A two-piece retainer ring is snap-fit together by protruding roll pins in mating holes forming a self-connected ring around a high-voltage cable engaging a cable plug flange. Parallel spring wires intruding into a central opening of a coupling nut engage an exterior groove in the retainer ring with a snap fit forming an interconnected mutually rotatable coupling nut assembly. A bend relief sleeve between the retainer ring and the cable extends away from the retainer ring along the cable. A ridge around the bend relief sleeve engages an interior groove in the assembled retainer ring. A D-shaped cable plug flange engages a D-shaped plug receptacle opening to align plug contact pins with receptacle sockets. Mating threads on the nut and receptacle secure the plug in the receptacle with an extending sleeve on the retainer ring bearing against the flange. Protruding sloping annular surfaces inside the nut and outside the assembled retainer ring mutually engage to force the retainer ring against the plug flange insuring a tight plug fit and ground continuity between the retainer ring and the flange and between the retainer ring and the nut. Relative motion between the sloping annular surfaces and between the retainer ring and the flange breaks surface oxide enhancing ground continuity.