Input Phase Loss

What does PF mean?

The Drive input power supply has an open phase or a large imbalance of input voltage. This can be caused by a missing phase, loose terminal screws, momentary power loss, or significant input voltage fluctuations. Operating with phase loss can lead to drive component stress and damage.

• One or more input power phases (R/L1, S/L2, T/L3) are missing due to a tripped upstream circuit breaker or blown fuse.
• Loose terminal connections at the drive's input power terminals (R/L1, S/L2, T/L3) or upstream power components.
• Significant voltage imbalance between input phases, exceeding the drive's tolerance (typically >5%).
• Momentary loss of one or more input phases during operation (e.g., power flicker, contactor chatter).
• Incorrect wiring of the input power supply, especially for single-phase operation if the drive is not designed for it.

Click steps to track your progress.

1. 1

   1. Using a multimeter, measure the AC voltage between R/L1-S/L2, S/L2-T/L3, and T/L3-R/L1 terminals and verify against nominal voltage.

2. 2

   2. Check all upstream circuit breakers and fuses for tripped, blown, or damaged conditions.

3. 3

   3. Confirm tightness of all power wiring connections at the drive's R/L1, S/L2, T/L3 terminals and the main disconnect.

4. 4

   4. Measure the current draw on each input phase with a clamp meter to detect significant imbalances under load.

5. 5

   5. Inspect input power contactors or relays for faulty contacts or chattering during operation.