GB1387288A - Current limiting fuse - Google Patents

Abstract

1387288 Fusible cut-outs WESTINGHOUSE ELECTRIC CORP 17 April 1972 [24 May 1971] 17616/72 Heading H2G A current limiting fuse comprises a first element and a second element being connected to the first at at least two separate positions. The first element has a lower electrical resistance than the second and thus carries the major part of the current in the protected circuit, but is designed to at least partially melt before the second under fault conditions thus causing the second to carry the full current and increase its temperature. This element, which is exothermic or explosive subsequently melts with an explosive force that completely fractures the already partly melted first fuse element. One type of second element that may be used has an aluminium core melting at 660‹ C. and an outer coating of palladium. In one embodiment of the invention the first fuse element, e.g. of silver or silver alloy has a number of spaced regions of reduced cross-sectional area, e.g. holes or notches. These may be filled with a low melting point material, e.g. tin or a cadmium based material or a lead of highly fusible tin composition or similar material may be positioned between the holes. In a second embodiment of the invention only a central portion of the second element may be of the explosive or exothermic type of fuse wire, the end parts being formed from, e.g. nickel-chrome or copper nickel. The fuse element, which can be in the form of a tapered wire spiral, may be contained in a cartridge fuse type cylinder that also contains a pulverulent arc quenching material, e.g. silica.