US3189712A

US3189712A - High interrupting capacity fuse

Info

Publication number: US3189712A
Application number: US259019A
Authority: US
Inventors: Frederick J Kozacka
Original assignee: Chase Shawmut Co
Current assignee: Chase Shawmut Co
Priority date: 1963-02-18
Filing date: 1963-02-18
Publication date: 1965-06-15
Anticipated expiration: 1982-06-15

Description

June 15,1965 J, Ko-ZACKA 3,189,712

HIGH INTERRUPTING CAPACITY FUSE Filed Feb. 18, 1963 3 Sheets-Sheetl 1 I l l l 4 ebaaa/ 9 8 INV EN TOR.

1754841422161# dlfozaaz BY MAMMWWJ F. J. KOZACKA vHIGH INTERRUPTING CAPACITY FUSE June l5, 1965 Filed Feb. 18, 1965 3 Sheets-Sheet 2 Spacing Units El Degrees INVENron Jlfozac'az,

BY www June l5, 1965 F. J. KozAcKA 3,189,712

l i HIGH INTERRUPTING CAPACITY FUSE Filed Feb. 18, 196s I f s sheets-sheet s Egea INV EN TOR.

BY Mmm Rm United States Patent Office 3,189,712 HGH INTERRUPTING CAPACITY FUSE Frederick I. Kozaeira, South Hampton, N.H., assignor to The Chase-Shawmut Company, Newburyport, Mass. Filed Feb. 18, 1963, Ser. No. 259,019 9 Claims. (Ci. m30-120) 'Ihis invention is concerned with electric fuses, and more particularly with high interrupting capacity currentlimiting fuses.

Achieving high interrupting capacity and a significant current-limiting 4action calls for the use of a pulverulent arc-quenching filler having a hig-h heat -absorbing capa-city an-d capable of generating high arc-voltage By far .the most effective pulverulent arc-quenching filler complying with .these requirements is quartz sand. Electric fuses which are filled with quartz sand must include casings which are heat resistant because quartz sand, being an excellent conductor of heat, tend-s to transfer large amounts of heat from the arcing zone inside the fuse to the casing thereof, imposing upon the latter a Isevere .thermal duty. The requirements in regard to the hea-t resistance imposed upon the material of which the casing is made lare particularly high when considering interruption of relatively smal-l protracted ovenloads as, for instance, overloads of the order of 200% of the rated current of the fuse. In such lan instance the quartz sand is heated to -a relatively high temperature before the fuse link melts, and before the interrupting process is initiated. Intense pre-heating of the quartz san-d -results in a drastic reduction of its 4arc-quenching ability. Consequently pre-heating of the quartz 4sand tends to increase the arc ener-g i.e. the .total electric energy which is converted inside of the fuse into heat in the interval of time between arc inception and arc extinction. The severity of the thermal duty imposed upon a casing of an electric fuse is increased in proportion to arc energy.

While the thermal duty which is imposed upon the casing of :a fuse varies with the amount of arc energy, all fuses comprising quartz `sand as an arc-quenching filler, lor arc-extinguishing medium, call for casings made of materials which are highly heat resistant, and heatshock resistant. Such materials are, for instance, ceramic materials and/or synthetic-resin-glass-cloth laminates. Heat resistant materials are relatively expensive. As a result, the cost of manufacturing electric fuses having an .arc-quenching filler of quartz sand and, therefore, calling for highly heat resistant casings, are likewise relatively high.

It is one object of this invention to provide high interrupting capacity current-limiting fuses which are lled with quantz sand, and which do not require casings of highly heat resistant and/or expensive materials.

The least expensive materials for making casings of electric fuses are cellulosic materials, eg. paper or fiber. In the past these materials have been used extensively Vfor making casings of fuses filled with .arc-quenching llers which 4are relatively poor thermal conductors "as, for instance, gypsum, but these materials were found to be Wholly inadequate for making high interrupting capacity current-limiting fus-es including quartz sand as a I filler.

some extent, upon the size of the casing of the fuse.

