US3152233A - Blade-type electric fuses - Google Patents

Description

Oct. 6, 1964 F. J. KOZACKA BLADE-TYPE ELECTRIC FUSES 2 Sheets-Sheet 1 Filed March 21, 1961 IIIIJ Oct. 6, 1964 Filed March 21,

F. J. KOZACKA BLADE-TYPE ELECTRIC FUSES 2 Sheets-Sheet 2 United States Patent 3,152,233 BLADE-TYPE ELECTRIC FUSES Frederick J. Kozacka, South Hampton, N.H., assrgnor to The Chase-Shawmut Company, Newburyport, Mass.

Filed Mar. 21, 1961, Ser. No. 106,994

Claims. (Cl. 200-120) This invention is concerned with electric fuses for protecting electric circuits against excessive currents, and it is more particularly concerned with current-limiting fuses.

It is a widely accepted practice to close the fuse tubes or casings of fuses intended to have a relatively high current carrying capacity and a relatively high interrupting capacity and to be current limiting by copper plugs the axially outer surfaces of which support a pair of aligned blade contacts.

Structures of this kind are relatively expensive. It is, therefore, one object of this invention tOl provide electric fuses of the blade contact type having a relatively high current carrying capacity and a relatively high interrupting capacity and which are current-limiting, which fuses are easier to manufacture and involve smaller manufacturing cost than the above referred-to type of fuses provided with terminals in the form of copper plugs.

Another object of this invention is to provide electric fuses having a particular kind of fuse links which will hereinafter be referred to as lattice links, in which fuses a pair of lattice links is associated with a pair of blade contacts for connecting that pair of lattice links into an electric circuit.

Another object of the invention is to provide electric fuses Whichhave terminal elements in the form of a pair of blade contacts projecting through a pair of caps closing both ends of the fuse tube or casing, which fuses have a very small voltage drop across said pair of blade contacts when performing their normal current carrying duty, wherein heat generation is thus minimized and which run cool as a result of minimized heat generation.

This application is a continuation-in-part of my copending patent application Ser. No. 764,293, filed September 30, 1958, for Time-Lag Fuses, now United States Patent 2,988,620, issued June 13, 1961.

It is a further object of this invention to provide improved versions of the electric fuse disclosed and claimed in my above referred-to copending patent application.

My above referred-to patent application is concerned with fuses of the time-lag type and it is, therefore, another object of this invention to provide improved electric fuses making it possible to achieve time-lag in the same fashion as disclosed and claimed in the above patent.

Another object of the invention is to provide currentlimiting fuses wherein the number of serially related points of reduced cross-section or necks is minimized without impairment of the current-limiting ability of the fuses.

Still another object of the invention is to provide current-limiting fuses wherein the current prevailing at the points of reduced cross-section or neck is relatively small.

Other objects of the invention and advantages thereof will, in part, be obvious and in part appear hereinafter.

For a more complete understanding of the invention reference may be had to the following description thereof taken inconnection with the accompanying drawings, in which:

FIG. 1 is a longitudinal section of an electric fuse embodying this invention taken along 11 of FIG 2;

FIG. 2 is a longitudinal section of the fuse shown in FIG. 1 taken along 2-2 of FIG. 1;

FIG. 3 is a longitudinal section of another electric fuse embodying this invention taken along 3-3 of FIG. 4; and

"ice

FIG. 4 is a longitudinal section of the fuse shown in FIG. 3 taken along 4-4 of FIG. 3.

