US2797279A

US2797279A - Electric fuse and method of constructing same

Info

Publication number: US2797279A
Application number: US571767A
Authority: US
Inventors: William E Brandt; William C Davis
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1956-03-15
Filing date: 1956-03-15
Publication date: 1957-06-25
Anticipated expiration: 1974-06-25

Description

June 25, 1957 W. E. BRANDT ETAL' ELECTRIC FUSE AND METHOD OF CONSTRUCTING SAME Filed March 15, 1956 Fig.2

Ihventors:

Williain C. Davis, William E. Brandt,

Unite States ELECTRIC FUSE AND METHOD OF CONSTRUCTEN G SAME Application March 15, 1956, Serial No. 571,767

8 Claims. (Cl. 20tl121) This invention relates to electric fuses and, more particularly, to improved indicating means for providing a visual indication of the operative condition of such fuses. The invention is also concerned with a method for constructing such indicating-type fuses.

The invention is especially applicable to the type of fuse indicator which comprises an indicator element that is spring-biased toward an indicating position but is held in a retracted non-indicating position by means of a fu sible current-sensitive conductor. In such indicators, the conductor is intended to fuse upon fuse operation, thus releasing the indicator and permitting its biasing spring to move it into an extended indicatingposition.

Heretofore, indicators of this type which have been acceptable from a cost viewpoint have not been entirely reliable and accurate in operation, and efforts to correct such deficiencies have unduly increased the cost and complexity of the overall fuse.

Accordingly, it is an object of our invention to provide a simple and inexpensive fuse indicator which is reliable and accurate in operation.

Another object is to provide a fuse indicator which can be quickly constructed as a self-contained sub-assembly of a type lending itself to convenient incorporation into the overall fuse.

Another object is to construct an indicating-type fuse by a method which requires a minimum of timeconsuming operations such as soldering and threading of the indicating conductor through small openings.

In carrying out our invention in one form, we indicate the operative condition of the fuse by means of an indicator sub-assembly which comprises a partition located in the fuse at one terminal thereof and a movable indicahle element slidably mounted adjacent the partition. The indicator element includes a projecting hook portion about which we loop a fusible current-sensitive conductor which normally restrains the indicator element in a retracted position against the action of suitable biasing means. The current-sensitive conductor extends from one terminal of the fuse to the other through a pair of spacedapart apertures formed in the partition and is anchored to the partition by pegs tightly fitted in said apertures. When that section of the conductor which is located between the pegs fuses in response to fuse operation, the indicator element is released and is driven by the biasing means into an extended indicating position.

Correct fusion of the indicator conductor is assured by constructing the conductor of multiple parallel segments throughout its length except in the section which extends between the anchoring pegs. This section is of a single segment construction, which because of its lower heat dissipating ability, fuses prior to the multiple segment portions. The individual segments of the multiple-- segment portions are conductively interconnected by the anchoring pegs, thus eliminating the need for soldering these segments together.

While the specification concludes with claims particuatent Patented June 25, 157

larly pointing out and distinctly claiming the subject matter which we regard as our invention, it is believed the invention will be better understood from the following description taken in connection with the accompanying drawing in which:

Fig. l is a cross-sectional view of an indicator subassembly constructed in accordance with our invention;

Fig. 2 is a cross-sectional view of a fuse constructed in accordance with our invention and including the indicator sub-assembly of Fig. 1;

Fig. 3 is an exploded view illustrating a method of constructing the sub-assembly of Fig. 1 in accordance with our invention; and

Fig. 4 is a cross-sectional view of a modified form of fuse and indicator.

Referring now to Fig. 1, the indicator sub-assembly shown therein comprises an indicator element 12, of insulating material, a cup-shaped housing 14 also of insulating material for slidably receiving the indicator element, and a compression spring 16 disposed between the housing 14 and the indicator element 12. The indicator element is shown in its retracted, or non-indicating position, where it is normally held by means of an indicator conductor in the form of a flexible wire 18 which is anchored to the housing 14 in a manner soon to be described.

