US3601739A

US3601739A - Indicating means for fuses

Info

Publication number: US3601739A
Application number: US889508A
Authority: US
Inventors: Donald D Blewitt
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1969-12-31
Filing date: 1969-12-31
Publication date: 1971-08-24
Anticipated expiration: 1988-08-24

Abstract

A fuse comprising an electrically insulating, generally tubular casing having a pair of terminal members mounted on the casing adjacent to the opposite ends of the casing and one or more fusible elements connected between the terminal members. A plunger is disposed in an axially extending opening in one of the terminal members and is biased outwardly from the opening by an associated spring. The plunger is normally restrained from movement under the influence of the spring by a restraining wire or high resistance fusible element which is connected between the plunger and the other terminal member of the fuse.

Description

United States Patent I [72] inventor Donald D. Blewitt Pittsburgh, Pa. 211 Appl. No. 889,508 [22] Filed Dee.31, 1969 [45] Patented Aug. 24, 1971 [73] Assignee Westinghouse Electric Corporation Pittsburgh, Pa.

[54] INDICATING MEANS FOR FUSES 12 Claims, 11 DrawlngFigs.

[52] US. Cl 337/244 {51] 1nt.Cl ...H01h85/30 [50] Field of Search n 337/7, 148, 158,159, 161, 164, 229,, 231, 232, 244, 248, 267, 293, 162, 241, 276

[56] References Cited UNITED STATES PATENTS 3,319,027 5/1967 Hitchcock 337/276 2,914,636 I 1/ 59 Kozocka 337/244 2,797,279 6/1957 Brandt et al. 337/244 2,794,096 4/1957 Kozocka 337/244 X FOREIGN PATENTS 1,167,427 4/1964 Germany 337/241 Primary Examiner-Hemard A. Gilheany Assistant ExaminerDewitt M. Morgan Attorneys-A. T. Stratton and C. L. McHale ABSTRACT: A fuse comprising an electrically insulating, generally tubular casing having a pair of terminal members mounted on the casing adjacent to the opposite ends of the PATENTEU AUB24 |97| SHEET 1 UF 2 FIGS.

INVENTOR Donald D. Blewitt ATTORNE Y INDICATING MEANS FOR FUSES BACKGROUND OF THE INVENTION In certain types of fuses, particularly those of the totally enclosed type, it is desirable or necessary to provide an externally visible means for indicating that the fuse has blown or operated to interrupt an abnormal or fault current. In certain applications, such an indicating means for a fuse may be required to perform an additional function, such as actuating the tripping of an associated circuit interrupter or circuit breaker. One general type of fuse construction includes an indicating means which employs a spring-biased member or plunger which is normally restrained from movement by one or more fusible elements or restraining wires disposed inside an associated casing, such as disclosed in U.S. Pats. Nos.

- 2,306,I53; 2,320,494; 2,417,268; 2,435,855; 3,134,874 and 3,179,774. It has been found that the indicating means of the various fuse constructions disclosed in the above patents have certain disadvantages in that the length of the spring is inherently limited by the available space in the overall construction of the indicating means or that the required. size or diameter of the associated restraining wire is greater than that which is desirable to insure proper operation of the indicating means. Other disadvantages of such known indicating means relate to the criticality which is required in the assembly of the parts of the indicating means when the plunger is disposed in its normally retracted operating position. It is therefore desirable to provide an improve indicating means for fuses which overcomes the disadvantages indicated above and which provides other advantages as well.

SUMMARY OF THE INVENTION sociated casing and which extends from the outer end of the terminal member axially inwardly beyond the adjacent end of the associated casingand a relatively smaller opening which extends from the first opening to the inner end of the terminal member. In one embodiment of the invention, a generally tubular housing is partially disposed in the first opening of the terminal member and extends axially outwardly beyond the adjacent end of the associated casing with a plunger normally disposed in said housing with the inner end of the plunger disposed adjacent to the inner end of the first opening in the associated terminal member. In order to bias the plunger outwardly from the housing, a coil spring is disposed in the housing and a restraining wire is connected between the plunger and the other terminal member of the fuse to normally restrain the plunger from outward movement under the influence of the biasing spring. The restraining wire passes through the second opening in the associated terminal member and extends diagonally from the second opening in the terminal member on one side of the longitudinal axis of the associated casing to the other terminal member of the fuse at a location on the other side of said longitudinal axis.

