Controller displays F11 Phase Imbalance; generator may continue running but alarms and may refuse to transfer.

Safety first: Open the generator output breaker and ATS before inspecting connections. Use lockout/tagout where applicable.

• Measure phase voltages: With the generator running unloaded, measure each line-to-line and line-to-neutral voltage. They should be within a few percent of each other. Large differences indicate a generator or sensing issue.
• Inspect terminal connections: Remove the alternator terminal box cover and check all phase and neutral connections for tightness and discoloration. Tighten loose lugs to the torque specified by Siemens.
• Check load distribution: Review the load wiring from the ATS or distribution panel. Excessive single-phase loads on one leg can cause imbalance. Redistribute loads across phases where possible.
• Inspect CTs and sensing wiring: Verify that current transformers are correctly installed and that their secondary wiring to the controller is intact. Loose CT connections can cause false imbalance readings.
• Stator testing (technician): If one phase voltage is consistently low or distorted, a stator winding fault may exist. This requires professional insulation resistance and winding tests.