This is a revised and expanded edition of a 1997 book. It is a comprehensive resource providing accessible information on circuit breakers, from basic design details and applications to equipment selection, specifications, and testing. The volume includes description of electric arcs and other electric systems during the interruption process; delineates the most significant design parameters of circuit breakers; highlights important electrical design standards; examines air, oil, sulfur hexafluoride, and vacuums as mediums; features new design concepts of breaker designs and revisions to governing standards; presents environmental issues for SF6 equipment; and introduces basic concepts for synchronous circuit breakers and condition monitoring.