US2157152A - Electrical fuse - Google Patents

Description

H. A. TRIPLETT ELECTRICAL FUSE May 9, 1939.

Sheets-Sheet 1 Filed Oct. 18 1937 www. H" II...

/ll'lll y 9, 1939- I H. A. TRIPLETT 2,157,152

ELECTRICAL FUSE Filed Oct. 18, 1937 5 Sheets-Sheet 3 Patented May 9, 1939 [UNITED STATES PATENT OFFICE ELECTRICAL FUSE Hugh A. Triplett, Wilmette, 11]., assignor to Schweitzer & Conrad, Inc., Chicago, 111., a corporation of Delaware Application October 18, 1937, Serial No. 169,611

18 Claims.

Y phases of the invention, wherever useful.

According to present practice, distribution systems usually operating at from 2,300 volts to 15,000 volts are protected by fuse devices of various construction and variously designated. Be-

cause of the large number required in a system of any extent, the item of initial expense and maintenance is a paramount consideration. The air break fuse has chiefly for this reason been widely adopted. Due to the location of these devices remote from the central station busses and with the reactance of the lines intervening, the amount of current that must be interrupted is limited to values which make air break fuses operating upon the expulsion principle fairly satisfactory. These fuses are disposed in or on various forms of mountings.

The typical commercial embodiment of the expulsion fuse early took the form of a tube of insulation with ferrules upon-the ends, and a closure for one end with the fusible portion of the link disposed adjacent said closed end. Great numbers of devices of this character have been employed, and are still in commercial use.

It was early recognized by my assignee that the simple expulsion fuse, while, in general; it operated fairly satisfactorily on relatively heavy overloads, came into difliculty on low overloads, as the expulsive force was not great enough to propel the link and cause separation of the ter- 40 minals, and interruption. Destruction of the device results. Fuses of large current carrying capacity are less subject to this particular difliculty because the blowing of a large capacity link releases enough energy to create a satisfactory expulsive effect. My present invention is particularly useful for 10w amperage fuses.

Another difficulty with fuses of this type has been the uncertainty as to time-current characteristics, particularly on low amperage fuses. A

further uncertainty resided in the uncertain lengths of arcing time of fuses as heretofore constructed. 1

The prior United States patent to Conrad, No.

1,466,423, largely overcame these difficulties by placing the fuse link under spring tension and surrounding the fusible element with a cork. Employment of spring tension was practicable because a method of relieving the fusible element from stress and possible injury by the spring load had been satisfactorily worked out, i. e., the use 5 of the so-called strain wire. Upon the occurrence of overload great enough to cause fusing of the fusible element, the terminals were promptly separated far enough to insure expulsive action and interruption of the current flow. 10

I have conceived the expulsion fuse as being, of necessity, a dual range device. According to my conception of the ideal expulsion fuse, it must have the capacity for operating in one fashion upon low overloads, and in another fashion upon high overloads, but these two modes must be so coordinated as to be mutually helpful or to overlap in producing the desired result In brief, the two modes of operation must work in the same general direction, so that in the intermediate 0 range when both actions occur, they may overlap and work to the common end; 'The device of my present invention is designed to do this.

In considering various forms of fuse devices upon the market, I have conceived the possibility 25 of incorporating within the fuse link itself the principle of operation of the aforesaid United States Patent to Conrad, No. 1,466,423, so that the resulting device employing such links will have the desired plural range action and suitable 0 time-current characteristics, short arcing time, etc.

One of the primary objects of my invention is to provide a fuse link for use in fuse holders of various forms or for various mountings to con- 35 stitute the same as plural range fuse devices with suitable predeterminable time-current characteristics and arcing time for each desired capacity.

For the accomplishment of this object and other objects, I have devised a form of link, which I 40 term a universal link, having such structural Another object of the invention is to provide an improved form of fusible element for the link, such element having a high temperature metal which is relatively free from corrosion, and has long life, accuracy in time-current characteristics, and the ability to stand momentary surges without deterioration.

A further object of the invention is to provide a fusible element which shall be suitable for withstanding the tension required in spring loaded or weight-loaded cutouts, such as automatic dropouts or reclosing fuses, and yet be satisfactory for use in cutouts putting no tension on the link.

