Input Phase Loss

What does PHF mean?

Detection of a loss of one or more phases in the main input power supply to the drive. This causes unbalanced operation, potentially damaging the drive's input rectifiers or internal DC bus capacitors. The drive will trip to protect itself and upstream equipment.

• Blown fuse or tripped circuit breaker on one or more incoming AC mains phases (L1, L2, L3) to the drive.
• Loose or corroded connection on one or more input phases at the main supply, input contactor, or drive terminals.
• Failure of the main input contactor (if present) to close one or more of its power contacts, leading to an open phase.
• Significant voltage imbalance between incoming phases (e.g., > 3-5% deviation) caused by upstream grid issues or single-phase loads.
• External utility power outage affecting one phase of the incoming supply.

Click steps to track your progress.

1. 1

   Using a true RMS voltmeter, measure the voltage across each pair of incoming phases (L1-L2, L2-L3, L3-L1) at the drive's input terminals.

2. 2

   Verify all incoming fuses or circuit breakers (e.g., F1, F2, F3) are intact and not tripped by measuring continuity or voltage across them.

3. 3

   Inspect and tighten all input power connections (L1, L2, L3) at the main disconnect, input contactor, and the drive itself.

4. 4

   Check for proper operation of any input line contactor; measure continuity across its main contacts (L1-T1, L2-T2, L3-T3) when energized.

5. 5

   If an input line reactor (choke) is installed, verify its connections and integrity (e.g., measure resistance of each winding).