Main Circuit Overvoltage

What does %U mean?

This fault indicates that the DC voltage of the main circuit has exceeded its safe limit. If occurring while stopped (warning state), it typically means the power supply voltage is too high. If occurring when the protective mechanism is actuated (during operation), it's usually due to excessive regenerative energy from the motor, often caused by short deceleration times or overshoot during acceleration, pushing the DC bus voltage above approximately 410V (or 820V for 400-VAC Class). Unresolved overvoltage can damage inverter components.

Additional Steps

Steps 1–2 are listed in Priority Fix.

1. 3

   For loads with high inertia or frequent deceleration, connect an appropriate braking resistor or braking resistor unit to dissipate excess regenerative energy.