Schneider Electric Altivar Machine ATV320 fault USF: Supply mains undervoltage
USF on a Schneider Altivar ATV320 is a supply mains undervoltage error: the supply voltage was too low or dipped transiently. It clears as soon as the cause is gone.
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Try Free Drive Diagnostic Upload a keypad photo, the fault history or a parameter export from your Schneider Electric Altivar Machine ATV320. InduQT compares the evidence and suggests the next useful checks.
When it happens
- During supply dips or brownouts
- When two or three input phases are lost
- At power-up on a weak supply
Likely causes and checks
1Supply voltage too low
- Points to it
- Persistent USF; mains voltage in the error record (ULP1) is low.
- Check
- Measure the supply at the drive input terminals under load.
2Transient voltage dip
- Points to it
- Brief trips that coincide with large loads starting or utility events.
- Check
- Compare trip times with power-quality records; review [Undervoltage handling] USB- settings.
3Two or three phases lost
- Points to it
- Fuses or breaker opened; drive ran on until it tripped.
- Check
- Check fuses and the input connection; Schneider notes that with 2 or 3 phases lost the drive keeps running until it trips on undervoltage.
4Loose or high-resistance input connection
- Points to it
- Intermittent USF or PHF under load; warm terminals.
- Check
- Lock out and check input terminal tightness and contactor contacts.
Telling it apart
- One missing phase shows as PHF (on load); losing 2 or 3 phases ends in USF.
- USF clears as soon as its cause disappears; [Undervoltage Resp] USB can make it a warning instead of a trip.
- CRF1 is a precharge relay or resistor error, not a supply problem.
Relevant parameters
| Parameter | Name | Why it matters |
|---|---|---|
| USB | Undervoltage Resp | Error triggered, error without relay, or warning. |
| USL | Undervoltage level | Detected undervoltage error level in volts; factory setting by drive rating. |
| UST | UnderVolt timeout | 0.2 to 999.9 s delay before the undervoltage is taken into account. |
| STP | UnderV. prevention | Maintain DC bus, ramp stop or freewheel lock when the prevention level is reached. |
Evidence to collect
- Error history entries and the mains voltage stored with them
- Supply measurements at the drive under load
- USB, USL, UST and STP settings
- Power-quality records
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