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What can cause an USF (undervoltage fault) on an ATV12 drive?

Published date: 09 September 2019

USF (undervoltage fault) on an ATV12 drive.

Product Line:
Altivar 12


Fault condition

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.

- Measure the the incoming line to line voltages
- Compare the line voltage to the Mains Voltage as shown under monitoring MON.
- 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. 
- Check to issues where line potential is dropping due to supply issues that may be caused by load pulling too much current.

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