Electricity: electrothermally or thermally actuated switches – Electrothermally actuated switches – Shunt or short circuit completion devices
Reexamination Certificate
1997-09-24
2001-02-20
Picard, Leo P. (Department: 2835)
Electricity: electrothermally or thermally actuated switches
Electrothermally actuated switches
Shunt or short circuit completion devices
C337S186000, C337S187000, C337S227000, C337S228000
Reexamination Certificate
active
06191678
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuse, and in particular, to a time lag fuse designed to withstand certain peak inrush currents.
2. Discussion of Related Art
Time lag or time delay fuses are well known in the art. See, for example, U.S. Pat. Nos. 4,517,544; 4,189,696; 4,189,696; 4,680,567; 4,445,106; and 4,409,729. Such fuses are frequently in the form of spiral wound fuses. In a spiral wound fuse, the fuse element is spirally wound around a core that is internal to the fuse body.
However, most prior art spiral wound fuses were at least 5 mm in diameter and 15 mm long, with a voltage rating of only 250 volts. In fact, most spiral wound prior art fuses are 6 mm in diameter and about 32 mm long.
However, certain applications require fuses having a diameter of 3 mm and a length of about 10 mm. Furthermore, the Underwriters Laboratories recently changed the standards for endurance testing of certain fuses. See §28.2 of UL Standard 497A. The new standard requires certain fuses to have endurance conditioning such that they can withstand a 14 amp pulse having {fraction (10/1000)} microsecond wave form. Under this standard, the fuse must be able to withstand 100 pulses that reaches 14 peak amps within 10 microseconds and will decay to half-value in 1000 microseconds. Fifty of these pulses are to be at one polarity, and then the pulses are to be repeated at the opposite polarity.
Prior to the present invention, no 3×10 mm fuses were able to be made which would comply with the standard and which would have a 350 mA continuous ampere rating and 600 volts DC rating.
OBJECTS AND SUMMARY
It is an object of the present invention to provide a fuse that, among other things, meets the new UL Standard 497A and is able to have a rating of 350 mA and 600 volts DC.
It is a further object of the present invention to provide a small, efficient spirally wound fuse that fits in a 3×10 mm package.
It is yet another object of the present invention to provide an efficient method of manufacturing a spirally wound fuse.
According to one embodiment of the present invention, a time lag fuse includes an insulative housing having first and second ends and an outer diameter of about 3 mm. The fuse further includes a nonconductive core arranged inside the insulative housing and a fuse element wound spirally around the nonconductive core. An end cap is mounted on each of the first and second ends of the insulative housing and each end of the fuse element is connected to a respective end cap. The fuse is rated at approximately 350 mA and 600 volts direct current and meets the UL endurance conditioning test of withstanding 100 pulses of 14 peak amps on a {fraction (10/1000)} wave form without damage.
According to another embodiment of the present invention, the fuse element is wound on the nonconductive core at about 120 to 150 turns per inch, and the fuse element is a Cu/Ag wire having a diameter of about 0.002 inches.
According to the present invention, one method of making such a fuse comprises the steps of spirally winding a fuse element on an elongated nonconductive core, threading sequentially on the wound core an assembly that includes a first conductive end cap, a fuse housing, and a second conductive end cap, repeating the above-identified threading step until a plurality of assemblies have been threaded on the wound core, soldering the fuse element to each end cap, and severing the wound core between each assembly.
REFERENCES:
patent: 4177444 (1979-12-01), Taki
patent: 4189696 (1980-02-01), Beswick et al.
patent: 4253080 (1981-02-01), Howard
patent: 4409729 (1983-10-01), Shah
patent: 4445106 (1984-04-01), Shah
patent: 4517544 (1985-05-01), Spaunhorst
patent: 4560971 (1985-12-01), Oh
patent: 4680567 (1987-07-01), Edwards
Standard for Safety; Underwriters Laboratories, Inc.; Jan. 15, 1990; pp. 1-54 and Appendix.
Secondary Protectors for Communications Circuits; Underwriters Laboratories, Inc.; Jan. 30, 1996; pp. 1-64 and Appendix.
Burns Doane , Swecker, Mathis LLP
Cooper Industries Inc.
Picard Leo P.
Vortman Anatoly
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