When sourcing a rotary converter, you must prioritize Phase Accuracy and Voltage Balance. Ensure the unit maintains a voltage deviation of less than 5% between phases to prevent motor overheating. Key specs include the Horsepower (HP) rating (ensure it is sized 2x the largest motor starting load), Input/Output Voltage (e.g., 220V Single-phase to 380V Three-phase), and the Starting Method (capacitor-start vs. soft-start). Look for units with high-quality bearings rated for at least 30,000 hours of operation.