Referring now to the drawing, and more particularly to FIGS. 1 and 2 thereof, numeral 1a has been applied to indicate a tubular casing of insulating material, e.g. of a synthetic resin-glass-cloth laminate. The axially outer ends of easing or fuse tube 1a are closed by a pair of metal caps 2a crimped on the axially inner ends thereof into casing 1a to establish a strong mechanical connection or tie between casing 1a and caps 2a. Aligned blade contacts 4a made of flat copper stock project from the outside of casing 1a transversely through the end surfaces of caps 2a into the inside of casing 1a. To this end each cap 2a is provided with a rectangular cutout 2a having substantially the same geometrical configuration as the cross-section of blade contacts 2a. Circular washers 3a having rectangular cut-outs similar to the cut-outs in caps 2a are interposed between caps 2a and the axially outer ends of casing 1a. Pins or pinshaped springs 4a project transversely across casing 1a and blade contacts 40. Pins 4a are intended to secure blade contacts 4a to casing 1a and to maintain the same axially aligned therein. The aforementioned pin structure has been only diagrammatically indicated in FIGS. 1 and 2. Preferably this structure is designed along the lines fully disclosed in my United States Patent 2,939,935 issued June 7, 1960, for Fuse Structures, and reference may be had to that patent for a full disclosure of the preferred pin structure intended for the embodiment of the invention shown in FIGS. 1 and 2. The axially inner ends of blade contacts 4a are conductively interconnected by a pair of ribbon-type fuse links 5a of sheet metal and easing 1a is filled with a pulverulent arcquenching filler 6a, e.g. quartz sand, in which fuse links 5a are submersed. Fuse links or fusible elements 5a have the same width as blade contacts 4a, the width W of which has been indicated at the left of FIG. 1. The width W is slightly less than the inner diameter of casing 1a. It is not absolutely necessary that the width of fuse links 5a be exactly equal to that of blade contacts 4a, but it is important that the width W of fuse links 5a be approximately, or substantially, equal to that of the blade contacts 41:, and that the latter is as large as possible. Each of links 5a defines a lattice consisting of parallel connected necks and of serially connected necks. A neck of a fuse link is a point thereof where the current density is larger than the current density prevailing at the points of the fuse link where its cross-sectional area is largest and its current-density accordingly smallest. Each fuse link 5a is provided with five transverse lines U, R, S, T, V defined by circular perforations forming five transverse lines of necks. The axially outer lines of perforations U, V are superimposed upon blade contacts 4a and the axially inner lines of perforations R, S, T define necks generating a circuit-interrupting arc voltage when the fuse blows. Reference characters x x x x have been applied to indicate the necks formed by transverse line of perforations R. Reference character x x x x have been applied to the center line of necks formed by the transverse center line S of perforations, and reference characters x x x x have been applied to indicate the necks formed by the line of perforations T. The aggregate width 2W of links 5;: is relatively larger, and the thickness of links 5a is relatively smaller, than the width and thickness of conventional fuses having a comparable current rating. This tends to greatly decrease the current density at each neck, and the magnitude of the arc current which flows across each gap formed upon blowing of the fuse at the point of each neck.

It is a generally accepted design principle to increase the number of series necks forming series breaks in proportion to the voltage of the circuit in which a particular fuse is intended to be used. Where a fuse is expected to exhibit a substantial current-limiting action the number of series necks forming series breaks is particularly high since it requires high initial arc voltages to rapidly force a major fault current down to zero. It is a generally accepted practice in the design of low-voltage currentlimiting fusesi.e. current-limiting fuses having a voltage rating of 600 volts or less-to provide the fuse links thereof with a relatively large number of series necks forming series breaks when the fuses blow.

The links or fusible elements of current-limiting fuses having a voltage rating of 600 volts, particularly if such fuses are intended for relatively high current ratings, have generally as much as five serially connected necks forming five series breaks when the fuses blow on major fault currents. FIGS. 1 and 2 (and also FIGS. 3 and 4) show a current-limiting fuse structure having a voltage rating of 600 volts but having only three effective transverse lines R, S, T of necks rather than five such lines. In the structure of FIGS. 1 and 2 the effective number of transverse lines of perforations is three rather than five since the perforations of the axially outer transverse lines U, V are shunted by knife blade contacts 4:: and, therefore, ineffective. This drastic reduction in the number of transverse lines of necks or circular perforations greatly reduces the voltage drop across the blade contacts 4a while the fuse is performing its normal current carrying duty, and it also reduces greatly the watt losses due to the voltage drop and thus tends to be conducive to a cool running fuse structure.

