Check the listing for details. Industrial Automatic Transfer Switch Grid to AC Generator 4 Poles 110V 220V 250A. Condition: New, Made in United States. Listed at 107.57 USD. Key Points: Auto mode: Common p ower supply must be City Grid Power. Backup power must be AC genarator. When there is only one power supply is working, the product will automatically switch to that power supply. When the common power supply and the backup power supply are supplied at the same time, the common power supply is used Preferentially.(Attention: in automatic mode, forcibly rotating the power switch handle will cause damage to the transfer switch) Manual mode: Power supply should be transfered manually by rotating the handle. Application: Industrial, residential and various occasions where continuous power failure is not allowed. Function: Auto mode and Manual mode for choise. Key Features: .