The z-source breaker is a new kind of breaker which is designed specifically for dc power systems. Without a zero crossing, interrupted dc currents produce arcing and hence ac breakers would not be applicable. The z-source breaker resolves this problem because it is designed to turn off as soon as it experiences a sharp transient in current. In this paper a new design for the z-source breaker is considered so that load transients are not identified as faults. The design is also modified to accommodate bi-directionality which is required in mediumvoltage dc ship power systems. A higher-level coordinated control scheme is discussed which enables multiple breakers to coordinate and isolate the fault in a simple medium-voltage dc ship power system architecture with a central control unit.