Generac 200-Amp Automatic Transfer Switch (NSE - 120/240V 3-Phase) #RTSN200J3Generac 200 Amp ATS 120 240 3 Phase NEMA 3R Cabinet. The transfer switch monitors utility power and signals the generator to start when utility power is interrupted. When utility power returns, the transfer switch returns the electrical load from the generator back to the utility. This ensures your most important electrical loads are powered, within seconds, even when youre away. All RTS transfer switches are housed in a NEMA UL Type 3R enclosure,