AC line phase fault

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A phase is missing on the AC line supply side of the adjustable frequency drive. This fault only activates in 3-phase AC line systems. It indicates an issue with the incoming power supply to the drive, such as a blown fuse, tripped breaker, or utility problem.

• Blown fuse or tripped circuit breaker in one of the incoming AC power lines (L1, L2, L3) to the drive.
• Loose or corroded connection on one of the incoming power terminals (R, S, T) on the drive or upstream contactor/breaker.
• Utility power instability or single-phasing condition from the grid.
• Faulty input rectifier section within the drive, though less common for a 'missing phase' fault.

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1. 1

   1. Using a multimeter, measure the phase-to-phase voltages (L1-L2, L2-L3, L3-L1) at the drive's input terminals (R, S, T). Verify all readings are within +/-10% of the rated supply voltage.

2. 2

   2. Inspect all fuses and circuit breakers upstream of the drive for continuity or tripped status; replace any blown fuses or reset tripped breakers.

3. 3

   3. Power down the drive, then inspect and re-torque all incoming power connections (R, S, T) for looseness or corrosion.

4. 4

   4. Check the upstream contactor or isolator for proper operation, ensuring all contacts close simultaneously and provide continuous power.

5. 5

   5. Monitor the utility power supply for single-phasing conditions or severe imbalances using a power quality analyzer over time.