Parallax Power Supply Line Generator Switch Model ATS 503. With a flick of the generator switch, the ATS 503 line generator switch from Parallax transfers power smoothly between shoreline power and generator/secondary power source, regardless of line voltage conditions. ATS 503 is engineered for superior reliability in 50 Amp, 120/240-volt electrical systems (per the new UL Standard 1008). Electronic circuit board design is proven in extensive cycle testing to withstand heat and torque. The low-profile chassis measuring just 3-1/2 high allows mounting in areas not possible with other 50 Amp transfer switches, and installation can be made without cover removal. Manual shut-off for time delay optimizes use with inverters.