Why does a VFD trip on overcurrent during startup?

An overcurrent trip during acceleration means the VFD has detected current beyond its permitted operating threshold. Resetting it repeatedly does not identify whether the demand is genuine, the drive configuration is unsuitable or a fault exists in the motor circuit.

Acceleration and load demand

A short acceleration time asks the motor to develop torque quickly. High-inertia fans, conveyors, centrifuges and loaded mechanisms may need more acceleration time than the current settings allow. A jam, seized bearing, brake that remains applied or process material resisting movement can create a similar demand.

Motor data and control mode

The drive relies on correct motor nameplate data and suitable control settings. Incorrect rated current, voltage, frequency, speed or autotune information can affect motor control and protection. Parameters should be reviewed against the actual motor and application rather than copied blindly from another machine.

Motor cable and motor condition

Damaged insulation, phase-to-phase faults, earth leakage, poor terminations and an incorrectly connected motor can cause a trip as output begins. Long motor cables, output filters and switching arrangements also need to match the drive manufacturer’s application requirements.

Supply and drive factors

Although the displayed code is overcurrent, incoming supply conditions, DC bus behaviour or an internal drive fault may influence what happens during startup. The exact trip code, subcode and operating point are more useful than the generic word “fault”.

Evidence that narrows the cause

• Does the motor begin to turn before the trip?
• Does it start successfully uncoupled or unloaded under an approved procedure?
• Has the ramp time, motor or process recently changed?
• What current does the drive display during acceleration?
• Does the fault occur cold, hot or on every start?
• What exact manufacturer fault code is recorded?

Drive output circuits require competent testing and correct isolation. Standard insulation tests must not be applied through connected electronic equipment.

When Truvo may help

Truvo Industrial investigates VFD, motor and machinery startup faults across Sheffield and South Yorkshire. A photograph of the drive display and motor nameplate, plus the exact point in the sequence where it trips, provides a useful starting point.