In another embodiment of the invention, the plunger of the indicating means is disposed directly in the first opening in the associated terminal member without a separate housing and one end of the associated biasing spring is secured to the plunger adjacent to the outer end of the plunger. The other end of the biasing spring is enlarged and retained in a recess provided in the associated terminal member adjacent to the inner end of the first opening provided in the terminal member. In this embodiment, the inn'er end of the plunger normally bears against the associated terminal member at the inner end of the first opening of the terminal member and,

where desired, the plunger includes an enlarged portion at the outer end-which also normally bears against the associated ter- BRIEF DESCRIPTION OF THE DRAWINGS Further objects of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a view, partly in side elevation and partly in section, of a fuse structure embodying the invention;

FIG. 2 is a view in end elevation of the fuse structure shown in FIG. 1, taken along the line II-II;

FIG. 3 is an end elevational view of the fuse structure shown in FIG. 1, taken along the line III-III;

FIG. 4 is an enlarged sectional view of an indicating means which forms part of the fuse structure shown in FIG. 1;

FIG. 5 is a plan view of the indicating means shown in FIG. 4, taken along the line V-V;

FIG. 6 is an enlarged view of a portion of the indicating means shown in FIG. 4, illustrating the manner in which a restraining wire is secured to an associated plunger which forms part of the indicating means shown in FIG. 4;

FIG. 7 is an enlarged view of a portion of a fuse structure, more specifically an indicating means which forms part of the fuse structure, illustrating a second embodiment of the invention;

FIG. 8 is an enlarged view of an indicating means which forms part of a fuse structure illustrating a third embodiment of the invention;

FIG. 9 is an enlarged view of an indicating means which forms part of a fuse structure illustrating a fourth embodiment of the invention;

FIG. 10 is an enlarged view of an indicating means which forms part of a fuse structure similar to tat shown in FIG. 1, illustrating a fifth embodiment of the invention; and

FIG. 11 is a graphical representation of certain operating characteristics of the indicating means which form part of the various disclosed fuse constructions;

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and FIG. 1 in particular, there is shown a fuse structure 20 which is of the current limiting type as illustrated. The fuse structure 20 includes a generally tubular, electrically insulating casing or fuse holder 30 which is formed from an electrically insulating material having sufficient structural strength to withstand the gas pressures and thermal conditions which may result during the operation of the fuse structure 20, such as a glass-reinforced melamine material. The fuse 20 also includes a pair of end members or terminal members T1 and T2 which are disposed adjacent to the opposite ends of the casing 30 to close off the ends of the casing 30 and to extend axially inwardly from the respective ends of the casing 30. The terminal members T1 and T2 are firmly secured to the ends of the casing 30 by suitable means, such as a bonding material which cements the end terminals T1 and T2 to the casing 30 and by a plurality of circumferentially spaced screws or spring pins 37 which pass through aligned openings provided in the casing 30 and the respective terminal members TI and T2. The terminal members T1 and T2 are formed from an electrically conducting material, such as copper, which may be silver plated over the outer surface thereof and, as illustrated, may have mounted thereon or formed integrally therewith the

contact blades

21 and 22, respectively, to facilitate the mounting of the fuse 20 in certain types of mounting arrangements.

In order to normally provide an electrically conducting path between the terminal members T1 and T2, one or more fusible elements or links 32 is disposed to extend axially between and to electrically and structurally connect the terminal members T1 and T2, as shown in FIGS. 1 through 3. As illustrated, each of the terminal members T1 and T2 may include a plurality of concentric, radially spaced groups of angularly spaced recesses or slots which are adapted to receive the ends of the associated fusible elements 32. The ends of each of the fusible elements 32 may be assembled into the recesses or slots provided in the associated terminal members T1 and T2 and secured thereto by suitable means, such as brazing or solder- 1ng.

As illustrated, each of the fusible elements 32 is ribbonlike in shape andis composed of a suitable fusible, electrically conducting material, such as silver. Each of the fusible elements 32 includes a plurality of axially spaced points of reduced cross-sectional area which may be formed by V-notching the ribbon material from which each of the fusible elements 32 is formed on both sides at spaced points along its length. This construction of each fusible element 32 results in a series of restricted areas or neck portions which fuse during an interrupting operation of the fuse 20 to provide a series of spaced arcs, the sum of the voltages across said arcs resulting in a relatively high total are voltage which is particularly desirable in a current limiting type of fuse. In order to increase the ability of each of the fusible elements 32 to withstand the stresses which may result during long periods of operation of the fuse 20, each of the fusible elements 32 may be generally bowed or follow an arcuate path between the points on the associated terminal members T1 and T2 at which the ends of each of the fusible elements 32 are secured.

In order to assist in arc extinction during an interrupting operation of the fuse 20, the balance of the space inside the casing 30 between the inner surfaces of the respective terminal members T1 and T2, may be substantially filled with a finely divided or pulverulent or granular, arc quenching material as indicated at 42, such as a high-purity silica sand as shown in FIG. 1. Other arc quenching fillers, such as calcium carbonate may be combined with silica sand in a particular application as described in detail in US. Pat. No. 3,213,242, which issued to F. L. Cameron on Oct. 19, 1965 and which is assigned to the same assignee as the present application. It is to be noted that after the terminal members T1 and 12, along with the fusible members 32, are assembled with the casing 30 as shown in FIG. 1, the arc quenching tiller 42 may be introduced into the space inside, the casing 30 through the opening provided in the terminal member T2 which is subsequently closed off by a threaded plug member 46, as shown in FIG. 1.

