US3122619A

US3122619A - Dual element electric fuse

Info

Publication number: US3122619A
Application number: US793415A
Authority: US
Inventors: Aloysius J Fister
Original assignee: McGraw Edison Co
Current assignee: McGraw Edison Co
Priority date: 1959-02-16
Filing date: 1959-02-16
Publication date: 1964-02-25
Anticipated expiration: 1981-02-25

Description

Feb. 25, 1964 A. J. FISTER DUAL ELEMENT ELECTRIC FUSE 2 Sheets-Sheet 1 Filed Feb. 16, 1959 Z a Iv a a 1 m 2 2 k a 6 a 2 9 9 v M 3 7 4 W4 9 W l 5 1 w m. H n m nu n 1O 0 z m 2 1 4 A 2 u 2H 4. 2 a wwu 6 q. 5 f k l/VVE/VTOR mom/us J Purse rent flows through the fuse.

United States Patent'() 3,122,l9 DUAL ELEMEN'I ELECTRE'C FUSE Aloysius l. Flster, St. Louis, Mo, assiguor to McGraw- Edison Company, Elgin, Ill., a corporation of Delaware Filed Feb. 16, @559, Ser. No. 793,415 17 (Ilaims. (ill. 200-126) This invention relates to improvements in protectors for electric circuits. More particularly, this invention relates to improvements in dual element fuses.

It is thererore an object of the present invention to relates to improvements in dual element fuses.

It is desirable, in the protection of many electric circuits, to equip those circuits with dual element fuses. Such fuses have thermal cut-outs that can respond to longcontinued low overloads to open, and thereby protect the circuits, and they also have fuse links that can respond to higher overloads to open, and thereby protect the circuits. Whether the dual element fuses open in their thermal cut-outs or in their fuse links, those fuses limit the current passing through the electric circuits and thereby protect those circuits. A number of such dual element fuses have been proposed, and some of them havcbecn sold Widely.

T he capacities of electric circuits have exhibited steady growths throughout the years, andhence it has become important to make some fuses with current limiting characteristics that are even greater than those possessed by prior dual element fuses. It would be desirable to have a fuse that possesses the time lag characteristics of a dual element fuse on light overloads but that responds to higheroverloads to open the circuit more rap-idly than can prior dual element fuses. Such a fuse could open the electric circuit, and thereby limit the current in that circuit, before that current reaches the capacity of that circuit. The present invention provides such a fuse; and it does so by providing a short-circuiting chamber which is equipped with fast-blowing fuse links and which is connected in series with a thermal cut-out. A heat generating conductor is disposed adjacent one end of the thermal cut-out and the short-ci-rcu-iting chamber is disposed adjacent the other end of that thermal out-out; and both the heart-generating conductor and the fuse links of the shortcircuiting chamber Will generate heat whenever curlt would not bedesirable to have unlimited interchange of heat between the heatgenerating conductor and the short-circuiting chamber, and such interchange of heat is prevented by the present invention by providing the heat-absorbing member of the thermal cu-out with a portion of reduced cross section.

The heat-generating conductor and the short-circuitinig chamber, and the connector and heat-absorbing member of the thermal curt-out are all intimately bonded together; and they essentially constitute one continuous and integral conductor. There is, as a result, minimum contact resistance between the various current-carrying components of the fuse provided by the present invention; and hence local heating due to contact resistance is avoided. While the present invention minimizes contact resistance between the various current-cawrying components of the fuse by intimately bonding those components together, it still limits the interchange of heat between the heat-genera-ting conductor and the fuse links of the short-circuiting chamber by reducing the cross section of that end of the 'heat-absorbing member which is bonded to the shortcircui-ting chamber. As a result, the heat-absorbing member can be intimately bonded to the short-circuiting chamher and tothe connector, and can be given enough mass and enough surface area to absorb sizeable quantities of seat and then to radiate appreciable portions or that heat, and yet not permit undue interchange of heat between the heat generating conductor and the fuse links of the short-circuiting chamber. It is therefore an object of the present invention to provide a heat-absorbing memher which has a large mass and a large surface area and which can be intimately bonded to the short-circuiting chamber and to the connector without permitting undue interchange of heatbetween heart-generating conductor and the fuse links of the short-circuiting chamber.

The heaogeneratingconductor of the fuse provided by the present invention supplies heat to heat-softenable material that normally holds the connector in mechanical and electrically-conrducting engagement with the heatgenerating conductor and with the heat-absorbing memher. That heabgenerating conductor must be kept from applying binding forces to the connector which could keep that connector from moving out of the said mechanical and electrically-conducting engagement when the heatasoftenable material softens; and yet the recur-rent and appreciable expansions and contractions of that heatgenerating conductor during the operation of the fuse can tend to warp and distort that heat-generating conductor and thereby tend to cause that heat-generating conductor to apply such binding forces to the connector. The expansions and contractions of the heatagenerating conductor can be appreciable where the fuse is subjected to high overloads that are continued long enough to raise the heat-softena-ble material to its softening temperature or to raise the fuse links of the short-circuiting chamber to their blowing temperature even though those high overloads are not continued long enough to soften the heat-softenable material or to blow the fuse links of the short-circuiting chamber. Expansions and contractions of the housing of the fuse can also tend to cause the heatgeneratin-g conductor to apply binding forces to the connector, and those expansions and contractions can easily be caused by varying conditions of temperature and humidity. The present invention compensates for such expansion and contractions of the heat-generating conductor and of the housing for the fuse and thereby keeps the heatagenerating conductor from applying binding forces tothe connectorby mounting the heat-absorbing member and the short-oircuiting chamber of the fuse so they can move relative to the housing of the fuse as the heatgenerating conductor or the fuse housing expands and contracts. That movement of the heat-absorbing mem her and of the sliort-circuiting chamber permits the heatgenerating conductor to remain substantially stress-free despite its expansion and contraction or that of the fuse housing; and that movement minimizes the likelihood that the heat-generating conductor will apply binding forces to the connector. present invention to provide an electric fuse wherein the heat-absorbing member and the shoe -ci-rcuiting chamber are mounted to move relative to the fuse housing as the heatgenerating conductor or the fuse housing expands and contracts.

The short-circuiting chamber of the fuse provided by the present invention has a casing that is shorter and is smaller in cross-section than the housing for thefuse; and that short-oircuiting chamber has end bells which close the ends of that casing. Those end bells coaot with that casing to provide a tight chamber for the fuse links of the fuse; and such a chamber confines any pressures that are generated when the fuse links blow, and those pressures help quench any arcs that may form when the fuse links blow. Further, those end bells and that casing hold arc-quenching filler in engagement with those fuse links while keeping that filler from impeding the movement of the heat-absorbing member and of the shortcircuiting chamber as the heatagenerating conductor or the fuse housing expands and contracts.

3,122,619 Patented Feb. 25, 1964 It is therefore an object of the The casing for the short-circuiting chamber is made of a sturdy, air-impervious and dimensionally-stable dielectric material. Such a casing is desirable because it makes it possible to use an inexpensive dielectric material in making the housing for the fuse. Further, such a casing is desirable because it can be given a tight fit with the end bells, and it can then be depended upon to maintain that tight fit. Such a casing is additionally desirable because it prevents the expulsion of vaporized metal or of hot gases when the fuse links blow.

To make the fuse links really fast-acting, those fuse links should be made quite short. However, short fuse link mean that the end bells of the short-circuiting chamber will be close together; and the closeness of those end bells creates the possibility of an arc traveling along the exterior of the short-circuiting chamber when the fuse links blow. Any such are would be momentary, and would be due to the fact that the voltage drop across the short-circuiting chamber can rise, during the blowing of the fuse links, to two or three times its normal value; but any such are could not be tolerated at the exterior of the fuse housing. However, by using the fuse housing to completely enclose the short-circuiting chamher, the present invention makes it possible to tolerate momentary arcs that could form at the exterior of the short-circuiting chamber during the blowing of the fuse links within that chamber; and it thereby makes it possible to use very short, and thus very fast-acting, fuse links.

The housing of the fuse protects the exterior of the short-circuiting chamber and keeps that exterior clean. In doing so, that housing keeps dirt or contaminants from providing paths, at the exterior of the short-circuiting chamber, which have low enough resistances to enable arcs to form and to follow those paths during the blowing of the fuse links of that short-circuiting chamber. Such paths could not only foster the striking of arcs, but they could also maintain those arcs; and hence the action of the fuse housing in keeping the exterior of the short-circuiting chamber clean is very important.

The fuse housing includes an elongated tube of insulating material; and that tube overlies and insulates the heat-absorbing member and its bonded connections to the short-circuiting chamber and to the connector. In doing so, that tube provides important protection against arcing which might otherwise occur if two of the fuses were set in adjacent recesses of a fuseholder equipped with cutaway insulating baftles. Such baffles are cut-away to provide openings, adjacent the centers of the fuses, to facilitate ready removal of the fuses from the fuseholders; and those openings could permit arcing between the heat-absorbing members of the adjacent fuses if those fuses were not provided with tubes of insulating material.