As shown in Fig. 1, the indicator conductor comprises a pair of double-

segment portions

19 and 26 in the form of loops located at opposite ends of the conductor and a single-segment intermediate portion 22 interconnecting the double-segment portions. The double-segment portions 19 and Zti extend through a pair of tapered spacedapart apertures in the housing 14 and are anchored in the apertures by means of a pair of tapered pegs 24 tightly fitted therein. The pegs 24 are preferably of a conductive material so as to insure good electrical connection between the individual segments of each doublesegment portion for reasons which will soon become apparent. The single-segment intermediate portion 22 is looped about an inwardly projecting hook 23 which is shown formed integral with the indicator element 12. This single-segment portion 22 is of such a length that when the double-

segment portions

19 and 20 are anchored as shown in Fig. 1, the indicator element 12 is restrained in a seated position against or near the end wall of housing 14.

The sub-assembly of Fig. 1 also comprises a fuse cap 26 which is provided with a central opening surrounded by a short inwardly-projecting annular lip 28. The housing 14 is secured to this fuse cap 26 by means of a tight fit provided between the cup-shaped housing 14 and the annular lip 28. A leak proof joint between these two parts is insured, preferably, by means of cement applied as shown at 29.

The lip 28 serves not only as a means for locating and securing the housing 14 with respect to the cap 26 but also as a motion-limiting stop for the indicator element 12 and additionally as a guide which insures against jamming of the indicator element. For example, when the singlesegment portion 22 fuses, in a manner soon to be described, the indicator element is driven by the spring 16 from its solid-line retracted position into its dotted-line extended, or indicating, position, where further motion is prevented by engagement of the lip 23 with an annular flange 30 formed on the indicator element. During this movement, the indicator element 12 is guided at its forward end by the inner periphery of the lip 23 and at its rear end by the sliding fit between the flange 30 and the cup-shaped housing 14. Guiding the indicator element at these widely spaced points effectively insures against cocking and resultant jamming of the indicator element. The fact that the lip 28 serves as a locating means for the cup-shaped housing 14 insures that the internal guiding surfaces on the housing 14 and the lip 28 are essentially coaxial, thus further contributing to the effectiveness of the guiding action.

In Fig. 2 the indicator assembly is shown incorporated into a fuse 32 of the multiple-link current-limiting type. This fuse 32 comprises a cylindrical insulating casing 34 provided with a pair of spaced-apart conductive terminals 36 and 37 fixed to opposite ends of the casing. These terminals 36 and 37 are conductively interconnected by a plurality of tightly-strung fusible links 38 which are located and supported near their ends by suitable conductive spacers t0. In the illustrated fuse, thesespacers 40 are of annular form and are held against theends of the casing 34 by internal shoulders formed on the terminals 36 and 37. The opposite ends of each fuse link are turned radially outward over the outer peripheral surface of the terminals where they are mechanically-fas tened by crimping the end caps 26 over suitable radiallyextending lips 41 provided on the terminals.

The indicator asembly of Fig. 1 is incorporated intothe fuse of Fig. 2 by a simple process which involves fastening the loops 19 and20 of the indicator wire to the terminals 36 and 37 by the same crimping operation which fastens the end caps 26 and links 38 to the terminals. Thereafter, the protruding ends of

theloops

19 and 20 as well as those of the links 38 are trimmed to provide a neat appearing construction.

The illustrated fuse is filled with a body 43 of pulveru- I lent arc-extinguishing material, such as quartz sand, which isintroduced into the casing 34, preferably, after the end cap of terminal 37 is attached and before attachment of the other end cap. The housing 14 acts as a partition which confines the filler material 43 to the main interrupting chamber of the fuse and excludes it from the indicator chamber. When the links 38 fuse in response to overcurrent of a predetermined character flowing between the terminals 36 and 37, the filler 43 acts, in va wellknown manner, to quickly extinguish the resultant .arcs.

