Abstract: A three-phase vacuum interrupter switch assembly for power distribution systems comprises an outer case having at least one window, a plurality of internal disconnect switch assemblies, and a plurality of vacuum interrupter bottle switch assemblies within the case. Each vacuum interrupter bottle switch is coupled in electrical series with a corresponding internal disconnect switch assembly. Because the open/closed state of a bottle switch is not directly observable owing to its sealed interior, a direct visible indication of the state of the three-phase vacuum interrupter switch assembly is provided by a visually detectable contact rod for each internal disconnect switch that is visible through the case window. To prevent potentially serious damage caused by arcing between the contacts of the internal disconnect switch, the internal disconnect switch is prevented from opening or closing when the bottle switches are closed. The case interior is preferably free of oil and/or SF6 gas.