The Parallax ATS line generator switches are the strongest in the industry and are the most trusted way to transfer power between shoreline and RV generators. With extreme ease, the improved ATS models transfer power smoothly regardless of the line voltage conditions. Users benefit from not having to handle plugs or electrical cords to transfer power. Parallax offers robust line generator switches specifically designed for 30 amp, 120V and 50 am 120/240V electrical systems. Both models are quality engineered for reliability and performance. ATS 503 sets new standards for 50-amp reliability, ease of installation, and diagnostics for field use. ATS 503 is listed to UL Standard 1008 for 50-amp transfer switches, uperceding the previous UL Standard 508. The printed circuit board design was developed and proven through extensive cycle testing, demonstrating the product's ability to withstand heat and torque. Field reliability is further enhanced by innovative diagnostics and controls. A fault indicator light provides easy trouble shooting, and a manual shut-off for the time delay feature optimizes operation when an inverter is used as the secondary power source.