GB1114804A - Improvements in or relating to electric fuses - Google Patents

Abstract

1,114,804. Fuses. J. R. McCAUGHNA. 6 Feb., 1967 [21 Feb., 1966], No. 7555/66. Heading H2G. An electric current-limiting fuse or multiple fuse having a powder-filled cartridge incorporates a fusible member, a portion of the surface of which is covered with metal or alloy of lower melting-point than the material of the fuse and this lower melting.point material is covered with a material having a higher melting-point than the material of the fuse. The fusible member 16 which may be a strip or wire or plurality of such is wound helically on a ceramic core 12 supported by fittings 13 and surrounded by quartz sand 17 in a cartridge 10 of insulating material having conductive end caps 11. Inclined arms 13a connected to annular elements 14 provide the electrical connection between the fusible member and end caps. Intermediate the ends of the helically wound fusible member at a position near the centre the member 16 is provided with four notches (16a), (Fig. 2, not shown), formed in opposite longitudinal edges, which define a short section 16b. This section is covered with a material (18) of lower melting-point than that of the fuse, such as tin, lead or zinc or an alloy thereof. Overlying this material is a further layer of material (19) having a higher melting-point than that of the fuse and may be a refractory material such as aluminium oxide, magnesium oxide or a ceramic. This material (19) holds the metal (18) in position of the fuse ribbon during slow fusion, and thus ensures that fusion occurs in the section 16b and that burning back towards the ends of the fusible member occurs.