A VFD overcurrent fault means the drive has detected output current above its allowable operating limit. The cause can be a mechanical bind, motor or cable problem, incorrect parameters, application conditions or a problem inside the VFD itself. Replacing or repeatedly resetting the drive without identifying the root cause can lead to recurring faults or additional equipment damage.
Common Causes of VFD Overcurrent Faults
- Motor or cable short circuit
- Ground fault or insulation breakdown
- Excessive mechanical load or a binding driven load
- Acceleration or deceleration time that is too short for the application
- Incorrect motor nameplate or drive parameters
- Motor starting into an already rotating load
- Failed output power components or current-sensing circuitry
- Loose, damaged or intermittent wiring connections
Start With the Fault History
Before resetting the VFD, record as much information as possible from the drive’s fault history. Useful information can include the fault code, output current, output frequency and DC bus voltage recorded at the time of the trip. Also determine exactly when the fault occurs—during startup, acceleration, steady operation or deceleration. The timing of the fault can provide valuable clues about its root cause.
Inspect the Mechanical Load
A mechanical problem can cause the VFD to produce excessive current even when the drive itself is operating correctly. With the equipment properly locked out and following the facility’s electrical and mechanical safety procedures, qualified personnel can verify whether the motor and driven equipment rotate freely and look for binding, bearing problems or other excessive mechanical loading.
If the motor or load may already be rotating when the VFD is commanded to start, the application may require the manufacturer’s flying-start or speed-search function. The correct feature and settings vary by VFD manufacturer and application.
Verify Motor and VFD Parameters
Confirm that the motor voltage, current, frequency and full-load amp information programmed into the VFD agrees with the motor nameplate and application requirements. Incorrect motor data or application settings can contribute to nuisance trips and poor motor performance.
If an overcurrent trip consistently occurs during acceleration or deceleration, the ramp settings and mechanical load should be reviewed. An aggressive ramp can demand more current than the motor-drive system can safely provide. Parameter changes should be made by qualified personnel and in accordance with the drive manufacturer’s recommendations and the requirements of the application.
Check Motor, Cable and Electrical Condition
Motor windings, motor cables and electrical connections should be evaluated before assuming the VFD has failed. Appropriate testing by qualified personnel can help identify insulation breakdown, leakage to ground, winding imbalance, loose connections or damaged wiring. These external problems can produce an overcurrent fault even when the VFD itself is healthy.
Free VFD Maintenance Training Can Help Prevent Problems
IPS offers a free VFD Maintenance Training program, typically performed at the customer’s facility, to help facility maintenance personnel become more familiar with VFD operation and practical preventive maintenance. Learn more about our VFD preventive maintenance and free training program.
While not every overcurrent fault can be prevented, good maintenance practices can help reduce conditions that contribute to some overcurrent events. Our training helps maintenance personnel understand items such as inspecting electrical connections, recognizing mechanical or cooling problems, recording fault information before resetting a drive, reviewing basic operating conditions and knowing when to involve a qualified VFD technician.
Better familiarity with the equipment can help facility personnel identify developing motor, load, wiring and application problems earlier—before they become repeated VFD trips or unplanned downtime.
When the VFD May Need Repair
If the motor, wiring, mechanical load and application settings have been verified and the overcurrent fault remains, the VFD may require bench evaluation. IPS can evaluate the drive for problems involving current sensing, control circuitry, power semiconductors and other components that may cause an overcurrent condition. If the drive is older or extensively damaged, our VFD repair vs. replacement guide can help explain the decision process.
Related VFD Fault
If the drive is tripping on excessive DC bus voltage rather than output current, see our VFD DC bus overvoltage troubleshooting guide.
Need Help Diagnosing an Overcurrent Fault?
IPS VFD field service can assist with on-site troubleshooting, or request a repair evaluation for the VFD. You can also contact IPS about scheduling free VFD Maintenance Training for your facility.