Yaskawa VFD Fault PF — What It Means
Fault PF on a Yaskawa drive (A1000, V1000, GA700, GA800 series) stands for Input Phase Loss. The drive’s input monitoring circuit detected that one or more of the three input AC phases (R/L1, S/L2, T/L3) is absent or significantly unbalanced relative to the others. The drive trips to prevent the DC bus capacitors and rectifier diodes from being overloaded by single-phase or unbalanced input.
Common Causes
- Blown fuse or tripped circuit breaker on one phase — A fuse upstream of the drive that opens on one phase leaves the drive on two-phase input, which the PF detection immediately catches.
- Loose or corroded input terminal — A loose wire on one input phase terminal causes high resistance and intermittent phase loss, often appearing as PF at higher load conditions.
- Contactor or disconnect failure — A single-phase welded or failed-open contact in an upstream contactor causes permanent or intermittent phase loss.
- Utility power phase imbalance — An unbalanced utility supply (more than 2–3% voltage imbalance between phases) can trigger PF on drives with sensitive phase-loss detection, even without a complete phase loss.
Step-by-Step Fix {#fix}
- Measure input voltage with main power on — Use a true-RMS multimeter and measure voltage between all three phase pairs at the drive input terminals: R-S, S-T, and R-T. All three readings should be within 2% of each other and within the drive’s input voltage range.
- Check upstream fuses — Inspect the input fuses or circuit breaker for the drive. A blown fuse on one phase is confirmed by measuring voltage on both sides of the fuse — voltage before, zero after = blown. Replace blown fuses; investigate why they blew before restarting.
- Tighten input terminals — With power off and lockout/tagout applied, check the torque on the input terminal block screws (R/L1, S/L2, T/L3). Tighten to the drive’s specification (typically 1.2–2.5 Nm depending on wire size).
- Inspect the upstream disconnect and contactor — Check that all three contacts of the main disconnect and any series contactors make and break cleanly. Measure voltage downstream of the contactor on each phase while it is closed.
- Clear the PF fault and restart — After correcting the cause, reset the fault via the keypad or digital input and attempt to restart. Monitor input voltages during startup.
Parts Often Needed
| Part | Notes |
|---|---|
| Input fuses (class J or similar) | Amazon | Match voltage, ampacity, and interrupt rating for the drive kW |
| Main contactor (3-pole) | Amazon | Replace if contacts show burning or one pole fails to make |
| Input terminal block | Amazon | Replace if terminals are corroded or cracked |
When to Call a Pro
Phase imbalance from the utility supply requires contacting the utility or a licensed electrician to investigate the power system. Single-phase loss events that repeatedly blow fuses indicate a fault in the upstream distribution system requiring a qualified electrician.