In order to provide an indication of the operation of the fuse 20 which is visible externally of the fuse 20 and to perform additional functions where required. in particular applications, the indicating means 50 is disposed or mounted on the terminal member T1 at a location which is generally offset or spaced from the longitudinal axis of the casing 30. In order to receive the indicating or actuating means 50, the terminal member Tl includes a first opening 43 which is offset or spaced from the longitudinal axis of the casing 30 and which extends from the outer end of the terminal Tl axially inwardly beyond the adjacent end of the casing 30 and a relatively smaller opening 47 which extends from the first opening 43 to the inner end or surface of the terminal member Tl.

More specifically, as best shown in FIGS. 1 and 4, the indicating means 50 comprises a generally tubular housing 46 which may be formed from any suitable material, such as brass. The housing '56 is partially disposed in the first opening 43 of the terminal member T1 and may include an externally threaded portion 56A which engages a threaded portion of the terminal member Tl around the opening 43. It is to be noted that the inner or lower end of the housing 56, as viewed in FIG. 4, is disposed adjacent to and spaced from the inner end of the opening 43 in the terminal member T1. It is also to be noted that the outer portion of the housing 56 projects axially beyond the outer end of the terminal member T1 and the adjacent end of the casing 30, as best shown in FIG. 1.

The indicating means 50 also includes a generally cylindrical indicating or actuating plunger 52 which is normally disposed in the inner bore of the housing 56 as shown in FIG. 4, with the inner end of the plunger 52 being normally disposed adjacent to the inner endof the opening 43 in the terminal member Tl. Theupper end of the plunger 52, as viewed in FIG. 4, may be tapered as indicated at 52C and the plunger 52 may include a circumferentially extending recess, as indicated at 528, adjacent to the outer end of the plunger 52. The plunger 52 may also include at its axially inner end an axially extending hole or opening, as indicated at 52A, for a purpose which will be explained hereinafter.

In order to bias the plunger 52 outwardly from the housing 56, a helically coiled compression spring 54 is disposed in the housing 56 with most 'of the turns of the spring 54 being disposed between the plunger 52 and the inner bore of the housing 56. As illustrated, the spring 54 includes a plurality of turns, with the upper or outer end turn 54B of the spring 54 being relatively smaller than the intermediate turns of the spring 54 and being disposed or retained in the recess 52B of the plunger 52 to thereby secure the upper end of the spring- 54 to the plunger 52 adjacent to the outer end of the plunger 52. The other or inner end turn 54A of the spring 54 is relatively larger than the intermediate turns of the spring 54 and is disposed or retained between the lower 'or inner end of the housing 56 and the inner end of the opening 43 in the terminal member Tl. Where desired, a washer 58 which, as illustrated, is metallic may be disposed between the end turn 54A and the inner end of the opening 43 to serve as one of the spring seats for the spring 54.

It is to be noted that the upper or outer end of the housing 56 may include a pair of transverse aligned

slots

56B and 56C which are adapted to receive a tool to facilitate the assembly of the housing 56 within the opening 43 of the terminal member T1.

In order to normally restrain the outward movement of the plunger 52 under the influence of the biasing spring 54, an auxiliary fuse element or restraining wire 34 is electrically and structurally connected between the plunger '52 and its associated terminal member T1 and the other terminal member T2. The restraining wire 34 is formed from a fusible material, such as stainless steel, having a relatively high electrical resistance compared with the electrical resistance of the fusible elements 32. One end of the restraining wire 34 is looped back on itself, as indicated at 34A in FIG. 6, and assembled inside the hole or opening 52A at the lower or inner end of the plunger 52 as shown in FIG. 6. The lower end or inner end of the plunger 52 is then crimped or deformed with a suitable tool to secure one end of the restraining wire 34 to the plunger 52. The restraining wire 34 extends from the plunger 52 through the central opening in the washer 58 and the relatively smaller opening 47 in the terminal member T1 and engages or contacts the terminal member T1 as indicated at 45 in FIG. 4 as the restraining wire 34 passes out of the opening 47. The restraining wire 34 then extends diagonally from the opening 47 in the terminal member T1 to the second terminal member T2 at a location which is on the other side of the longitudinal axis of the casing 34 from that on which the opening 47 is located. The restraining wire 34 then passes through an opening 39 in the terminal member T2 which extends axially through the terminal member T2 and is only slightly larger than the size of the restraining wire 34. The restraining wire 34 then passes through or is disposed in the relatively shallow, radially extending groove 35 at the outer end of the terminal member T2 and is wrapped or twisted twice around an eyelet member 48. The eyelet member 48 is then driven into the outer surface of the terminal member T2 to secure the adjacent end of the restraining wire 34 to the terminal member T2. It is to be noted that the diagonal path followed by the restraining wire 34 increases the length of the restraining wire 34 which reduces the possibility of an arc current persisting along the restraining wire 34 during an operation of the fuse 20. It is also important to'note that since the restraining wire 34 engages the terminal member T1 at the inner edge or corner of the opening 47 as indicated at 45 in FIG. 4, any electrical current which flows in the restraining wire 34 transfers or flows from the restraining wire 34 to the terminal member T1 at the location indicated at 45 to completely or substantially eliminate the possibility of the restraining wire 34 melting or fusing in the housing 56 in which the spring 54 is disposed.