Accuracy in blowing time of fuse links would be of little or no importance if heavy short-circuit currents were possible at the points where most cutouts are installed. The fact is that on most systems, and particularly rural systems, heavy short-circuit currents are the exception rather than the rule. Therefore, this means that most cutouts sold are subjected to an interrupting duty which is out on the long time blowing end of the time-current curve. Out on the low current end of the curve, reliable accuracy in blowing time andcurrent is essential if a power company insists on good operating results. By good results, I mean that the accuracy of the fuse link is such that its blowing can be so coordinated with the circuit breaker at the head of the feeder, and so co-ordinated with any other fuse in sequence on the line, that when a fault occurs, on the load side of the cutout, a fuse link will isolate the fault in time to prevent these other fuses or breakers from opening and thus dropping the load in adjacent territory. This requires, in a fuse link, both accuracy in time-current characteristics and reliable short arcing time. No matter how accurate the melting of the link, long and indefinite arcing time will undo the benefit of such accuracy by causing other devices in seically weak with respect to spring tension, and

entirely unsuited to be installed in a cutout employing a tensioning spring, the fuse oi the present invention permits the use of a heavier wire which is entirely adequate in tensile strength. The link of the present invention will melt and part at the same overload or fault currents which would melt the wire of hairlike proportions. The fuse of the present invention will withstand the spring tension which is found in all of the cutouts of my assignee and in the cutouts of the new dropout type which are coming into the market.

In carrying out this phase of the invention, I" employ a pair of wires; preferably of nickelchromium alloy, having hooked engagement with each other. The wires are of adequate mechanical strength to resist the necessary spring tension but the hooked connection will readily yield under the spring tension which is provided by straightening out the hooked or bent parts of one or both of the wires. By' provision of a molded bead of a low melting point metal or alloy which encases or embeds the hooked engagement, the Pulling apart of the hooked engagement is prevented until the bead softens suiiiciently to permit the end of the hook to swing about through the body of the low melting point metal and straighten out sufliciently to. pull clear of the cooperating anchorage.

A further object of this invention is to provide a fuse link which has a very sharp melting and parting point on the temperature curve, that is a link which does not soften and stretch and thus reduce its cross-section as the temperature closely approaches the definite melting point. In the present construction, the bead of tin or other low melting point material either allows the hooked engagement to pull apart or it will not permit the bent portion of the hook to straighten out at all. The present fuse link, therefore, does not result in a progressive lengthening of the fusible section, as would be the case if the two wires were soldered together or otherwise connected through the body of low melting point metal.

Another object of the invention is to provide a fuse link with a novel and distinctive form of time-current characteristic curve, as illustrated in exaggerated form in Figure 4. A fuse having such a characteristic curve, that is, with the short and medium time blowing points elevated permits the momentary surges or transients, such as lightning or induced current, to pass through the device without melting of the bead. There is, therefore, less cumulative effect of repeated surges which might otherwise cause the link to melt and part at normal load current. In that part of the curve corresponding to long time blowing there is a relatively sharp dip beyond the duration time of surges and transients. Being at the long time end of the curve, and being a substantial drop in the curve, it serves as a protection against detrimental thermal effect in the transformer to which this link is applied as a protection. It is known that long continued overload of the order of 50% or possibly 100% on the transformer results in destruction of the insulation. It is therefore desirable to have the long time end of the curve as low as possible with respect to the normal load current of the transformer while the medium and short blowing time of the curve should be higher with respect to the normal load current of the transformer. It is desirable, therefore, that these two sections of the curve be joined by a section which is as nearly vertical as it is possible to provide. This object is particularly desirable for fuses of the order of one to two ampere ratings which blow on currents ranging from one to three or four amperes.

In addition'to the foregoing objects there are other and numerous objects of the present invention which will be apparent from the following detailed description and the appended claims.

Now in order to acquaint those skilled in the art with the manner of constructing and operating a device in accordance withmy invention I shall describe, in connection with the accompanying drawings, several specific embodiments of the invention.

