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What will cause the input current on one phase of a three phase variable speed drive to be lower than the other two phases?

Issue: 
What will cause the input current on one phase of a three phase variable speed drive to be lower than the other two phases?

Product Line:
ALTIVAR 212, ALTIVAR 21, altivar 61, altivar 71, altivar 312, altivar 12

Environment:

All 3 phase VFD

Cause:
The in current on a single phase is much lower than the other 2 phases.

Resolution:
To verify if the issue is the VFD or the incoming power, first rotate 2 of the phases on the input of the VFD terminals.  If the problem remains on the same phase of the VFD, then the VFD is the issue.  Is the VFD is inoperative ? If yes, then you will need to check the input rectifier, replace the input diodes if applicable or replace the VFD.   
If the problem follows the rotated phase then the problem is with the incoming power.   Check the connection on the incoming power and resolve the issue with the incoming power or transformer.. 
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