Power device terminal backup switch unit

A system comprising:

• an AC power source;
• a plurality of loads
• an uninterruptable power supply comprising:
• one or more output terminals;
• an input power conversion circuit;
• an output power conversion circuit;
• an energy storage device, wherein the input power conversion circuit is electrically connected between the one or more input terminals and the energy storage device one or more input terminals;
• and
• a backup switch unit, wherein the backup switch unit comprises:
• a controller,
• a power relay, and
• a fast switch device;
• a neutral conductor, wherein the neutral conductor is electrically connected between the input power conversion circuit and the output power conversion circuit, wherein the power relay is in a closed configuration on startup, wherein the fast switch device is in an open configuration on startup, and wherein the controller is configured to:
• close the fast switch device responsive to a voltage difference between the neutral conductor and a ground terminal being greater than a first threshold,
• open the fast switch device responsive to a voltage difference between the neutral conductor and the one or more input terminals being greater than a second threshold, and
• close the fast switch device responsive to a voltage difference between the neutral conductor and the one or more input terminals being less than the second threshold.