In the operation of the electrical current which is normally 20, it is to be noted that normally the restraining wire 34 carries a negligible amount of current due to the relatively high electrical resistance of the restraining wire 34 compared with that of the fusible elements 32. Upon the occurrence of a predetermined overload condition for a time period which varies with the magnitude of the overload current, the electrical current through the main fusible elements 32 will cause each of the fusible elements 32 to fuse or melt and the electrical current which is nonnally carried by the fusible elements 32 will then temporarily transfer to the restraining wire 34 which is electrically connected in parallel with the fusible elements 32 between the terminal members T1 and T2. The electrical current which is transferred to the restraining wire 34 will produce significant heating of the restraining wire 34 due to the relatively high electrical resistance of the restraining wire 34. The restraining wire 34 will then melt and vaporize and the electrical current which is momentarily carried by the restraining wire 34 will be returned to the main fusible elements 32 where the current will be finally interrupted by the generation of a plurality or series of arc voltages and the formation of a fulgurite as is well known in the art. During the time interval that the electrical current is carried by the restraining wire 34 during an interrupting operation of the fuse 20, the restraining wire 34 will melt to thereby release the plunger 52 which will then move outwardly from the normal position shown in FIG. 4 to the indicating position as indicated in phantom at 52"in FIG. 4 in which the plunger 52 extends axially beyond the outer end of the housing 56 to thereby indicate the operation of the fuse 20 or to actuate the operation of an associated circuit interrupter or circuit breaker where desired. When'the plunger 52 is released and actuated to the position indicated in phantom at 52' in FIG. 4, the spring 54 whose outer end turn 54B is secured to the plunger 52, limits the outward movement of the plunger 52 under the influence of the spring 54 and prevents the plunger 52 from being separated from the housing 56.

It is important to note that the indicating means construction just described is uniquely adapted to the use of a relatively longer coil spring 54 than would be possible in similar in- ,dicating means such as disclosed in the patents previously mentioned. Referring to FIG. 11, the advantages of a relatively longer biasing spring in indicating means 50 is illustrated graphically. For example, if the minimum forces required to be exerted on the plunger 52 at the corresponding travel points or distances are as indicated at 302 and 304, the minimum force requirements of the biasing spring will be indicated by the line 300 in FIG. 11. In other words, as long as the force exerted on the plunger by the associated spring is above the line 300 at any particular point in the travel of the plunger, the spring characteristic will be adequate for a particular application. Referring to the characteristic line for a relatively shorter spring as indicated at 100 in FIG. 11, if the minimum force provided by the characteristic line 100 were equal to that indicated by the line 300 at the point 304, the force exerted by such a relatively short spring on the plunger 52 and the associated restraining wire under static conditions as indicated at 102 would be relatively greater than the minimum force required, as indicated by the line 300 if extended. On the other hand, for a relatively longer spring, such as the spring 54 in the indicating means 50, the force characteristic would be that indicated by the characteristic line 200 in FIG. 11 and, if the minimum force provided by such a relatively longer spring were adequate at the point 302 on the characteristic line 300, the force provided by the relatively longer spring corresponding to the travel at the point 304 will be relatively greater than that required in a particular application. It is important to note that for a relatively longer spring as indicated by the characteristic line 200, the force exerted by this spring under static conditions as indicated at 202 would be relatively much less on the plunger 52 and the associated restraining wire 34 to therefore reduce the cross-sectional size or area of the restraining wire 34 which is required in a particular application. The use of a relatively smaller size or diameter restraining wire would substantially reduce the tendency of the restraining wire 34 to maintain the arc which results during the operation of the fuse 20 and which might otherwise prevent the transfer of the arc back to the main fusible elements 32 which would render the fuse 20 inoperative for the desired interrupting purpose.

Referring now to FIG. 7 there is illustrated a second embodiment of the invention. More specifically, a fuse structure is shown which is identical to the fuse structure 20 previously described except that an indicating means 150 is disposed on one of the terminal members Tl instead of the indicating means 50 previously described. In general, the indicating means 150 is similar to the indicating means 50 previously described except that the indicating means 150 does not require a separate housing and therefore the cross-sectional size or diameter of the biasing spring 154 included in the indicating means 150 may be relatively larger than is possible where a housing is disposed in the opening in the associated terminal member tl More specifically, the terminal member Tl includes a first opening 143 which is offset or spaced from the longitudinal axis of the associated casing and which extends from the outer end of the terminal member Tl axially inwardly beyond the adjacent end of the associated casing and a relatively smaller opening 147 which extends from the first opening 143 to the inner endor surface of the terminal member T1. The first opening 143 includes an enlarged portion or recess 143A at the inner end thereof. The indicating means 150 also includes a generally cylindrical plunger 152 which is partially disposed in the opening 143 of the terminal member T1 and which includes an enlarged portion 152A at its outer end. It is to be noted that the inner end of the plunger 152 normally bears against the terminal member T1 at the inner end of the opening 143 in the terminal member T1.

