What is an USF fault on the ATV28 drive?

FA177899

22/05/2020

Issue:
ATV28 USF fault. 

Product Line:
Altivar ATV28

Environment:
All

Cause:
Mains undervoltage is to low on L1 L2 L3.

Resolution:
USF is an undervoltage fault. 
Check the Mains voltage on L1 L2 L3 with a digital meter.
Check the DC bus voltage on PA and PC