Sourcing Requirements
If your system is for a home or small business The most common setup would be something like Transfer switch 120/240 V single-phase 60 A or 100 A Even if you use loads at 110/120 V, many devices are rated as 120/240 V single phase Important note You need to define if your alternate source will be Grid / generator Grid / inverter Two different supplies And also If you change only the phase Or phase and neutral Practical recommendation For what you describe, I would request it like this "Single-phase transfer switch, 120/240 V, 60 Hz, 100 A, for 110/120 V service" This gives you flexibility and is easier to find If you want, I can provide it in a bill of materials format or make you a basic connection diagram