As shown in FIG. 1 each link 5a is provided with a system of circular perforations having centers arranged in a lattice pattern. These perforations define a system of necks which are likewise arranged in a lattice pattern. Thelattice pattern of circular perforations includes a first family of parallel lines R, S, T extending transversely across each link 5a and a second family of parallel lines at right angles to said first family and extending in a direction longitudinally of casing in. The second family of lines includes seven parallel spaced lines. There are six parallel lines of series necks between each of said second family of lines of perforations, namely lines of necks x x x x x x x x x x x x" It will be apparent that the number of the above referredto longitudinal lines exceeds by far the number of transverse lines R, S, T. This is but one way of saying that the number of necks arranged, or connected, in parallel in each of the three transverse lines R, S, T exceeds by far the number of serially connected lines of necks, the first mentioned number being six and the last mentioned number being three. The number of the serially connected lines R, S, T of necks determines the magnitude of the arc voltage immediately upon blowing of the fuse under major fault conditions. That arc voltage increases in proportion to the number of serially connected lines of necks.

Upon having reached a peak value the arc voltage decays at each point of break more or less rapidly, the rate of decay depending inter alia upon the heat generated at the particular point of break and the latter depending upon the density of the arc current at each point of break.

It will now be apparent why the lattice structure shown in FIGS. 1 and 2 makes it possible to achieve in a 600 volt circuit substantially the same current-limiting action which, in comparable prior art current-limiting fuses, called for five series breaks, or five serially connected lines of breaks. The reduction in a number of series necks, or the number of serially connected lines of necks, greatly reduces the initial arc voltage, but the increase of the number of necks in each transverse line of necks greatly reduces the current at each neck or point of break, the heat generated at each point of break and consequently the rate of the decay of the arc voltage at each point of break. This is conducive to a more or less steady or stable arc voltage, or flat top are voltage, which is the ideal type of arc voltage. This ideal can never be fully attained. Fuse links of the type shown in FIGS. 1 and 2 are, however, conducive to generating a fair approximation to the ideal arc voltage.

The reduction of the number of series necks, or serially connected lines of necks, and the concomitant increase of the number of parallel connected necks per line are not only conducive to arc voltages having relatively small initial peaks and relatively small rates of subsequent decay, but are also conducive to relatively small voltage drops across the fuse while the latter is performing its normal current carrying duty before occurrence of a major fault current.

The cross-sectional area Q max. of a fuse link of perforated sheet stock at any point thereof where the fuse link is not perforated is largely determined by the current carrying capacity which is required of the fuse of which the fuse link forms a part. The cross-sectional area Q min. of a fuse link of perforated sheet stock at any point where its cross-section is reduced to a minimum is determined by the required fusing i -t value of the fuse of which the fuse link forms a part. To decrease in any given design the number of transverse lines of perforations and to increase the number of perforations per line without changing the voltage rating and current rating and the current-limiting ability of the particular fuse structure therefore means to greatly reduce the thickness of the sheet metal of which the fuse link is made, varying its Q max. Within limits, and maintaining its Q min. unchanged.

In order to minimize the current per neck two links 5a are connected in parallel, and each of the two links 5a is made as wide as possible, i.e. approximately as wide as the pair of wide blade contacts 4a projecting through caps 2a. If a fuse intended for a given current carrying capacity is designed in this fashion the ribbon links thereof have a tendency to become thinner than those in conventional fuses having the same current carrying capacity or current rating. This, in turn, makes the fuse links 5a considerably more fragile. To prevent damage to the very thin and fragile fuse links 5a each link 5a is supported by an insulating plate 7a preferably made of a synthetic resin-glass-cloth laminate, e.g. a melamine-glass-cloth laminate. Plates 7a are arranged on juxtaposed sides of links 5a. Links 5a may be affixed to insulating plates 7:: by means of staples 9a projecting transversely through the links 5a and the insulating plates 7a. In addition to supporting links 5a, plates 7a form effective barriers against the flow of products of arcing into the space between links 5a. The transverse lines of perforations, U, V superimposed upon blade contacts 4a facilitate soldering of the axially outer ends of links 5a to the axially inner ends of blade contacts 4a. These two lines of perforations do not perform any function upon assembly of the fuse when the latter performs its current carrying and interrupting duty and may, therefore, be omitted, if desired. Each link 5a has axially outer bent portions 5a enclosing an angle of degrees with the general plane of blade contacts 4a. Bends 5a are situated between the axially outer ends of metal ribbons 5a and the axially outer edges of insulating plates 7a. Bent portions 5a impart increased flexibility, or give, tothe link structure, which properties are required because of the fragility of the latter. It

