GB701076A - Improvements in current-limiting electric cartridge fuses - Google Patents

Abstract

701,076. Fusible cut-outs. CHASE-SHAWMUT CO. Feb. 13, 1952, No. 3838/52. Class 38 (1) In a current-limiting cartridge fuse of the type comprising a fusible link surrounded by an arc-quenching filler, e.g., quartz sand, which is converted upon blowing of the fuse into a hot semi-conducting fulgurite, steps are taken to cool the fulgurite by convection and render it non-conductive, by means of the gases produced by the fuse blowing. The Specification describes the theory underlying the construction. An inner insulating casing 1 encloses a fusible link 2 of silver surrounded by quartz sand 3 and having a number of perforations 2a. An outer insulating casing 4 forms with the casing 1 an annular chamber 5 connected to the interior of the casing 1 by a number of (e.g., four) radial vents 1c. A cellulosic tape 6 prevents egress of the sand 3 from the casing 1. On low-current interruption the link 2 vapourizes and the gas pressure produced breaks the tape 6, and gases flow along the casing 1 towards its centre and through the vents 1c into the chamber 5, thereby cooling the fulgurite formed by the sand 3 and preventing post-interruption failure of the fuse. In the case of short-circuit interruption, there is less heating of the fuse and the circuit is successfully interrupted without, in general, breakage of the tape 6 and the cooling effect of the gases. To withstand the high pressures, the casings 1, 4 are closed by triple pairs of metal caps 7a, 8a, 9a. In a modification Fig. 3 (not shown), a tin rivet is inserted in one of the perforations 2a towards one end of the link 2, the rivet forming with the silver link 2 a low-melting-point alloy where arcing is initiated upon low-current interruption, the rivetcarrying end of the link being surrounded by a gas-producing filler, e.g., chalk, separated by a partition from the quartz sand.