This device is a rack-mounted Automatic Transfer Switch (ATS) or Inverter Redundancy Controller.
It is designed to manage dual power configurations, specifically alternating between two distinct inverters to ensure an uninterrupted power supply (UPS) for critical rack-mounted equipments like servers, computers and other network devices.
MASTER (Green LED): Indicates that the system is currently running on the designated main power source and that the power output is stable.
INVERTER 1 MASTER / INVERTER 2 MASTER (Rotary Selector Switch): This manual override knob allows you to designate which inverter acts as the primary ("Master") source.