GB496731A - Improvements in or relating to electric cables employing pulverulent mineral insulation - Google Patents

Abstract

496,731. Cable end sleeves; cable joints. DEAN, W. J., and CLOTHIER, M., [Representatives of CLOTHIER, H. W.], CLOTHIER, G. D., and PYROTENAX, Ltd. June 3, 1937, No. 15467. [Classes 36 and 38 (i)] A method of sealing the end of a cable of the kind comprising one or more conductors insulated from a surrounding metal sheath by compressed mineral insulating powder, such as magnesia or steatite, comprises applying endwise-pressure to the cable insulation so as radially to expand the sheath and to form an end recess into which non-hygroscopic, insulating and sealing material, or a bush of solid insulating material may be inserted. The bush may be provided with a central tubular conductor so that the recessed and expanded ends of two cables may be connected together and sealed by the bush. Figs. 1 and 2 show apparatus for recessing and expanding a cable end. The conductor A<2> is bared at the cable end and the sheath A is gripped near its end between a pair of clamping plates B, B<1> which are grooved to accommodate the cable, the grooves being flared at their ends adjacent the cable end. Bolts C extending through the clamping plates B, B carry a head D which may be urged towards the end of the sheath by nuts D<2>. The head D has an aperture D<1> through which the conductor A<2> passes and is formed with a recess D<3> in which fits an apertured conical die E. To recess and expand the cable end, the nuts D<2> are tightened so that the die E is forced into the cable insulation A<1>, as shown in Fig. 2. If the die is of insulating- material it may remain in the cable end and serve as an insulating bush, otherwise the die is removed and a separate bush fitted in the recess. The end of the sheath is then swaged on to the bush. In effecting a joint between two cable ends, the ends are recessed and expanded as described with reference to Figs. 1 and 2 and a jointing element comprising a tubular conductor J, Fig. 5, separated from a sheath J<2> by an insulating layer J<1> having conical ends and preferably consisting of the same material as that used in the cables, is inserted between the cable ends. The ends of the sheath J<2> fit over the enlarged ends of the cable sheaths A. Clamps B are then attached to each sheath A and are drawn together by bolts C so that the conical surfaces of the cable and joint insulation are pressed firmly together. The ends of the sheath J<1> are then swaged to the cable sheaths. In a modified process the insulating layer J<2> is of solid material and is used to expand the cable ends, a separate expanding operation being unnecessary. In the case of a multicore cable, the expansion of the sheath is effected in a number of stages by a succession of dies having successively larger spacing between the holes through which the cores pass and additional insulation is introduced into the cable end after each die is withdrawn.