In a number of instances, sand is used as an arcquenching filler at one end of a short-circuiting chamber, and an inert material is provided at the other end of that short-circuiting chamber. The sand can respond to arcs, that form during the blowing of the fuse links of that short-circuiting chamber, to form fulgurites during the quenching of arcs. The inert material keeps those fulgurites from extending all the way between the two end bells of the short-circuiting chamber, and thereby keeps those fulgurites from establishing after-blow, currentcarrying paths between those end bells. Different inert materials have been used to keep the fulgurites from extending all the way between the end bells of the shortcircuiting chamber; and while most of those inert materials do keep the fulgurites from extending all the way between those end bells, those inert materials seem to respond to the blowing of the fuse links to permit afterblow, current-carrying paths to form in the short-circuiting chamber. Those paths are undesirable, and they can be obviated by using anhydrous calcium sulphate as the inert material in the short-circuiting chamber. It is therefore an object of the present invention to provide 1 anhydrous calcium sulphate as the inert material in a short-circuiting chamber.

The heat-absorbing member of the fuse provided by the present invention has the heat-generating conductor adjacent one end thereof and has the fuse links of the short-circuiting chamber adjacent the other end thereof, and that heat-absorbing member can become quite warm. A terminal will be connected to the opposite end of the short-circuiting chamber, and that terminal will be kept cool by the fuse clips of the fuse holder; and that terminal will cool the said opposite end of the short-circuiting chamber. The present invention disposes the arcquenching sand adjacent the said opposite end of the short-circuiting chamber, and thereby keeps the sand cool. This is desirable because the cooler the sand, the smaller the cross-section that can be given the fuse links; and small cross-section fuse links can be very fast-acting fuse links.

The heat-absorbing member of the fuse provided by the present invention is not cylindrical because a cylindrical heat-absorbing member would have its periphery immediately adjacent the inner surface of the fuse housing and could have its heat-absorbing action materially affected by the temperature of that fuse housing. The heat-absorbing member of the fuse provided by the present invention is flat; and the greatest portion of the surface of that heat-absorbing member is spaced from the inner surface of the fuse housing to provide an air space. That air space acts as an insulator and thereby keeps the temperature of the fuse housing from materially affecting the heat-absorbing action of the heat-absorbing member of the fuse.

Electric fuses are usually made in standard sizes. Thus, fuses that are to be used to protect circuits utilizing currents in the range of zero to thirty amperes will be of one size, fuses that are used to protect circuits utilizing currents in the range of thirty-one to sixty amperes will be of a larger size, fuses that are used to protect circuits utilizing currents in the range of sixty-one to one hundred amperes will be of a still larger size, and so on. Heretofore the current-limiting abilities, of the fuses that had the same physical dimensions but had different ampere ratings, differed; and therefore to be sure that fuses, made to have ampere ratings that differ from the standard and usual ampere ratings, would have the desired currentlimiting abilities, it was necessary to make detailed tests of the current-limiting abilities of those fuses. Such tests are expensive and time-consuming; and the present invention minimizes the need of such tests. It does so by providing current-limiting fuse links, for the shortcircuiting chamber, that can be used with most of the differently rated fuses having the same physical dimensions. As a result, to make a fuse that has a desired ampere rating, a desired size, and a known current-limiting ability, it is only necessary to make up a thermal cutout having the desired ampere rating and then intimately bond the heat-absorbing member of that thermal cut-out to the short-circuiting chamber for the desired size fuse. It is therefore an object of the present invention to provide a short-circuiting chamber which can provide predetermined current-limiting characteristics and to use that short-circuiting chamber with thermal cut-outs of different ampere ratings to provide fuses with predetermined current-limiting characteristics but with different ampere ratings.

When the connector of a dual element fuse is separated from the heat-generating conductor of that fuse to open the circuit, an arc can tend to form. It is impractical to surround the connector with arc-quenching filler because that filler would interfere with the requisite ready separation of the connector from the heat-generating conductor; and hence an are at the connector could continue to burn. Such an arc can be of appreciable duration where the fuse opens a circuit which utilizes direct current. The present invention obviates arcing at the connector when that connector moves to open the circuit; and it does so by placing a readily fusible shunt wire in parallel with the heat-generating conductor. That shunt wire will be unable to carry the rated current of the fuse, much less overload currents, and it will fuse and open the circuit after the connector moves. However, that shunt wire will take a fraction of a second to heat up to its fusing temperature; and it will carry all of the current through the fuse as it does so, thereby preventing arcing when the connector moves. The shunt wire will be embedded in filler, and any are that might form when the shunt wire fuses will quickly be quneched by the filler. it is therefore an object'of the present invention to provide a shunt wire for the heat-generating conductor of a dual element fuse and to embed that shunt wire in filler that will quench arcs that form when that shunt wire fuses.

Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.

In the drawing and accompanying description, several preferred embodiments of the present invention are shown and described but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

in the drawing, FIG. 1 is a =longitudinal section through one embodiment of fuse that is made in accordance with the principles and teachings of the present invention,

FIG. 2 is a broken, longitudinal section, on a greatly enlarged scale, of the lefthand portion of the fuse shown in FIG. 1,

FIG. 3 is a sectional View through the fuse shown in FIG. 1, and it is taken along the plane indicated by the line 33 in FIG. 1,

FIG. 4 is another sectional view through the fuse shown in PK 1, and it is taken along the plane indicated by the line 44 in FIG. 1,

FIG. 5 is another sectional view through the fuse shown in FIG. 1, and it is taken along the plane indicated by the line 5--5 in FIG. 1,

FIG. 6 is a perspective view of the heat-absorbing member of the fuse shown in FIG. 1,

PEG. 7 is an end view, on a large scale, of the shortcircuiting chamber of the fuse shown in FIG. 1 before the end bells are affixed to that short-circuiting chamber,

PEG. 8 is a perspective view of the heat-generating conductor of the fuse shown in FIG. 1,

FIG. 9 is a perspective view of one of the fuse links in the short-circuiting chamber of the fuse shown in PEG. 1,

PEG; 10 is a sectional View, on a considerably enlarged scale, through the short-circuiting chamber of FIG. 7, and it is taken along the'plane indicated by the line 1ti1-tl in FIG. 7,

PEG. 1-1 is a longitudinal section through another embodirnent of fuse that is made in accordance with the principles and teachings of the present invention,

FIG. 12 is a sectional view through the fuse shown in FIG; 11, and it is taken along the plane indicated by the line 12-42 in FIG. 11,

FIG. 13 is another sectional view through the fuse shown in FIG. 11 and it is taken along the plane indicated by the line 1313 in FIG. 11,

FIG. 14 is a perspective view of the right-hand terminal of the fuse shown in PEG. 11, and it shows that terminal after it has been provided with protuberances at of fuse that is made in accordance with the principles and teachings of the present invention.

Referring to the drawing in detail, the numeral 20 denotes the tubular housing for one embodiment of fuse that is made in accordance with the principles and teachings of the present invention. That housing can be made of a readily available, inexpensive, insulating material such as That housing has a smooth and uninterrupted interior surface, and it has threaded openings 22 adjacent the ends thereof.

A terminalfi i, that is rectangular in plan, has a width that is less than the inner diameter of the housing 20. That terminal has an opening 3i) adjacent the right-hand end thereof, and it has a second opening 28 spaced to the left of the opening 3ft. A bar-like pin 25 is pressed into and fixedly held, by the opening 28, and that pin extends transversely of that terminal. That pin has a length equal to the outer diameter of the housing 29. As a result, the pin 26 limits the extent to which the right-hand end of the terminal 24 can be telescoped into the lefthand end of the housing 2b. When the flat face of the pin abuts the lefbhand end of the housing 2%, the opening lit) in the terminal 24 is disposed within that housing.

The nut eral 32 denotes a cup-shaped closure for the left-hand end of the housing 26, and that closure has an inside diameter which is slightly larger than the outer diameter of that housing. The closure 32 has a slot34- in it, and that slot is just slightly larger than the cross section of the terminal 24. The closure 32 also has openings 35 which can be set in register with the openings 22 in the housing 2b. The

alin ed openings

22 and 35 receive threaded fasteners 36, and the threaded shanks of those fasteners extend through the openings 35 and seatv in the openings 22 to rigidly secure the closure 32 to the housing Also, the fasteners 36 enable the closure 32 to hold the pin 26 and the terminal 24 rigidly fixed relative to the housing 20. i

The numeral 3-8 denotes a conductor which is made so it will generate appreciable amounts of heat whenever currents greater than the rated current or" the fuse pass through it. That conductor has an opening 45 adjacent the left-hand end thereof, which can be set in register with the opening 36 in the terminal 2 The conductor 33 has two portions 42 and 4d of reduced cross section, and those portions of that conductor will be the hottest portions of thatconductor. The conductor 38 also has a reduced cross-section, right-hand end as. As indicated particularly by FIGS. 1 and 2, the conductor 38 is bent upwardly at a point to the right of the opening iii, and it is bent downwardly at a point adjacent the left-hand end of the reduced cross-section portion 46.

The numeral E52 denotes a support which has the form of a circular disc; and that support is made small enough, relative to the inner diameter of the housing 20, to enable that support to move freely relative to that housing in the axial direction. The support 52 is of insulating material, such as fiber, and it has two slots '54- and as in it. The slot 5 accommodates the reduced crosssection, right-hand end 46 of the heat-generating conductor 38, and the slot 56 accommodates the reduced cross-section, lefbhand end of a heat-absorbing member 62. That reduced cross-section end of the heat-absorbing member has an opening od in it, and that openin g'wiil disposed to the left of the support 52 whenever that heat-absorbin-g member is assembled with that support. The heat-absorbing member is fiat and it is wide, but its edges are spaced inwardly of the interior surface of the housing 2% to provide an insulating air space intermediate the heat-absorbing member and the housing. The right-hand end 63 of the heat-absorbing member 62 is also reduced in cross-section, but it is wider than the reduced cross-section, left-hand end of the eat- The numeral 50 denotes a sleeve-like rivet that is telescoped through the aligned openings 3% and it? of the terminal 24 and heat-generating conductor 38, respectively; and it is also telescoped through a washer That rivet permanently secures the terminal and the heat-generating conductor together; and it coacts with the support 52 to hold the heat-generating conductor 38 adiacent the geometric axis of the housing 20.

