Industrial Engineer · phase 14 of 16
Input Phase Loss
Loss or severe imbalance of an incoming AC phase that increases rectifier and DC-bus stress.
The Explain card
- Plain English
- Input phase loss means one of the three incoming phases has gone missing or is badly unbalanced. The rectifier is left working on two phases, the bus ripple climbs, and the capacitors take the strain.
- Example
- A fuse on one incoming phase blows. The drive keeps running for a moment on the remaining two, then trips on input phase loss as the bus ripple exceeds its limit.
- Why it matters
- Running on two phases cooks the bus capacitors and the remaining diodes, so the trip is protecting the drive. Check the incoming fuses and the disconnect before you look at anything inside.
- Hook
- One leg of the supply is gone and the drive is limping.
Where it sits in the deck
Phase 14: VFD Safety, Faults, and Diagnostics
What a drive does when it trips, what the fault codes are telling you, and how safe torque off stops the motor without killing the panel.