3,189,712 Patented June 15, 19655 It is apparent that the .aforementioned thermal duty might greatly be reduced by increasing the dimensions of the casings of electric fuses. That is, however, practically not feasible because the dimensions of electric fuses are standardized. Most manufacturers of fuses follow these size standards, and some manufacturers of fuses make fuses having smaller dimensions than provided in the fuse standards. Fuses having larger dimensions than provided in the fuse standards are, however, unacceptable. Therefore it is unacceptable to increase the size of casings of fuses above and beyond standard dimensions in order to reduce the thermal duty which is imposed upon casings of electric fuses.

It is, therefore, still another object of this invention to provide high interrupting capacity current-limiting fuses having casings of standard dimensions-or eve-n smal-ler dimensions than standard dimensions-which casings are made of cellulosic materials such as paper, or fiber, and are filled with quartz sand.

Still another object of this invention is to provide novel and improved electric fuses which, while operating fast on occurrence of major fault currents, such as shortycircuit currents, have a considerable time lag on occurrence Iof small protracted overloads, and whose time 'lags are sufliciently long to allow application of the fuses in motor circuits Where lblowing of fuses must not occur as a result of harmless motor starting inrush currents.

These and other objects of the invention and advantages thereof will become more apparent from the ensuing detailed description of the invention :and the features of novelty which characterize the invention will 'be pointed out with particularity in the claims annexed to this specification and forming a part thereof.

.For a better understanding of the invention reference may be had to the accompanying drawings illustrating the invention wherein- LFIG. 1 is a side elevation of a fuse embodying the prese-nt invention;

FIG 2 is an end view of the structure shown in FIG. 1;

FIG. 3 is a section of the structure of FIGS. l and 2 taken along 3 3 of FIG. 1 and showing some of the parts in front elevation rather than in section;

FIG. 4 is an isometric view of the link structure of the fuse shown in FIGS. l-S;

IFIGS. 5a to 5d lare front views and cross-sections, respectively, of link sub-assemblies for structures of the kind show-n in FIGS. 1-3;

FIG. 6 is a diagram showing the melting times for a given constant current plotted against the angle of the bend in the llink assemblies of FIGS. 5a and 5b;

,-FIG. 7 is a diagram showing the melting times for a given lconstant current plotted ,against the spacing between Athe two fuse links of the structure of FIGS. 1-3; and

FIGS. 8a, 8b, 9a, 9b, 10a and 10b are transverse sections across electric fuses embodying this invention and illustrate some geometrical relations which are characteristie of such fuses.

Referring now to the drawing, and more particularly to FIGS. 14!` thereof, reference numeral 1 has been applied to indicate a tubular casing of insulating material. Casing 1 is made of a cellulosic insulating material such as fiber. Casing 1 may also be made of layers of paper which are wound spirally one upon the other until the desiredY wall thickness for the casing is obtained. Terminal caps 2 close casing 1 on each end thereof. A Washer 6 of a fibrous heat resistant material is interposed between each rim of casing 1 and each terminal cap 2. Caps 2 as well as washers 6 are each provided with a cut-out, or stamped out, opening for the passage of knife blade contacts 5.

`gard to casing 1l is eccentric.

caps 2 and washers d, into the inside of casing 1. Leaf springs formed to the shape of pins 3 extend transversely across caps 2, casing l and knife blade contacts 5, thus Y supportingpthe latter and firmly securing caps 2 to casing 1. The central portion of each pin-shaped spring 3 upon which knife blade contacts 5, are mounted is compressed, and the axially router ends of pin-shaped springs 3 are expanded by means yof drive screws 4 driven into the axial- I. Kozacka, Fuse Structures, Oct. 31, 1961. Reference may be had to these two patents for further details regarding the way in which knife blade contacts 5 are supported in. position and caps 2 secured to housing 1. The axially inner endsV of knife blade contacts 5 are conductively interconnected by a pair of ribbon fuse links 8sandwichin g the axially inner ends of knife blade contacts 5. Each fuse link 8 is provided with five transverse lines 8a. of circular perforations and the center line of perforations of each vfuse link is associated with a link-severing overlay 9 of a low fusing point metal, c g. of tin. Fuse linksV 8 are preferably made of copper oranother metal having a relatively high fusing point, c g. silver. Overlays 9 are preferably arranged on fuse links 8 in the fashion disclosed and claimed in United Statesk Patent 2,988,620 to Frederick I. Kozacka, TimeLag Fuses, June 13, 1961. Each fuse link 8 is in the shape of a substantially channel-.shaped element and the arrangement of both fuse links 8 in re- As best shown in FIG. 4 each fuse link comprises a center strip ,8' and a pair of Vlateral extensions 8 enclosing angles ry with the center strip 8. A gap 10 is formed between the juxtaposed longitudinal edges of lateral extensions 8". The width of that gap may vary, and the angle y may vary, aswill be explained below more in detail. The angle 'y should preferably be in the order of 30 degrees. As best shown in FIG. 4 each center strip 8' of fuse links 8 is provided with an axial extension 8c in the form of a tab to be brazed, or soldered, or otherwise conductively connected to an axially inner end of one of the knife blade contacts 5. A crease or pleat 8b is formed between axial extensions Sc and center strips 8c to impart a sucient degree of flexibility to the fuse link structures. Fuse links 8 are entirely submersed in a body of quartz sandv 7 inside of casing 1.

