Plain-English Summary
A VFD controls motor speed and torque by changing the power delivered to the motor. When it faults, the drive is reporting a condition it cannot continue through safely or properly.
Why It Matters
Repeatedly resetting a VFD without understanding the fault can damage motors, drives, belts, gearboxes, pumps, fans, conveyors, product, and people. A VFD fault may be electrical, mechanical, programming-related, environmental, or process-related.
Field Rule of Thumb
Read and record the exact fault before resetting the drive. Do not clear the clue before you understand what the drive is telling you.
Walt - Simple Man Takeaway
A VFD fault is the drive raising its hand. Do not slap its hand down with reset until you find out why it raised it.
Core Formula / Concept
Common VFD fault families include overcurrent, overload, overvoltage, undervoltage, ground fault, phase loss, overtemperature, communication fault, encoder/feedback fault, stall/torque limit, acceleration/deceleration fault, and external fault. A drive fault may appear electrical while the real cause is a jammed conveyor, seized bearing, tight belt, plugged pump, product pileup, misalignment, or wrong parameter.
Worked Example
A conveyor VFD trips on overcurrent during startup. First checks find the conveyor is loaded with product, a roller bearing is seized, and the acceleration ramp was shortened during a recent speed change. The drive was not the root problem; it was responding to excessive load and aggressive startup conditions.
Common Mistakes
- Resetting faults repeatedly.
- Blaming the drive before checking the machine.
- Changing parameters without recording original values.
- Ignoring cooling, blocked filters, failed fans, dust, or cabinet temperature.
- Measuring VFD output with the wrong meter or method.
- Ignoring motor cable, grounding, moisture, and insulation condition.
First Checks / Troubleshooting Flow
- Record exact fault code/message.
- Record machine state when fault occurred.
- Ask what changed recently.
- Check whether fault occurs at startup, running, speed change, stopping, or under load.
- Inspect mechanical load for jams, binding, bearings, belts, pumps, fans, or product buildup.
- Check motor, cable, grounding, and visible wiring condition.
- Check drive cooling, cabinet temperature, filters, and fans.
- Check control commands and external fault inputs.
- Review recent parameter changes.
- Compare against OEM and drive manufacturer fault guidance.
- Document parameter values before changing anything.
Walt says STOP! - Safety First
Make these checks prior to proceeding.
Stop when the drive cabinet is open, live testing is required, the motor may start unexpectedly, stored DC bus voltage may be present, terminals are exposed, the fault involves ground fault/overcurrent/smoke/heat, or parameter changes could affect speed, torque, direction, braking, safety, or process control.
Source Notes / References
This page is original Dingfelder practical field guidance. Verify controlled requirements against drawings, OEM documentation, current standards, site procedures, customer requirements, and qualified authority where applicable.