Troubleshooting guide

Why Does a VFD Trip on Overcurrent or Overvoltage?

The common causes of variable frequency drive overcurrent, overvoltage and overload faults, what points to each, and what to check.

Electrical & Power · Last reviewed October 15, 2026

A drive trips to protect itself and the motor. The fault name and the moment it happens (during acceleration, at steady speed, or during deceleration) narrow the cause quickly.

Drives hold dangerous voltage on the DC bus after the power is removed. Wait for the bus to discharge and verify it with a meter before opening the drive. Settings and measurements belong with qualified personnel following lockout/tagout.

Fault and timing	Likely cause	What to check
Overcurrent during acceleration	Acceleration time too short for the load inertia, or a high-torque start	Increase the acceleration time. Check the torque boost and the current limit setting
Overcurrent at steady speed	Mechanical overload, jam, or a failing bearing	Measure the motor current against the nameplate. Turn the shaft by hand with power off
Overcurrent immediately on start	Short circuit or ground fault in the motor or cable, or a failed output stage	Insulation test of the motor and cable (drive disconnected). Check for damaged cable and moisture
Overvoltage during deceleration	Regenerated energy raises the DC bus. High-inertia load decelerated too quickly	Lengthen the deceleration time, enable bus-voltage control, or add a braking resistor or regenerative unit
Overvoltage at any time	High supply voltage, or line transients	Measure the incoming voltage. Check for capacitor switching or lightning events
Overload (thermal) trip	Sustained current above the setting, or wrong motor data programmed	Compare the programmed motor nameplate values with the real nameplate. Check cooling at low speed
Undervoltage	Supply dip, loose connection, or a blown fuse on one phase	Check supply voltage on all phases, fuses and connections

The deceleration case, step by step

A fan with a lot of inertia coasts down more slowly than a short deceleration ramp demands. The motor then acts as a generator and sends energy back into the drive. With no braking resistor, the energy goes into the DC bus capacitors and the bus voltage rises until the drive trips on overvoltage. Longer deceleration, a braking resistor, or a regenerative drive removes the energy.

Write a useful problem statement

Drive model, rating and firmware. Motor nameplate. Cable length and type.
Exact fault code and when it occurs (accelerating, running, decelerating, on stop).
Programmed acceleration and deceleration times and motor data.
Recent changes: load, settings, cable, supply, environment.

A second example: how much braking energy?

A fan with a total moment of inertia of 2 kg·m² turns at 1,500 rpm and is stopped in 5 seconds.

Angular speed = 1,500 × 2π ÷ 60 = 157 rad/s.
Kinetic energy = ½ × J × ω² = 0.5 × 2 × 157² = 24,700 J (24.7 kJ).
Spread over 5 seconds, the average power returned to the drive is about 4.9 kW, and more at the start of the ramp.

Friction and the load absorb part of that energy. If the drive cannot absorb the rest in its DC bus capacitors, the bus voltage rises and the drive trips on overvoltage. A braking resistor or a regenerative unit sized for that energy removes it.

For a 480 V supply, the normal DC bus voltage is about 1.414 × 480 = 679 V. Many drives trip on overvoltage at some level near 800 V or above, so check the manual for the drive in question.

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Questions

Can a long motor cable cause overcurrent trips?

Yes. Long cables add capacitance, which causes current spikes at each voltage edge. Output reactors or filters, and a lower carrier frequency, help. The drive manual gives the limits.

Why is the motor data in the drive important?

The drive uses it to control torque and to protect the motor. Wrong values give the wrong current limit and the wrong thermal model.

What is a braking resistor?

A resistor, switched by the drive, that converts the energy returned by the motor during deceleration into heat, so the DC bus voltage stays below the trip level.

What is the DC bus voltage?

The internal DC voltage of the drive after the input rectifier. For a three-phase supply it is about 1.414 times the line voltage at no load.

Where do I find the fault history?

Most drives keep a fault log on the keypad or in the configuration software, with the fault code, the time and often the current, voltage and speed at the moment of the trip.

Educational material. Examples use simplified, hypothetical inputs and are not a design, a construction document or professional engineering advice. Confirm requirements with the codes and standards adopted where the work is built and with a licensed engineer.

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