As willbe evident from Figs. 1 and 2, the indicator wire 18 is connected in parallel circuit relationship with the main fuse links 38. Since the indicator wire is preferably of a high resistance material and since it is of a very small cross'section compared to that of links 38, it will carry only a very slight amount of current during normal fuse operation. So long as the links 38 remain intact, this slight current will be insufficient to melt the indicator Wire. However, when the main links 38 fuse, say in response to an overcurrent condtion, all of the circuit current is forced to flow throu h the indicator wire.18, which responds by quickly melting at its single segment portion 22. As previously described, this releases .the indicator element 12 and permits the spring 16 to quickly force it into its extended or indicating position, thus providing a visual indication that the fuse has .operated.

Successful operation of the indicator is assured only if that section of the indicator wire 18 inside the housing 14 fuses in response to fusion of the main link 38 since. it is this particular section of the indicator wire which restrains the indicator element in its retracted position. In the disclosed indicator, fusion of this particular section of the indicator Wire is assured by virtue of the fact that this section includes the single-segment portion 22 of the wire whereas the remainder of the wire is of a multiple-parallel-segment construction. Thus, less current is required to fuse the section within the housing 14 than is required for the remainder of the indicator wire. As a result, the section in the housing 14 fuses first and the remainder of the indicator wire, which is embedded in the filler material 43, fuses later to effect interruption of the follow current.

To prevent the indicator spring 16 from contacting the indicator wire 18 in such a manner as to short out the important single-element portion 22, we have located one of the plug-receiving apertures substantially coaxial with the generally cylindrical spring 16. This insures that at least the centrally-disposed length of the single-segment portion 22 will be out of contact with the spring 16, thus insuring that at least this length will be subjected to melting current upon fuse operation.

The indicator sub-assembly lends itself most advantageously to a high-speed, inexpensive assembly process. As one step of this process, the double-segment portions 19 and of the indicator wire are formed by tieing the extreme ends of the wire to the body of the wire at spaced points on the wire. This yields a pair of spaced loops respectively forming the double-

segment portions

19 and 20 and also the intermediate single- 1 element portion 22. As will be apparent from Fig. 3,

the resultant wire is then threaded through one of the openings in the housing 14 and the double-segment portion, or loop, 20 is anchored in the opening by pressing one of the tapered pegs 24 into place within this opening. The other loop 19 is then threaded through the other opening leaving a U-shaped portion of the wire inside the housing 14. This U-shaped portion of the wire is drawn through the center of spring 16 and is then snared about the book 23 of the indicator element. The relationship of the various components just prior to this snaring operation is illustrated in Fig. 3.

Tension is then applied to the free loop 19 to retract the indicator element against the force of spring 16 into a seated position against the end wall of housing 14. The loop 19 is then anchored in place within its opening by the other peg 24, thus holding the indicator element in seated position. Thereafter the housing 14 is pressed about the lip 28 and the cemented joint 29 is applied, thus completing the indicator sub-assembly.

It should be appreciated from the above description that the presence of hook portion 23 significantly contributes to the speed at which the assembly operation can be performed. All that is required to couple the indicator wire 18 to the indicator element 12 is to snare the wire about the hook. This obviates the need for the timeconsuming threading operations which have been required with prior constructions having one or more holes formed in the indicator element for receiving the wire.

It should also be appreciated from the above description that it is unnecessary to solder the individual segments of each loop together at the knots in order to provide for good electrical connection between the individual segments. This is the case because a highly elfective intersegment connection is provided for by the tapered conductive pegs 24. The tight fit between these tapered pegs and their corresponding tapered apertures assures that the segments will be forced into intimate electrical contact with the pegs over a substantial length. The fact that the pegs and apertures are tapered also insures that the indicator wire is securely anchored in the correct position and additionally insures that the indicator chamber is effectively sealed against the entry of filler material 43'through the apertures. This sealing action also effectively prevents any surrounding air from entering the main fuse chamber through the apertures, and is desirable in this respect because any moisture contained in such air could detrimentally alfect the arc-quenching ability of the filler material.