The numeral 66 denotes a wire that has a cross section that is much smaller than the cross section of the heatgenerating conductor 38, and that wire will blow whenever it has to carry all of the rated current of the fuse. That wire is encased in asbestos or some other heat-insensitive insulating material. One end of the wire as is stripped of its insulation and is extended up through the sleevelike rivet t and the other end of that wire is stripped of its insulation and is extended up through the opening 64 in the reduced cross-section, left-hand end of the heat-absorbing member 62. Bonding material 63, such as solder, holds the wire 66 in electrically-conducting relation with the terminal 2 and with the heat-absorbing member 62. The Wire 66 is made long enough so it can be spaced from the heat-generating conductor, and thereby kept from being heated appreciably by that heat-generating conductor. An inert filler 1%, such as calcium sulfate, is disposed in the compartment defined by the closure 32 and the support 52, and that filler will help keep the wire 66 from being appreciably heated by the heat-generating conductor 33. Also, that filler will help quench any are that may form when the wire 66 blows.

The numeral 7% denotes a connector that is made from two U-shaped pieces of metal, from a square piece of metal, and from one end of a helical extension spring 72. One of the U-shaped pieces of metal is lighter in weight than the other, and it is disposed so its open end faces to the left, as that connector is viewed in FIG. 2. The other U-shaped piece of metal is disposed so its open end faces to the right, and so its upper arm overlies the lower arm of the upper U-shaped piece of metal. The square piece of metal is disposed within the other U-shaped piece of metal; and it underlies the lower arm of the upper U- shaped piece of metal. The left-hand end of the helical spring 72 is disposed between the square piece of metal and the lower arm of the other U-shaped piece of metal.

The two U-shaped pieces of metal, the square piece of metal, and the left-hand end of the spring 72 are set in position, and then a heavy pressure is applied to the upper and lower faces of the upper and lower arms, respectively, of the other U-shaped piece of metal. That pressure is heavy enough to clamp the arms of that other U-shaped piece of metal tightly enough to hold all four components of the connector '70 in permanently assembled relation. When the connector 7% is completed, its upper U-shaped piece of metal will define a recess that can telescope freely over the right-hand end 46 of the heat-generating conductor 3%). A. mass 74, of heat-softenable material such as solder, fills that recess and also engages the heat-absorb ing member 62. That mass normally holds the connector 70 in mechanical and electrically-conducting engagement with the heat-generating conductor 38 and with the heatabsorbing member 62. However, that mass can respond to heat to soften and release that connector for movement out of that engagement; and when that connector moves it will move as a unit.

A support 58 of insulating material has the form of a notched circular disc; and the diameter of that disc is smaller than the inner diameter of the housing Ztl. As a result, that support can move freely relative to the housing 2% in the axial direction. The notch 59 in the support 58 is wide enough to slip over the reduced cross-section end 63 of the heat-absorbing member 62, as shown by FIG. 5. A hook 659 is set in a slot in the support 58, and the right-hand end of that hook is riveted over to maintain that hook in assembled relation with that support. That hook receives and holds the other end of the t. helical extension spring '72, and that spring biases the connector 7% for movement out of its normal engagement with the heater 38 and with the heat-absorbing member d2. As a result, when the heat softenable material 74- responds to heat to soften and release the connector ill, that connector will respond to the spring 72 and move out of its normal mechanical and electrically-conducting engagement with the heater and with the absorber 62.

The numeral 76 denotes an end bell of metal which has its right-hand face machined away to form a shallow, cup-like recess. The numeral '73 denotes an end bell of metal which has its left-hand face machined away to form a shallow, cup-like recess; and the end bell 73 is materially thicker and thus has more thermal capacity than the end bell '76. The end bells 76 and 73 are made so their diameters are smaller than the inner diameter of the housing 243; and therefore those end bells can move freely relative to the housing 29 in the axial direction. The reduced cross-section portion 63 of the heat-absorbing member d2 is permanently connected to the left-hand face of the end bell 76, as by silver solder or the like; and a terminal 82 is permanently connected to the righthand face of the end bell '73, as by silver solder or the like. The terminal 32 is rectangular in plan, and it is narrow enough to permit the left-hand end thereof to telescope within the right-hand end of the housing 20; but it is as wide as the diameter of the end bell '78. The terminal as has protuberances 83 thereon, and those protuberances are conveniently formed by a staking operation.

A closure 36 of cup-shaped configuration has an inner diameter which is slightly larger than the outer diameter of the housing 2%, and that closure can be telescoped over the right-hand end of that housing. A slot 38 is provided in the closure 86, and that slot is sufficiently larger than the terminal 82 to enable that terminal to move longitudinally relative to that closure. The closure 86 will be telescoped over the terminal 82 and over the right-hand end of the housing 26* before the protuberances 83 are formed on that terminal, and those protuberances will prevent unlimited movement of the terminal 82 to the left. The closure 86 has openings which can be set in register with the threaded openings 22 in the housing 2t adjacent the right-hand end of that housing. Fasteners 84 with threaded shanks can be passed through the openings 85 and seated in the threaded openings 22 to fixedly prevent separation of the closure 86 from the housing 29.

The numeral 9% denotes a right-circular cylinder which is made of a high-alumina ceramic; and one such highalumina ceramic is Frenchtown Porcelain Company No. 4462. That cylinder is resistant to abrasion, corrosion, thermal shock and mechanical shock, and it has good dielectric properties. The cylinder htl has a number of cylindrical passages 92 through it; and in the embodiment shown by FIGS. 1-10, there are three passages d2. However, more or fewer passages 92 can be formed in the cylinder hit. The end faces, and the end portions of the outer surface, of the cylinder are provided with thin coatings 93 of metal; and those coatings are preferably formed by a metallizing process. ln that process, a material such as Frenchtown Porcelain Company Nicote is painted on, or otherwise applied to, the end faces and the end portions of the outer surface of the cylinder 99, and then that cylinder is fired at a high temperature. Soft solder is then applied to the metallized coatings to tin them; and then the cylinder 9% is cleaned to free it of solder flux.

The numeral '94 denotes a fusible conductor or fuse link which has a number of transversely-directed narrow openings $6 therein and which has a circular opening 97 therein. That conductor will preferably be made of silver; and it is dimensioned so it can be disposed within one of the cylindrical passages 92 Without having any portion thereof touch the wall of that passage. The fuse shown in FIGS. llO has three fusible conductors 94; one for each passage 92.

Cup shaped Washers 98 provided to close the ends of the passages 92 in thecylinder 9d; and the tapered walls of those washers engage and are centered by the passage-defining portions of that cylinder, as shown particularly by FIG. Each of the cup-shaped washers 98 has a diametric slot 100 therein, and those slots are made slightly larger than the cross sections of the fusible conductors 94. The tapered walls of the cup-shaped washers 98 will center the slots 1% relative to the passages 92, and those slots will center the fuse links 94 relative to those passages 92. The overall result is that the fusible conductors 94 are positively centered with regard to the passages 92. Solder 101 engages the cup-shaped washers 9 8 and also engages the tinned coatings 93 of metal and the fuse links '94. That solder hermetically seals the ends of the passages 92 and electrically bonds the fuse links 94 and the cup-shaped washers 98 and the tinned metal coatings 93 together. The cup-shaped Washers '98 not only center the links 94 but also provide adequate contact areabetween those links and the

end bells

76 and 78.

The numeral W2 denotes quantities of anhydrous calcium sulfate that are disposed within the passages 92 of cylinder W and that embed the left-hand ends and the left-handmost openings 96 of the fusible conductors 94.

i The numeral lit 2- denotes quantities of quartz sand that are disposed within the passages 92 of cylinder 9% and that embed the circular openingsl 7 and the remaining openings 96 of the fusible conductors 94. The interfaces between the quantities of anhydrous calcium Sulfate and quartz sand will be intermediate the circular openings 97 andthe left-handmost openings 960i thefusible conductors 94-. The quartz sand can respond toblowing of the fuse links to form fulgurities during extinction of arcs that form when those fuse links blow: The anhydrous calcium sulfate keeps the fulgurities from spanning the full lengths of the passages 92. of the cylinder 90, and it also prevents the establishment of after-blow resistance paths through thepassages 92 of cylinder 90.

In assembling the fuse links 9'4 with the cylinder 9%,

each of the fuse links 194 has one of its ends bent, and

94 are telescoped through the passages 92 until the tapered walls of the cup-shaped Washers 93 intimately engage and are held and centered by the passage-defining portions of the cylinder ill; and at that time further solder 101 is used to seal those cup-shaped washers to the tinned metal coatings Q3.

