
Line power and DC bus faults
Power loss, under-voltage, over-voltage, or trips that happen when line power changes or the machine decelerates.
Likely causes
- Input fuse or disconnect issue.
- Supply sag, interruption, or high transient voltage.
- Regeneration during deceleration driving the DC bus high.
- Aggressive decel time on high inertia loads.
Checks
- Measure line voltage while the machine is under the same operating condition that produced the fault.
- Review drive DC bus value and whether the fault happens during acceleration, deceleration, or steady state.
- Inspect input power wiring, branch protection, line reactor, and upstream contactor or safety power device.
- For over-voltage during stopping, compare decel time, stop mode, load inertia, and dynamic brake hardware.
Corrective actions
- Correct line supply or fuse issues before resetting the drive.
- Increase deceleration time or adjust stop behavior when regeneration is the trigger.
- Evaluate braking resistor or dynamic brake options for high inertia applications.
- Document the actual voltage readings, not only the fault name.
Motor overload, stall, and overcurrent faults
Drive faults during start, speed change, jam, heavy process load, or shortly after a motor or mechanical change.
Likely causes
- Mechanical binding, jammed load, high friction, or an overhauling load.
- Motor nameplate or overload parameters do not match the installed motor.
- Acceleration time, boost, current limit, or DC braking settings are too aggressive for the load.
- Motor or cable insulation problem that only shows under load.
Checks
- Compare measured current against motor FLA and drive output current display.
- Verify motor FLA, base voltage, base frequency, poles, overload current, and overload class where applicable.
- Run the load unloaded or uncoupled only when the machine procedure allows it.
- Check recent belt tension, gearbox work, pump valve position, fan damper position, or process blockage.
Corrective actions
- Fix the mechanical load first if current rises before the fault.
- Correct motor data and overload settings before increasing limits.
- Lengthen acceleration or deceleration where the trip is caused by the profile.
- Use the correct autotune or motor identification workflow after motor or drive replacement.
Ground fault, phase-to-ground, and output short faults
Fault returns immediately, appears when output is enabled, or follows a wet motor, damaged cable, or recent wiring work.
Likely causes
- Grounded motor winding or damaged motor lead.
- Short between output phases.
- Moisture, coolant, metal dust, or crushed cable at the motor junction box.
- Incorrect contactor, bypass, or output switching arrangement.
Checks
- Inspect motor leads at the drive and motor end for damage, heat, loose strands, and incorrect shield termination.
- Disconnect the motor from the drive before insulation testing.
- Check each motor lead phase-to-phase and phase-to-ground using the approved test method.
- Verify the drive output is not feeding a device that opens under load unless the drive manual allows it.
Corrective actions
- Repair the motor cable or motor before returning the drive to service.
- If the fault remains with the motor leads removed, stop and evaluate the drive output section with the manufacturer procedure.
- Do not keep replacing drives without proving the motor/cable path.
- Record insulation readings and environmental evidence.
Thermal faults
Fault appears after runtime, hot weather, cabinet door closed, filter loaded, or line speed increased.
Likely causes
- Blocked or dirty heat sink fins.
- Failed or obstructed fan.
- Enclosure ambient temperature above rating.
- Insufficient panel cooling or drive spacing.
Checks
- Check actual cabinet temperature and airflow with the door closed.
- Inspect fan operation, filter condition, heat sink contamination, and spacing around the drive.
- Review carrier frequency, load profile, and duty cycle after process changes.
- Look for multiple drives heating the same enclosure zone.
Corrective actions
- Restore airflow before resetting and returning to production.
- Clean filters and heat sinks using the approved maintenance method.
- Repair cooling fans or panel air conditioning.
- Reduce thermal load only after process and equipment constraints are understood.
Analog, safety, and communication faults
Drive is electrically healthy but faults from missing reference, open safety chain, or network ownership loss.
Likely causes
- Loose 4-20 mA or 0-10 V reference wiring.
- Analog loss parameter configured to fault on signal loss.
- Safety input not made or safety circuit not reset.
- Embedded EtherNet/IP, DSI, option card, or external network interruption.
Checks
- Measure the analog reference at the drive terminals and compare it to PLC raw/scaled values.
- Verify the drive start source and speed reference source match the intended control method.
- Check safety input status at the drive and through the safety relay or safety PLC diagnostics.
- For EtherNet/IP, check link, IP settings, controller I/O tree status, switch logs, and duplicate IP evidence.
Corrective actions
- Repair wiring or scaling before changing analog loss behavior.
- Restore the safety chain using the approved safety reset procedure.
- Correct adapter settings and network faults before resetting communication faults.
- Capture switch port and controller fault evidence before cycling power.
Evidence to capture
- Fault code, timestamp, and whether it is active or historical.
- Drive model, firmware, parameter file, and network address.
- Output current, DC bus, commanded frequency, output frequency, motor FLA setting, start source, and reference source.
- Line voltage readings, motor current readings, and cabinet temperature.
- Photos of drive terminals, motor junction box, enclosure airflow path, and any visible heat or moisture evidence.
- PLC/HMI command bits, drive status word, safety status, and controller I/O fault message.
Escalate when
- Fault returns immediately with motor leads removed.
- Ground/short fault evidence suggests a damaged motor or cable that requires electrical testing beyond normal reset work.
- Drive power unit fault cannot be cleared after line, load, cooling, and wiring checks.
- Safety input is involved and the approved machine safety validation process is not available.
- Fault occurs after a parameter download and no verified backup exists.