Undervoltage

What does USF mean?

This fault indicates that the incoming line supply voltage to the drive has dropped below its safe operating threshold, or there is an internal issue with the drive's precharge resistor. This can be caused by insufficient line supply, transient voltage dips, or a damaged internal component. An undervoltage condition will cause the drive to trip to protect its internal circuitry and ensure stable operation.

Additional Steps

Steps 1–2 are listed in Priority Fix.

1. 3

   If persistent undervoltage occurs and line conditions are stable, an internal component like a precharge resistor may be damaged.

2. 4

   If internal damage is suspected, the drive may need to be replaced by a qualified technician.