It will be apparent from the foregoing that in fuses embodying this invention the fuse link structure including all the current carrying portions thereof is arranged relatively close to the axis of the tubular casing 1 and relatively remote from the inner surface 0f the latter. The fuse link structure includes substantially juxtaposed' portions `forming parallel current paths and being more narrowly spaced from each other than each from theinterior surface of casing I. Both ribbon fuse links 3 are bent to form a pair of eccentric, substantially congruent,

' substantially channel-shaped or tubular structures extending in a direction longitudinally of casing 1. The spacing between the axes of said pair of channel-shaped or tubular link structures is substantially less than the spacing between each of said axes and said casing. In FIG. 8a showing diagrammatically the structure of FIGS. 1-4 reference character m has been applied to indicate the spacing between the axes of channel-shaped ortubular fuseV link structures 3 and reference character n has been applied to indicate the minimum spacing between each of said axes and the inner surface of casing 1, and it is apparent that The cross-section of the fuse links does not necessarily have to be triangular as in FIGS. 1-7 and in FIG. 8a but may, for instance, take the shape illustrated in FIG. 8b wherein reference character 8a hasbeen applied to indil c-ate a pair of substantially tubular fuse link structures havingall the essential structural characteristics of the fuse link structures described in connection with FIGS. 1 4, except for the fact that the fuse link structures 8a have more or less the shape of an elongated Yoval rather than the triangular shape shown in FIGS. 1-4 and 8a. lnFIGS 8a and Sb reference character F1 has been applied to indicate the portion of the total cross-sectional area of casing 1 situated outside of fuse link structures 8 or Smrespectively, and reference characters F2 have been applied to indicate the portion of the Vtotal crossfsectional area of' casing 1 situated inside of

tubular structures

8, or 8a, respectively. It is apparent that the first mentioned portion of the cross-sectional area of casing 1 by far exceeds the last mentioned portion thereof, i.e. that It Will be further apparent from FIGS. 1-4 and 8a that fuse; links S are arranged in spaced relation each having a center portion S situated in `one of a pair of substantially parallel planes. In FIGS. 8a and 8b reference character X has been applied to indicate the spacing between said pair of parallel planes. Y

FIGS. 9a an-d 9b are identical t-o FIGS. 8a and 8b and illustrate some additional important geometrical relations of the constituent parts of fuses embodying this invention. In FIGS. 9av and 9b reference Vcharacter X has been applied to indicate the spacing between fuse links 8 and 3a, respectively. Reference character b has been applied to indicate the smallest spacing between

fuse links

8 and 8a, respectively, from the interior of casing 1. apparent that Vi.

e. fuse links

8 and 8a, respectively, are morenarrowly spaced from each other than from the interiorsurface of casing l. As a general rule Y n b x i.e. the minimumk spacing of the fuse links S from casing I should by far exceed the spacing between the fuse links. In FIGS. 9a and 9b reference character r hasv been applied to indicate the maximum spacing of the lateral extensions 81 and ila, respectively, of rthe fuse links from the center vstrips thereof marked 8 andV 8a', respectively.V

The spacing ris much smaller than the minimum spacing b of each pair of lateral extensions S, 8a fromthe i11- terror surface of casing 1, i.e.

