an electric plug that has a retractable ground terminal in addition to the customary two terminals . this ground terminal is connected to the ground wire in the plug cable and when the ground terminal cannot be used , it is swung into a retracted or inoperative position and concealed from view . a ground outlet wire is used when the ground terminal is in inoperative position and this ground wire is wound around a spool when the ground terminal is used . this ground wire is connected by novel means to the ground terminal only when the latter is swung into inoperative position whereby the ground wire may be unwound from its inoperative position on the spool , and electrically connected to the outlet box and thus establish a ground connection from the outlet box to the ground terminal and thence to the ground wire in the outlet cable for the plug .