A126 External alarm via binary input in ABB DCS800 drive indicates that an external alarm signal has been received through a designated digital input. This signal can be triggered by various external devices or systems, such as safety interlocks, sensors, or PLCs.

Troubleshooting Steps:

1. Verify that the external alarm input is not physically activated.
2. Ensure that the input is configured correctly in the drive's parameters.
3. Visually inspect the wiring between the external alarm source and the drive's digital input module.
4. Check for any loose connections, damage, or short circuits.