In order to bias the plunger 152 outwardly from the opening 143 and the terminal member Tl, a helically coiled compression spring 154 is disposed between the inner end of the opening 143 and the enlarged portion 152A of the plunger 152. The outer end turn of the spring 154 is indicated at 1548 is disposed in a circumferentially extending recess 152D provided adjacent to the outer end of the plunger 152 with the outer end turn 1548 being relatively smaller than the intermediate turns of the spring 154, as shown in FIG. 7. The inner end turn 154A of the spring 154 is enlarged and is retained or disposed in the recess 143A at the inner end of the terminal member T1. The inner portion 1528 of the plunger 152 also includes a hole or opening, as indicated at 152C, in which one end of the associated restraining wire 34 is secured by the method previously described. It is to be noted that the restraining wire 34 engages or contacts the terminal member Tl similarly to the manner in which the restraining wire 34 engages or contacts the terminal member T1 previously described at the inner edge of the opening 147 as indicated at in FIG. 7, to transfer any electrical current flowing in the restraining wire 34 to the terminal member T1 at that point or location. It is to be noted that the plunger 152 projects axially beyond the outer end of the terminal member T1 by a predetermined distance indicated at d1 in FIG. 7.

In the operation of a fuse structure which includes the indicating means 150, when the restraining wire 34 melts or fuses, the plunger 152 is released and moves outwardly from the position seen in FIG. 7 under the influence of the biasing or actuating spring 154 to thereby indicate the operation of the overall fuse structure or to actuate the tripping of an associated circuit interrupter or circuit breaker similarly to the operation of the fuse 20 previously described.

Referring now to FIG. BREE is shown a portion of a fuse an indicating means 250 rather than the indicating means 50 of the fuse structure 20. More specifically, the indicating means 250 is similar to the indicating means 150 just described except that the plunger 252 of the indicating means 250 includes an enlarged outer portion 252A which normally bears against the outer end of the associated terminal member T1" around the opening 243 in which the plunger 252 is partially disposed. Similarly to the terminal T1, the terminal Tl" includes a first opening 243 which is offset or spaced from the longitudinal axis of the associated casing and which extends from the outer end of the terminal member T1" axially inwardly beyond the adjacent end of the associated casing and a relatively smaller opening 247 which extends from the first opening 243 to the inner end or surface of the terminal member T1 Similarly, to the indicating means 150, the indicating means 250 includes a helically coiled spring 254 which is disposed in the opening 243 to bias the plunger 252 outwardly from the opening 243. The spring 254 includes a relatively smaller outer end turn 2543 which is disposed and retained in a circumferentially extending recess 252D in the plunger 252 and a relatively larger inner end turn 254A which is disposed and retained in a recess 243A which is provided in the terminal member T1 at the inner end of the opening 243.

The indicating means 250 also includes a restraining wire 134 which has one end disposed in a hole or opening 252C at the inner end of the inner portion 2528 of the plunger 252 and is secured thereto in similar fashion to the indicating wire 34 in the indicating means 50 and 150 previously described. The restraining wire 134 engages or contacts the terminal member T1" at the inner edge 245 of the terminal member T1 around the opening 247 as shown in FIG. 8.

The operation of the indicating means 250 is substantially the same as the operation of the indicating means 50 and 150 previously described. In particular, when the restraining wire 134 melts or fuses, the plunger 252 is released and moves outwardly under the influence of the biasing spring 254 with the outward movement of the plunger 252 being limited by the spring 254 which is secured to the plunger 252 adjacent to the outer end thereof as just described. It is to be noted that the plunger 252 normally projects out of the opening 243 in the terminal member Tl" by a predetermined distance, as indicated at d2 in FIG. 8. It is also to be noted that the enlarged outer portion 252A of the plunger 252 normally closes off the outer end of the opening 243 to thereby prevent the entrance of moisture or other contaminants into the opening 243 which might otherwise effect the life or characteristics of the spring 254.

Referring now to FIG. 9, there is shown a portion of a fuse structure illustrating a fourth embodiment of the invention. In general, the portionof the fuse structure as shown in FIG. 9 is identical to the fuse structure 20 previously described except that the portion of the fuse structure shown in FIG. 9 includes an indicating means 350 rather than the indicating means 50 of the fuse structure 20 previously described. More specifically, the indicating means 350 includes a generally tubular housing 356 which is partially disposed in a first opening 343 in the associated terminal member T31. Similarly to the terminal member T1 previously described, the terminal member T31 includes a first opening 343 which is offset or spaced from the longitudinal axis of the associated casing and which extends from the outer end of the terminal member T31 axially inwardly beyond the adjacent end of the associated casing and a relatively smaller opening 347 which extends from the first opening 343 to the inner end or surface of the terminal member T31. The housing 356 projects axially beyond the outer end of the terminal member T31 by a predetermined distance, as indicated at d3. The housing 356 also includes at its outer end a transverse portion 356A having a central opening 356B which is relatively smaller than the opening or inner bore in the balance of the housing 356.

v The indicating means 350 also includes a generally cylindrical plunger 352 which is normally disposed in the housing 356. The plunger 352 includes a relatively smaller outer portion 3528 which is adapted to pass through the opening 3568 at the outer end of the housing 356 and a portion 352C having a relatively larger cross-sectional area at the inner end of the plunger 352 with the inner end of the plunger 352 normally bearing against the associated terminal member T31 at the inner end of the opening 343 as shown in FIG. 9. The plunger 352 also includes a shoulder or flange portion 352A intermediate the axial ends of the plunger 352.