Preferably the bent ends of the fuse links 94 will be adjacent the right-hand end of cylinder 94 and the other ends of those fuse links will be adjacent the left-hand end of that cylinder, as that cylinder is viewed in FIG. 1. Where that is the case, the cylinder 9d can be rotated ninety degrees inthe clockwise direction from the position shown in FIG. 1, and quartz sand 2G4 can be introduced into the passages 92. That sand will embedthe circular opening SW and the three, narrow openings 96 intermediate that circular opening and the lower end of each of the fuse links 94. Once this has been done, anhydrous calcium sulfate will be introduced, into and will be used to fill, the upper ends of the passages 92. That anhydrous calcium sulfate will embed the uppermost opening 96 in each of the fuse links 94.

Three additional cupshaped'washers 93 Will then have the slots 10%} tlereof telescoped over the upper ends of the'fuse links 9 and those upper ends will then be bent over to maintain those cup-shaped washers inassembled relation with those fuse links.

Further solder 1M will it! i be used to bond those cup-shaped washers as to the upper ends of the links 94, and also to secure those cup-shaped washers to the tinned metal coatings 93 on the ends of the cylinder as. This further solder Th1 coacts with the solder M l at the opposite end of the cylinder 93, and with the cup-shaped washers 9% at both ends of the cylinder dd, to hermetically seal the passages )2. The cylinder with its fuse links $4 and its fillers Th2. and res, serves as the shoit-circuiting chamber of the fuse shown in FIGS. 1-10.

At this time the end bell 78, to which the terminal 82 has previously been permanently secured, is set so its recessed end is uppermost. That end bell is then heated to the melting point of solder, the cylinder 9% is set so the sand-filled end thereof is within the recessed end of end bell '78, solder is applied to that recessed end. and is caused to melt and bond that cylinder and end bell together, and. then the end bell and solder are permitted to cool. That solder will mechanically and electrically bond the short-circuiting chamber to the end bell 78.

The end hell 7%, to which the absorber62 has previously been permanently secured, is then setwith its recessed end uppermost. That end bell is then heated to the melting point of solder, the shortcircuiting chamber with its attached end bell '78 and terminal 82 will then be inverted and set in the recess of the end bell 7'6. Solder will then be applied to the recess in the end bell 76, and that solder will melt and intimately bond that end bell to the short-circuiting chamber; and then that end bell and the solder will be permitted to cool.

The support 52 will then have its slot 54 telescoped over the reduced cross-section, lefthand end of the absorber 62; and the heater 3-3, which has previously been riveted to the terminal 2 5-, will have its reduced crosssection portion 46 telescoped through the slot 54 in that support 52. The axis of the terminal 2-4 will then be alined with the axis of the absorber 6'2, and thereafter the connector 70 will be set so the lower loop thereof rests upon the absorber 62 and so the upper loop thereof telescopes over the reduced cross-section end 45 of the heater 38'. Heat-softenahle material "Id will then be applied to the connector 7h, to the heater 33, and to the absorber 62; and that heat-softenable material will mechanically and electrically bond the connector '76 to that heater and absorber. I

The notch 59 in the support 53 willithen be telescoped down over the reduced cross section portion-63 of the absorber 62;; and that support will thus be intermediate the end bell '76 and the fulhwidth portion of the heatabsorbing member d2. The right-hand end of the helical extension spring 72 will then be secured to the upper end of thehook till. That spring will be under tension and will bias the connector its for movement out of its mechanical and electrically-conducting engagement with the heater 38 and absorber s2.

The opposite ends of the wire 66 will be stripped of their insulation and will then be telescopes upwardly through the rivet 59; and through the opening as in the absorber 62. Solder 58- will be applied to those ends of that wire to bond those ends to the terminal 24 and to the absorber 62. At this time, all of the electricallyconducting components of the fuse will be electrically bonded together to constitute one, continuous, integrated conductor.

The wire 66 will be in parallel with, and will thus shunt the heater -38. The overall resistance of the Wire 56 will be materially greater than that of the heater 38; and, therefore, as long asthe connector 76 is in its normal, electrically-conducting engagement with the heater 38 and absorber as, the shunt wire 66 will carry very little current. However, When the connector 7a is moved out of its normal, electrically-conducting engagementwith the heater 3% and absorber 62, the wire 66 will have to carry all of the current; and that current will cause that who to blow.

The fusible conductors 94 are in parallel with each other, and each of those fusible conductors will carry its proportionate share of the total current passing through the fuse. The openings 95 and d7 provide weak spots in those fusible conductors, and those weak spots will generate the great-est temperatures generated by those fusible conductors. The amount of heat generated by those fusible conductors will be great enough to blow those fusible conductors on heavy overloads and on short circuits. Because the quartz sand 1% within the passages 92 is kept relatively cool by the end bell 7S and the terminal 82, the fuse links 94 can be made of smaller-than-normal cross section, and the

openings

96 and 97 can be made larger than normal. The overall result is that the fuse links 94 are very fast-acting and can provide important and desirable current-limiting characteristics.

The overall integrated conductor, including the terminals 24 and 82, the heater 38 and the shunt wire 6%, the connector 7d, the absorber 62, the short circuiting chamber .Btl, and the end balls '76 and 73 is then telescoped into the housing 269. That telescoping will be done by passing the terminal 82 all the way through the housing and that telescoping will be limited by the eugage ment of the pin 26 with the left-hand end of the housing 2d. Once the overall integrated conductor has been telescoped within the housing 2%, the compartment defined by the support 52 and the left-hand end of the housing 24 will be filled with a filler such as calcium sulfate 1%. Thereupon, the closure 32 will have its slot 34 alined with, and telescoped over, the terminal 24-; and then that closure will be moved into holding engagement with the pin 25. The fasteners 35 can then be passed through the openings 35 in the closure 32. and seated in the threaded openings 22 adjacent the left-hand end of the housing 29 to permanently secure the overall integrated conductor and the closure 32 to the housing Ztl. Thereafter, the closure 86 will have its opening 88 alined with, and telescoped over, the terminal 82; and that closure will be moved until its openings 85 are in register with the threaded openings 22 adjacent the right-hand end of the housing 20. At this time, the fasteners 84 will have their threaded shanks passed through the openings 85' and seated in those openings 22. Those fasteners will permanently secure the closure 86 to the housing Ell; but the terminal 82, the end bell '78, the cylinder the end bell '76, the support 58, the absorber 62, the connector "iii and the support 52 will be free to move axially of the housing 22. Thereafter, the terminal 32 will be staked to form the protuberances $3 at each side thereof; and those protruberances are spaced a short distance to the right of the closure 86, and they project outwardly beyond the sides of the slot 3% of closure 36. Those protuberances will keep a heavy pressure or a severe blow from driving the terminal 82, the end bell 78, the cylinder 90, the end bell 76 and the absorber 62 to the left to cause binding between the connector 70 and the heater 3%.

Under normal conditions of operation, the fuse of FIGS. l-lO will carry its rated current and will occasionally carry transient overloads. The reduced

cross-section portions

42 and 4 of the heater 38 will respond to the passage of the rated current through the fuse to generate heat, and the weak spots in the fuse links 94 formed by the openings 9t? and 97, will also respond to the passage of that current to generate heat. The heat absorber 62 will respond to the heating of the heater 33 and of the fuse links 94 to become heated, but that absorber will not become hot enough to permit the heat-softenable material '74 to soften. Only where an objectionable overload is continued for an objectionable length of time will be heat supplied to, and held by, the absorber 62 be great enough to soften the heat-softenable material 74. However, once that material does soften, it will release the connector 7%; and the spring 72 will thereupon move that connector out of its electrically-conducting engagement with the heater 33 and absorber 62. At such time, the circuit through the iii.

heater 38 will be interrupted, but the circuit through the shunt wire 65 Will be intact. The circuit through the shunt wire 66 will prevent or minimize arcing in the compartment defined by the

supports

52 and 58; and this is very desirable. The shunt wire 66 will be unable to carry the rated current of the fuse, much less any overloads that cause the heat-softenable material '74 to soften; and hence that wire will blow. However, any arcs that form when that wire blows will be quickly extinguished by the filler 1% which embeds that Wire.

if the overloads to which the fuse is subject are extremely heavy overloads or are short circuits, the fuse links 9-3 will blow in one or more of their openings 96. Any arcs that form will be extinguished by the fillers 102 and 104-. The fuse links 94 will open very promptly, and thus they will limit the current that has to be carried by the circuit whenever a heavy overload or a short circuit occurs.

Where heavy overloads of short duration are recurrently applied to the fuse, the heater 38 will expand and contract appreciably; and that heater can tend to force the connector 70 to move axially of the housing 2%. Such movement will not cause binding of that connector because that movement will be compensated for by the axial movement of the absorber 62 and of the short circuiting chamber with its end bells. That axial movement thus compensates for expansions and contractions of the heater 38; and it also compensates for changes in the overall length of the housing 20 due to expansion or contraction of that housing.

The fuse of FIGS. 1-10 thus provides the desirable time lag of a dual element fuse on low overloads, and provides current-limiting operation on heavy overloads and on short circuits. Thus, the fuse of FIGS. 1-10 provides exceptionally desirable circuit protection.

FIGS. 11-14 show a fuse which is very similar to the fuse of FIGS. 1-10. The principal difference between the fuse of FIGS. 11-14 and the fuse of FIGS. 1-10 is the substitution of stamped end bells for the machined end bells of the fuse of FIGS. 1-10.

The fuse of FIGS. 11-14 has a tubular housing 124) of a readily available, inexpensive insulating material such as fiber, That housing has an unobstructed interior surface, and it has threaded openings 122 adjacent the opposite ends thereof. A terminal 124 has an opening, not shown, adjacent the right-hand end thereof, and it also has a second opening, not shown, to the left of the first opening. That second opening receives and fixedly holds a transversely-directed, bar-like pin 126; and that pin bears against the left-hand end of the housing 120.

