The USF fault occurs when the DC bus voltage level drops below the threshold set in 1.8 Fault Management > Undervoltage Management > Undervoltage level.
For N4, 480V drives at factory setting of 480VAC, the threshold is 430VDC on the DC bus or 304VAC on the line terminals.
For M3, 240V drives at factory setting of 260VAC, the threshold is 230VDC on the DC bus or 163VAC on the line terminals.
For Y, 575V drives at factory setting of 690VAC, the threshold is 571VAC on the DC bus, or 404VAC on the line terminals.
- Measure the the incoming line to line voltages
- Compare the line voltage to the Mains Voltage as shown under Menu 1.2 Monitoring and also the measurement of the DC bus voltage.
- If the standard line voltage is low, you can adjust the Mains voltage setting
- Adjust the Undervoltage time out to compensate for line contactors, or add time delay before a fault would occur.