In FIGS. 10a and 10b showing the same structure as FIGS. 8a and 9a, and FIGS. 8b and 9b, respectively,

i.e. the spacing between the axes of

fuse links

8 and 8a,

' respectively, is substantially less than the minimum spacing between said axes and the inner surface of casing l. FIGS. 8a, 8b, 9a, 9b, 10a and 10b have beendrawn t0 better show the aforementioned relations, but these figures `do not indicate the most desirable proportions of a structure embodying the present invention. FIGS. 1-3, inclusive, are, however, scale drawings of a fuse embodying th1s invention, having a current rating of 400 amps and a Voltage rating of 600 volts, and having `been successfully subjected to a wide variety of low current interrupting tests and of high current interrupting tests.

As a result of the aforementioned geometrical relations the fuse links 8 and Sa, respectively, require a larger amount o-f metal than comparable prior art fuses, i.e.

It will be 'y prior art fuses having a comparable current-carrying-capacity and interrupting capacity at a predetermined voltage rating and tested in a predetermined circuit having predetermined characteristics, particularly as far as the rate of rise of the recovery voltage is concerned. Because fuses having the aforementioned relations between the constituent parts thereof require a relatively larger amount of link metal than comparable prior art fuses to achieve the same current-carrying-capacity, or the same current rating, or the same minimum fusing current, the ohmic resistance of their fuse links is relatively small. Hence their watt losses tend to be relatively small. The drastic limitation of watt losses coupled with a relatively large spacing between the fuse link structure and the inner surface of the casing makes it possible to use cellulosic casing materials in spite of the fact that the arc-quenching liller is quartz sand, or another arc-quenching filler material having a similarly high thermal conductivity and, therefore, resulting in a relatively small temperature gradient between the wallrof the casing and the region inside the casing where the fuse links are arranged.

The following data give some indication of the reduction of watt losses resulting from the above fuse link geometry and casing geometry. A fuse structure as shown in FIGS. 1-3, inclusive, having a current rating of 400 amps and a voltage rating of 600 volts had a voltage drop of 80 millivolts when carrying its rated current. Comparable modern prior art fuses exhibited under the same conditions a voltage drop of 95 millivolts.

A reduction of Watt losses is desirable irrespective of whether or not it is desired to make the casing of a cellulosic material. Therefore the above geometry 4of the fuse link and of the casing is not limited to casings of cellulosic material but is indicated wherever it is desired to have a cool running fuse in spite of the presence of an arc-quenching liller which is such a good thermal conductor as quartz sand and tends to minimize the radial voltage gradient within the tubular casing.

Since the above geometry of the fuse links and of the casing tends to increase the relative amount of link metal, or the ratio of the amount of link metal to the currentcarrying-capacity of the fuse structure, it is conducive to relatively long delay times for fusion of the link-severing overlays 9, and concomitant initiation of the interrupting process on occurrence of relatively small overload currents. In other words, the above geometry of the fuse links and of the casing tends to result in time delay, or time lag, at relatively small overload currents and is, therefore, indicated wherever a time delay action is required, or desired. Since the time delay action is primarily a result of the geometry of the fuse link and of the casing, the application of this geometry is indicated whereever time delay is a desired operating characteristic, i.e. the application of this geometry may be desirable irrespective of the nature of the material of which the casing is made and irrespective of the thermal characteristics of the pulverulent arc-quenching ller interposed between the fuse link structure and the casing.

Referring now to FIGS. Srl-5d, each of these ligures shows a pair of spaced blade contacts 5 conductively interconnected by a pair of identical perforated stampings of sheet copper forming fuse links 8. According to FIG. 5a the pair of stampings conductively interconnecting blade contacts 5, comprise a center strip 8 having two lateral extensions 8 forming therebetween a narrow gap 10. The lateral extensions 8 enclose angles of 26 degrees with center strip 8. FIG. 5b differs from FIG. 5a in that in the former the langle enclosed between the center strips 8 and the lateral extensions 8 thereof is 45 degrees. As shown in FIG. 5 c this angle is increased to 90 degrees. According to FIG. 5d the center strips 8 and the lateral extensions 8 of each fuse link 8 are arranged in the same plane or, in other words, the above angle has been increased from 90 degrees to 180 degrees.