will be apparent from FIGS. 1 and 2 that forces of compression, tension or torsion resulting from misalignment of blade contacts 4a are not transmitted to the fragile neck portions of links 5a.

Each link 5a is made of a metal having a relatively high conductivity and a relatively high fusing temperature, preferably silver or copper. The conductivity of silver is 62.6 and the fusing point of silver is 960.5 deg. C. The conductivity of copper is 58.8 and the fusing point of copper is 1083 deg. C. The conductivity of 'point metal such as silver and copper.

tin is 9.4 and the fusing point of tin is 231.8 deg. C. Tin is a typical low fusing point metal. Zinc has a conductivity of 16.95 and a fusing point of 419.4 deg. C., i.e. its conductivity is less than one third of that of a high conductivity metal such as silver and copper, and its fusing point is less than one half of that of a high fusing High conductivity, high fusing point metals such as silver and copper have small fusing i -t values and are, therefore, necessary and desirable for making fuse links for current limiting fuses. Each link 5a is provided with an overlay 8a of a metal having a relatively low fusing point, e.g. tin, capable, upon fusion thereof, to destroy the base metal by a metallurgical reaction and thus to form a break. Such overlays are well known in the fuse art as a means for achieving time-lag and forming breaks on the occurrence of relatively small protracted overloads, as distinguished from major fault currents. Overlays 8a are arranged on remote sides of links 5a. It will be apparent from FIG. 1 that overlays 8a are coextensive with the entire Width of ribbons 5a and substantially parallel to the transverse family of lines defining a lattice pattern of necks, and the lattice pattern of circular perforations, respectively. Overlay 8a has a family of longitudinal projections extending to, but not beyond, the transverse line S along which necks x x x x are aligned. As a result of this geometry, on occurrence of major fault currents all necks aligned in line S will fuse substantially simultaneously with all necks aligned in lines R and T, whereas on occurrence of small but protracted and inadmissible overloads but the necks aligned in transverse line S will be severed by the action of overlay 8a. Thus necks x x x x are dual function necks, forming breaks on occurrence of major fault currents as well as on occurrence of relatively small overloads of inadmissible duration. This dual function feature of the necks aligned along transverse line S makes it possible to rapidly interrupt circuits having a circuit voltage of, and as high as, 600 volts by resorting to but three serialy connected lines R, S, T of necks.

The structure shown in FIGS. 3 and 4 is similar to that shown in FIGS. 1 and 2 and operates in substantially the same fashion as the latter. Referring now to FIGS. 3 and 4, tubular casing 1b is closed on both ends thereof by caps 2b having rectangular cutouts 2b through which blade contacts 4b project from the outside of the casing into the inside thereof. Casing 1b is filled with a pulverulent arc-quenching filler 6b, e.g. quartz sand, and washers 3b preclude the same from leaking out of casing lb. Pin springs 4b project through casing 1b and blade contacts 4b, integrating these two parts into a structural unit. A pair of ribbon type fuse links 5b sandwiches at the axially outer ends thereof the axially inner ends of blade contact 4b. Each fuse link is provided with a lattice of circular perforations defining a lattice of necks, both lattices being the same as those shown in FIGS. 1 and 2 and more fully described in connection therewith. The lattice area of both fuse links 5b is backed up by insulating plates 7b which are coextensive with said area. Staples 9b projecting through links 5b and insulating plates 9b maintain the latter in their proper position. The center line S of perforations and necks is associated with an overlay 8b of tin or other low fusing point metal for severing the base metal by a metallurgical reaction on occurrence of relatively small overloads of inadmissible duration. Each fuse link 5b is provided with a substantially semicircular bend 5b situated between the axially inner edges of blade contacts 4b and the axially outer edges of insulating plates 7b. These bends impart a certain flexibility to the structure and help to protect the perforated portion of the links 5b against stresses and strains which may result from external forces acting on blade contacts 4b.

