US 4,054,858 AGranted

Electric fuse capable of interrupting small overload currents by series multibreaks

AssigneeGould Inc.

InventorPhilip C. Jacobs, Jr.

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Abstract

The fusible element of a fuse that needs series multibreaks for interrupting small currents is provided with a shunt current path including an arc gap in the center region thereof. That current path does not normally carry any current on account of the presence of the arc gap in it. The shunt current path shunts a portion of the fusible element including a so-called M-effect causing overlay. When that overlay becomes operative it causes formation of an arc gap in the fusible element which, in turn, causes a voltage to appear across the arc gap. When that voltage is sufficiently high the arc gap breaks down. The ensuing arc current is too small to allow formation of series breaks in the fusible element. The fusible element or the above shunt thereof are provided with beads that evolve gases under the action of the arc. These gases are directed to the points of junction of the fusible element and its shunt and due to this artificial gap contamination by hot gases the arc current becomes sufficiently high to produce series breaks in the fusible element.

Claims9

Dependent claims

An electric fuse adapted to form multibreaks at the occurrence of small protracted overload currents including

a. a tubular casing of electric isulating material;
b. a pulverulent arc-quenching filler inside said casing;
c. a pair of metallic terminal elements closing the ends of said casing;
d. conductive means interconnecting said pair of terminal elements, said conductive means including a fusible element and a shunt shunting a portion of said fusible element;
e. said fusible element having a relatively small resistance and forming a plurality of serially related points of reduced cross-section area and said fusible element further having means situated between two of said points of reduced cross-sectional area for causing formation of a break therein at the occurrence of small protracted overloads;
f. said shunt shunting said point of break formation, having an arc gap in the center region thereof and having ends conductively connected to said fusible element;
and
g. bead means mounted on said conductive means of a material evolving a gas when heated and generating jets of hot gas directed at the points of connection of said fusible element and said shunt to help in the ionization of these points.

5 more elements

Dependencies are inferred from the claim text.