GB212821A - An electric safety fuse - Google Patents

Abstract

212,821. Koloman, T. H. Aug. 2, 1923. Fusible cut-outs.-Magazine fuses comprise a number of independently movable fusible members connected at one end to a common circuit contact and carrying at the other end a contact adapted to be placed at will in connection with a second circuit contact. Plug fuses comprise a shell 1 of insulating material carrying contacts 2, 4 and an insulating cover 7 with a slot 6 in which lie the upper ends of a number of fusible members 5 twisted together and connected to the contact 4 at their lower ends. The fusible members are copper coated at their upper portions to make good contact in turn with a clip contact 3 in connection with the fuse contact 2; they are coated at their lower portions with a heat resisting substance such as water glass to prevent the heat of fusing affecting adjacent members, and the upper extremities have insulating heads 8 which, for indicating purposes, may be of a low melting point or of a material (such as cupromercuric iodide) which changes colour upon heating. To reset a blown fuse the head of the fused element is withdrawn and the head of the next drawn to the end of slot 6 and' into the clip 3. In another form (Fig. 3) a spring strip 9 with a central slot and a surface coating of insulating material is secured at one end to the plug casing and connected to the contact 2. The heads of the fuse members 11 are adanted to make contact in turn with an uncovered portion at the free end of the spring where the slot is closed. As each fusible member is severed, by fusion or by fracture whilst softened by excessive current, its head it thrown out of the casing by the spring which may project through a slot 14 on a cap 13 to give an indication. In high voltage fuses the lower ends of the fuse strips are kept apart by being secured around the periphery of a cylindrical contact member or a screwed member adapted to be removably secured in the casing by the contact member. The casing may be formed with a recess 20 in which the fuse elements are retained and shielded by a spring flap cover 21 as shown in section in Fig. 9.