Abstract: A sleeve having a central channel for receiving a prong of an electrical connector and preventing use of the connector is provided. A locking stud in the form of a projection extends on a flexible arm into the channel. Upon insertion of the prong in the channel the locking stud engages a hole in the surface of the prong as is commonly provided. In one embodiment there are two such locking studs on opposite sides of the channel to engage opposite sides of the hole in the prong. The tip of the locking stud is beveled to facilitate insertion of the prong and the opposite face of the locking stud is perpendicular to the channel to prevent removal of the prong. A key having two slightly divergent blades with beveled ends is inserted in the channel. The blades slide by the end of the prong deflecting the arms and withdrawing the locking studs from the holes in the prong permitting removal of the prong. The sleeve can be constructed from two identical components.