Cause : Input phase loss comes when input R,S,T have phase loss or imbalance. An Input Phase Loss "Err12" fault will occur when the DC bus ripple exceeds a pre-defined level. One (or more) of the input phases were lost.

1. Large imbalance of voltage exists on the input of the drive.
2. Drive is not properly sized for single phase input.
3. Check input voltage.
4. Check rectifier section using multimeter.