In the drawings, the same or similar reference characters designate the same or similar parts, throughout.

Figure 1 is a side elevational view of a low amperage fuse link of the order of one to two amperes, the specific fuse link shown is a two ampere link;

Figure. 2 is a vertical, longitudinal sectional view through the fuse link of Figure 1, taken along the line 2-2;

Figure 3 is a view of the fuse link and terminals taken at right angles to the view of Figure 2;

Figure 4 is a diagram illustrating the type of time-current characteristic curve which is secured by the fuse of Figure 1;

Figure 5 is a time-current characteristic curve showing the relation between current in amperes and time in seconds to blow fuses of the present invention plotted on a logarithmic scale; and

Figures 6 through 13 show, at an enlarged scale, different embodiments of bead-construction.

Referring first to Figures 1, 2, 3, and 6, I have shown a fuse link I which necessarily involves three essentials. First, a terminal portion 2, such as is suitable for attachment to one electric terminal and support, a fusible section 3 (Figure 2), and a flexible lead and terminal portion 4 for' making connection with another elec- 7 connector, the outer end of which as shown at 6, is tinned to hold the strands together. It will be observed that the terminal portion 4 is provided with a collar member I which has an intermediate portion 8 that is pinched or flattened upon the body of the lead 4 and which is provided with a flared or conical wedging contact IQ for engagement in a cooperating stationary wedging contact such as shown in Patent No. 2,091,453, of Allan Ramsey.

The upper terminal 2 comprises a cylindrical stud member I 3 (Figure 3), the outer end of which is threaded at l4. The intermediate portion comprises a flange [5 which may represent the original diameter of the stock from which the stud is out, as by a screw machine. Adjacent the flange I 5 there is a groove l6 and beneath the same a knurled portion H. The inner end of the stud 13 comprises a tubular socket portion l8 into which is inserted. the upper end of the fuse wire l9 of the fusible link 3. The tubular portion I8 is then flattened or pinched upon the end of the wire to make good electrical and mechanical connection with said wire l9.

The threaded stud I3 is adaptable to a wide variety of situations for making connection between the link and a suitable terminal, either stationary or movable, as the case may be. For connection with a stationary mounting wherein an annular seat and a cooperating cap or clamp argemployed, a flanged 'head 29 is provided. This flanged head comprises a tubular sleeve or shank internally threaded to cooperate with the threads l4 of the stud l3 and having its upper end flanged or flared out as indicated at 21 as by a spinning operation. Where the annular seat is of greater extent than would be suitably engaged by' the flange 21, a dished washer 23 is provided (Figure 1), this washer being passed over thelink from the opposite end and resting under the flange 21. The end of the stud I3 is substantially flush with the top of the flange 21 and provides a'good clamping surface additional to the top ofthe conical flange 21.

The wires l9 and 29 have hooked engagement at 22, as shown in detail in Figure 6. A molded bead 23 of low melting point metal or alloy, such for example, as solder or tin, is molded on the hooked engagement 22 and embeds the ends of the wires l9 and 20 where they make engagement. The lower end of the wire 20 is folded back on itself like the upper end of the wire l9 and is disposed in a tubular fitting 29, the upper end of which provides a socket 30 which is flattened upon the end of the wire 20 to grip it mechanically and to make connection electrically. The lower end of the fitting 29, which is preferably made of a piece of copper tubing or the like, is similarly pinched or flattened upon the upper end 40 of the flexible lead 4.

The fitting 29 therefore forms a coupling or junction member between the lower end of the fusible element 3 and the lead 4. It also forms an anchorage for the tension spring 33, which has its upper coil flattened against the flat sides of the pinched socket 30 and is prevented from disengagement by the shoulders 34 of the flattened part of the socket 32, since the flattened portions of the sockets 30 and 32 are so disposed that their planes are substantially at right angles to each other.

The spring 33 has its opposite and anchored directly to the flattened collar 35 which is pinched upon the flexible lead 4. Indirectly, the spring is anchored to the cap or plate 36 through the medium of the fitting I, which has its adjacent end 31 in engagement with the plate or cap 36.