In order to bias the plunger 352 outwardly from the housing 356, the helically coiled compression spring 354 is disposed inside the housing 356 with the inner end of the spring 354 bearing against the inner end of the opening 343 in the terminal member T31 and the outer end of the spring 354 bearing against the shoulder portion 352A of the plunger 352. Similarly to the indicating means 50, and 250 previously described, the plunger 352 is normally restrained from out ward movement under the influence of the spring 354 by a restraining wire 34 which is secured at one end in a hole or opening 352D in the plunger 352 in the same manner as the restraining wire 34 in the fuse structures previously described. The restraining wire 34 similarly engages or contacts the terminal member T31 at the inner edge around the opening 347 in the terminal member T31 at the inner edge around the opening 347 in the terminal member T31 as indicated at 345 in FIG. 9. It is to be noted that the housing 356 may be secured to the terminal member T31 by a suitable bonding material, such as a thennosetting resin, which may be applied around the portion of the housing 356 which is disposed in the opening 343 or the housing 356 may include an internally threaded portion similarly to the housing 56 of the indicating means 50 previously described.

The operation of the indicating means 350 is similar to that of the indicating means previously described. In general, when the restraining wire 34 melts or fuses to thereby releasethe plunger 352 under the influence of the biasing spring 354, the plunger 352 will move axially outwardly until the shoulder portion 352A of the plunger 352 engages or bears against the transverse portion 356A of the housing '356 which limits the outward movement of the plunger 352 under the influenceof the spring 354. It should be noted that the inner portion 352C of the plunger 352 functions as a spring guide during the operation of the indicating means 350. It is also important to note that the retracted position of the plunger 352 as shown in FIG. 9 is readily determined when the inner end of the plunger 352 bears against the terminal member T31 at the inner end of the opening 343.

Referring now to FIG. 10, there is shown a portion of a fuse structure illustrating a fifth embodiment of the invention. The portion of the fuse structure which is shown in FIG. 10 is identical to the fuse structure 20 previously described in detail except that the portion of the fuse structure shown in FIG. 10 includes an indicating means 450 rather than the indicating 'means 50 of the fuse structure 20. Similarly to the terminal members previously described, the terminal member T41 of the portion of the fuse structure shown in FIG. 10 includes a first opening 443 which is offset or spaced from the longitudinal axis of the associated casing and which extends from the outer end of the terminal member T41 axially inwardly beyond the adjacent end of the associated casing and a relatively smaller opening 447 which extends from the first opening 443 to the inner end of the terminal member T41. A generally tubular housing 456 is partially disposed in the opening 443 and maybe secured thereto by a suitable bonding material, such as a thermosetting resin, or may be externally threaded similarly to the housing 56 previously described. The housing 456 projects axially beyond the outer end of the terminal member T41 by a predetermined distance, as indicated at d4 in FIG. 10. The housing 456 includes at its outer end a transverse or flange portion 456A having a central opening as indicated at 456B. The housing 456 may be formed from the same material as indicated for the housing 56 previously described.

The indicating means 450 also includes a generally tubular or cup-shaped plunger 452 which-is normally disposed in the housing 456. As shown in FIG. 10, the outer end of the plunger 452 is closed off by a transverse portion as indicated at 452B. It is to be noted that the outer portion of the plunger 452 is adapted to pass through or move axially through the central opening 4568 of the associated housing 456. In order to limit the outward movement of the plunger 452 under the influence of a helically coiled compression spring 454 which is disposed inside the inner bore of the plunger 452, the plunger 452 includes a flange portion or shoulder portion 452A which is adapted to bear against the flange portion 456A of the housing 456 during the operation of the indicating means 450. The plunger 452 may beformed from any suitable material, such as brass.

In order to normally restrain the outward movement of the plunger 452, under the influence of the biasing spring 454, the restraining wire 34 is connected at one end to the plunger 452. More specifically, one end of the restraining wire 34 as shown in FIG. 10 may be secured to the outer transverse portion 4528 of the plunger 452 by suitable means, such as brazing or soldering. It is to be noted that the restraining wire 34 engages or contacts the terminal member T41 at the inner edge 445 of the opening 447 in the terminal member T41 to thereby transfer any electrical current flowing in the restraining wire 34 to the terminal member T41 without the current flowing in the portion of the restraining wire which is disposed in the housing 456.

