GB738344A - Improvements in electric fuses - Google Patents

Abstract

738,344. Fusible cut-outs. E.M.P. ELECTRIC, Ltd. Oct. 7, 1953 [June 23, 1953], No. 17358/53. Class 38 (1). A powder-filled cartridge fuse has a number of elements connected in parallel, one or more of which has an inherently different fusing characteristic from another or others of the elements but all of the elements have similar current-carrying characteristics and fuse simultaneously under short-circuit. In Fig. 1, the end caps 8 of the cartridge enclose metal blocks 9 to which the elements are connected. Three elements 11 ... 13 are shown consisting of silver strip with reduced centre portions having holes 16 to ensure optimum short-circuit operation. The strips carry equal proportions of current and strip 12 is severed at 17 and united by low-melting-point material 18 which causes the strip to fuse first on moderate overload, the proportion of current diverted to the remaining strips then causing them to fuse. It is stated that this construction results in a low fusing factor. Instead of severing the strip, indentations may be provided on opposite sides or the strip may simply be surrounded by a blob of low-melting-point metal. Fig. 5 shows a modification wherein a compression spring 20 located between projections 21 on the strip 12 pushes apart the ends of the strip on fusing. An indicator plunger 22 is provided operated either by release of tension in a wire 27, Fig. 5, or by fusing of a wire 25, Fig. 1. Fig. 6 shows another embodiment wherein strips 11, 13 are formed of silver and strip 12 is formed of tin, the cross-sections of the strips being such that they have equal resistances.