The margins of the plate or cap 36 are so formed as to center it upon the lower end of a fiber tube 38. The upper end of the tube 38 is securely bound to'the upper terminal stud [3 in axial alignment therewith and rigid for both rotary or axial motion with respect thereto. This engagement is secured preferably by wetting the end of the fiber tube 38, pushing it over the knurled portion l1, and then shrinking the end into the groove under the flange l5. Such shrinkage may be facilitated by pinching.

It will be observed that the spring 33 does not apply any tension to the portion 40 of the flexible conductor 4 between the terminal 29 and the collar 35. Any desired tension may be applied to the flexible lead 4 externally, either by springs in the housing or by the lineman in refusing the.

housing, without imposing on the link 3 any stress in addition to that already imposed by the spring 33 unless this stress imposed by the spring 33 is exceeded. This type of spring arrangement and fastening therefor provides a non-cumulae tive type of replaceable spring link. It constitutes a distinct advance in the art. However, the non-cumulative arrangement 'of the spring 33 forms no part of my invention. It is disclosed and claimed in the copending application of Lindell, Serial No. 70,280, filed March 23, 1936, and assigned to the assignee of this application.

The spring 33 is arranged to place the link 3 under a tension which, in the present instance, is of the order of seven pounds. In the S 8: C cutouts of the type shown in United States Patent 1,818,382, the tension of the spring which tends to separate the terminals of the fusible link ranges from to 12 pounds.' This amountof tension is necessary in view of the unavoidable mass of the terminal and cable assembly which is required to extend the rating of any particular .cutout 'to include links of higher ampere rating,

say up to 60 amperes.

Now inasmuch as the present link is designed and adapted to be inserted in cutouts of that type as well as in other forms of mountings, fuse tubes and the like, it is desirable that the fusible element be capable of withstanding spring tension of that order, that is, from 10 to 12 pounds' I have provided the hooked engagement 22 and the soft metal bead 23 as a means for permitting the employment of wires i9 and 20, which. are ample in cross section and mechanical strength to withstand spring loads or other loads of from 10 to 12 pounds. The wires 59 and 2t will not fuse at from 1 to 3 or 4 amperes, which is the definite overload value at which the fuse shall open, but the hooked engagement, combined with the minimum spring tension, is designed to do this under the control of melting of the molded metal bead 23. That is to say, the wires it and 20 must maintain good mechanical strength throughout the life of the device and must maintain substantially unchanged cross-section. These wires are made of metal which does not corrode, deteriorate due to oxidation, or is not otherwise attacked by atmospheric ingredients or components. Preferably, I use an alloy of nickel and chromium which appears on the market under the trade name of Chromel A. Obviously, I do not wish to be limited to this specific material, as any other metal which has noble characteristics may be employed.

The critical point of the construction resides in the straightening out, or release, or pulling apart of the hooked connection.

I am aware that it is old to have parts soldered together or held together by a solder or soft metal rivet or the like, but these devices are subject to change in characteristics due to an approach to the melting point and a recession therefrom. In the 1 ampere fuse size I employ wires for 1 ampere rating of the order of 0.016 inch in diameter, and for a 2 ampere rating of the order of 0.018 inch in diameter of the aforesaid material, and where the total length of the fusible link between the tubular end portions l8 and 30 may be of the order of 1 inch.

