Socket connector of a socket cover

The retainer (1) has a measuring and evaluating unit (5) with a sensor (4) for determining a measuring parameter, and passage openings (12) provided for passage of contact pins (13) of a plug (14) to be retained. An electrically conductive, capacitive or inductive unit supplies power to the retainer, and a display outputs the parameter. The power supply unit has an electrically conductive contact for electrically contacting with a plug socket bush (6) during mounting of the retainer at a flush-mounted plug socket insert (3). The sensor reads a radio frequency identification (RFID) chip.