The numeral 132 denotes a cup-shaped closure that can telescope over the left-hand end of the housing 12 and that closure has a slot 134 which telescopes over the terminal 124. That closure can abut the pin 1% and fixedly hold that pin and the terminal rigid relative to the housing 12%. The closure 132 has openings that can be set in register with the threaded openings 122 adjacent the left-hand end of the housing 126; and fasteners 136 have threaded shanks which pass through the openings in the cup-shaped closure 132 and seat in the threaded openings 122. Those fasteners fixedly secure the terminal 124, the pin 126 and the closure 132 to the housing 129.

The numeral 138 denotes a heater that has an opening, not shown, in the left-hand end thereof which can be set in register with the first opening in the terminal 124. That heater has two reduced cross-section portions 1d and i ll, and it also has a reduced cross-section, right-hand end 146. A washer 143 has the opening therein alined with the opening in the heater 138 and with the first opening in the terminal i2 3; and a sleevelike rivet 159 telescopes through those openings and is riveted over to fixedly secure the heater 138 in permanent engagement with the terminal 124.

The numeral 152 denotes a support of insulating material, and that support has the form of a circular disc.

ine outer diameter of the support 152 is less than the 13 inner diameter of the housing 12d, and therefore the support 1522 can be moved relative to that housing in the axial direction. That support has a slot 154 therein that accommodates the reduced crosssection, right-hand end fl t-6 of the heater 138, and it has a slot 156 that accommodates the reduced cross section, left-hand end of a heat-absorbing member M2. That left-hand end of the absorber 162; has an opening. not shown, through it; and that opening accommodates one end of a shunt wire 166 which is encased in asbestos or some otner heat-insensitive insulating material. The other end of that shunt wire extends upwardly through the sleeve-like rivet 15d; and solder 168 bonds the ends of the wire 166 to the terminal 124 and to the absorber 162. Filler mat rial 2% will embed the wire res and will quench any arcs that may tend to form when that Wire blows.

A connector 170, which is identical to the connector 7% of the fuse of FIGS. 1-10, is bonded to the heater 233 and to the absorber 162 by heat-sottenable material 174. That connector is normally bonded in mechanical and electrically-conducting engagement with the heater lfiti and the absorber 162; but it can move out of that engagement when that heat-softenable material softens.

The right-hand end of the absorber 162 has a reduced cross-section portion 163, and that reduced cross-section portion has a width approximately one half of the width of the absorber 162. The reduced cross-section portion 163 accommodates a notch H in a circular support 158 of insulating material. That support receives and holds a'hook 16!); and that book receives and holds the righthand end of a helical extension spring 172.. That spring biases the connector llll for movement out of its electrically-conducting engagement with the heater 138 and absorber 162.

The reduced cross-section, right-hand en 1163 of the absorber M2 is permanently secured, as by silver solder or the like, to a cup-shaped end bell 1176. That end bell is preferably formed by a stamping operation; and while that end bell is not as thick as the end bell '76 of the fuse of FZGS. 1-10, that end bell has appreciable thermal mass. Bonded to the right-hand face of the end bell 1% by solder is a short-circuiting chamber including the cylinder 19 9, three {use links 194, and six cupshaped washers 1% which have diametric slots 24% to accommodate the fuse links 1%. The right-hand end of that short-circuiting chamber is bonded, by solder, to a cup-shaped end bell E73; and that end bell is preferably formed by a stain ing operation. That end bell is permanently secured, as by silver solder or the like, to the left-hand end of a terminal 182; and that terminal is longer than the terminal 82 of the fuse of FIGS. 1-18. That terminal has protuberances lit?) at the sides thereof comparable to the protuberances $3 on terminal 820i the fuse of FIGS. 1-10.

The right-hand end of the housing 126 is covered by a cup-shaped closure 136; and that closure has a slot 188 which loosely accommodates the terminal 182. Fasteners 1&4 extend through openings in the closure 186 and seat in threaded openings 121% adjacent the right-hand end of the housing 12%); but while the fasteners 134 fixedly hold the closure res in assembled relation with the housing i2 0, they do not preclude axial movement of the terminal 182, of the short-circuiting chamber and its

end bells

176 and 178, of the absorber 162 of the connector 17b, and of the

supports

152 and 158.

Because of the substitution of the

stampedend bells

176 and 178 for the machined end bells 176 and '78, the current-limiting characteristics of the fuse of FIGS. l1- 14 will not be as great as those of the fuse of FIGS. 1-10. However, the fuse of Fl'G-S. 11-14- will have important and desirable current-limiting characteristics; and it will provide important and valuable circuit protection, as by permitting the connector 176 to move on low overloads and by permitting the links in the short-circuiting chamher to blow on heavy overloads and short circuits.

Referring to FEGS. l5 and 16, the numeral denotes a tubular housing of a readily available, inexpensive insulating material such as fiber. That housing has an unobstructed interior surface, and it has threaded openings 222. adjacent the opposite ends thereof. A terminal 224, similar to the terminals 24 and 12.4, has an opening, not shown, adjacent the right-hand end thereof; and it has a second opening, not shown, to the left of the first opening. That second opening receives and holds a bar-like, transversely-extending pin 226. That pin is longer than the inner diameter of the housing 22%, and the fiat face of that pin abuts the left-hand end of that housing. A cup shaped closure 232 has a slot 234 which accommodates the terminal and it also has openings which can be alined with the threaded openings 22. adjacent the left-hand end of the housing 226. Fasteners 236 have threaded shanks that extend through the openings in the closure 232 and seat in the threaded openings of the housing 22%.

The numeral denotes a heater which has reduced I cros section portions 242 and 244 and which has a reduced cross-section, right-hand end 246. That heater is substantially identical to the

heaters

38 and 138 of the fuses of FIGS. 140 and 11-14, respectively. An opening, not shown, in the left-hand end of the heater 238 is alined with the first opening in the right-hand end of the terminal 234; and a washer has its opening alined with those openings. A sleeve-like rivet 250 extends through the alined openings in the heater 2.38, the terminal 224, and the washer; and that rivet permanently secures the heater 238 to the terminal 224.

A support 252; of insulating material has the form of a circular disc; and that support has a diameter smaller than the inner diameter of the housing 220. The support Z'b'Z has a slot 254 that accommodates the reduced cross-section, right-hand end 246 of the heater 23S, and it also has a slot 25d to accommodate the reduced crosssection, left-hand end of a heat-absorbing member262. That left-hand end of the absorber 262' has an opening through it; and one end of a shunt wire 266 extends through that opening. The other end of that shunt Wire extends through the sleeve-like rivet 25%; and the ends of that shunt wire are bonded tothe absorber 262 and to the terminal 224. That wire is encased in asbestos or some other heat-insensitive insulating material. material 3% Will embed the Wire 266 and will quench any arcs that may tend to form when that wire blows.

The numeral 258 denotes asupport which is smaller than the housing 22% and which can move freely within the housing 224} in the axial direction; and that support has a notch 25h That notch telescopes over the reduced cross-section, right-lend end 263 or" theabsorber 262. That support carries a hook 269, and that book receives and holds the right-hand end of a helical extension spring 272. That spring biases a connector 27% out of its normal, mechanical and electrically-conducting engagement with the heater 2.38 and the absorber 2&2. The connector 27% is identical with the connectors 79 and 17d of the fuses of P168. 1-10 and ll-14, respectively. Heat softenable material 274- normally holds the connector 270 in that mechanical and electrically-conducting engagement, but it will respond to heat to soften and release that connector. When that heat-softenable material softens, the spring ZWZwill move the connector 270 to the right and open the circuit of the fuse.

The numeral 2'76 denotes an end bell which is permanently secured, as by silver solder or the like, to the reduced cross-section end 263 of the absorber 262. That end bell is a solid, cylindrical, metal disc, but it has a number of radially-extending openings at the periphery thereof. The numeral 278 denotes a similar end bell, and those end bells are dimensioned to telescope within a sleeve 2% of glass'melam-ine.

imensionally stable, and it can be made so it ha a very close lit with the peripheries of the

end bells

276 and 278. The sleeve 2% has openings adiacent the ends thereof, and those openings will accommodate steel pins Filler That sleeve will be 291. Those pins will have press fits with the radial openings at the peripheries of the end bells 276 and 27?, and those pins will permanently secure the sleeve 25% to the

end bells

276 and 278. The inner diameter of the sleeve 2% is larger than the Width of the absorber 2522 but is smaller than the Width of the terminal 2'62.

Intermediate the end bells 27d and 278 are a number of fusible conductors 294; and each of those fusible conductors has four narrow openings 2J6 therein plus one circular opening 29'? therein. As indicated particularly by FIG. 15, the circular opening 297 is adjacent the lefthand end of the fusible conductor 2% but is spaced from that left-hand end by an intermediate narrow opening The ends of the fusible conductors 2% are permanently secured to the confronting faces of the

end bells

276 and 278, as by solder. Where desired, slots or notches can 'be formed in the confronting faces of the end bells 276 and 2,73, and those slots or notches will accommodate the ends of the fuse links 2%. Anhydrous calcium sulfate as; embeds the left-hand ends of the fusible conductors 2%, and quartz sand embeds the middlcs and also the right-hand ends of the fusible conductors 2%. This arrangement of fillers is exactly the same as the arrangement of fillers in the fuse of FIGS. 1-10.

