Fault Code 427
Cummins
Three-Phase Voltage Imbalance
Generator shuts down; controller shows Fault Code 427 – Phase Imbalance / Voltage Unbalance
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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
Uneven loading across phases, Loose connection on one phase, Internal stator winding issue, Faulty sensing wiring to controller
How to Fix / Troubleshooting
Safety first: Open the generator output breaker or transfer switch. Disable automatic start before opening any terminal boxes.
- Measure phase voltages: With a multimeter, measure L1-L2, L2-L3, and L3-L1. Significant differences indicate imbalance.
- Check load distribution: Review the load panel to ensure large single-phase loads are balanced across phases. Have an electrician rebalance circuits if necessary.
- Inspect connections: Tighten all phase and neutral connections at the generator terminals and in the transfer switch.
- Sensing wiring: Verify that the controller’s voltage sensing leads are correctly connected and secure on all phases.
- Reset and test: After corrections, clear the fault and run under load while monitoring phase voltages.
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Repair Difficulty
Hard
4/5
Required Part
Generator Stator Assembly
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