Sealed box for tapping a cable

A sealed tapping box comprising at least one opening provided in a wall for the purpose of inserting a loop of a cable folded over to form a U-loop into the box, said opening being edged by a gasket seat for receiving a gasket and surrounded at each of its ends by external necks which are carried by the box and which are laterally split facing the opening so as to receive a portion of the cable inserted through said opening, said gasket comprising a strip for closing off the opening and two tubular stoppers projecting from the ends of the strip and provided with respective through ducts to enable the portion of the cable to pass into the box in sealed manner from the outside through the necks that are plugged by the stoppers, and a compression device which fixes to the box and which comprises first auxiliary sealing means for pressing the strip against the gasket seat, and second auxiliary sealing means for pressing the stoppers into the necks and onto the cable portion that passes through them.