A terminal 2-32 is permanently secured, as by silver solder or the like, to the right-hand face of the end bell 278. That terminal has protuberances 283 at the opposite side thereof. That terminal has t .e left-hand end thereof loosely lodged Within a slot 238 in a cup-shaped closure 2236 for the right-hand end of the housing 22%. That closure has openings which accommodate fasteners 284; and the threaded shanks of those fasteners extend through those openings and seat in threaded openings 22?, adjacent the right-hand end of the closure 22%.

In fabricating the short-circuiting chamber which includes the sleeve 2%, the

end bells

276 and 278, the fusible conductors 294, and the filler materials 362 and 304, the end bells 2'76 and 278 are first equipped with the absorber 262 and the terminal 232, respectively; and thereafter the fusible conductors 294 are soldered to the

end bells

276 and 278. At such time, the end bell 276 is telescoped part Way into the tube 2%, and then anhydrous calcium sulfate 31692 is poured into the sleeve 2%. The end bell 273 is then telescoped within the right-hand end of the tube 296, and thereupon the threaded plug 31th can be removed from the threaded opening in the end bell 278. Quartz sand 364 i then introduced through that opening; and once the compartment defined by the

end bells

276 and 278 and the sleeve 29%; is filled, the threaded plug 316 can be replaced.

The fuse of FIGS. and 16 differs from the fuses of FIGS. 1-10 and 11-14 in the construction of the shortcircuiting chamber; but the operation of the fuse of FIGS. 15 and 16 is the same as the operations of those other fuses. The short-circuitin=g chamber shown in FIGS. 15 and 16 is cheaper and easier to make than are the shortcircuiting chambers of the fuses of FIGS. 1-10 and 11-14.

Referring to FIG. 17, the numeral 329 denotes a housing of a dimensionally stable dielectric material, and one such material is glass melamine. Disposed Within, and located adjacent the left-hand end of, the housing 329 is an end bell 3'75 which differs from the end bell '76 of FIGS. 1-10 because it has radially-directed openings 377 at the periphery thereof and because it has a terminal, rather than a heat-absorbing member, permanently secured to it. An end bell 378, which is identical to the end bell 376, is disposed Within and adjacent the other end of the housing 32% and that end bell has radiallydirected peripheral openings 37 7, and has a terminal 332 permanently secured to it, as by silver solder or the like. Steel pins 379 extend through openings in the housing 329 and seat in the radially-directed peripheral openings 377 in the end bells 376 and 373 to permanently secure those end bells to that housing.

The contror ing faces of the end bells 376 and 373 are machined to form cup-like recesses, and those cup-like recesses accommodate the ends of a cylinder 3% which is identical to the cylinder t of the fuse of FIGS. 1-10. That cylinder has metal coatings at the opposite ends thereof, has cup-shaped washers, and has fusible conductors 394 extending through the cylindrical passages 392 therein. The only differences between the short-circuiting chamber of FIGS. 10 and 17 are that each of the fusible conductors 3% has a mass 3% of alloying material pressed into the circular opening 397 thereof and that insulating discs 399 are intermediate the

filler materials

382 and 3%. The masses 3% are made of an alloying material such as tin, which will respond to heat to alloy with the metal of the fusible conductors 394 and thereby causes blowing of those conductors. This alloying action will occur whenever objectionable overloads continue for objectionable periods of time.

The fuse of FIG. 17 will protect against heavy overloads and short circuits by blowing at the openings 396 of the links 394; and that fuse will protect against lesser overloads by the alloying action between the masses 395 and the metal of the fusible conductors 3%. Thus the fuse of FIG. 17 provides full circuit protection.

Whereas the drawing and accompanying description have shown and described several preferred embodiments of the present invention, it should be apparent to those skilled in the art that various changes may be made in the form of the invention without affecting the scope thereof.

What I claim is:

1. In a protector for electric circuits, a tubular housing of insulating material, a terminal that is carried by one end of said housing and that is held against movement relative to said housing, a heat-generating conductor that has one end thereof fixedly secured to said terminal and that has the other end thereof disposed Within said housing and spaced from said terminal, a heat-absorbing member having one end thereof adjacent said other end of said heat-generating conductor and having the other end thereof directed toward the other end of said housing, a connector that is adjacent said other end of said heatgenerating conductor and said one end of said heatabsorbing member, heat-softenable material that engages said heat-generating conductor and said heatabsorbing m mber and said connector and normally holds said heat-generating conductor and said heat-absorbing member and said connector in mechanical and electricallyconducting engagement, a spring that has one end thereof secured to said connector and that biases said connector for movement out of said electrically-conducting engagement With said heat-generating conductor and said heat-absorbing member and that responds to softening of said heat-softenable material to move said connector out of said electrically-conducting en agement with said heatgenerating conductor and said heat-absorbing member, a second tubular housing of insulating material that is disposed Within the first said housing and that is movable reiative to the first said housing, said inner housing being intermediate said other end of said heat-absorbing member and said other end of the first said housing, end bells for said inner housing, a fusible conductor disposed Within said inner housing and electrically connected to said end bells, one of said end bells being in mechanical and electrically-conducting engagement with said other end of said heat-absorbing member, a second terminal, said second terminal having one end thereof in mechanical and electrically-conducting engagement with the other end bell of said inner housing, a support that is disposed Within but is movable relative to the first said housing and that supports said other end of said heatgenerating conductor and said one end of said heatabsorbing member, a second support that is disposed Within but is movable relative to the first said housing and that supports the other end of said spring, and a closure heat-absorbing member and said inner housing and second terminal being movable relative to the first 17 for said other end of the first saidhousing, said closure supporting said one end of said second terminal while permitting movement of said second terminal relative to it, the first said support and said heat-absorbing member and said second support and said inner housing and said second terminal being movable relative to the first said housing as said heat-generating conductor expands and contracts, whereby said connector is not bound but is free to move out of said electrically-conducting engage- 'ment with said heat-generating conductor and said heatabsorbing member whenever said heat-softenable material softens, said second terminal having motion-limiting protuberances thereon that are disposed outwardly of, and that are normally spaced from, saidclosure for said other end of said housing, said protuberances preventing inward movement of said heat-absorbing member and said inner housing and said second terminal that could bind said connector and prevent movement of said circuitopening connector. i

2. In a protector for electric circuits, a housing, a tenninal that is carried by one end of said housing and that is held against movement relative to said housing, a heatgeneratin'g' conductor that has one end thereof fixedly secured to said terminal and that has the other end thereof disposed within said housing and spaced from said terminal, a heat-absorbing member having one end thereof adjacent said other end of said heat-generating conductor and having the other end thereof directed toward the other end of said housing, a connector that is adjacent said other end of said heat-gener ating conductor and said one end of said heat-absorbing member, heat-softenable material that normally holds said heat-generating conductor and said heat-absorbing member and said connector in electricallyconducting engagement, a spring that biases said connector for movement out of said electricallyconducting engagement with said heat-generating conductor and said heat-absorbing member and that responds to softening of said heat-softenable material to move said connector out of said electrically-conducting engagement with said heat-generatingconductor and said heat-absorbing member, a second housingthat is disposed within the first said housing and that is movable relative to the first said housing, said inner housing being intermediate said other end of said heat-absorbing member and said other end of the first said housing, end bells for said inner housing, a fusible conductor disposed within said inner housing and electrically connected to said end bells, one of said end bells being in mechanical and electrical engagement with said other end of said heat-absorbing member, a second terminal, said second terminal having one end thereof in mechanical and electrical engagement with the other end bell of said inner housing, and a closure for said other end of the first saidhousing, said closure supporting said one end of said second terminal while permitting movement of said second terminal relative to it, said said said housing as said heat-generating conductor expands and contracts, whereby said connector is not bound but is free to move out of said electrically-conducting engagement with said heat-generating conductor and saidheahabsoibing member whensaid heat-softenable material softens, said second terminal having a motion-limiting protuberance thereon that is disposed outwardly of andis normally spaced from said closure for said other end of said housing, said protuberance preventinginward movement of said heat-absorbing member and said inner housing and said secondterminal that could bind said connector and prevent movement of said connector.

3. In a protector for electric circuits, a housing, a terminal that is carried by one end of said housing and that is held against movement relative to said housing, a heat generating conductor fixedlysecured to said terminal, a heat-asborbing member, a connector, heat-softenable material that normally holds saidheat-generating conduc 18 tor and said heat-absorbing member and said connector in electrically-conducting relation, a spring that biases said connector formovement out of said electrically-conduc ing relation and that responds to softening of said heatsoftenablematerial to movesaid connector out of said electrically-conducting relation, a second housing that is disposed within the first said housing and is movable relative to the first said housing, said inner housing being intermediate said heat-absorbing member and said other end of the first said housing, a fusible conductor disposed Within said inner housing, said fusible conductor being in electrically-conducting relation with said heatabsorbing membena second terminal, said second terminal having one end thereof in electrically-conducting relation with said fusible conductor, and a closure for said other end of the first said housing, said closure supportingsaid one end of said second terminal While permitting movement of said second terminal relative to it, said heat-absorbing member and said inner housing andsa id second terminal being movable relative to the first said housing as said heat-generating conductor expands and contracts, whereby said connector is not bound but is free to move out of said electrically-conducting relation Whenever said heat-softenable material softens, said second terminal having a motion-limiting protuberance thereon that is disposed outwardly of and is normally spaced from said closure for said other end of said housing, said protuberance preventing inward movement of said heat-absorbing member and said inner housing and said second terminal that could bind said connector and prevent movement of said connector.