The hooked engagement 22 is preferably that shown in detail in Figure 6, wherein the wire I9 has a closed loop or eye 42 formed upon the end thereof, this eye being, for example, circular and formed by bending the stdck adjacent the end into a circular annular loop, with the end of the wire, as at 43, brought parallel with the main body thereof, and welded or otherwise secured thereto. The wire 20 likewise has a loop 44 of similar configuration, but having its end 115 free. A bead of low melting point metal, for example, tin, solder or the like, is then cast about this hooked engagement, and this device thereupon forms a mechanical relay controlled by temperature. Obviously, instead of forming one loop completely closed by welding the end 43 as shown in Figure 6, the ends of both wires may be left open, as shown in Figure '7, at 22'. In the sizes of wire shown without the metal bead 23 cast in'place, a tension of only 3 to 4 pounds is sufficient to straighten out the hooked engagement sufli'ciently to allow the wires i9 and 20 to pull apart. But with the head 23 in place the hooked engagement is stronger than the main part of the wires 89 and 20, until it is softened by heat. When the bead 23 is softened by heat generated in the wires l9 and 20 by current flow, the Wires i9 and 20 can be pulled apart by straightening out the hooked engagement with a force of 7 pounds or less. The conductivity of the bead 23 surrounding the hooked engagement is so great that this part of the fusible element does not become s'ufiiciently elevated in temperature by current flow but heat is generated in the intermediate parts of the wires i9 and 20, that is, between the bead 23 and the terminals 88 and 30, and the heat is conveyed to the bead 23, bringing it up to a temperature where it softens sufficiently to permit the tension of the spring to separate the parts. The wires i9 and 2t) will not soften sumciently under heat to cause any weakening thereof short of approximately 800 C. to 900 C., but the metal bead 23 will soften between 200 C. and 300 C. There is, therefore, a wide difference in the effective temperatures of the two parts of the fusible link.

It is to be understood that the amount of spring tension which is placed upon the fusible link affects the time-current characteristic of the link. That is to say, if the spring tension is excessive, obviously it will break the link without any current flow. If the current flow is great enough to affect the temperature of the link, it

- will affect the mechanical strength, even though the link be but a straight wire. If the wire alone be considered, no appreciable weakening in mechanical strength will be caused by current flow until the wire reaches a critical temperature, whereupon the spring tensionwill have a marked effect upon the time-current characteristic. The fusible element 3 shownin Figures 2, 3, and 6 of the drawings is a compound device in which it is intended, as hereinabove stated, to secure an offset in the time-current characteristic curve which is idealized in Figure 4.

In that curve I have shown only the general contours and not absolute values. ous full line curve shows the characteristics desired. The dot-and-dash curves indicate continuations of the two independent curves which are combined by my invention. The part of the curve running from P to M is a part of a curve for one capacity of fuse. The part of the full line curve running from N to Q is part of the curve of a lower capacity link. Assume that the line MN is a substantially vertical line and that this line is placed at substantiallythe second value, for example, it will be assumed that for values of current greatly in excess of the normal load current, the blowing time is relatively short, but a marked increase of current is required if the fuse is to blow in less than 60 seconds. Within this range the wire H3 or 20 itself melts. Within the range N-Q the bead melts and releases the link. It is desirable that this should occur at as small an increase above normal load current as it I is possible to secure in order that apparatus on the line, such as transformers, will not be subjected, for any appreciable period of time, to values of current flow substantially in excess of the normal rating.

In practice it is not possible to have as sharp a junction as indicated by the vertical line MN in Figure 4. In Figure 5 of the drawings, I have shown the shape of actual curves as plotted from tests made on fuses of this character. The curves, marked Nos. 1 and 2, are curves representing the performance of one and two ampere fuses constructed in accordance with the disclo sure of Figures 1, 2, 3, and 6 of the drawings. It will be observed that these curves are of the general shape indicated by Figure 4, the relatively sharp dips indicated in the region MN' showing the pronounced efifectwhich is produced by the introduction of the bead and hook construction heretofore described.

The continu- As above indicated, the hook and bead principle may be embodied in quite different forms. For example, in Figure 6, the hooked free end 45 may be considered as a lever hinged to the main shank portion of the wire 20 with a predetermined friction at the pivot as representing the force required to swing it into the unhooking position. Obviously, as indicated in Figures 10 and 11, the principle would not be changed by hav-' ing the free end 45' pivoted to the main shank portion of the conductor 20, for example, without friction. In other words, the end 45', which constitutes a lever, might be pivoted to the main shank by an actual pivot joint giving a known leverage of relatively high value. The real resistance to unhooking of the connection of these two wires resides in the molded head 23. In order to move to an unhooking position, the free end 45 must swing sidewise through the metal of the bead. To permit this the metal of the bead must be soft enough to allow the arm 45' to swing therethrough. This mode of operation is entirely different from prior devices, in which a straight wire or a wire bent into zig-zag or coiled form is embedded in a bead, since according to that construction, spring tension allows a slow creepage or lengthening of the link to occur, thereby changing its ratingand rendering the device unreliable. In the present case, even if the free lever-like end 45' should begin to swing and then be halted, no appreciable lengthening of the wire 20 or of the link 3 as a whole could be detected. Hence, the time-current characteristic of the link would not be changed, and thatwould be true of any position of the. wire 45' short of allowing an actual unhooking or slipping through the eye 42.

