GB832503A - Improvements relating to electric heating cables - Google Patents

Abstract

832,503. Electric heating cables. BRITISH INSULATED CALLENDER'S CABLES Ltd. Jan. 16, 1957 [Jan. 17, 1956], No. 1616/56. Class 39(3) An electric heating cable comprises at least two metal conductors separated by semi-conducting inorganic material, the whole being enclosed within a surrounding layer of pulverulent mineral insulating material and an outer metal sheath. As shown, Fig. 1, a tubular conductor 3 is concentric with a central conductor 4 and separated from it by semi-conductive material 5, the whole being insulated from an outer metal sheath 1 by an annular body 2 of pulverulent insulant. In Fig. 2, two D-shaped conductors 23 and 24 separated by semi-conductive material 25 are insulated from the outer metal sheath 21 by an annular body 22. Other embodiments described are two symmetrically placed circular conductors within a tubular conductor and separated from it and each other by semi-conductive material (Fig. 3, not shown), two D-shaped conductors wholly embedded in the semi-conductive material so as to be separated by it from one another and from the insulating body (Fig. 4, not shown); and two circular conductors which together with the separating semi-conductive material, form a central assembly which is elliptical in section (Fig. 5, not shown). The metal sheath and conductors may be of copper or aluminium, the tubular conductors being in the form of a seamless tube, a tape folded longitudinally, or a tape wrapped helically, and the other conductors being of solid or stranded construction. The pulverulent insulant may be of magnesium oxide or talc. The semi-conductive material may consist of mixtures of magnesium oxide with carbon or metallic oxides or titanates. The cables may be made by the mechanical working, e.g. rolling, swaging or drawing, of the metal components and semi-conductive and insulating compositions assembled in the appropriate relationship. Alternatively, the cable may be made by an extrusion process.