4. In a protector for electric circuits, a housing, a terminal at one endof said housing that is held against movement relative to said housing, a heat-generating conductor that has one end thereof fixedly secured to said terminal and that hasthe other end thereof disposed within said housing and spaced from said terminal, a heat-absorbing member, a connector, heat-softenable material that normally holds said heat-generating conductor and said heat-absorbing member and said connector in electrically-conducting relation, a spring that biases said connector for movement out of said electricallyconducting relation with said heat-generating conductor and said heat-absorbing member and that responds to softening of said heat-softenable material to move said connector out of said electrically-conducting relation with said heat-generating conductor and said heat-absorbing member, a fusible conductor disposed within said housing,

ductor, said heat-absorbing member and said fusible conductor and said second terminal normally having only a' frictional connection, plus their connection through said heatgenerating conductor, to said housing whereby said heat-absorbing member and said fusible conductor and said second terminal can move relatively freely relative to said housing, said heat-absorbing member and said fusible conductor and said second terminal being movable relative tosaid housing as said heat-generating conductor expands and contracts, whereby said connector is not bound but is free to move out of said electrically-con ducting relation with said heat-generating conductor and saidheaflabsorbing member wheneve'r said heat-softenable material softens. i

5. In a protector for electric circuits, a tubular housing of insulating material, a terminal that is carried by one end of said housing and that is held against movement relative to said housing, a heat-generating conductor that has one end thereof fixedly secured to said terminal and that has the other end thereof disposed within said housing and spaced from said terminal, a heat-absorbing member having one end thereof adjacent said other end of said heat-generating conductor and having the other end thereof directed toward the other end of said hous ing, a connector that is adjacent said other end of said heat-generating conductor and said one end of said heatabsorbing member, heat-softenable material that engages said heat-generating conductor and said heat-absorbing member and said connector and normally holds said heatgenerating conductor and said heat-absorbing member and said connector in mechanical and electrically-conducting engagement, a spring that has one end thereof secured to said connector and that biases said connector for movement out of said electrically-conducting engagement with said heat-generating conductor and said heatabsorbing member and that responds to softening of said heat-softenable material to move said connector out of said electrically-conducting engagement with said heatgenerating conductor and said heat-absorbing member, a second tubular housing of insulating material that is disposed within the first said housing and that is movable relative to the first said housing, said inner housing being intermediate said other end of said heat-absorbing member and said other end of the first said housing, end bells for said inner housing, a fusible conductor disposed Within said inner housing and electrically connected to said end bells, one of said end bells being in mechanical and electrically-conducting engagement with said other end of said heat-absorbing member, a second terminal, said second terminal having one end thereof in mechanical and electrically-conducting engagement with the other end bell of said inner housing, a support that is disposed within but is movable relative to the first said hosuing and that supports said other end of said heat-generating conductor and said one end of said heat-absorbing member, a second support that is disposed within but is movable relative to the first said housing and that supports the other end of said spring, and a closure for said other end of the first said housing, said closure supporting said one end of said second terminal while permitting movement of said second terminal relative to it, the first said support and said heat-absorbing member and said second support and said inner housing and said second terminal being movable relative to the first said housing as said heatgenerating conductor expands and contracts, whereby said connector is not bound but is free to move out of said electrically-conducting engagement with said heatgenerating conductor and said heat-absorbing member whenever said heat-softenable material softens.

6. In a protector for electric circuits, a housing, a terminal that is carried by one end of said housing and that is held against movement relative to said housing, a heatgenerating conductor that has one end thereof fixedly secured to said terminal and that has the other end thereof disposed within said housing and spaced from said terminal, a heat-absorbing member having one end thereof adjacent said other end of said heat-generating conductor and having the other end thereof directed toward the other end of said housing, a connector that is adjacent said other end of said heat-generating conductor and said one end of said heat-absorbing member, heatsoftenable material that normally holds said heat-generating conductor and said heat-absorbing member and said connector in electrically-conductmg engagement, a spring that biases said connector for movement out of said electrically-conducting engagement with said heat-generating conductor and said heat-absorbing member and that responds to softening of said heat-softenable material to move said connector out of said electrically-conducting engagement with said heat-generating conductor and said heat-absorbing member, a second housing that is disposed within the first said housing and that is movable relative to the first said housing, said inner housing being intermediate said other end of said heat-absorbing member and said other end of the first said housing, end bells for said inner housing, a fusible conductor disposed within said inner housing and electrically connected to said end bells, one of said end bells being in mechanical and electrical engagement with said other end of said heatabsorbing member, a second terminal, said second terminal having one end thereof in mechanical and electrical engagement with the other end bell of said inner housing, and a closure for said other end of the first said housing, said closure supporting said one end of said second terminal while permitting movement of said second terminal relative to it, said heat-absorbing member and said inner housing and said second terminal being movable relative to the first said housing as said heatgenerating conductor expands and contracts, whereby said connector is not bound but is free to move out of said electrically-conducting engagement with said heat-generating conductor and said heat-absorbing member when said heat-softenable material softens.

7. In a protector for electric circuits, a housing, a terminal that is carried by one end of said housing and that is held against movement relative to said housing, a heatgenerating conductor fixedly secured to said terminal, a heat-absorbing member, a connector, heat-softenable material that normally holds said heat-generating conductor and said heat-absorbing member and said connector in electrically-conducting relation, a spring that biases said connector for movement out of said electricallyconducting relation and that responds to softening of said heat-softenable material to move said connector out of said electrically-conducting relation, a second housing that is disposed within the first said housing and is movable relative to the first said housing, said inner housing being intermediate said heat-absorbing member and said other end of the first said housing, a fusible conductor disposed within said inner housing, said fusible conductor being in electrically-conducting relation with said heat-absorbing member, a second terminal, said second terminal having one end thereof in electrically-conducting relation with said fusible conductor, and a closure for said other end of the first said housing, said closure supporting said one end of said second terminal while permitting movement of said second terminal relative to it, said heat-absorbing mem er and said inner housing and said second terminal being movable relative to the first said housing as said heatgenerating conductor expands and contracts, whereby said connector is not bound but is free to move out of said electrically-conducting relation whenever said heat-softenable material softens.

8. In a protector for electric circuits, a housing, a heat-- generating conductor that is disposed Within said housing, a heat absorbing member having one end thereof adjacent said heat-generating conductor and having the other end thereof directed toward the other end of said housing, a connector that is adjacent said heat-generating conductor and said one end of said heat-absorbing member, heatsoftenable material that normally holds said heatgenerating conductor and said heat-absorbing member and said connector in electrically-conducting engagement, a spring that biases said connector for movement out of said electrically-conducting engagement with said heat-generating conductor and said heat-absorbing member and that responds to softening of said heat-softenable material to move said connector out of said electrically-conducting engagement with said heat-generating conductor and said heat-absorbing member, a wire that is disposed within said housing and is connected in parallel with said heatgenerating conductor, said wire being fusible whenever it carries the rated current of said protector for electric circuits, said connector being separable from said heatgenerating conductor to cause said wire to carry the rated current of said protector for electric circuits, and filler material embedding said wire to quench any arcs that form when said wire fuses, said Wire minimizing arcing. adjacent said heat-absorbing member when said connector is moved out of said electrically-conducting engagement and susbequently fusing at a point spaced from said heatabsorbing member, whereby any are that may form as the circuit is opened will be spaced from said heat-absorbing member and can not be fed by the metal of said heatabsorbing member.

9.- In a protector for electric circuits, a housing, a heatgenerating conductor that is disposed within said housing, a heat-absorbing member having one end thereof adjacent said heat-generating conductor and having the other end thereof spaced from said heat-generating conductor, a connector that is adjacent said heat-generating conductor and said one end of said heat-absorbing member, heatsoftenable material that normally holds said heatgenerating conductor and said heat-absorbing member and said connector in electrically-conducting engagement, a spring that biases said connector for movement out of said electrically-conducting engagement with said heatgenerating conductor and said heat-absorbing member and that responds to softening of said heat-softenable material to move said connector out of said electrically-conducting engagement with said heat-generating conductor and said heat-absorbing member, and a wire that is disposed within said housing and is connected in parallel with said heatgenerating conductor, said wire being fusible whenever it carries the rated current of saidprotector for electric circuits, said connector being separable from said heatgenerating conductor to. cause said wire to carry the rated current of said protector for electric circuits, said wire minimizing arcing adjacent said heat-absorbing member when said connector is moved out of said electricallyconducting engagement and subsequently fusing at a point spaced from said heat-absorbing member, whereby any are that may form as. the circuit is opened will be spaced from said heat-absorbing member and can not be fed by the metal of said heat-absorbing member. I

10. In a protector for electric circuits, a housing, a heat-generating. conductor that is. disposed within said housing, a heat absorbing member having'one end thereof adjacent said heat generating. conductor and having the other end thereof directed toward. the other end of said housing, a connector that is adjacent said heat-generating conductor and said one end. of said heatabsorbing member, heat-softenable material that normally holds said heat-generating conductor. and. said heat-absorbing member and said connector in electrically-conductingengagement, a spring. that biases said connector for movement out of said electrically-conducting engagement with said heat-generating conductor and said heat-absorbing member and that responds to-softening of said heat-softenable material to move said connector out of said electricallyconducting engagement with said heat-generating conductor and said heat-absorbing member, a wire that is disposed Within said housing and is connected in parallel with said heat-generating conductor, said wire being fusible whenever it carries the rated current of said protector for electric circuits, said connector being separable from said heat-generating conductor to cause said wire to carry the rated current of said protector for electric circuits, and filler material embedding said wire to quench any arcs that form when said wire fuses, said wire minimizing arcing adjacent said heat-absorbing member when said connector is moved out of said electrically-conducting en-, gagement and subsequently fusing at a point spaced from said heat-absorbing member, whereby any are that may form as the circuit opened will be spaced from said heat-absorbing member and can not be fed by the metal of said heat-absorbing member, said wire having the major portion thereof spaced away from said heat-generating conductor to minimize heating of said wire, said filler material helping to minimize heating of said wire by said heat-generating conductor.