For reasons of clarity the section plane 1-1 of FIG. 2 and the section plane 33 of FIG. 4 are shown in spaced relation from the upper surface of blade contacts 4a and 41;, respectively, and from the upper surface of fuse links 5a and 5b, respectively. Actually both these section planes are supposed to coincide with the upper surfaces of the blade contacts and of the upper surfaces of the fuse links. Each circular perforation in fuse links 5a and 511 respectively accommodates a thin layer of pulverulent arc quenching filler 6a and 6b respectively clearly shown in FIGS. 1 and 3, and therefore the portions of the blade contacts and the portions of the insulating plates below that thin layer are not exposed to view.

When the fuse structure shown in FIGS. 1 and 2 is carrying current a temperature gradient is established in the direction longitudinally of links So as well as in transverse direction. The highest spot temperatures occur in necks x and x When the overlay 8a covering necks x and x melts, these two necks are severed by metallurgical reaction and the current continues to flow through the remaining necks x x x x in line S. Soon the overlay on necks x x melts and all the current is then concentrated in necks x x After these two necks have been severed by the aforementioned metallurgical reaction the current paths through links 5a are interrupted.

Interruption on occurrence of major fault currents such as short-circuit currents is effected in a similar sequence of partial link-severing processes. The temperature is highest in necks x x x x x x immediately adjacent the center perforations and decreases toward the two immediately adjacent radially outer perforations. Melting begins at the points Where the temperature is highest. Small droplets of liquefied link metal are formed at these points. These droplets have a tendency to flow in transverse direction toward cooler points of the link, this tendency being due to the surface tension of the liquefied metal. There is thus a tendency of formation of transverse gaps beginning with a transverse en largernent of the perforations intersected by plane 22, or a transverse restriction of necks x x x x x x When these necks are completely severed by fusion, fusion and severance of necks x x x x x x begins. When fusion and severance of these necks has been completed, necks x x x x x x are caused to fuse and to be severed. Arcing begins when the last mentioned necks are fused and severed. It has been found that arcing is not limited to the points where fusion occurs last. When links 5a are completely severed in transverse direction along lines R, S, T arcing occurs along the entire width of the transverse gaps thus formed. Back burning occurs likewise along the entire width of these gaps, and thus the heat generated during the arcing period is evenly distributed, minimizing the decay of the arc voltage after kindling of series are at lines R, S, T.

The operation of the structure of FIGS. 3 and 4 is, in substance, the same as that of FIGS. 1 and 2.

Where there is no need for overload protection involving time lag, but merely one for protection against major fault currents or short-circuit currents, overlays 8a (FIGS. 1 and 2) and 8b (FIGS. 3 and 4) may be omitted.

The fuse structures shown in FIGS. 1-4 are primarily intended for A.C. circuits having a circuit voltage up to and of 600 volts. They are not adapted for interrupting high D.C. currents at voltages as high as 600 volts, but may be used in DC. circuits if appropriately derated. The back-burning of the ribbon links of these fuse structures is very limited. Hence the total length of ribbons 5a and 512, respectively, can be less than 3 inches.

For reasons of greater clarity a different direction of the hatching lines has been adopted in FIGS. 2 and 4 to indicate the arc-quenching filler in the space between the ribbon links 5a, 5b and outside of the same. It will be understood, however, that there is actually an integral body pulverulent arc-quenching filler throughout the entire casing.

It will be apparent from the foregoing that this invention provides a novel type of high interrupting capacity or current-limiting fuses which is strictly opposed to the current trend in the design of high interrupting capacity or current-limiting fuses inasmuch as the current trend is toward increasing the number of serially connected necks for any given circuit voltage, whereas this invention is predicated upon decreasing the number of serially connected necks for any given circuit voltage. This is made possible by reducing the thickness of the ribbon links and concomitantly increasing both the width thereof and the number of perforations per transverse line of perforation. It thus becomes possible to successfully interrupt circuits having a circuit voltage of 600 volts with ribbon fuse links having but three transverse lines of perforations, or one line of transverse perforations per 200 volts, or for each 200 volts, circuit voltage.

