US2143037A - Fuse - Google Patents

Description

Jan. 10, 1939. s. R. SMITH, JR

FUSE

Filed May 25, 1937 Irv/d@ 31'`l d Sidne: .Smit 1'? Zw H is Attorney.

Patented Jan. l0, 939l PATENT OFFICE FUSE Sidney B Smith. Jr.,

General tric New York Lenox, Mass., asslgnor to Company, a corporation of Application May 25. 1987, Serial No. 144,851 1a claim. (oi. zoo-12e) 'Ihe present invention relates to fuses and has for an object the provision of an improved fuse of simple, compact, and inexpensive construction, of such small-size as to require only a minimum of installation space and particularly adapted for use in relatively high voltage electric circuits in commotion with apparatus such as capacitors and generators, although not necessarily limited to such use.

Another object of the invention is the provision of an improved fuse of the current limiting type, capable not only of limiting the magnitude and duration of a short circuit current but also of interrupting satisfactorily the flow of current over a wide range of power faults including a relatively low current overload.

'In the construction of fuses of the current limiting type, it has been common practice to embed a fusible conductor in an arc quenching material disposed in an enclosing casing, the fusible element extending more or less directly from a terminal at one end of the casing to a terminal at the other end of the casing. This conventional construction has, however. failed to meet satisfactorily present day fusing requirements for relatively high voltage'service since it has been found that to obtain in a single tube construction of the conventional type the required length of fusible conductor for successful operation at high circuit voltages necessitates a much greaterv overall length of enclosing casing than is` permissible in those installations wherein space requirements are an important consideration.

A form of fuse construction which lends itself readily to the obtaining of required conductor length with minimum overall length of enclosing casing is that in which the conductor is threaded back and forth successively through a plurality of individual compartments or tubes. However, the plural compartment or tube fuse constructions heretofore employed have proved unsatisfactory for other than relatively low voltage service because they have been subject to the limitations, among others, that they have not embodied any means capable, upon subjection of the fusible conductors to relatively high voltage current overloads. of effectively preventing arcing between courses of the conductors in adjacent compartments or tubes or between courses of the conductors and end terminals of the fuses, with resultant short-circuiting and loss of effect of portions of the conductors, and also that they have not embodied any means for properly `venting Ithe compartments or tubes to obtain successful operation at high voltages and currents, which latter limitation is especially undesirable in those fuses wherein a gas producing type of arc quenching filler is employed.

A further and more specific object of the 5 present invention is, therefore, the provision of a fuse of the enclosed type, particularly suited for lhigh voltage service, embodying a plurality of tubes or compartments with a fusible conductor threaded back and forth successively therel through in order to obtain the required length of conductor in a minimum of space and having an improved construction and arrangement of parts for insuring proper venting of the fuse and for preventing short-circuiting of any porl tion of the fusible conductor by an arc attendant upon fuse operation.

For an understanding of other objects of the inventionand of that which I believelto be novel and my invention, attention is directed to the following detailed description and the claims appended thereto, taken in conjunction with the accompanying drawing wherein are illustrated exemplary embodiments of the invention.

In the drawing, Fig. l illustrates in longitudinal section one vform of enclosed fuse embodying the present invention; Fig. 2 shows a transverse cross-section along the line 2-2 of Fig. 1; Fig. 3 illustrates in longitudinal section a second form of enclosed fuse embodying the present inventlonand which is somewhat similar to the embodiment of Fig. 1, differing materially only` in the construction and arrangement of the inner tubes; Fig 4 shows a transverse cross-section taken along the line l-4 of Fig. 3; Fig. 5 is an 35 exploded view illustrating diagrammatically a modiication of the form of fuse illustrated in Fig. 3, and Fig. 6 shows a transverse section through a fuse embodying the tubes of Fig. 5 in assembled form.