In Figure '7, I have indicated open hooks on both the wire I9 and the wire 20 to give the hooked connection 22'. In practice it is not necessary or doesirable to have more than one of the wires provided with an open hook, inasmuch as there is a tendency for the bead 23 to be rotated and, as the bead is oblong, it mightcome into a position in the fiber tube 38 which would interfere with its free rotation and expulsion. Furthermore, contact of the head 23 with the inside of the fiber tube is not desirable, as it tends to alter the time-current characteristics of the device.

In Figures 8 and 9, I have shown the eye 42 as provided with a smaller roller 41 of a definite exterior diameter, so as to control accurately the pivotal point about which the free end 45 of the wire 20 willrotatefi By thus providing a definite radius and conforming the end of the wire 20 to that radius, a snug and certain fit may be obtained, showing very definitely the yielding point of the link.

Also, it is to be understood that instead of the two wires directly hooking with each other, they .may hook with an intermediate link which provides either the hook portion or the eye portion. Such a construction is shown in Figures 12 and 13 of the drawings. As there illustrated, the wires I 9 and 20 terminate in eyes 49 and 50 which may be formed by suitably bending the adjacent ends of the wires I9 and 20 back and welding them to the shank portions, as indicated at 5| and 52 respectively. The eyes 49 and 50 are interconnected by a link 53 which, may comprise a generally c-shaped member. The entire assembly is embedded, as shown, in the bead 23 for the reasons set forth hereinbefore.

the wires I9 and 20, each may be chosen, as to material, with respect to its separate function. That is, the wires I9 and 20 may be chosen with respect to the tension stress applied thereto and the means employed for fastening them in the sockets I8 and 30, Figure 3, while the link 53 may be composed of a difierent kind or size of material or both and with reference to the timecurrent characteristics desired and its relation to the melting of the bead 23.

In the operation of blowing of a fuse link in a fuse housing, such as an expulsion tube employing the fuse link-shown in Figures 1, 2, and 3, there are two ranges of operation wherein different modes of action are secured, all to. a common end of accurate predetermined operation.

Assume that the excess current is in the lower ranges wherein the wires I9 and 20 are heated by the fiow of current but not to the point where these wires lose their mechanical strength, that is, in a region to the right of the hump in the curves indicated at MN in Figure 5. The wires I9 and 20, transmit heat to the low melting point bead 23 and, if the current is maintained for a period of time which will permit the bead to become softened to the point of allowing the end 45 of the wire 20 to swing about through the body of the bead and become unhooked, the fuse thereupon operates to interrupt the circuit. Inasmuch as certain types of expulsion fuse housings are provided with springs which exert a pull of the order of 10 to 12 pounds, whereas the spring 33 has a pull of the order of 7 pounds, the total stress upon the fusible link is only 10 to 12 pounds. Hence, no substantial deviation from the type of curve shown in Figure 5 is occasioned by this form of mounting.

For higher values of current fiow above the hump indicated at MN, Figure 5, the fiow of current tends to soften the wires I9 and to such an extent that they yield mechanically before sufficient heat is transmitted to the bead 23 to cause softening of the same, and fusion of the bead is not depended upon to secure opening of the circuit. In this event the wire I9 or 20 pulls apart, due to the spring tension, and the circuit is opened as above described, with the combined action of the springs and the gases formed upon blowing of the fusible link.

