When your VFD throws a fault code at 6 AM and your production line grinds to a halt, the temptation is to assume the worst. But most VFD faults aren't actually drive failures—they're the drive telling you something else is wrong.
Understanding the difference between "the drive is protecting itself" and "the drive has failed" can save you thousands in unnecessary replacements and hours of downtime chasing the wrong problem.
The Most Common VFD Faults (And What's Really Happening)
Overcurrent
What the drive is saying: "I'm seeing more current than I should."
What's usually wrong: This is rarely the drive itself. Check for mechanical binding on the motor, a shorted motor winding, loose connections at the motor terminals, or undersized wiring that's creating voltage drop. If the motor runs fine on bypass, suspect the drive's output transistors—but try the simple stuff first.
Overvoltage
What the drive is saying: "The DC bus voltage is too high."
What's usually wrong: The motor is regenerating energy back into the drive faster than it can dissipate. This happens during rapid deceleration or when the load is overhauling (gravity-fed conveyors, for example). Solutions include extending deceleration time, adding a dynamic braking resistor, or using a regenerative drive. The drive itself is usually fine.
Ground Fault
What the drive is saying: "Current is going somewhere it shouldn't."
What's usually wrong: Insulation breakdown in the motor windings or the cable between drive and motor. Disconnect the motor leads at the drive and megger test the motor and cable separately. If the fault clears with the motor disconnected, you've found your culprit.
Overtemperature
What the drive is saying: "I'm too hot."
What's usually wrong: Blocked ventilation, failed cooling fan, ambient temperature above rating, or drive mounted too close to other heat sources. Clean the heatsink, verify the fan is spinning, and check that you're within the drive's ambient rating (usually 40°C max without derating).
Faults That Actually Indicate Drive Failure
Some fault codes do point to internal drive problems that require repair or replacement:
| Fault Type | Common Codes | What It Means |
|---|---|---|
| IGBT/Output Fault | F005 F029 IGBT |
Power stage failure—drive needs repair or replacement |
| Control Board Fault | F100+ CPU Error |
Main processor or control circuitry issue |
| Memory Error | F200+ EEPROM |
Parameter storage corruption—sometimes recoverable with factory reset |
| Bus Capacitor Fault | Varies by manufacturer | DC bus capacitors failing—drive needs service |
Before You Order a Replacement
If you've determined the drive itself has failed, there's still a decision to make: repair or replace?
When Repair Makes Sense
The drive is a high-value unit (30HP+), the failure is a known serviceable component (fan, capacitors, single IGBT), and you have a spare to keep production running during repair.
When Replacement Makes Sense
The drive is smaller/lower cost, repair turnaround is too long for your needs, or the unit has multiple issues suggesting end-of-life.
Keeping Spares On Hand
For critical applications, having a shelf spare of your most common drive models eliminates the downtime equation entirely. A 10HP PowerFlex 525 sitting on your shelf costs the same as two hours of production downtime at most facilities.
Smart spare strategy: Stanlo Automation stocks surplus drives from Allen-Bradley, Siemens, ABB, Schneider, Yaskawa, and more—often at 40-60% below new OEM pricing, with full testing and 12-month warranty.