Referring particularly to Fig. l, the fuse illustrated therein is provided with an elongated tubular enclosing casing Il which is illustrated as being constructed of insulating fibrous material but which, if desired, may be constructed of other suitable insulating material such as glass. The opposite ends of the casing are provided with metal terminal caps Il and I2 respectively which are secured to the ends of the casing in any suitable'manner as by means of 50 self-threading screws I3. These terminal caps il and l2 are formed with axially projecting cylindrical bosses i4 and l5 respectively by means of which the fuse may be mounted in any commonly employed form of terminal clips (not "5 insulating material, although, if desired, they may beconstructed of other suitable insulating materials such, for example, as glass. More than three Y of the inner tubes may be employed but only three are shown for the purpose of illustrating the manner of carrying outthe present invention. `VA'IWo i of the inner tubes Il and i8, are closed at lone end by means of metal end caps, the tube Il being closed by means of cap 2 I while the tube I8 is' closed by means of cap 22. The other ends of tubes Il and i8 and both ends of tube is are left open. The inner tubes are so arrangai within casing Iii that the closed ends of tubes Il and I8 are respectively adjacent opposite ends of the casing, While the third inner tube iii is disposed in parallel side by side relationship with the innermost lapped portions of the tubes I1 and i3, the

tube I9 being of sumcient length to span the distance between the open inner ends of tubes Il and I8. In order to facilitate the assembly of the inner tubes within the outer casing and also to maintain the inner tubes in their proper physical relationship, a band of paper or other suitable material is wrapped around the three inner tubes as indicated at 23.

lA fusible conducting element 24 is threaded back and forth successively through inner tubes I1, I8, and IS in such manner that it extends from end cap 2I on the outermost end of tube II, through tube I1, out of the open inner end o-f tube I1 and into the adjacent open end of tube I9, through tube I9 and out the other end thereof into the adjacent open inner end of tube I8 and thence'through tube I8 to end cap 22 on the outermost end of tube I8. 'I'his element 24 may be made of any suitable fusible material such as commonly employed in fuse devices and may comprise either a single conductor strip or a. plurality of conductor strips connected together in such manner as to provide a continuous fusible element. End caps 2I and 22 provide electrical terminals for the opposite ends of the fusible element and are connected by means of wires 25 and 26 respectively to the terminal caps II and I2 on the opposite ends of casingl I0.

With the arrangement just described, the required length of fusible conductor may be accommodated in an outer .casing of relatively short overall length while at the same time it is rendered impossible for an arc attendant upon fuse operation to short-circuit any portion of the con'- ductor with resultant loss of effect of such shortclrcuited portion. The walls of the inner tubes effectively insulate the major portion of the conductor so'asto prevent short-circuiting arc-over between different courses thereof, and the looped portions a and b, which extend between the open ends of the inner tubes located remotely from the end terminalsand which connect the courses of the conductorlying in the inner tubes, are spaced such substantial distances from the en-d' terminals II, 2i lat o ne end of the fuse casing, and the end terminals I2, 22 at the other end of the fuse casing as to prevent short-circuiting arc-over between these looped portions of the conductor and the end terminals.

amaca? A relatively finely divided arc quenching filler material 27, such as commonly employed in high voltage fuses, is disposed within the interior of outer casing I and the interiors of inner tubes il, I8, and I9 and embeds the fusible conductor extending therethrough. This filler may consist, as in the illustrated embodiment, of a gas producing material such as a calcium or boric acid compound, or may consist of an inert filler material such as sand, pulverized quartz or the like. In order to prevent escape of the filler material from the fuse casing through openings I6, while at the same time providing for proper venting of the casing, disks 28 of porous material are placed 1n the opposite ends of the casing to cover the f openings IB.