The fiber tube 38 is not intended to be expelled with the fuse terminal 29, as it is anchored firmly to the stud member I3. The tube 38 seryes the useful purpose of confining the gases and assisting in the expulsive effect, particularly on the lower current values. Also, it protects the inside of the permanent fuse tube from injury by the arc. Also, it serves to assist in evolving deionizing gases, as it appears that the decomposition of the fiber by the arc is helpful in the action of deionizlng the are by driving gases evolved from the walls of the tube endwise of the arc to sweep out the ionized product and metal vapors. The sleeve 38, while it is preferably made of plain gray fiber, may be specially constructed to assist in the evolution of gases as by impregnating the same with a liquid or solid arc extinguishing medium, as disclosed in the United States patent to Ringwald, Reissue No. 19,097.

From the above it will now be apparent that I have provided a fuse link suitable for employment in a wide variety of mountings, in which there is a predetermined spring tension to controlthe time-current characteristic according to a desired mode of operation. This spring tension is great enough for the very low ampere fuses, such as one or two amperes, to overcome the hooked engagement of the fuse wires when the bead melts. Mere melting of the bead does not release the hooked connection of the wires, and this spring tension is therefore necessary to secure opening of the circuit for current values which are lower than those which would actually melt the wires, such as the wires i9 and 2b. In this manner it is possible to secure a very delicate response to low current values while employing parts of ample mechanical strength and dimensions.

I believe that the hook and bead principle is broadly new. I am aware that it has been attempted to hold parts together by solder, wax and various other expedients, but in all of the structures with which I am familiar, there is no positive mechanical engagement such as I have obtained by the use of the hook and eye, independently of the bead or solder.

Numerous other advantages in manufacture and operation will be apparent to those skilled in the art.

I do not intend to be limited to the details shown and described.

I claim:

1. In an electric fuse, a fusible current carrying element of predetermined rating comprising a pair of wires of relatively high melting point having portions coupled mechanically by hooked connection, and a body of metal fusible at a relatively low temperature and holding said hooked connection against disconnection by bending a hooked part of the wire, said wires being fusible by large increase of current, and said body of metal being fused by current flow insufficient to melt said Wires when continued over a period of time.

2. In a fuse of small current carrying capacity adapted to withstand spring tension, a pair of wires of relatively high mechanical strength and relatively high melting point having hooked connection, and a head of meal of relatively low melting point embedding said hooked connection of said wires.

3. In a small capacity fuse element adapted to be placed under substantial tension, a pair of nickel-:chromium alloy wires having hooked connection with each other, and a bead of metal comprising tin embedding said hooked connection.

4. In a device of the class described, a fuse element comprising a pair of wires of high tensile strength, high melting point and resistant to corrosion, a closed loop formed on one wire, an open loop on the other wire hooked through said closed loop, and a bead of low melting point metal embracing said open loop to keep it from opening by tension imposed upon said elements until the heat from said wires softens the metal of said bead.

5. In combination in a fuse, a pair of wires of high tensile strength and small cross section having hooked connection, and a bead of tin formed about said hooked connection and being subject to being softened by the heat of said wires to release said hooked connection under tension.

6. In a fuse of a given ampere rating, the combination of a conducting link comprising a member having an eye, a member having a hook cooperating with said eye, and a body of low melting point metal coupling the open side of the hook to the shank thereof, at least one of said members being heated up by current flow in exawaits cess of said rating to raise said body of metal substantially to its melting point whereby it loses its coupling effect, and a spring imposing sufficient tension upon said members to pull. the hook out of the eye when the hook is freed by softening of said body of metal.

7. In combination in a fuse, a fusible link comprising a pair of high tensile strength wires of small cross section having hooked connection, a bead of low melting point metal embedding said hooked connection, and means placing said hooked connection under predetermined mechanical tension sufficient to straighten the hooked part of one wire when said bead is melted.

8. A fusible link comprising a pair of corrosion resisting wires of relatively high tensile strength having hooked connection with each other, and a soft metal body of relatively low melting point in good thermal contact with at least one of said wires preventing unfolding of said hooked connection.

9. A fusible link comprising a corrosion resisting wire of relatively high tensile strength and high melting point, said wire having a hook formed in one end thereof, an anchorage which said hook engages, and a body of relatively low melting point metal which holds the hook from straightening out and releasing itself from the anchorage, said body of metal being in good heat conducting relation to said wire to be heated thereby upon the flow of abnormal current through the link.