Fig. 4 shows a modified form of our indicator assembly as applied to a different type of fuse terminal structure from that shown in Fig. 2. Since the indicator assembly of Fig. 4 operates in essentially the same manner as that of Figs. '1 and 2, corresponding parts in the twofuses have been assigned like reference numerals. The terminal structure37 of Fig. 4 comprises a tubular extension 50 having an axially-extending opening 52 at its outer end. The indicator element 12 is slidably received in this opening and is restrained in its retracted position by an indicat or conductor 18 corresponding to that of Fig. 2. When the single segment portion 22 of the conductor 18 fuses in response to fuse operation, the spring 16 is free to drive the indicator element from its retracted position shown into an extended indicating position, in the same 7 general manner as described in connection with Fig. 2.

The indicator assembly of Fig. 4 differs from that of Fig. 2 primarily in the physical relationship which the housing 14 bears to the rest of the assembly. This housing 14 of Fig. 4 is tightly fitted into the tubular extension 50 and is provided at its inner end with an annular locating flange 54 that abuts against a disk portion of the terminal structure 37. The cylindrical portion of the housing 14 receives the spring 16 and effectively locates it in spaced-apart relationship to the tubular extension. Accordingly, this cylindrical housing portion effectively prevents the spring 16 from forming a possible shunt path around the important single-segment portion 22 of the indicator conductor. The indicator element 12 in its retracted position is located adjacent the housing 14 but does not extend into the housing, as in Fig. 2. The indicator conductor 18 is anchored to the housing 14 in the same manner as in Figs. 1 and 2 and is conductively connected in a similar manner at its ends to the fuse terminals.

The indicator assembly and the overall fuse of Fig. 4 are constructed and assembled by essentially the same manufacturing process as described in connection with the fuse of Figs. 1-3.

While we have shown and described a particular embodiment of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from our invention in its broader aspects and We, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

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

1. In an electric fuse, an insulating casing provided with a pair of spaced-apart electrically-conductive terminals, at least one main fuse link conductively interconnecting said terminals, an indicating assembly for indicating fusion of said main link comprising an insulating partition located at one fuse terminal and having a pair of spacedapart apertures therein, a movable indicator element slidably mounted adjacent said partition and having a projecting hook portion secured to said element, a fusible current-sensitive conductor looped about said hook portion and extending from one terminal of said fuse to the other terminal through said apertures in the partition, sealing pegs tightly fitted in said apertures for anchoring said conductor to said partition to normally restrain said indicator element in a retracted position, and biasing means for driving said indicator element into an extended indicating position upon fusion of said conductor in response to fusion of said main link.

2. In an electric fuse, an insulating casing provided with a pair of spaced-apart electrically-conductive terminals, at least one main fuse link conductively interconnecting said terminals, an indicator assembly for indicating fusion of said main link comprising an insulating partition located at one fuse terminal and having a pair of spaced-apart apertures therein, a movable indicator element slidably mounted adjacent said partition, currentsensitive means for normally restraining said element in a retracted position comprising a fusible conductor interconnecting said terminals, said conductor comprising spaced-apart, multiple-parallel-segment portions interconnected by a single-segment portion, means for anchoring said multiple-segment portions to said partition comprising conductive pegs tightly fitted in said apertures and conductively engaging the individual segments of said multiple-segment portions, the section of said conductor extending between said apertures including said singlesegment portion, means for coupling said indicator element to said section of the indicator conductor, and biasing means for driving said indicator element into an ex- 6 tended indicating position upon fusion of said conductor in response to fusion of said main link.

3. The fuse of claim 2 in which said pegs and apertures are of the tapered configuration.

4. The fuse of claim 2 in which the coupling means between the indicator element and the indicator conductor comprises a projecting hook portion secured to said indicator element and receiving said conductor in looped-about relationship.