Upon subjection of fusible conductor 24 to current overload, the conductor fuses and volatilizes with the formation of an arc along the path formerly occupied by the conductor. The resultant fuse particles, as well as the heat and are gases, are dissipated through and to some extent absorbed by the immediately surrounding filler material, while, with a gas producing ller, as in the embodiment illustrated, the heat of the arc at the same time causes large amounts of gas to be driven oi from the filler, resulting in an extreme turbulence which exerts a rapid cooling and disintegrating action on the are, tending to extinguish the arc and interrupt current iiow.

i Moreover, from tests made upon fuses embodying the construction and arrangement of the present invention, it is indicated that the structure illustrated in Fig. 1 simulates to some extent three expulsion fuses connected in series in that there is created a forced movement of gases axially of the inner tubes and toward their open ends, the portion of the gases which is not completely absorbed by the filler material either within the inner tubes or the outer casing being discharged through porous disks 28 and openings I6 at the ends of the casing. This forced axial movement of the gases also contributes to the interruption of the arc and the current iiow. Thus, although the fuse of the present invention is not strictly an expulsion type fuse, yet it is apparent that some of the benefits of the expulsion type fuse are derived from the disclosed construction and arrangement. In the case of a short-circuit current particularly, the actions above described take place so rapidly that the current does not have time to build up to the value which it would otherwise attain but, on the contrary, is limited to a value appreciably less than that corresponding to the short-circuit characteristics of the circuit so that there results a material reduction in the short-circuit stresses on the system as Well as in the possibility of distress and damage to the apparatus being disconnected by the fuse. i

In lorder to provide a visual indication of fuse operation, a. wire 3i) is connected in shunt with the fusible element 24 and is brought out, as indicated at 3l, through the wall of fuse casing I0 into contact with a small body 32 of gunpowder or other similar mixture which preferably is held in place by means of a small paper label 33. Preferably wire 30 is of higher resistance metal than that of fusible element 24 and is connected in shunt with only a portion of the fusible conductor. as, for example, the portion of the fusible element which extends through intermediate tube I9. In order to insure that the portion of the fusible element with which wire 3I'I is connected in parallel shall rupture rst on fuse operation, any well known expedient forac- 7A complishing this purpose may be employed, such for example as a reduction in the cross-section of this portion of the element throughout all or a. part of its length. A small opening such as that indicated at 34 may be provided to accomplish the desired result. when the fusible element is subjected to an overload, the middle section passing through tube il melts first because of its reduced cross-section and causes current to flow through the indicating wire 30 which, due to its higher resistance, heats up to a point suilclent to cause the gunpowder or like mixture 32-to ignite, thus giving a readily observable visual indication of fuse operation.

The fuse illustrated in Fig. 3 is similar in construction and operation to the fuse illustrated in Fig. 1 and described hereinbefore. However, in the fuse construction illustrated in Fig. 3, all three of the inner tubes 35, 30, and 31 are of substantially the same length as the outer tubular casing 38 and both ends of all three of the inner tubes are left open. As previously pointed out, more than three of the inner tubes may be employed, if desired, and the inner tubes as well as the outer casing may be made of ilbrous insulating material as illustrated or of any other suitable insulating material such as glass. On opposite ends of casing 38 are mountedterminal caps 39 and Iii respectively which are formed with axially projecting cylindrical mounting bosses Il' and-40 respectively. 'I'he terminal caps may be fastened on the ends of the casing in any suitable manner as, for example, by means of self-threading screws 42, as illustrated. In the ends of the terminal caps adjacent the bases of their projecting mounting bosses are provided vent openings 43. Disks M of porous material are placed between the terminal caps and the outer ends of the inner tubes, in the' same manner as described in connection with the embodiment of Fig. 1, to prevent escape of illiing material from the fuse while providing for escape of gases from the interior of the fuse casing through openings 43.

A fusible conducting element ll, similar to lthe fusible element 24 described in connection with the embodiment of Fig. l, is threaded suc- `cessively back and forth through the inner tubes 35, 36, and 31. The opposite ends of the fusible element have portions which are bent out around the edges of the disks M respectively at opposite ends of the casing as indicated at 46 and the extreme ends of the element -are then brought out through vent openings 43 in the opposite terminal caps and fastened in any suitable manner as by soldering to the outside surfaces of the terminal caps as indicated at 41. Thus, the fusible element is electrically connected between the two terminal caps. As will be seen from the drawing, the fusible element does not pass from one tube to the next through openings at or in proximity to the ends of the tubes, which, if this were the case, might result in arcing over between the looped ends ot the fusible element and the terminal caps or other portions of thefiusible element adjacent thereto, but the fusible lelement ls threaded through openings Il provided in the walls of the inner tubes at points remote from the ends of the tubes. Thus, there is no danger of short-circuiting arc-over, upon fuse operation, between courses of the fusible element lying in diiferent ones of the tubes or between any portion of the element and the end terminal caps 33 and 4l, since the major portion With this arrangement,

