A connector assembly includes a preassembly frame to which the ends of a number of high-voltage transmission lines are connected, whereupon the preassembly frame is mounted in an open-ended chamber contained in a connector housing. The frame includes a first end wall having openings that receive intermediate portions of the transmission lines, which first end wall carries a grounding plate having projections for engaging exposed portions of braided shielding layers of the transmission lines. The free ends of the transmission lines are provided with contact members that are supported by insulation sleeves in wall openings contained in a second end wall of the preassembly frame. A coding arrangement prevents the connector assembly from being connected to an unauthorized companion electrical device.