GB1397097A - Current limiting fuse - Google Patents

Abstract

1397097 Fusible cut-outs WESTINGHOUSE ELECTRIC CORP 9 Aug 1972 [30 Sept 1971] 37153/72 Heading H2G A fuse structure includes at least one fusible element 60 on an insulating support member 30 inside an insulating casing 20, in which at least an intermediate part of member 30 is made of a normally solid material which, upon arcing evolves a gas but is substantially non- tracking, and the space between the casing and the member 30 is filled with pulverulent arc quenching material 50, such as silver or quartz sand. As shown, member 30 is formed from nine tubular support pieces placed end to end and made of boric acid compressed by a minimum isostatic pressure of 25,000 Ibs. p.s.i., or compressed calcium carbonate. A notched silver ribbon 60 is wound round the support, the ends, which may be doubled over to increase the cross-sectional area, being trapped between caps and terminal members 82 and 72 and 84 and 74 respectively. The ends of elements 60 may be bound to support 30 by glass tapes. A bead of tin or solder material which melts between 182‹ and 232‹ C. is provided on element 60 to promote melting of the fuse. Terminal members 72 and 74 also hold the flattened ends of support member 30. The casing 20 is of glass-reinforced melamine or epoxy-resin material. When arcing takes place the boric acid support member emits water vapour and quenches the arc. As the member is non-tracking no leakage current flows and the support member does not break down. If a calcium carbonate member is used, carbon dioxide or monoxide is evolved. The support member may be made of a single block, and may be solid or have a core which does not evolve gas, e.g. a ceramic or other inorganic material. If the member is hollow a high resistance fusible wire, co-operating with indicating means, may be placed in it.