Why AC Dual-Source Transfer Is Harder Than It Looks In many substations, industrial plants, and rail facilities, the “information brain” of the site still runs on AC: station control servers and engineering workstations industrial switches and firewalls DCS/PLC controllers remote terminal and gateway equipment A brief disturbance on the incoming AC feeder, or one maintenance pull of a plug-in breaker, can be enough to black out an entire panel. Screens go dark, communication