Abstract: A computer-controlled system protects electric circuits where power and branch load circuits are all disposed outside the pressure hull of a submersible in a marine environment. The system generally comprises a combined inboard operator panel and computer arrangement and an inboard or outboard circuit breaker computer operatively connected by a data link to the panel computer. A multiplexer/demultiplexer arrangement is provided for the system to minimize the passage of electric lines through the hull. The circuit breaker computer compares its stored information with the output of circuit current sensors to detect whether a circuit fault condition exists and if so to open the interrupter of the fault-detected circuit. Moreover, if a circuit fault is detected greater than a predetermined value, e.g., greater than 500% normal load current value, the circuit breaker computer not only opens the fault detected branch circuit but also the power circuit.