Loss of a Line Phase

What does PHF mean?

One or more incoming line phases to the soft starter are either completely missing or have significantly reduced voltage. This leads to single-phasing conditions which are highly destructive to three-phase motors and can damage the soft starter.

• Blown fuse or tripped circuit breaker in one of the incoming line phases (L1, L2, or L3) to the soft starter.
• Broken conductor or loose connection in the incoming power wiring to the soft starter (e.g., at main contactor, isolator, terminal block).
• Failure of a power contactor pole upstream of the soft starter preventing one phase from reaching the unit.
• Severe voltage sag on one phase from the utility supply, indicating an upstream power issue.
• Faulty voltage sensing circuit within the soft starter leading to an incorrect phase loss detection.

Click steps to track your progress.

1. 1

   1. Measure the incoming line voltages (L1-L2, L2-L3, L3-L1) at the soft starter's input terminals using a voltmeter; identify the missing or significantly reduced phase.

2. 2

   2. Check all fuses and circuit breakers upstream of the soft starter in the identified faulty phase for continuity or tripped status.

3. 3

   3. Inspect all power connections from the main incoming supply to the soft starter's input terminals (L1, L2, L3) for tightness, corrosion, or signs of damage.

4. 4

   4. Perform continuity checks on individual power conductors in the faulty phase from the source to the soft starter input.

5. 5

   5. Verify that the soft starter's phase loss trip level (e.g., P6-02 (Phase Loss Voltage Trip Level)) is correctly configured.