GB947995A - Dual element fuses - Google Patents

Abstract

947,995. Electric cut-outs. FEDERAL PACIFIC ELECTRIC CO. Nov. 13, 1962, No. 42913/62. Heading H2G. A cartridge fuse comprises a fuse link 14 (Fig. 1), of relatively high melting temperature, held within a tube of insulating material 12 by two brass (or similar metal) end caps 10, 11, the link having an aperture 20 filled by an annular body of metal 22 of low-melting temperature and one or more regions of reduced cross-section 16, 18 (Fig. 2, not shown), which may be constituted by apertures, spaced from the aperture 20 along the link. The link may be of silver or copper and the annular body 22 of solder, being either an apertured filling of metal alloyed to the link around the edge of the aperture 20, or a hollow rivet secured mechanically in the link. Aperture 18 may also be filled with solder and extra apertures may be provided between member 20 and the end caps. The tube 12 may be filled with sand. Prolonged overcurrent causes localized high temperature regions at 16, 18 and 20; heat flow from the region 18 accentuates the heating at 20. The annular solder body then begins to melt and spreads laterally mainly towards 18 (Fig. 5), reducing the cross-section at 20, the formation of a menicus film being prevented by the annular shape. Continued overcurrent causes further increase in the hole in the solder body, the resistivity of the adjacent part of the link increases, owing to the further alloying with the solder, and the fuse link quickly ruptures at 20.