US 4,344,058 AGranted

Low voltage cartridge fuse design

AssigneeGould Inc.

InventorsEdward J. Knapp, Jr., Richard J. Perreault

Life of this patent

Estimating the term…

Loading patent…

Abstract

This invention relates to electric fuses meeting the requirements of Underwriter's RK1 classification. It includes a high-current interrupter in the form of a fusible element having serially arranged points of reduced cross-section and a low-current interrupter in the form of a plunger soldered to the high-current interrupter. The plunger is spring biased, and when the solder joint softens, the plunger separates under the action of the spring from the fusible element leaving a large gap between them. The separation of the plunger from the fusible element is allowed to be particularly large on account of the fact that the plunger may be allowed to move into a special fuse cap, known as a cap having a rejection feature as described, for instance, in U.S. Pat. No. 2,943,295 to V. N. Stewart; June 28 1960 for REJECTION TYPE FUSE CLIP and in many other patents.

Claims13

Dependent claims

An electric fuse comprising a casing of electric insulating material closed on both ends thereof by a pair of terminal caps;

separate means for interrupting major fault currents and for interrupting overload currents arranged in said casing and serially connected to each other;
said means for interrupting major fault currents including a fusible element of sheet metal having serially arranged points of reduced cross-section;
said means for interrupting overload currents including a spring-biased contact inserted into the circuit by one or more solder joints;
and a pulverulent arc-quenching filler inside said casing wherein the improvement comprises
(a) a contact in the form of a plunger soldered by a first solder joint to one of the ends of said fusible element and acted upon by a helical spring tending to break said first solder joint;
(b) a tubular metal sleeve surrounding said plunger with a clearance between said metal sleeve and said plunger;
(c) a second solder joint precluding entry of said arc-quenching filler into said metal sleeve by way of said clearance between said metal sleeve and said plunger;
(d) a heating element of sheet metal extending along the outer surface of said metal sleeve for heating said metal sleeve and said plunger, said heating element having current-carrying tab means interposed between the outer surface of said casing and one of said pair of terminal caps;
and
(e) electric insulating means interposed between said heating element of sheet metal and said metal sleeve for insulating said heating element from said metal sleeve, said insulating means including an insulating sleeve surrounding said metal sleeve.

7 more elements

An electric fuse comprising

(a) a casing of electric insulating material;
(b) a pair of terminal caps including a first terminal cap and a second terminal cap closing the ends of said casing;
(c) said first terminal cap having a relatively small distance from the axially inner end thereof to the axially outer end surface thereof, and said first terminal cap having a cylindrical lateral wall uninterrupted by rejection means in form of a circular groove;
(d) said second terminal cap having a relatively large distance from the axially inner end thereof to the axially outer end surface thereof and said second terminal cap having a cylindrical lateral wall interrupted by rejection means in form of a circular groove.
(e) an elongated fusible element having a plurality of serially arranged points of reduced cross-section inside said casing at the end thereof closed by said first terminal cap and conductively connected to said first terminal cap;
(f) a plunger arranged inside said casing and conductively connected by a first solder joint to the end of said fusible element remote from said first terminal cap and biased by a helical spring arranged in coaxial relation to said plunger away from said first terminal cap toward said second terminal cap;
(g) an electric strip heater conductively connected with one end thereof to said second terminal cap and a second solder joint conductively connecting the other end of said strip heater to said plunger, a portion of said strip heater extending substantially along said plunger and reducing when energized by current flow the holding power of said first solder joint and the holding power of said second solder joint;
and
(h) the travel of said plunger under the action of said helical spring away from said first solder joint being sufficiently large to cause abutting engagement of said plunger and of said axially outer end surface of said second terminal cap.

6 more elements

Dependencies are inferred from the claim text.