The operation of the indicating means 450 is similar to that of the indicating means previously described. In general, when the restraining wire .34 melts or fuses, to thereby release the plunger 452, the plunger 452 moves axially outwardly until the shoulder portion 452A of the plunger 452 engages the flange portion 4568 of the housing 456. It is important to note that in the operation of the indicating means 450, the construction of the indicating means 450 indicating means 450 permits the use of a relatively long biasing spring 454 compared with known indicating means for fuses and that such a relatively long biasing spring provides the operating advantages previously discussed in connection with the fuse structure of FIG. I, which includes the indicating means 50, and the graphical representation of FIG. 11.

It is to be understood that in certain applications the manner in which the restraining wire. 34 is secured to the associated plunger in certain embodiments of the invention is disclosed may be other than the particular construction disclosed, such as by brazing one end of the restraining wire 34 to the associated plunger member. It is also to be understood that in certain applications, the other end of the restraining wire away from the associated plunger in certain embodiments of the invention as disclosed may be secured to the associated terminal member by means other than the eyelet device as disclosed, while retaining the balance of the teachings of the applicants invention.

The various fuse structures embodying the teachings of the invention have several advantages. For example, the manner in which one end of the restraining wire in each of the disclosed embodiments of the invention engages or contacts the associated terminal member on which the associated indicating means is disposed substantially eliminates the possibility of the restraining wire melting within the opening or housing in which the associated plunger moves which might otherwise cause a malfunction of the overall fuse structure. Another advantage of the applicants invention is that at least several of the different embodiments disclosed lend themselves to use of a biasing spring having a relatively long axial dimension and in some cases having a relatively large cross-sectional area to thereby provide the advantages of a relatively smaller size restraining wire or to provide a more reliable force which is applied to the associated plunger during the travel of the plunger. In addition, the manner in which the restraining wire passes through a shallow groove in one terminal member and is secured thereto by an eyelet avoids damage to an overstressing of the restraining wire and the manner in which the restraining wire is secured to the associated plunger in the different embodiments of the invention increases the reliability of the electrical and mechanical connection of the restraining wire to the associated plunger. The diagonal disposition of the restraining wire within the overall casing of the fuse structure also substantially prevents the melting of the restraining wire within the opening or housing of the associated indicating means. A further advantage of the applicant's invention is that in at least several embodiments the retracted position of the plunger which forms part of the indicating means is more conveniently established by the plunger bearing against certain portions of the associated terminal member to thereby eliminate the criticality of the assembly of the parts which form the different indicating means. A final advantage of the applicants invention is that, in a fuse structure as disclosed in the different embodiments of the invention, the likelihood of an arc current persisting or hanging on the restraining wire in the different embodiments is substantially reduced or eliminated by the construction of the overall fuse and the indicating means which forms part of the fuse It is also to be noted in certain embodiments, the outward movement of the plunger which forms part of the indicating means is limited during the operation of the indicating means by the construction of the indicating means without the use of a retaining housing to thereby permit a biasing spring having a relatively larger cross-sectional size.

Since numerous changes may be made in the above described fuse structures and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. I claim as my invention:

1. A fuse comprising a generally tubular, electrically insulating casing, a pair of terminal members disposed adjacent to the opposite ends of said casing, one or more fusible elements disposed in the casing and connected between said terminal members, one of the terminal members including a first opening which is spaced from the longitudinal axis of said casing and which extends from the outer end thereof axially inwardly beyond the adjacent end of said casing and a relatively smaller opening which extends from the first opening to the inner end of the terminal member, a generally tubular housing partially disposed in said first opening and extending axially outwardly beyond the adjacent end of said casing, a generally cylindrical plunger normally disposed in said housing with one end disposed adjacent to the inner end of the first opening in said terminal member, a coil spring having a plurality of turns disposed in the housing for biasing said plunger outwardly from the housing, and a restraining wire connected between said plunger and the other of said terminal members for normally retaining the plunger within said housing against the influence of said spring, said restraining wire passing through said second opening and extending diagonally from said second opening on one side of the longitudinal axis of said casing to the other of said terminal members at a location on the other side of said axis.

2. The combination as claimed in claim 1 wherein one end of said coil spring is secured to the plunger adjacent to the outer end thereof and the other end of said spring is retained between said housing and said terminal member.

3. The combination as'claimed in claim 1 wherein said one end of said plunger includes an opening into which one end of said restraining wire is assembled and looped back on itself, said one end of said plunger being crimped to secure said one end of said restraining wire to said plunger.

4'. The combination as claimed in claimed I wherein said plunger is generally cup-shaped with an outwardly projecting flange portion at its inner end and said housing includes an inwardly projecting flange portion at its outer end, said spring being disposed inside said plunger.

5. The combination as claimed in claim 1 wherein said housing includes a transverse portion at its outer end having a relatively smaller opening therein than the opening in the balance of said housing and said plunger includes an outer portion adapted to pass through said smaller opening and an intermediate shoulder portion disposed to engage said transverse portion of said housing when said restraining wire ruptures to thereby release said plunger to move under the influence of said spring.

