DC power distribution systems in marine applications are in the process of being established as the preferred solution for shipboard power distribution systems. This paper presents a bus-tie switch topology for the protection of such systems. The device is based on a four quadrant switch with single active semiconductor and is designed to be modular and scalable, so it can be adapted to different interruption current and bus voltage levels. The developed prototype has been experimentally validated for its thermal behaviour in continuous conduction and switching performances, as well as in standalone operation with digital controller added to the power stage. The simplicity of the device topology offers interesting prospects for DC power distribution systems.