Abstract: A protective device protects low-voltage lines such as telephone lines of a cable. It is fitted to a cable connection head which comprises two junctions for connecting two conductive wires of each cable line to two conductive wires of a switching exchange. Each junction includes two separable leaf-spring contacts or a rigid contact. Each line is protected by an overvoltage protective circuit having a first terminal and a second terminal which is connected to ground referenced voltage. Conductive contacts secured to the body of said protective device connect the first terminal of the protective circuit to a contact junction of the head after the protective device is fitted to the head. The fitting of the protective device to the head does not require unwiring of the conductive wires with respect to the contact junctions of the head.