GB1476870A - Fuse element - Google Patents

Abstract

1476870 Fuses DORMAN SMITH FUSES Ltd 29 April 1976 [17 May 1975] 21088/75 Heading H2G A fuse element comprises a metal strip made of for example silver or copper formed with a trough containing a low melting point metal, for example tin or tin/lead alloy, wherein the strip is reduced in section, to create a zone of relatively high resistance, immediately adjacent the trough. As shown the high resistance zones 13 are formed by forming notches. Further notched zones 15, 16 are provided further from the trough. A cartridge fuse (Fig. 3) may contain one or more elements 17 disposed in a ceramic tube 18 filled with arc-quenching silica sand 19, the tube being closed at each end by a pair of end caps 20, 21, enclosing an asbestos disc. Various modifications of the element are disclosed including forming the zone of reduced section by providing holes (Figs. 7 and 8, not shown), or a surface channel (Figs. 9 and 10, not shown). The trough may be rectangular (Figs. 11 and 12, not shown), and the alloy may be a rod in a semicircular trough (Figs. 13 and 14, not shown). In a further modification a reduced-section zone is bounded by a pair of troughs (Figs. 15 and 16, not shown). The arrangement provides for short-time current surges to be withstood, the heat developed in the reduced zone melting the alloy and thereby delaying fusing, whilst more persistent overloads melt the fuse. The remote zones 15, 16, respond to short-circuit overloads