Time delay fuse

• US 5,345,210 A
• Filed: 07/19/1993
• Issued: 09/06/1994
• Est. Priority Date: 07/19/1993
• Status: Expired due to Term

• Current Assignee: Littlefuse Incorporated
• Original Assignee: Littelfuse Incorporated
• Inventors: Swensen, Robert G., Kowalik, Joseph W.
• Primary Examiner(s): DONOVAN, LINCOLN D
• Application Number:
  US08/094,376
• Time in Patent Office: 414 Days
• Field of Search: 337/163, 337/164, 337/165, 337/166, 337/234, 337/236, 337/238, 337/239
• US Class Current: 337/163
• CPC Class Codes: H01H 2085/383 with insulating stationary parts
• CPC Class Codes: H01H 85/0052 Fusible element and series heating means or series heat dams
• CPC Class Codes: H01H 85/055 Fusible members
• CPC Class Codes: H01H 85/38 Means for extinguishing or suppressing arc by powder filling H01H85/18; by mechanical tension applied to fusible member H01H85/36

Abstract

A time delay fuse and various subassembly components for that time delay fuse. The fuse includes a housing made of an insulating material. The housing encloses a short-circuit fusible element, preferably a copper or copper alloy strip having a plurality of slots. The housing also encloses one or more rigid meltable fusible elements, preferably a plurality of solder bars. A body of resilient, compressible insulating material has at least one passageway through which each of the time delay fusible elements extends. When the rigid meltable fusible elements melt, the circuit through the fuse opens. In addition, the passageway which surrounded the rigid meltable fusible elements collapses upon its melting. This provides protection against "arc-back."

Claims

1. A subassembly component for mounting within the housing of a time delay fuse, said subassembly component for mounting between the axial ends of said fuse, said subassembly component comprising:

a. a rigid meltable fusible element having a pair of ends and said rigid meltable fusible element melting upon exposure to a current overload for a given period of time; and

b. a body of resilient, compressible insulating material spaced apart from conductive terminals of said fuse, said body having a passageway through which a portion of said rigid meltable fusible element extends, and said passageway being defined by surrounding walls, said walls collapsing upon the melting of said rigid meltable fusible element due to the resiliency of said body of material.

2. The subassembly component of claim 1, wherein said rigid meltable fusible element expands said walls of said passageway to accommodate said rigid meltable fusible element, and wherein when said current overload flows through said rigid meltable fusible element for said given period of time, said rigid meltable fusible element melts to effect collapse of said passageway.

3. A subassembly component for a time delay fuse, said subassembly component comprising:

a. a rigid meltable fusible element having a pair of ends, said ends being securable to spaced-apart conductive terminals of an electrical circuit, and said rigid meltable fusible element melting upon exposure to a current overload for a given period of time; and

b. a body of resilient, compressible insulating material, said body having a passageway through which a portion of said rigid meltable fusible element extends, and said passageway being defined by surrounding walls, said rigid meltable fusible element expanding said walls of said passageway to accommodate said rigid meltable fusible element, said walls collapsing upon the melting of said rigid meltable fusible element when said current overload flows through said rigid meltable fusible element for said given period of time, due to the resiliency of said body of material, said body of material further comprising vent holes to provide any molten portions of said rigid meltable fusible element with an escape path.

4. A time delay fuse, comprising:

a. a housing with first and second conductive terminals at the opposite axial ends of said housing;

b. a short-circuit fusible element within said housing, said short-circuit fusible element having first and second opposite ends, said first opposite end being conductively connected to said first terminal;

c. a rigid meltable fusible element in said housing, said rigid meltable fusible element being conductively secured between said second end of said short-circuit fusible element and said second terminal; and

d. a body of resilient, compressible insulating material, said body having a passageway through which said rigid meltable fusible element extends, said passageway being defined by surrounding walls, and said walls collapsing because of the resiliency of said insulating material upon melting of said rigid meltable fusible element.

5. The time delay fuse of claim 4, wherein said rigid meltable fusible element extends along a first longitudinal axis, and includes a pair of end portions and a central portion between said end portions, said central portion of said rigid meltable fusible element being retained within said passageway of said body of insulating material, and the end portions of said time delay fusible element projecting axially beyond said body.

6. The time delay fuse of claim 5, wherein said short-circuit fusible member is a thin copper strip or copper alloy strip, and where said rigid meltable fusible element melts to interrupt current flow when overload current flows through said rigid meltable fusible element for a given period of time.

7. The time delay fuse of claim 6, wherein said rigid meltable fusible element and said short-circuit fusible element are longitudinally-spaced and extend along a first longitudinal axis of said housing.

8. The time delay fuse of claim 4, wherein said housing encloses a quantity of a pulverulent arcquenching material.

9. The time delay fuse of claim 8, wherein said pulverulent arc-quenching material is sand.

10. The time delay fuse of claim 4, further comprising a heater element connecting said rigid meltable fusible element with said second conductive terminal.

11. The time delay fuse of claim 4, wherein said body of resilient, compressible insulating material includes vent holes to provide any molten portions of the initially rigid meltable fusible element with an escape path.

12. A component for a time delay fuse, said component comprising:

a. a short-circuit fusible element that is heatable and fusible by short-circuit current;

b. a rigid meltable fusible element that is electrically connected to one end of said short-circuit fusible element, said rigid meltable fusible element comprising at least one body of solder conductively secured to said short-circuit fusible element; and

c. a body of resilient, compressible insulating material collapsed around said rigid meltable fusible element, a collapsible passageway within said resilient body being defined by said body of solder;

the walls of said passageway collapsing to form an arc and current barrier when said body of solder melts.

13. The component for a time delay fuse as set forth in claim 12, wherein said short-circuit fusible element is a copper or copper alloy strip.

14. The component for a time delay fuse as set forth in claim 13, wherein said copper or copper alloy strip forming said short-circuit fusible element includes at least one elongated slot and at least one enlarged elongated slot along its length, said portion of said short-circuit fusible element adjacent said elongated and said enlarged elongated slots providing increased resistance to current flow, to encourage blowing of said short-circuit fusible element adjacent said enlarged elongated slots upon short-circuit or high overload current conditions.

15. A time delay fuse having a housing with first and second conductive terminals at the opposite axial ends of said housing, and a subassembly for said time delay fuse, said subassembly including:

a. at least a pair of laterally-spaced, axially-extending rigid meltable fusible elements that are heatable and fusible by modest overload electrical current over a given time;

b. a short-circuit fusible element that is disposed between one end of said pair of rigid meltable fusible elements and said first terminal; and

c. a body of resilient, compressible insulating material collapsed around said pair of rigid meltable fusible elements, a collapsible passageway being defined by said rigid meltable fusible elements and by passageway walls in the insulating material;

the walls of said passageway collapsing to form an arc and current barrier when said rigid meltable fusible elements melt.

16. The time delay fuse of claim 15, further comprising a heater element connecting said rigid meltable fusible element with said second conductive terminal.