IndustrialDriveDataDrive Board & Diagnostic Database
Schneider Electric fault record

USF: Undervoltage / Supply Loss Fault

The drive reports USF, drops ready state, or trips when supply voltage collapses during operation.

Meaning of the indication

The drive does not have adequate input/DC-link voltage. The route begins at line supply, fuses, contactor, precharge and DC-link condition.

Checking order

  1. Measure all input phases at the drive terminals.
  2. Check fuses, disconnect, contactor and supply sag evidence.
  3. Separate power-up undervoltage from undervoltage under load.
  4. Listen for abnormal precharge/contactor sequence only as supporting evidence.
  5. Inspect DC-link and rectifier path after safe isolation when input evidence is normal.

Suspect areas

Mains supplyInput fuseContactorPrechargeRectifierDC-link capacitors
Fault-specific caution

An undervoltage message does not prove the DC link is safe to touch.

Diagnostic workflow

Workflow
Schneider ATV61 / ATV71 OSF and USF DC-Link Diagnostic Workflow

ATV61/ATV71 reports OSF overvoltage or USF undervoltage during power-up, run or deceleration.

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