of the element is insulated by the walls of the surrounding inner tubes while the portion of the conductor intermediate tubes Il and I8 and the portion of the element intermediate tubes '3l and 31 are spaced respectively such substantial inner tubes. However. if desired in the practice of the present invention, the space within the outer casing also may be filled. In either case, the operation of the fuse will be substantially the same as that previously described in detail in connection with the fuse of Pig. ll, with the.exo`eption that upon fuse operation. resultant gases which are not absorbed by the lling material'within the inner tubes are forced outwardlythrough openings 5I, provided in the side walls of the inner tubes, as well as axially out through the open ends of the inner tubes, and naliy are discharged through the porousdisks u and openings I3 to atmosphere. The resultant turbulence and expulsionlike action along with the heat and gas dissipating and absorbing of the filler operate in the manner previously' described to extinguish the are and interrupt the current ilow.v

An important feature of the construction just described is that the vent openings Ii in the walls o1' each ci the inner tubes are so located that they are not opposite any portions of the fusible element which extend through the respective inner tubes. In other words, the fusible element extends through only a portion of each of the inner tubes and care is taken to locate the vent holes li in the walls of those portions of the inner tubes which are l ible element. Thus, th'eopenings Il cooperate with the openingsin the ends of the inner tubes to insure adequate venting while being so located as to prevent any possibility of short-circuiting arcs being formed between courses of the fusible conductor in adjacent inner tubes due to the discharge of ionized gases from the vent openings.

The ruse or m. a may it desired be provided with an indicating 'arrangement such as that previously described in connection with the embodiment of Fig. 1or maybe provided with some other suitable indicating arrangement such, for example, as that disclosed inthe application oi' R. S. Bennett, Serial No.` 144,660, nled May 25, 1937, and assigned t'o the assignee of the present invention.

In some cases it may be found desirable, in order to' provide the required length of fusible conductor in an outer easing of a given permissible length, to employ imore than three inner tubes in the practiceof the present invention. An exemplary five-tube arrangement is illustrated diagrammatically in the exploded view of Fig. 5, although it will be obvious that even more than ilve tubes may be'employed, if desired. In the exemplary arrangement'illustrated, the five cylindrical tubes, numbered II, I1, Il, Il, and It, are adapted to be assembled in close parallel not traversed by the fusside by side relationship within an outer cylinl7l drical casing Si, as illustrated in Fig. 6, with the opposite ends of the casing closed by means of terminal caps 52 and 63. These terminal caps have vent openings 54 and it is contemplated that porous disks 55 be inserted between the ends of the inner tubes and the terminal caps in the manner described in connection .with the embodiment of Fig. 3. A fusible conductor 56 is shown threaded back and forth successively through inner tubes 55, 51, 58, 59, and 58, with its opposite ends arranged to .be connected respectively to the terminal caps 62 and 63.

