AL17
SDMO
Phase Sequence / Phase Loss Fault
Controller indicates AL17 phase sequence or phase loss; generator may not connect to load or ATS.
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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 phase rotation at alternator terminals, Open phase due to loose cable or breaker pole, Faulty phase sequence relay in SDMO panel, Miswired ATS output to load
How to Fix / Troubleshooting
Safety first: De-energize generator and mains before opening any terminal boxes. Use a phase rotation meter for verification.
- Verify phase rotation: With the generator running and isolated, use a phase rotation meter on L1-L2-L3. Ensure it matches the required rotation (e.g., L1-L2-L3 clockwise). Swap two phases at the alternator or breaker if needed.
- Check for phase loss: Inspect all three phases from alternator to main breaker and ATS. Tighten loose terminals and replace damaged cables.
- Test phase sequence relay: If fitted, verify correct operation of the SDMO phase sequence/phase failure relay. Replace if it falsely indicates a fault.
- Inspect ATS wiring: Confirm that the ATS output to load maintains correct phase order and that no phase is missing.
- Reset AL17: After corrections, clear the alarm and test transfer to load while monitoring phase voltages.
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Repair Difficulty
Hard
4/5
Required Part
Phase Sequence Relay
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