Input Phase Loss

What does PF mean?

The PF fault occurs when the inverter detects the loss of one or more incoming AC power phases. This is determined by monitoring the DC bus voltage ripple; if the voltage difference (∆V) exceeds a threshold for 0.5 seconds, the fault is declared, and the motor coasts to a stop to prevent damage.

• Blown fuse or tripped circuit breaker in one of the incoming AC power phases before the inverter's input terminals (R, S, T).
• Loose or corroded connection at the input power terminals (e.g., L1, L2, L3) of the inverter or upstream disconnect.
• Failure of an upstream power component like a contactor or main circuit breaker, preventing one phase from reaching the inverter.
• Utility power sag or complete loss of one phase from the grid upstream of the facility.
• Misconfigured phase loss detection parameters, such as sensitivity (if adjustable in the drive).

Click steps to track your progress.

1. 1

   1. Using a multimeter, measure the AC voltage across all three incoming phases (R-S, S-T, T-R) at the inverter input terminals to confirm phase presence and voltage balance (e.g., 480V ±5%).

2. 2

   2. Inspect all upstream fuses and circuit breakers for continuity or trip status, resetting or replacing as necessary.

3. 3

   3. De-energize the circuit, then visually inspect and manually tighten all input power terminal connections on the inverter and any upstream disconnects or contactors.

4. 4

   4. Check the status of any upstream contactors or relays to ensure all poles are closing properly when energized.

5. 5

   5. Verify the DC bus voltage (terminals P+ and N-) after power is applied; it should be stable with minimal ripple (typically 1.35 * peak AC line voltage).