Thus, there may be 3 types of AC power sources. Transfer switches are used to configure switching of the AC power sources in such a way that the priority of the AC sources goes towords one of following:

- Electric utility power

- Genset (generator)

- Inverter

Determining which circuits you will require during a power outage is the first step in selecting the proper backup generator / inverter and respective the transfer switch. Since most home appliances operate intermittently, a 3000 watt generator / inverter and a 30 A Transfer Switch can provide adequate power to circuits for the most common appliances, such as furnace, lights, refrigerator, freezer, microwave oven, and TV.

If your home has a deep well pump with up to 1 HP motor, a 5000 watt generator and 50 A Transfer Switch will be required to provide the starting capacity for the pump. Larger wattage units can be selected for simultaneous starting and operation of multiple appliances.