What is an USF fault on the ATV312 drives?

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Issue
USF showing on the ATV312 drives.

Product Line:
Altivar ATV31 and ATV312

Environment:
All

Cause:
Drive is tripping on USF or undervoltage fault.

Resolution:
USF means undervoltage fault.
Get a digital meter and check your input line voltages on L1 L2 L3
ATV312........M2 drive will trip on USF if the line voltage is 160VAC or less
ATV312........M3 drive will trip on USF if the line voltage is 160VAC or less
ATV312........N4 drive will trip on USF if the line voltage is 300VAC or less
ATV312........S6 drive will trip on USF if the line voltage is 430VAC or less