It Will be further understood that I have illustrated and described herein preferred embodiments only of my invention and that various alterations may be made in the details thereof without departing from the spirit and scope of my invention as defined in the appended claims.

I claim:

1. An electric high interrupting capacity fuse comprising in combination:

(a) a substantially tubular casing of insulating material having a predetermined inner diameter;

(b) a pair of terminal caps closing the ends of said casing;

(c) a pair of aligned knife blade contacts having a predetermined Width but slightly less than said diameter each projecting from the outside of said cas ing through the end surface of one of said pair of terminal caps into the inside of said casing;

(d) a pair of spaced thin sheet metal ribbons of a metal having a relatively high conductivity and a relatively high fusing point approximately equal in width to said predetermined width conductively interconnecting the axially inner ends of said pair of blade contacts, each of said pair of ribbons including a lattice pattern area of necks connected in parallel and of serially connected necks, said lattice pattern area being formed by substantially transverse lines of perforations, each of said lines of perforations including a predetermined number of perforations per line, the number of perforations per line being substantially in excess of the number of lines of perforations, each of said pair of ribbons having axially outer ends sandwiching therebetween the axially inner ends of said pair of knife blade contacts, and each of said pair of ribbons having a pair of flexible bends situated adjacent to one of the axially outer ends thereof;

(2) a filled of quartz sand inside of said casing embedding said pair of ribbons; and

(1) two pairs of insulating plates each substantially coextensive with said lattice pattern area of one of said pair of ribbons and each affixed to one of said pair of ribbons on juxtaposed sides thereof.

2. An electric high interrupting capacity fuse compris ing in combination (a) a substantially tubular casing of insulating material having a predetermined inner diameter;

(12) a pair of terminal caps closing the ends of said casing;

(c) a pair of aligned knife blade contacts having a predetermined width but slightly less than said diameter each projecting from the outside of said casing through the end surface of one of said pair of terminal caps into the inside of said casing;

(d) a pair of spaced thin sheet metal ribbons of a. metal having a relatively high conductivity and a relatively high fusing point approximately equal in width to said predetermined width conductively interconnecting the axially inner ends of said pair of blade contacts, each of said pair of ribbons including a lattice pattern area of necks connected in parallel and of serially connected necks, said lattice pattern area being formed by substantially transverse lines of perforations each including a predetermined number of perforations per line, the number of perforations per line being approximately twice the number of lines of perforations, each of said pair of ribbons having axially outer ends sandwiching therebetween the axially inner ends of said pair of knife blade contacts, each of said pair of ribbons having a pair of flexible bends situated adjacent to one of the axially outer ends thereof;

(e) a filler of quartz sand inside of said casing embedding said pair of ribbons; and

(f) two pairs of insulating plates each substantially coextensive with said lattice pattern area of one of said pair of ribbons and each affixed to one of said pair of ribbons.

3. An electric high interrupting capacity fuse comprising in combination:

(a) a substantially tubular casing of insulating material having a predetermined inner diameter;

(/5) a pair of terminal caps closing the ends of said casing;

(c) a pair of aligned knife blade contacts having a predetermined width but slightly less than said diameter each projecting from the outside of said casing through the end surface of one of said pair of terminal caps into the inside of said casing;

(d) a pair of spaced thin sheet metal ribbons of a metal having a relatively high conductivity and a relatively high fusing point approximately equal in width to said predetermined width conductively interconnecting the axially inner ends of said pair of blade contacts, each of said pair of ribbons including a lattice pattern area of necks connected in parallel and serially connected necks, said lattice pattern area being formed by substantially transverse lines of perforations each including a predetermined number of perforations per line, the number of said transverse lines being three and the number of perforations per line being at least six, each of said pair of ribbons having axially outer ends sandwiching therebetween the axially inner ends of said pair of knife blade contacts, each of said pair of ribbons having a pair of flexible bends situated adjacent to the axially outer ends thereof;

(6) a filler of quartz sand inside of said casing embedding said pair of ribbons; and

(f) two pairs of insulating plates each substantially coextensive with said lattice pattern area of one of said pair of ribbons and each aflixed to one of said pair of ribbons.

