Cause : Brake acknowledge comes when unexpected state of brake acknowledge signal. This signal is essential for the drive to safely control the motor's braking process.

The fault code FF74 in your ABB ACS800 drive indicates a problem with the brake acknowledge signal. This signal is used by the drive to verify that the mechanical brake on the motor has been released successfully.

1. See parameter group 42 BRAKE CONTROL.
2. Check connection of brake acknowledgement signal.