FIG. 6 shows the times required to initiate interruption in fuses embodying the structures of FIGS. Saz-5d when carrying the same current plotted against the angle enclosed between the center strips 8 and the lateral extensions 8". It is apparent that the fusing time increases rapidly as the aforementioned angle is increased and decreases rapidly as the aforementioned angle is decreased. Hence to achieve the same current-carrying-capacity, or the same minimum fusing current, with the structure of FIGS. 5a or 5b requires significantly thicker sheet metal than with the structure of FIG. 5a'. Hence with the structures of FIGS. 5a and 5b watt losses are significantly smaller and time lags significantly longer than with the structure of FIG. 5d.

In FIG, 7 'the times required to initiate fusion of the links in the structure of FIGS. 1 3 when carrying a predetermined constant current are plotted versus the spacing X between center strips S. It is apparent from FIG. 7 that fusing time increases rapidly as the aforementioned spacing X is increased, and decreases rapidly as the aforementioned spacing X is decreased. Hence to achieve the same current-carrying-capacity, or the same minimum fusing current, with a structure having a relatively small spacing X calls for significantly thicker sheet metal than with a structure having a relatively large spacing X. As a result watt losses are significantly smaller, and time lags significantly larger, as the spacing is reduced to the order of the thickness of the blade contacts, as shown in FIG. l.

Although this invention has been described in considerable detail, it is to be understood that such description is illustrative rather than limiting, as the invention may be variously embodied, and is to be interpreted as claimed.

I claim as my invention:

1. An electric fuse comprising in combination:

(a) a tubular casing of cellulosic insulating material;

(b) a pulverulent silicious high heat conductivity arcquenching filler within said casing;

(c) a pair of metallic terminal elements closing the ends of said casing;

(d) a pair of fuse-link-severing elements of a relatively low fusing point metal; and

(e) a pair of ribbon fuse links of a relatively high fusing point metal arranged inside said casing, subrnersed in said filler, conductively interconnecting said pair of terminal elements and each supporting yone `of said pair of fuse-link-severing elements, each `of said pair of link-severing elements extending transversely across one of said pair or" fuse links, said pair of fuse links being bent to form a pair of eccentric substantially congruent substantially tubular structures extending in a direction substantially longitudinally of said casing, and the spacing between the axes of said pair of tubular structures being substantially less than the spacing between each of said axes and the inner surface of said casing.

2. An electric fuse comprising in combination:

(a) a tubular casing of insulating material;

(b) a pulverulent arc-quenching iller within said cas- (c) a pair of metallic terminal elements closing the ends of said casing;

(e) a pair of ribbon fuse links of a relatively high fusing point metal arranged inside said casing, subrnersed in said iiller, conductively interconnecting said pair of terminal elements, and each supporting one of said pair of fuselinksevering elements, each of said pair of link-severing elements forming an overlay on one of said pair of links extending continuously from one lateral edge to the other lateral edge thereof, said pair of fuse links being bent to form a pair of eccentric substantially congruent narrowly spaced substantially tubular structures extending in a direction substantially longitudinally of said casing, the portion of the cross-sectional area of said casing situated outside of said pair of tubular structures by far exceeding the portion of the cross-sectional area of said casing situated inside of said pair of said tubular structures.

3. An electric fuse comprising in combination:

(a) a tubular casing of hard fiber;

(b) a high heat conductivity quartz sand `liiler within said casing;

(c) a pair of metallic terminal elements closing the ends of said casing;

(d) a pair of ribbon fuse links of copper inside said casing submersed in said filler conductively interconnecting said pair of terminal elements, saidpair of fuse links including juxtaposed web portions forming parallel current paths being more narrowly spaced from each other than the spacing of any point thereof from the interior surface of said casing and each of said pair of fuse links including a pair of flange portions enclosing angles of less than 45 degrees with the web portion thereof; and

(e) a pair of link-severing overlays of a metal having a substantially lower fusing point than copper each affixed to one of said pair of fuse links, said pair of overlays extending transversely across said web portions of said pair of fuse links and transversely across said pair of flange portions of each of said pair of fuse links, and said pair of overlays reducing the minimum fusing current of said pair of fuse links sufliciently to preclude substantial thermal damage to the hard liber of said casing on occurrence of protracted currents in the order of said reduced minimum fusing current.