4. In combination an electric circuit having a predetermined circuit voltage and an electric high interrupting capacity fuse inserted into said circuit, said fuse including:

(a) a substantially tubular casing of insulating material having a predetermined inner diameter;

(b) a pair of terminal caps closing the ends of said casing;

(c) a pair of aligned knife blade contacts having a predetermined width but slightly less than said diam eter each projecting from the outside of said casing through the end surface of one of said pair of terminal caps into the inside of said casing;

(d) a pair of spaced thin sheet metal ribbons of a metal having a relatively high conductivity and a relatively high fusing point approximately equal in width to said predetermined Width conductively interconnecting the axially inner ends of said pair of blade contacts, each of said pair of ribbons including a lattice pattern area of necks connected in parallel and serially connected necks, said lattice pattern area being formed by substantially transverse lines of perforations each including a predetermined number of perforations per line, the number of said transverse lines being equal to said circuit voltage divided by 200 and the number of perforations per line being approximately twice said number of lines, each of said pair of ribbons having axially outer ends sandwiching therebetWeen the axially inner ends of said pair of knife blade contacts, each of said pair of ribbons having a pair of flexible bends situated adjacent the axially outer ends thereof;

(2) a filler of quartz sand inside of said casing embedding said pair of ribbons; and

( two pairs of insulating plates each substantially coextensive with said lattice pattern area of one of said pair of ribbons and each affixed to one of said pair of ribbons.

5. In combination an electric circuit having a circuit voltage of 600 volts and an electric high interrupting capacity fuse inserted into said circuit, said fuse includmg:

(a) a substantially tubular casing of insulating material having a predetermined inner diameter;

(b) a pair of terminal caps closing the ends of said casing;

(c) a pair of aligned knife blade contacts having a predetermined width but slightly less than said diameter each projecting from the outside of said casing through the end surface of one of said pair of terminal caps into the inside of said casing;

(d) a pair of spaced thin sheet metal ribbons of a metal having a relatively high conductivity and a relatively high fusing point approximately equal in width to said predetermined width conductively interconnecting the axially inner ends of said pair of blade contacts, each of said pair of ribbons including a lattice pattern area of necks connected in parallel and serially connected necks, said lattice pattern area being formed by but three transverse lines of perforations each including about six perforations per line, each of said pair of ribbons having axially outer ends sandwiching therebetween the axially inner ends of said pair of knife blade contacts, each of said pair of ribbons having a pair of flexible bends situated adjacent the axially outer ends thereof;

(e) a filler of quartz sand inside of said casing embedding said pair of ribbons; and

(1) two pairs of insulating plates each substantially coextensive with said lattice pattern area of one of said pair of ribbons and each affixed to one of said pair of ribbons.

References Cited in the file of this patent UNITED STATES PATENTS 1,278,322 Eustice et al. Sept. 10, 1918 1,290,860 Bender Jan. 7, 1919 2,313,373 Sundt Mar. 9, 1943 2,665,348 Kozacka Jan. 5, 1954 2,864,917 Sundt Dec. 16, 1958 2,988,620 Kozacka June 13, 1961 FOREIGN PATENTS 20,483 Great Britain Sept. 19, 1902 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5,152,253 October 6, 1964 Frederick J, Kozack'a It is hereby certified that error appears in'theabove numbered patent reqiiring correction and that the said Letters Patent should read as oorrectedbelow.

