Input Phase Loss

What does PF mean?

A PF fault indicates that one or more of the input AC phases to the drive has been lost. The drive's detection circuit monitors DC bus current ripple and activates if the difference (ΔV) between maximum and minimum DC bus voltage values reaches or exceeds an internal detection level for 0.5 seconds. This can lead to imbalanced current draw, potential damage to the drive's input rectifier, and motor instability.

• Loss of one or more incoming AC supply phases (L1/R, L2/S, L3/T) due to a tripped circuit breaker, blown fuse, or utility power outage.
• Loose or corroded connection on one of the main power input terminals of the drive or upstream wiring.
• Faulty main power contactor or disconnect switch with one or more open poles.
• Unbalanced three-phase supply voltage, where one phase voltage is significantly lower than the others, mimicking a phase loss condition.

Click steps to track your progress.

1. 1

   Using a multimeter, measure the incoming AC line voltage at the drive's L1/R, L2/S, L3/T terminals to confirm the presence of all three phases and balanced voltages (e.g., 480V L-L).

2. 2

   Inspect the main circuit breaker or fuses upstream of the drive, confirming they are in the 'ON' position and fuses are intact (test continuity across fuses).

3. 3

   Tighten all power wiring connections at the drive's input terminals (L1/R, L2/S, L3/T) and at any upstream contactors or disconnects.

4. 4

   If a main input contactor is used, verify all three sets of its main contacts close properly by checking continuity or observing contact engagement.

5. 5

   Monitor the DC bus voltage ripple (dC bus monitor value) on the drive during operation, observing for excessive fluctuation indicating an input phase imbalance.