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What is a possible cause of OSF fault on the ATV31 or ATV312 drive?

What is a possible cause of OSF fault? 

Product Line:
Altivar 312 , ATV312


Line voltage is too high
Problem with the line supply
Voltage spike on line side affecting DC bus voltage
Switching power factor correction capacitors by the facility or by the utility company

OSF is a  mains overvoltage fault (DC bus voltage too high).  OSF is displayed if the drive is not in a run state when overvoltage is detected.  If the drive is in a run state and an overvoltage occurs the drive will display ObF (over bus fault).  When the drive is running it is possible for the motor to regen voltage back into the drive.  If this causes the DC bus voltage to go too high the drive will trip on ObF.  One possible cause for ObF to occur is a decel time that the drive is not able to meet because of excessive inertia from the motor load.  See FAQ on ObF for resolutions.
Check the line voltage at L1, L2, L3 on the drive terminals
Compare the line voltage reading with the ULn display ( SUP menu)
Measure the DC Bus voltage
Monitor line power for voltage spikes
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