AL16
Kohler-SDMO Incorrect Phase Rotation / Phase Sequence Fault

Controller displays AL16 / Phase Sequence Error when transferring load

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Incorrect connection of generator output phases, Reversed phases at ATS (Automatic Transfer Switch), Faulty phase sequence sensing in controller

How to Fix / Troubleshooting

Safety first: Isolate both utility and generator sources. Lock out and tag out the ATS before opening any covers. Only qualified personnel should work on live power circuits.

  • Verify phase rotation: Using a phase rotation meter, check the phase sequence (e.g. L1-L2-L3) at the generator terminals and at the ATS load side. They must match the installation design.
  • Correct wiring: If rotation is reversed, swap two phases at the generator output or ATS input terminals to restore correct sequence.
  • Check controller settings: In the APM controller, verify that phase sequence monitoring is enabled and configured correctly for the installation.
  • Test transfer: After corrections, clear AL16 and perform a test transfer from mains to generator and back, monitoring motor loads for correct rotation.

Incorrect phase sequence can damage three-phase motors; ensure all corrections are done by a qualified electrician.

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Repair Difficulty

Professional Required 5/5

Required Part

Automatic Transfer Switch (ATS) Wiring
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