Column 1, line 59, for "neck" read necks column 3, line 68, for "a" read the column 6, line 17, 'for "X 8.1'ld X4" read x and x column, .7 line 53, column .8 lines l3 and 48 column 9 line- 11, and column 10 line 13 after "bends", each occurrence, insert each column 7, line 55, for "filled" read filler column 7 line 57', column 8.,- lines 17 and 52, column 9, line 15, and column 10, line l7, strike out "pairs of" each occurrence I Signed and sealed this 24th 'day of August 1965 (SEAL) Attest:

ERNEST w. SWIDER EDWARD J. BRENNER Atlnsting Officer Commissioner of Patents,

UNITED STATES PATENT OFFICE Q CERTIFICATE OF CORRECTION Patent No 3,152 ,235 October 6, 1964 Frederick J, Kozecka It is hereby certified that error appears in'the above numbered patent reqliring correction and that the said Letters Patent should read as oorrectedbelow.

Column 1, line 59, for "neck" read necks column 3,

line 68, for "a" read the column .6, line 17, for "x mand X4" read X3 and 20 column, [7 line 53, column .8 lines 15 and 48, column 9, line 11, and column 10, line 13, after "bends", each occurrence, insert each column 7, line 55, for "filled" read filler column 7, line 57', column 8,- lines 17 and 52, column 9, line 15, and column 10, 'line 17, strike out pa irs' of" each occurrence. s

Signed and sealed this Z4th-"day of August 1965.,

(SEAL) Attest:

ERNEST w. SWIDER EDWARD J. BRENNER Ancsting Officer Commissioner of Patents

Claims (1)

1. AN ELECTRIC HIGH INTERRUPTING CAPACITY FUSE COMPRISING IN COMBINATION: (A) A SUBSTANTIALLY TUBULAR CASING OF INSULATING MATERIAL HAVING A PREDETERMINED INNER DIAMETER; (B) A PAIR OF TERMINAL CAPS CLOSING THE ENDS OF SAID CASING; (C) A PAIR OF ALIGNED KNIFE BLADE CONTACTS HAVING A PREDETERMINED WIDTH BUT SLIGHTLY LESS THAN SAID DIAMETER EACH PROJECTING FROM THE OUTSIDE OF SAID CASING THROUGH THE END SURFACE OF ONE OF SAID PAIR OF TERMINAL CAPS INTO THE INSIDE OF SAID CASING; (D) A PAIR OF SPACED THIN SHEET METAL RIBBONS OF A METAL HAVING A RELATIVELY HIGH CONDUCTIVITY AND A RELATIVELY HIGH FUSING POINT APPROXIMATELY EQUAL IN WIDTH TO SAID PREDETERMINED WIDTH CONDUCTIVELY INTERCONNECTING THE AXIALLY INNER ENDS OF SAID PAIR OF BLADE CONTACTS, EACH OF SAID PAIR OF RIBBONS INCLUDING A LATTICE PATTERN AREA OF NECKS CONNECTED IN PARALLEL AND OF SERIALLY CONNECTED NECKS, SAID LATTICE PATTERN AREA BEING FORMED BY SUBSTANTIALLY TRANSVERSE LINES OF PERFORATIONS, EACH OF SAID LINES OF PERFORATIONS INCLUDING A PREDETERMINED NUMBER OF PERFORATIONS PER LINE, THE NUMBER OF PERFORATIONS PER LINE BEING SUBSTANTIALLY IN EXCESS OF THE NUMBER OF LINES OF PERFORATIONS, EACH OF SAID PAIR OF RIBBONS HAVING AXIALLY OUTER ENDS SANDWICHING THEREBETWEEN THE AXIALLY INNER ENDS OF SAID PAIR OF KNIFE BLADE CONTACTS, AND EACH OF SAID PAIR OF RIBBONS HAVING A PAIR OF FLEXIBLE BENDS SITUATED ADJACENT TO ONE OF THE AXIALLY OUTER ENDS THEREOF; (E) A FILLED OF QUARTZ SAND INSIDE OF SAID CASING EMBEDDING SAID PAIR OF RIBBONS; AND (F) TWO PAIRS OF INSULATING PLATES EACH SUBSTANTIALLY COEXTENSIVE WITH SAID LATTICE PATTERN AREA OF ONE OF SAID PAIR OF RIBBONS AND EACH AFFIXED TO ONE OF SAID PAIR OF RIBBONS ON JUXTAPOSED SIDES THEREOF.

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