A103 DC-Breaker acknowledge fault in ABB DCS800 drive indicates a "DC-Breaker Acknowledge Missing." This means that the drive is expecting an acknowledgment signal from an external DC breaker, but it's not receiving it. 

1. This fault typically occurs when the DC breaker fails to close or when the acknowledgment signal is not transmitted correctly.
2. Check DC BreakAck (10.23), if necessary invert the signal (group 10).