an electrical power protection technique which is especially suitable for use in three - phase high voltage switch gear applications is disclosed herein . this technique utilizes an electrically insulated housing for each phase of the electrical circuit . each housing contains a fuse intended for placement in circuit with the switch gear and a source of high voltage and has an entry door for gaining access to the fuse from outside the housing . each fuse is disengagably connected to a power terminal , outside the housing through a utility opening in the latter . the terminal is , in turn , connected in circuit with the source of high voltage and switch gear . a component interlock assembly is provided for automatically disconnecting each fuse from its terminal and thereafter closing the cooperating utility opening sufficient to physically shield the terminal from its fuse when the entry door is opened . the same interlock assembly automatically opens each utility opening and reconnects its associated fuse with its cooperating terminal when the entry door of its housing is closed .