GB893800A - Improvements in electric heating elements - Google Patents

Abstract

893,800. Electric heating elements. BRITISH INSULATED CALLENDER'S CABLES Ltd. July 13, 1960 [July 14, 1959], No. 24237/59. Class 39(3) An electric heating element consists of a length of insulated wire folded on itself at its midpoint and the halves placed side by side and enclosed in a single lead sheath, the insulation being provided by applying two or more layers 2, 3, 4, Fig. 1, of glass fibre as helical lappings with alternating directions of lay, and after each layer has been applied impregnating it with an insulating compound and burnishing its surface. The glass fibre is applied in the form of a composite yarn or roving. In one embodiment the insulation is applied as a roving built up from a number of strands of 130's count in the glass system, e.g. one of the kind designated as 130/40. Composite yarns of counts 225/2/3 and 150/2/2 may also be used, but the use of yarns with a count number greater than 300 should be avoided. The resistance wire 1 may be of 0À036 inches diameter and insulated by three 130/40 rovings, the 40 continguous glass fibre filaments preferably being "untwisted". The composite layer thus formed has a radial thickness of 40 mils. A suitable length 5, Fig. 2, of insulated conductor (e.g. 220 ft.) is folded on itself at its midpoint and the two halves are enclosed in a lead sheath 6 formed by extrusion. The end 7 of the sheath is shaped to form a cap over the conductor 5 and soldered to form a waterproof covering therefor, the free ends 8 and 9 of the conductor being left uncovered to enable current to be supplied to the element. The transverse cross-section of the element may be a flattened oval, a "Figure 8" or a dumb-bell. The element may be used in a floor heating system or for pipe heating.