5. In an electric fuse, an insulating leasing provided with a pair of spaced-apart electrically-conductive terminals, at least one main fuse link conductively interconnecting said terminals, an indicator assembly for indicat ing fusion of said main link comprising an insulating partition located at one fuse terminal and having a pair of spaced-apart apertures therein, a movable indicator element slidably mounted adjacent said partition, currentsensitive means for normally restraining said element in a retracted position comprising a fusible conductor interconnecting said terminals, said conductor comprising spaced-apart, multiple-parallel-segment portions interconnected by a single-segment portion, means for anchoring at least one of said multiple-segment portions to said partition comprising a conductive peg tightly filled in one of said apertures and conductively engaging the individual segments of said one multiple-segment portion, the section of said conductor extending between said apertures including said single-segment portion, means for coupling said indicator element to said section of the indicator conductor, and biasing means for driving said indicator element into an extended indicating position upon fusion of said conductor in response to fusion of said main link.

6. In an electric fuse, an insulating casing provided with a pair of spaced-apart electrically-conductive terminals, one of which has an opening therein surrounded by an annular axially-inwardly projecting lip, at least one main fuse link conductively interconnecting said terminals, means for indicating operation of said fuse comprising a cup-shaped housing fitted about said lip, a movable indicator element comprising a first portion of a diameter larger than the internal diameter of said lip slidably received in said cup-shaped housing and a second portion of smaller diameter guided for sliding motion by said annular lip, means biasing said indicator element toward an extended position indicating operation of the fuse, and current-sensitive means for normally restraining said element in a retracted position comprising a conductor interconnecting said terminals and coupled to said indicator element, the conductor being adapted to fuse upon fuse operation to permit said indicator element to move to indicating position.

7. In a method of constructing an electric fuse of the type which includes a casing provided with spaced terminals and an indicator assembly comprising an indicator element biased for movement with respect to a partition which is located adjacent one of the fuse terminals; the steps of providing a fusible restraining wire for the indieating element, securing the ends of the wire to spaced points on the wire body to form a pair of spaced loops at opposite ends of the wire and a single-segment portion interconnecting said loops, threading the wire through an opening formed in the partition and anchoring one of the loops within the opening, threading the other loop through another opening formed in the partition, snaring the wire about a hook secured to the indicator element, seating and restraining the indicator element in a retracted position by a process which comprises applying tension to said other loop and thereafter anchoring said other loop in said other opening with the single segment portion drawn taut between said element and said partition, and there after joining the resulting indicator assembly to the fuse casing by a process which comprises connecting said loops to the fuse terminals.

8. In a method of constructing an electric fuse of the type whi h includes a casing provided with spaced terminals and an indicator assembly comprising an indicator element biased for movement with respect to a partition which is located adjacent one of the fuse termina1s;the steps of providing a fusible restraining wire for the indicating element, securing the ends of the wire to spaced points on the wire body to form a pair of spaced loops at opposite ends of the wire and a single-segment portion interconnecting said loops; seating and restraining the indicator element in a retracted position with respect to the partition by a process which includes snaring the restraining wire about ahook secured to the indicator element, threading the wire through spaced apertures formed in said partition and anchoring said loopsin place in said apertures, thus providing a self-contained indicator assembly; and thereafter joining the indicator assembly to the 15 fuse casing by a process which comprises connecting said loops to the fuse terminals.

References Cited in the file of this patent UNITED STATES PATENTS Conant Dec. 9,1913 Weissberg Apr. 7, 1914 Bennett Jan. 10, 1939 'Biermanns et a1. Q. Dec. 22, 1942 Wald Aug. 13, 1946 Strang et a1. June 3, 1947 "Schuck Feb. 3, 1948 FOREIGN PATENTS Denmark Dec. 9, 1935 Great Britain Apr. 7, 1932 Germany June 8, 1932 Francev Oct. 15, 1929