GB514522A - Improvements in or relating to electric fuses - Google Patents

Abstract

514,522. Fusible cut-outs. HOPE, V. May 9, 1938, Nos. 13729, 14913 and 18625. [Class 38 (i)] A fuse element is constructed of a non-fusing portion 38, e.g. of copper or an alloy thereof, of high specific heat, a fusing portion 35, e.g. of silver of an allov thereof of lower specific heat that fuses on heavy overloads and a fusing portion 36, associated with the portion 35, of low-melting metal, e.g. lead, tin, or their alloys, that fuses on sustained overload. The non- fusing parts are connected to the contacts of the fuse, so that during the fusing of the middle portion the temperature of the ends does not rise appreciably. The parts 35 may be necked or slotted to localize the point of rupture and the low-melting point metal may be applied thereto to restore the original cross-sectional area. A coating 37 of boric acid may be applied to the portion 36 as described in Specification 411,861. The elements may be constructed by rolling out juxtaposed blocks of copper and silver so that the pressure between the blocks forms a " coherence diffusion joint." The rolled out strip is cut transversely to make the fuse element. The silver portion may be encased in a layer of copper. The fuse element may be enclosed in a cartridge filled with arc quenching material 43, 49. Specifications 217,625, [Class 38 (i)], 493,100 and 508,959 are referred to in the Provisional Specifications.