11. An electric fuse that comprises a heat-generating conductor adjacent one end of said fuse, a short-circuiting chamber adjacent the opposite end of said fuse, a

22' connector and a heat-absorbing member that are disposed between said heat-generating conductor and said shor t-circuiting chamber and that connect the confronting ends of said heat-generating conductor and said shortcircuiting chamber, said sbort-circuiting chamber having a fusible conductor therein that generates heat, a terminal that is connected to the other end of said short-circuiting chamber and that thus adjacent said opposite end of said fuse and that conducts heat away from said shortcircuiting chamber, whereby said other end of said shortcircuiting chamber is cooler than said confronting end ofsaid short-circuiting chamber, an inert filler in saidshortcircuiting chamber that surrounds one part of said fusible conductor and is adjacent said confronting end of said short-cirouiting chamber, and sand in said short-cirouiting chamber that surrounds another part of said fusible conductor and is adjacent said other end of said short-circuiting chamber and thus adjacent said opposite end of said fuse.

12. An electric fuse that comprises a hea t-gener-ating conductor adjacent one end of said fuse, a short-circuiting chamber adjacent the opposite end of said fuse, a connector and a heat-absorbing member that are disposed between said heat-generating conductor and said shortcircuiting chamber and that connect the confronting ends of said heat generating conductor and said short-circuiting chamber, said short-circuiting chamber having a fusible conductor therein that generates heat, a terminal that is connected to the other end of said short-circuiting chamber andthat is thus adjacent said opposite end of said fuse and that conducts heat away from said shortcircuiting chamber, whereby said other end of said shortcircuiting chamber is cooler than said confronting end of said short-circuiting chamber, an inert filler in said short-circuiting chamber that surrounds one part of said fusible conductor and is'adjacent said confronting end of said short-circuiting chamber, and sand in said shortcircuiting chamber that surrounds another part of said fusible conductor and is adjacent said other end of said short-circuiting chamber and thus adjacent said opposite end of said fuse, said inert filler bein anhydrous calcium sulfate, said fusible conductor having a reduced crosssection. portion that is embedded within said sand.

13. In a protector for electric circuits, a housing, a heat-generating conductor within said housing and adjacent one end of said housing, a fusible conductor within said housing and adjacent the opposite end of said housing, and a' heat-absorbing member and heat softenable material intermediate and electrically connecting said heat-generating conductor and said [fusible conductor, said heat-generating conductor and said fusible conductor generating appreciable but different amounts of heat whenever said protector for electric circuits carries overloads, said heat-absorbing member having a crosssection which is dimensioned to cause said heat-absorbing member to provide a predetermined delay in the softening of said heat softenable material, said heat absorbing member having a portion of reduced cross section that limits heat interchange between said heat-generating conductor and said fusible conductor so said he at-so ftenable ma-' terial is not prematurely heated to its softening point, the cross section of said portion of reduced cross section not being dependent upon the cross section of said heat-absor'bing member.

14. In a protector for electric circuits, a housing, a heat-generating conductor within said housing and adjacent one end of said housing, a fusible conductor within said housing and adjacent the opposite end of said housing, and a heat-absorbing member and heat softenable material intermediate and electrically connecting said heat-generating conductor and said fusible conductor, said heat-generating conductor and said fusible conductor generating appreciable but different amounts of heat whenever said protector for electric circuits carries overloads, said heat-absorbing member having a cross section which is dimensioned to cause said heat-absorbing member to provide .a predetermined delay in the softening of said heat softenable material, said heat-absorbing member having a portion of reduced cross section that limits heat interchange between said heat-generating conductor and said fusible conductor so said heat-softenable material is not prematurely heated to its softening point, said portion of reduced cross section having a width approximately one half the width of said heat-absorbing member, said heat-absorbing member being fiat.

15. In a protector for electric circuits, a housing, a heat-generating conductor within and adjacent to one end of said housing, a short-circuiting chamber within and adjacent to the opposite end of said housing, a fusible conductor Within said short-circuiting chamber, and a heat-absorbing member and a connector intermediate and electrically connecting said heat-generating conductor and said short-circuiting chamber, said heat-generating conductor and said fusible conductor generating appreciable but different amounts of heat, said heat-absorbing memher having a cross section which is dimensioned to cause said heat-absorbing member to provide a predetermined delay in the releasing of said connector, said heat-absorbing member having a portion of reduced cross section that limits heat interchange between said heat-generating conductor and said fusible conductor so said connector is not prematurely released, the cross section of said portion of reduced cross section not being dependent upon the cross section of said heat-absorbing member, said connector being adjacent said heat-generating conductor and being remote from said short-circuiting chamber.

16. In a protector for electric circuits, a housing, a heat-generating conductor within and adjacent to one end of said housing, a fusible conductor within and adjacent to the opposite end of said housing, and a heat-absorbing member and heat softenable material intermediate and electrically connecting said heat-generating conductor and said fusible conductor, said heat-generating conductor and said fusible conductor generating appreciable but different amounts of heat whenever said protector for electric circuits carries overloads, said heat-absorbing member having a cross section which is dimensioned to cause said heat-absorbing member to provide a predetermined delay in the softening of said heat soften- .able material, said heat-absorbing merrnber having a portion of reduced cross section that limits heat interchange between said heat-generating conductor and said iusibie conductor so said heat-softenable material is not prematurely heated to its softening point, the cross section of said portion of reduced cross section not being dependout upon the cross section of said heat-absorbing member,

24 said heat-generating conductor and said fusible conductor and said heat-absorbing member being bonded into one overall integrated conductor.

17. In a protector for electric circuits, a housing, a terminal that is carried by said housing, a heat-generating conductor fixedly secured to said terminal, a heat-absorbing member, a connector, heat-softenable material that normally holds said heat-generating conductor and said heat-absorbing member and said connector .in electrically-conducting relation, a spring that biases said connector ifor movement out of said electrically-conducting relation and that responds to softening of said heat-softenable material to move said connector out of said electricallyconducting relation, a second housing that is disposed Within the first said housing, said inner housing being intermediate said heat absorbing member and said other end of the first said housing, a fusible conductor disposed within said inner housing, said fusible conductor being in electrically-conducting relation with said heat-absorbing member, and a second terminal, said second terminal having one end thereof in electrically-conducting relation with said fusible conductor, said second terminal being wider than the inner diameter of said inner housing, said heat-absorbing member being narrowed than said inner diameter of said inner housing, whereby substantial amounts of heat can flow from said fusible conductor to said second terminal but only limited amounts of heat can flow from said fusible conductor to said heat-absorbing member.

References (Jilted in the file of this patent UNITED STATES PATENTS 2,159,423 Bussmann May 23, 1939 2,293,953 Taylor Aug. 25, 1942 2,300,620 Duerkob Nov. 3, 1942 2,321,711 Taylor June 15, 1943 2,563,536 Laing Aug. 7, 1951 2,662,140 Kozacka Dec. 8, 1953 2,678,980 Hitchcock May 18, 1954 2,688,677 Laing Sept. 7, 1954 2,694,124 Laing et a1. Nov. 9, 1954 2,734,111 Kozacka Feb. 7, 1956 2,809,254 Edsall Oct. 8, 1957 2,837,614 Fister June 3, 1958 2,859,307 Enk Nov. 4, 1958 2,871,314 Swain et a1. Jan. 27, 1959 FOREIGN PATENTS 22,106 Great Britain Oct. 10, 1902 480,044 Great Britain Feb. 16, 1938

Claims

13. IN A PROTECTOR FOR ELECTRIC CIRCUITS, A HOUSING, A HEAT-GENERATING CONDUCTOR WITHIN SAID HOUSING AND ADJACENT ONE END OF SAID HOUSING, A FUSIBLE CONDUCTOR WITHIN SAID HOUSING AND ADJACENT THE OPPOSITE END OF SAID HOUSING, AND A HEAT-ABSORBING MEMBER AND HEAT SOFTENABLE MATERIAL INTERMEDIATE AND ELECTRICALLY CONNECTING SAID HEAT-GENERATING CONDUCTOR AND SAID FUSIBLE CONDUCTOR, SAID HEAT-GENERATING CONDUCTOR AND SAID FUSIBLE CONDUCTOR GENERATING APPRECIABLE BUT DIFFERENT AMOUNTS OF HEAT WHENEVER SAID PROTECTOR FOR ELECTRIC CIRCUITS CARRIES OVERLOADS, SAID HEAT-ABSORBING MEMBER HAVING A CROSS SECTION WHICH IS DIMENSIONED TO CAUSE SAID HEAT-ABSORBING MEM-