4. An electric fuse comprising in combination:

(a) a tubular casing of cellulosic insulating material;

(b) a pulverulent high heat conductivity quartz ller Within said casing;

(c) a pair of metallic terminal elements closing the ends of said casing;

(d) a pair of fuse-link-severing elements of a relatively low fusing point metal;

(e) a pair of blade contacts projecting from the outside of said casing through said pair of terminal elements into the inside of said casing;

(f) a pair of separate ribbon fuse links of a relatively high fusing point metal inside said casing submersed in said ller conductively interconnecting said pair of blade contacts and each supporting one of said pair of fuse-link-severing'elements, each of said pair of fuse-link-severing elements extending transversely across one of said pair of fuse links, said pair of fuse links having portions arranged in a pair of substantially parallel planes having a narrower spacing from each other than the average spacing of each of said pair of fuse links from said casing, each of said pair 0f fuse links having a pair of integral lateral extensions arranged outside of said pair of parallel planes, and each of said pair of lateral extensions being substantially juxtaposed to one of said portions of said pair of fuse links.

5. An electric fuse comprising in combination:

(a) a tubular casing of cellulosic insulating material;

(b) a pulverulent silicious high heat conductivity arcquenching ller within said casing;

(c) a pair of metallic terminal elements closing the ends of said casing;

(e) a pair'of separate ribbon fuse links of a relatively high fusing point metal arranged inside ofV said casing, submersed in said filler, conductively interconnecting said pair of terminal elements and each supporting one of said pair of link-severing elements, each of said pair of fuse-link-severing elements extending transversely across one of said pair of fuse links, said pair of fuse links including portions arranged in spaced relation in a pair of substantially parallel planes having a smaller spacing from each other than the minimum spacing of each of said pair of fuse links from said casing, each of said pair of fuse links having a pair of lateral extensions integral therewith enclosing acute angles with said portions of said pair of fuse links, and each of said portions of said pair of fuse links having a smaller maximum spacing from said pair of lateral extensions thereof than the minimum spacing of each of said pair of lateral extensions from the interior surface of said casing.

n 6. An electric fuse comprising in combination:

(a) a tubular casing of insulating material;

(b) a pulverulent arc-quenching filler within said cas- (c) a pair of metallic terminal elements closing the ends of said casing;

(d) a pair of fuse-link-severing elementsV ofa relatively low fusing point metal; and Y (e) a pair of separate ribbon fuse links of a relatively high fusing point metal arranged inside of said casing, submersed in said filler, conductively interconnecting said pair of terminal elements, `and each supporting one of said pair of fuse-linkssevering elements, each of said pair of fuse link severing elements extending transversely across one of said pair of fuse links, said pair of fuse links having portions arranged in spaced relation in a pair of substantially parallel planes having a smaller spacing from each other than the 4minimum spacing of each of said pair of `fuse links from said casing, each of said pair of fuse links having a pair of lateral extensions integral therewith enclosing acute angles with said portions of said pair of fuse links, and each of said pair of lateral extensions having a smaller maximum spacing from said portions of said pair of fuse links than the minimum spacing of eachrof said portions of said pair of fuse links from the interior surface of said casing. Y

'l'.` An electric fuse comprising in combination:

(a) a tubular casing of insulating material having a predetermined cross-sectional area;

(b) a pulverulentarc-quenching filler within said cas- (c) a pair of terminal elements closing the ends of said casing;

(d) a pair of substantially tubular fuse links of sheet metal arranged in spaced eccentric relation inside said casing, submersed in said filler and conductively interconnecting said pair of terminal elements, the total cross-sectional area encompassed by said pair of fuse links being substantially less than said predetermined cross-sectional area', and the spacing of the longitudinal axes of said pair of fuse links from each other being substantially less than the spacing of said longitudinal axes from said casing; and

