A111 Mains low voltage alarm in ABB DCS800 drive indicates that the mains voltage supplied to the drive has dropped below a predefined threshold.

Troubleshooting Steps:

1. Use a voltmeter to measure the actual mains voltage supplied to the drive.
2. Ensure that the voltage is within the specified range.
3. Check for loose connections, damaged cables, or faulty terminals.
4. Ensure that all circuit breakers and fuses are in good condition and not tripped.
5. Check the drive's parameter settings related to the low voltage threshold.