As pointed out in connection with the embodiments previously described, it is important that the connecting portions of the conductor, which extend exteriorly' of the inner tubes between the courses of the conductor lying in the inner tubes, be so arranged as to prevent arcing between these connecting portions and the terminal caps at the ends of the enclosing casing. It is important also, in a multi-tube arrangement such as that illustrated in Fig. 5, that these connecting portions be so arranged with relation to each other as to prevent arcing between dierent connecting portions upon fuse operation. Hence, in the arrangement illustrated, openings 61. through which a connecting portion of the conductor passes intermediate tubes 56 and 51 and openings 68 through which a connecting portion of the conductor passes intermediate tubes 58 and 59, are located at points remote from the ends of the respective tubes which in the nal assembly are adjacent terminal cap 53, thereby to prevent arc-over between the last mentioned connecting portions and cap 63. Similarly, openings 69 through which a connecting portion of the conductor passes intermediate tubes 59 and 68 and openings 10 through which a connecting portion of the conductor passes intermediate tubes 51 and 58, are located at points remote from the opposite ends of the respective tubes which in the finalassembly are adjacent terminal cap 82 so as to prevent arc-over between these last mentioned connecting portions and cap 62. However, upon fuse operation, the potential gradient along the path of the conductor will cause successive portions of the conductor, taken at progressively greater distances along the length of the conductor from one of the terminal caps, to be at progressively higher potentials with respect to that terminal cap. Therefore, as to those connecting portions of the conductor which in the nal assembly are located near the end of the casing closed by cap 59', the

be at a higher potential with` respect to cap 63 than will be the connecting portion intermediate openings 58 since the former connecting portion is at a greater distance along the length of the conductor from cap 63. Likewise, as to the connecting portions of the conductor which in the final assembly are located near the end of the casing closed by cap 62, there will be a greater potential difference between cap 62 and the connecting portion of the conductor intermediate openings 69 than between cap 52 and the connecting portion intermediate openings 10. For these reasons, openings 58 may be located, as illustrated, closer to the ends of the tubes 58 and 59 than the openings 61 are located from the ends of tubes 56 and 51, and openings 18 may be located, as illustrated, closer to the ends of tubes 51 and 58 than the openings 69 are located from the ends of tubes 59 and 60. By means of the aieaosv lize larger portions of the lengths of tubes 51, 58 and 59, in order to accommodate maximum possible length of conductor, while still providing sufilcient arcing distances between the terminal caps and the connecting portions of the conductor. The arrangement has the further advantage that it provides increased arcing distance between the portions of the conductor lying intermediate openings 81 and intermediate openso as to eliminate any possibility of arcing between courses of the conductor in diierent ones of the tubes due to discharge of ionized gases from the vent openings. Also, it is contemplated that, in the arrangement illustrated diagrammatically in Fig. 5, the inner tubes will be filled with an arc-quenching material and that some means will beV provided for giving visual indication of fuse operation, as pointed out in connection with the previously described embodiments.

An important advantage-of the fuse construcb tions described hereinbefore is that' they make possible the use of fusible conductors o'f considerable length in a relatively short outer casing. Moreover, although a fuse constructed in accordance with the present invention is of relatively v.,

short overall length, the arc path provided thereby is very long in proportion to the dimensions of the fuse so that an extremely eiective arcextinguishing action is secured with a fuse which requires only a minimum of installation space.

A .further important advantage of the constructions described is that the arc resultant upon fuse operation is definitely confined in a small space throughout its whole length and, due to the eiective isolation of the different sections of the fusible element with respect to each other, it is rendered impossible for'a short-circuiting arc to be formed between adjacent courses of the fusible conductor or between connecting portions of the fusible element and the fuse terminals, which arcs would be highly u`ndesirable in that they would result in a shortcircuiting and loss of eiect of a portion of the fusible element. As a result of the features above pointed out, the operation of a fuse constructed in accordance with the present invention is reliable and highly consistent in operation over a wide range of conditions and, due to its current limiting action" described hereinbefore, has ythe characteristics of resistor type 'fuses heretofore employed without requiring any auxiliary resistance element. It will be seen therefore that the constructions described lend themselves most readily to the manufacture of small fuses of high current interrupting capacity and particularly adapted for high voltage service.

What I claim as new and desire to secure by Letters Patent of the United States'is:

1. In a fuse device, a casing, terminals carried thereby, at least three tubes disposed Within the casing and having openings of substantial size for the ready relief of gases therefrom, a fusible conductor connected between said terminals and threaded back and forth successively throughr said tubes, said conductor passing from one to-the next of said tubes at points remote from each other and from said terminals in order to prevent short-circuiting arcs between the connecting portions of the conductor intermediate the tubes or between said connecting portions and said terminals upon fuse operation, a filler of arc-quenching material in each of said tubes embedding said conductor, and means for venting gases from said casing upon fuse operation.

