Abstract: In one embodiment a protective housing adapted to be locked upon and cover a prong of an electrical plug is disclosed. The housing has a chamber to receive a prong of the plug and has a collared recess and threaded bore on one side communicating with the chamber to receive a lock screw that impinges upon the prongs. The head of the lock screw is guidably received in the collared recess and has a side slot. A key is provided with a tab at one end that engages the slot and the collared recess allows the key to turn the lock screw to and from its locked position against the prong.