Cause : Over-voltage during constant speed comes when the DC bus voltage within the drive has exceeded a set limit while the motor is running at a constant speed.

The ovn error code on your Delta MS300 drive indicates an Over-voltage During Constant Speed Operation condition. This means the DC bus voltage within the drive has exceeded a specific limit while the motor is running at a constant speed.

1. Connect the brake resistor, braking unit or DC bus to the drive.
2. Reduce the load.
3. Replace the drive with a larger capacity model. 
4. Adjust the braking level (Pr.07-01 or bolt position of the brake unit).
5. Use a braking unit or DC bus.