2. In a fuse device, an elongated tubular casing, terminals elements at the ends of said casing, means providing at least three compartments extending longitudinally within the casing and having at least one end open for the venting of gases therefrom, a fusible conductor threaded back and forth successively through said compartments and passing from one to the next of the compartments at points spaced substantial distances from the ends of said-casing in order to prevent short-circuiting arc-over between said terminals and intermediate points along the length of the conductor upon fuse operation, means electrically connecting the opposite ends of said conductor respectively to said terminals, a' ller of arc-quenching material surrounding the courses of the conductor lying within each of said tubes, and means at the ends of said casing for the venting of gases therefrom.

3. In a fuse device, a casing, terminals carried thereby, means providing at least three compartments extending in substantially side by side relationship within said casing and having at least one end open for the venting of gases therefrom, a fusible conductor threaded back and forth successively through said compartments with its opposite ends electrically connected respectively to said terminals, the portions of the conductor interconnecting the courses of the conductor lying within the compartments being spaced remotely from said terminals, bodies of arcquenching material embedding the courses of the conductor lying within each of said compartments and means providing for the venting of gases from said casing. Y

4. In a fuse device, an elongated tubular casing, metal terminal caps disposed on `opposite ends of the casing and having perforations for the venting of gases from the casing, a plurality of tubes disposed in the casing in parallel side by side relationship and having at least one end open for the venting of gases therefrom, a fusible conductor threaded back and forth successively through said tubes with its opposite ends electrically connected respectively to said terminal caps, said fusible conductorpassing from one to the next of said tubes through openings located substantial distances from the terminal caps at the ends of the casing, bodies of relatively flnely divided arc-quenching material embedding the courses of the conductor within said tubes and gas-pervious screening means arranged tov prevent escapev of said material through the perforations in said terminal caps. 1

5. In a fuse device, an enclosing casing, terminals carried thereby, a rst tube disposed within said casing and having both ends open, a pair of tubes disposed in said casing in parallel side by side relation with said first tube, one of said pair of tubes having an open end adjacent one of thej open ends of said first tube and the other of said pair of tubes having an open end adjacent the otherof the open ends of said first tube, the other ends of said pair 4of tubes extending to points spaced longitudinally substantial distances from each other and from the open ends of said first tube, a fusible conductor electrically connected between said terminals and threaded back and forth successively through said three tubes, relatively finely divided arc-quenching material embedding said conductor in said casing and said three tubes, and vent means for the relief of gases from said casing upon fuse operation.

6. In a fuse device, an elongated tubular casing having metal terminal caps closing the ends thereof, a pair of tubes disposed in parallel relationship in said casing with the innermost portions of the tubes in lapped relationship and the outer ends of the tubes respectively adjacent the opposite ends of the casing, metal end caps mounted on the outer ends of said tubes and electrically connected respectively with the terminal caps on the opposite ends of the casing, the inner ends of said pair of tubes being open, a third tube open at both ends and extending from a point adjacent the inner open end of one of said pair of tubes to a point adjacent the inner open end of the other of said pair of tubes, a fusible element extending back and forth successively through said three tubes and having its ends respectively connected to the metal end caps on the outer ends of said pair of tubes, a body of relatively i'lnely divided arc-quenching material substantially nlling said casing and said tubes, means providing openings for venting gases'from said casing and screen means for preventing escape of said material through said venting openings.

7. In a fuse device, a casing having terminals at opposite ends thereof, means providing a plurality of substantially parallel longitudinally extending compartments within said casing, a fusible conductor connected between said terminals and threaded back and forth successively through said compartments, said conductor traversing only a portion of each of the compartments and sively through said compartments, and bodies of arc-quenching material embedding the courses of the conductor lying within the compartments, said conductor extending from one to the next of the compartments through openings providedI lin the walls of the compartments at points remote from the ends thereof in order to prevent shortcircuiting arc-over at the ends of the compartments between different courses of theA conductor or between the conductor and said terminal caps. 9. In a fuse device, a tubular casing, terminals carried thereby, a plurality of tubes disposed in said casing in substantially parallel relationship and having openings in the side walls thereof for the passage of gases from the interiors of the tubes to the space within said casingA around the tubes, a fusible element electrically connected between said terminals and extending successively through said tubes. bodies of arc-quenching material embedding said fusible element within said tubes, and means for venting said casing.