(e) a pair of substantially annular link-severing overlays of a metal having a substantially lower fusing point than said sheet metal each on one of said pair of fuseY links.

d. An electric fuse comprising in combination:

(b) a pulverulent arc-quenching filler within said cas- (c) a pair of terminal elements closing the ends of i ranged in spaced relation inside of said casing and submersed in said filler, the total cross-sectional area encompassed by said pair of fuse links being substantially less than said predetermined cross-sectional area, said pair of fuse links having a pair of juxtaposed sides having a spacing in the order of said predetermined thickness of said pair of blade contacts, each of said pair of opposite sides of said pair of fuse links being provided at the end thereof with a pair of connector tabs each forming a V-shaped crease and each being conductively connected to one of said pair of blade contacts; and

(f) a pair of substantially triangular link-severing overlays of a metal having a substantially lower fusing point than said sheet metal each on one of said pair of fuse links.

9. An electric fuse comprising in combination:

(a) a tubular casing of insulating material;

(b) a pulverulent arc-quenching ller Within said cas- (c) a pair of terminal caps closing the ends of said casing;

(d) a pair of blade contacts having a predetermined thickness each projecting from the outside of said casing across one of said pair of terminal caps into the inside of said casing;

(e) a pair of link-severing overlays of a relatively loW- fusing point metal; and

(f) a pair of ribbon fuse links of a relatively high fusing point metal conductively interconnecting said pair of blade contacts and each supporting one of said pair of link-severing overlays, each of said pair of fuse-link-severing overlays extending transversely .across one of said pair of fuse links, said pair of fuse links including a pair of center strips having a spacing substantially equal to said predetermined thickness of said pair of blade contacts and each of said pair of fuse links including a pair of lateral extensions integral with one of said pair of center strips and enclosing an angle of less than degrees with said one of said pair of center strips.

References Cited by the Examiner UNITED STATES PATENTS 1,396,255 11/21 Conner 200-135 1,774,252 8/30 Bussmann 200-135 2,004,191 6/35 Bussmann 200-135 2,988,620 6/61 Kozacka 20G-135 3,007,019 10/61 Kozacka 200-135 3,020,372 2/62 Kozacka 200-120 FOREIGN PATENTS 497,223 5/30 Germany.

BERNARD A. GILHEANY, Primary Examiner.

Claims

1. AN ELECTRIC FUSE COMPRISING IN COMBINATION: (A) A TUBULAR CASING OF CELLULOSIC INSULATING MATERIAL; (B) A PULVERULENT SILICIOUS HIGH HEAT CONDUCTIVITY ARCQUENCHING FILLER WITHIN SAID CASING; (C) A PAIR OF METALLIC TERMINAL ELEMENTS CLOSING THE ENDS OF SAID CASING; (D) A PAIR OF FUSE-LINK-SEVERING ELEMENTS OF A RELATIVELY LOW FUSING POINT METAL; AND (E) A PAIR OF RIBBON FUSE LINKS OF A RELATIVELY HIGH FUSING POINT METAL ARRANGED INSIDE SAID CASING, SUBMERSED IN SAID FILLER, CONDUCTIVELY INTERCONNECTING SAID PAIR OF TERMINAL ELEMENTS AND EACH SUPPORTING ONE OF SAID PAIR OF FUSE-LINK-SEVERING ELEMENTS, EACH OF SAID PAIR OF LINK-SEVERING ELEMENTS EXTENDING TRANSVERSELY ACROSS ONE OF SAID PAIR OF FUSE LINKS, SAID PAIR OF FUSE LINKS BEING BENT TO FORM A PAIR OF ECCENTRIC SUBSTANTIALLY CONGRUENT SUBSTANTIALLY TUBULAR STRUCTURES EXTENDING IN A DIRECTION SUBSTANTIALLY LONGITUDINALLY OF SAID CASING, AND THE SPACING BETWEEN THE AXES OF SAID PAIR OF TUBULAR STRUCTURES BEING SUBSTANTIALLY LESS THAN THE SPACING BETWEEN EACH OF SAID AXES AND THE INNER SURFACE OF SAID CASING.