6. The combination as claimed in claim 5 wherein said plunger is normally disposed in said housing with the inner end of said plunger bearing against said one of the terminal members at the inner end of said first opening.

7. A fuse comprising a generally tubular electrically insulating casing, a pair of terminal members disposed adjacent to the opposite ends of said casing, one or more fusible elements disposed in the casing and connected between said terminal members, one of the terminal members including a first opening which extends from the outer end thereof axially inwardly beyond the adjacent end of said casing and a relatively smaller second opening which extends from the first opening to the inner end of said one of the terminal members, a generally cylindrical plunger having a first portion normally disposed in said first opening with one end of said first portion normally bearing against said one of the terminal members at the inner end of said first opening and a second portion which normally projects out of said first opening a predetermined distance axially beyond the end of the adjacent terminal member, a coil spring normally disposed at least partially in said first opening and disposed to bias said plunger outwardly from said first opening, one end of said. spring being secured to the plunger adjacent to the outer end of said first portion and the other end of said spring beingenlarged and retained in a recess in the adjacent terminal member adjacent to the inner end of said first opening, and a restraining wire connected between said plunger and the other of said terminal members for normally retaining said one end of the first portion of said plunger against said one of the terminal members against the influence of said spring.

8. The combination as claimed in claim 7 wherein said second portion of said plunger is enlarged normally bears against the outer end of said one of the terminal members.

9. The combination as claimed in claim 7 wherein said first opening in said one of the terminal members is spaced from the longitudinal axis of said casing and with said restraining wire passing through said second opening and extending diagonally from said second opening on one side of the longitudinal axis of said casing to the other of said terminal members at a location onthe other side of axis. 7

10. The combination as claimed in claim 7 wherein said one end of said plunger includes an opening into which one end of said restraining wire is assembled and looped back on itself,

said one end of said plunger being crimped to secure said one end of said restraining wire to said plunger. 7

11. The combination as claimed in claim 8 wherein said first opening in said one of the terminal members is spaced from the longitudinal axis of said casing and with said restraining wire passing through said second opening and extending diagonally from said second opening on one side of the iongitudinal axis of said casing to the other of said terminal members at a location on the other side of said axis.

12. The combination as claimed in claim 8 wherein said one end of said plunger includes an opening into which one end of said restraining wire is assembled and looped 'back' on itself, said one end of said' plunger being crimped to secure said one end of said restraining wire to said plunger.

Claims

3. The combination as claimed in claim 1 wherein said one end of said plunger includes an opening into which one end of said restraining wire is assembled and looped back on itself, said one end of said plunger being crimped to secure said onE end of said restraining wire to said plunger.

4. The combination as claimed in claimed 1 wherein said plunger is generally cup-shaped with an outwardly projecting flange portion at its inner end and said housing includes an inwardly projecting flange portion at its outer end, said spring being disposed inside said plunger.

7. A fuse comprising a generally tubular electrically insulating casing, a pair of terminal members disposed adjacent to the opposite ends of said casing, one or more fusible elements disposed in the casing and connected between said terminal members, one of the terminal members including a first opening which extends from the outer end thereof axially inwardly beyond the adjacent end of said casing and a relatively smaller second opening which extends from the first opening to the inner end of said one of the terminal members, a generally cylindrical plunger having a first portion normally disposed in said first opening with one end of said first portion normally bearing against said one of the terminal members at the inner end of said first opening and a second portion which normally projects out of said first opening a predetermined distance axially beyond the end of the adjacent terminal member, a coil spring normally disposed at least partially in said first opening and disposed to bias said plunger outwardly from said first opening, one end of said spring being secured to the plunger adjacent to the outer end of said first portion and the other end of said spring being enlarged and retained in a recess in the adjacent terminal member adjacent to the inner end of said first opening, and a restraining wire connected between said plunger and the other of said terminal members for normally retaining said one end of the first portion of said plunger against said one of the terminal members against the influence of said spring.

9. The combination as claimed in claim 7 wherein said first opening in said one of the terminal members is spaced from the longitudinal axis of said casing and with said restraining wire passing through said second opening and extending diagonally from said second opening on one side of the longitudinal axis of said casing to the other of said terminal members at a location on the other side of said axis.

10. The combination as claimed in claim 7 wherein said one end of said plunger includes an opening into which one end of said restraining wire is assembled and looped back on itself, said one end of said plunger being crimped to secure said one end of said restraining wire to said plunger.

11. The combination as claimed in claim 8 wherein said first opening in said one of the terminal members is spaced from the longitudinal axis of said casing and with said restraining wire passing through said second opening and extending diagonally from said second opening on one side of the longitudinal axis of said casing to the other of said terminal members at a location on the other side of said axis.

12. The combination as claimed in claim 8 wherein said one end of said plunger includes an opening into which one end of said restraining wire is aSsembled and looped back on itself, said one end of said plunger being crimped to secure said one end of said restraining wire to said plunger.