Powerswitch® mechanical interlock devices incorporate a safety disconnect switch and IEC receptacle in a non-metallic watertight enclosure. The interlock mechanism prevents making and breaking of power under load. The switch cannot be actuated to the ON position until an IEC compatible plug is fully inserted and the plug cannot be removed until the switch is in the OFF position. The complete IEC 60309 system of plugs, connectors, inlets and mechanical interlock devices can be used for both retrofit and new installations for enhanced safety and performance in critical power connections.