Abstract: According to the present invention, n (n=S is a positive integer) pieces of interrupting grids (22-1, 22-2, 22-3, - - - , 22-(n-1) and 22-n) are provided, each of the interrupting grids encompasses P pieces of narrow cut-off canals arranged in parallel. The both side of each of the narrow cut-off canals are concaved so that the narrow cut-off canal has a waisted-mortar shape. The waisted-mortar shape is delineated by m pieces of elliptical holes (Q1, Q2, Q3, - - - , Qm-1 and Qm (m=P?1 is a positive integer)) arranged adjacently in parallel and semi-elliptical holes (cut ID portions) provided on both sides the alignment of elliptical holes. Then, n pieces of the interrupting grids 22-1, 22-2, 22-3, - - - , 22-(n-1) and 22-n are arranged in series through jointing zones (heat-radiation zones) (21-1, 21-2, 21-3, - - - , 21-(n-) and 21-n) having a length of 2.5 millimeters or less measured in the series direction.

Abstract: A vacuum fuse includes a pair of metallic spiral elements of different wrapping directions mounted on inner end portions of axially aligned conductor rods. The radial inner ends of spiral elements are electrically connected to respective conductor rods and the radial outer ends are electrically connected to outer metallic rings, respectively. Arcing electrode disks are mounted to opposite axial ends of the outer rings to define confronting spaced apart and parallel arcing surfaces. A fusible element is connected between the conductor rods. When the fusible element is broken by an excess current, an arc is produced between the arcing surfaces and a magnetic flux is induced by the current flowing through the spiral elements. The magnetic flux causes the arc to move so that each arcing electrode is prevented from being locally heated, thereby improving the current interrupting property of the fuse.