Apparatus for the electrical powering of a removable unit (3) connected to a data processing system through electrical connection pins (7,8,9), comprising circuits (10,11,12,13,14,15) for detecting the insertion of the removable unit in the system, through the grounding of one (7) of the pins by the removable unit, for applying a gradually increasing voltage to the powering pins (8,9) of the removable unit and for connecting the powering pins (8,9) of the removable unit to a system voltage source (1) by switching on electromagnetic switches (16,17) once the powering pins have been electrically biased, the energization of the electromagnetic switches being enabled through the grounding, by the removable unit, of one(7) of the pins.