10. As an article of manufacture, a fuse link comprising a conductor having a fusible portion comprising a corrosion resisting wire of relative ly high tensile strength and high melting point, said wire having a hook formed in one end thereof, an anchorage which said hook engages, and a body of relatively low melting point metal which holds the hook from straightening out and releasing itself from the anchorage, said body of metal being in good heat conducting relation to said wire to be heated thereby upon the flow of abnormal current through the link, means carried by the link for imposing a predetermined tension upon said fusible parts great enough to bend the hook and release it from the anchorage when the body of metal is melted, and releasable terminal means by which the link is supported for connecting said link in an electric circuit to be protected.

11. The combination of a high tensile strength and high melting point conductor having a hook which is adapted to sustain a tension less than that required to cause the conductor to part, a cooperating anchor member with which said hook is in hooked engagement, and a mass of low melting point metal for holding the hook against opening and for improving the conductivity of gle joint between the hook and the anchor mem- 12. In combination in a fuse of low but predetermined time-current rating, a pair of members having hooked connection capable of sustaining a tension of approximately three pounds before they will disconnect, a spring operatively connected to said members and exerting a tension upon saidmembers of approximately seven pounds, and a fusible mass of melting point substantially lower than the melting point of either of said members for reinforcing said hooked connection to make it capable of resisting a tension substantially in excess of ten pounds.

13. A fuse of two or three amperes or less continuous current rating, comprising a pair of of withstanding said pull while carryingcon- 9,157,152 terminals, a link comprising a pair of nickelchromium wires having hooked connection with each other capable of withstanding a pull of approximately three to four pounds, said wires themselves being capable of withstanding a pull of more than ten to twelve pounds and capable tinuously a current substantially twice the continuous ampere rating, a spring operatively connected to one of the terminals to place said link under a tension of approximately seven to eight pounds, and a low melting point connection for reinforcing said hooked connection to make it capable of withstanding continuously a pull of more than ten to twelve pounds.

14. In a fuse device, a first strand anchored at one end and having a loop at the other end, a

second strand substantially in alignment with the first strand and having aportion extending through said loop and carried back to the body of said second strand whereby said strands have a hooked engagement, 8. body of low melting point metal holding the end and the body of the second strand together, and means connected to said second strand placing said strands and said hooked engagement in tension and tending to swing said end from said body of the second strand to unhook the second strand from the first strand.

15. In a fuse, a pair of wires of relatively-high mechanical strength and melting point, a lever pivoted on one end of one of said wires, a loop at one end of the other of said wires interfltting CERTIFICATE OF Patent No. 2,157,152.

with said lever, and a bead of relatively low melting point metal embedding said lever and said' loop.

16. In a fuse, a pair of wires of relatively high mechanical strength and melting point, a roller carried by one of said wires, a hook forming a part of the other of said wires and engaging said roller thereby providing a mechanical connection between said wires, and a bead of relatively low melting point metal embedding said roller and said hook.

17. In a fuse, a pair of wires of relatively high mechanical strength and melting point, each of said wires terminating in a loop portion, a link joining said loop portions, and a bead of relatively low melting point metal embedding said loop portions and said link.

18. In a fuse adapted to withstand spring ten- ,sion, a pair of wires of relatively high mechanical strength and melting point having a mechanical connection therebetween, and a bead of relatively low melting point metal embedding said connection and arranged and adapted to act at a mechanical advantage therewith to prevent separation of said wires on application of said spring tension in such manner that stress is not transmitted directly therethrough, said wires fusingunder high current conditions to open the circuit and said bead softening under low current conditions to permit. separation of said wires to open the circuit.

HUGH A. 'I'RlPLE'I'I'.

CORRECTION.

May 9, 1959.

HUGH A. TRIPIIETT It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 6, first column, line 1 .3, claim 2., for the word "meal" read metal; and-that the said Letters Patent should be read with this'correction therein that the same may conform to the record of the case inthe Patent Office.

Signed and sealed this 11th day of July, A. D. 19 9 (Seal) I Henr VanA'rsdale Acting omnissioner of Patents.

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