10. In a fuse device, an elongated tubular casing, terminals carried thereby, a plurality of tubes disposed in said casing in substantially parallel relationship, certain of said tubes having solid walls along a portion of the length thereof and vent openings in the walls of another portion of the length thereof, fusible stri electrically interconnected with said terminals and traversing portions of said tubes including only the solid wall portions of said certain of the tubes, bodies oi' arc-quenching material disposed in said tubes embedding said fusible strips, and means for venting said casing.

11. In a fuse device, an elongated tubular casing, a plurality of open ended tubes disposed in substantially parallel relationship in said casing with opposite ends of the tubes respectively adjacent opposite ends of the casing, fusible conducting strips extending through at least portions of each of said tubes, bodies of relatively nely divided lling material in said tubes surrounding said fusible strips, metal terminal caps on the ends of said casing electrically connected to said fusible strips and having perforations therein for the venting of gases from said casing, and discs of porous material interposed between the ends of said tubes and said terminal caps for preventing the escape of said finely divided material through said perforations while providing for the escape of gases through the perforations.

12. In a fuse device, a casing having terminals at opposite ends thereof, a plurality of substantially parallel longitudinally extending'tubes in said casing, and a fusible conductor threaded back and forth successively through said tubes: the openings through which connecting portions of the conductor pass, intermediate successive tubes, being spaced substantial distances from said terminals in order to prevent short-circuit arc-over between the terminals and said con-` necting portions of the conductor; the openings CERTIFICATE lPatent No 2,1).5 ,O57

sans? between which connecting portions of the conductor pass adjacent one end oi' the casing being arranged also to provide progressively greater arcing distances between the terminal at said one end of the casing and successive ones ofsaid last mentioned connecting portions lying at progressively greater distances along the length of the lconductor from the terminal at said one end of the casing; the openings between which connecting portions of the conductor pass adjacent the other end of the casing being arranged to provide progressively greater arcing distances between the terminal at said other end of the casing and successive ones of the last mentioned connecting portions of the conductor lying at progressively greater distances along the length of the conductor from the terminal at said other end of the casing.

13. In a fuse device, a casing having terminals at opposite ends thereof, a plurality of substantially parallel longitudinally extending tubes in said casing, a fusible conductor electrically connected between said terminals and threaded back and forth successively through said tubes, said conductor passing from one to the next of the tubes through openings in the side of the tubes spaced substantial distances from said terminals and from each other to prevent short-circuiting arc-over across said distances upon fuse operation, and bodies of relatively iinely divided arcquenching material disposed in said tubes, the ones of 'said openings adjacent one end of the casing being spaced from the terminal at that end of the casing distances proportional to the voltages likely to appear across such distances upon fuse operation assuming linear voltage distribution along the course of the conductor and the ones of said openings adjacent the other end of thecaslng being spaced in like manner from the terminal at said other end of the casing.

SIDNEY R. SMITH, Jn.

OF CORRECTION'.

January lO, v1959.

` SIDNEY R. SMITH, JR.

It is hereby certified that *error appears in the printed specification of the4 above numbered patent requiring correction a's follows: Page li, first column, line T5, after'the word "possible" insert to; page 5, first co1- umn, line ll, claim 2, for "terminals" read terminal; page 6, first coll umn, line 59, clam 12, for 'i' short-circuit" read short-cireui'eing; and that the said Letters yPatent should be read with this correction therein that the same may conformi to the record of the case in the 'Patent Office.

I Signed and sealed this 21st day o f February, yA.. D., 1959s (Scali Henry Van' Arsdale Acting VCommissioner of Patents.

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