US3061700A

US3061700A - Protectors for electric circuits

Info

Publication number: US3061700A
Application number: US829455A
Authority: US
Inventors: Aloysius J Fister
Original assignee: McGraw Edison Co
Current assignee: McGraw Edison Co
Priority date: 1959-07-24
Filing date: 1959-07-24
Publication date: 1962-10-30
Anticipated expiration: 1979-10-30

Description

Oct. 30, 1962 A. J. FISTER PROTECTORS FOR ELECTRIC CIRCUITS Filed July 24, 1959 0 Cd 2 4 w 4 e9 7 H 5 M 9 H e 6% 9 4 w k F L +4 4 4 5 MW 8 7 6 Q0 k 0 M5 6 M w y n 2 0.8 .w 6 9 J 8 n 2 3 w a 3 7 F H a w a 4 2 8 2 9 a United States Patent ware Filed July 24, 1959, Ser. No. 829,455 Claims. (Cl. 200-120) This invention relates to improvements in protectors for electric circuits. More particularly, this invention relates to improvements in electric fuses.

It is therefore an object of the present invention to provide an improved electric fuse.

When an electric fuse blows, at least a part of the metal of the fuse volatilizes and an arc tends to form; and where an arc does form it will volatilize even more of the metal of the fuse. The overall volatilization of the metal of the fuse will generate a pressure within the housing of the fuse. If that pressure is moderate, it will help to extinguish the arc; but if that pressure is excessive, it could cause the housing of the fuse to burst. The pressure generated during the blowing of a fuse is a function of the severity of the arcing that occurs during blowing; and the severity of the arcing increases as the cube of the voltage. As a result the problem of pressure generation within the housings of fuses used to protect high voltage circuits is more severe than is the problem of pressure generation within the housings of fuses used to protect low voltage circuits. The present invention solves the pressure generation problem of fuses used to protect high voltage circuits by subdividing the fusible elements of those fuses into a number of short fusible elements and by disposing those fusible elements in series relation indifferent but contiguous compartments within the housings of the fuses. It is therefore an object of the present invention to subdivide the fusible element of a fuse into a number of short fusible elements and to dispose those short fusible elements in series relation in separate but contiguous compartments within the housing of the fuse.

The subdividing of the fusible element of a fuse into a number of short fusible elements, and the disposing of those short fusible elements in series relation in separate but contiguous compartments within the housing of the fuse, reduce the voltage across each short fusible element below the value of the voltage to which the fuse will be subject, at the time it blows. Further, where all of the short fusible elements blow at the same time, the total voltage across the fuse will be divided between all of those short fusible elements. As a result, the blowing of each short fusible element will generate only a moderate pressure; and each individual compartment will be able to withstand the pressure generated within it. The atmospheres in the various compartments within the housing of the fuse are largely isolated from each other, and that isolation tends to enable the pressure generated in each compartment to help quench the arc that forms when .the short fusible element in that compartment blows. Consequently, when all of the short fusible elements in the various compartments of the housing of the fuse blow at the same time, desirable moderate arcquenching pressures will be generated in the various compartments; and effective and quiet opening of the circuit will be effected.

It is therefore an object of the present invention to subdivide the fusible element of a fuse into a number of short fusible elements and to dispose those short fusible elements in series relation in separate but contiguous compartments within the housing of the fuse which have their atmospheres largely isolated from each other.

The various compaltments within the housing of the fuse must not be completely isolated from each other;

but, instead, small cross-section passageways must be provided between those compartments. While those passageways keep the compartments within the housing of the fuse largely isolated, they obviate the generation of excessively high pressures in any one of the compartments within the housing of the fuse. For example, even if the short fusible element in just one of the compartments Within the housing of the fuse were to blow and the short fusible elements in the rest of those compartments were to remain intact, the pressure in that one compartment could not become excessive because the small cross-section passageways would enable some of the gases and vapors, from the blowing of that one fusible element, to escape into the adjacent compartments. Without those small cross-section passageways, the pressure within that one compartment might become great enough to cause the housing of the fuse to burst, because the full voltage across the fuse would have to be interrupted by just that one short fusible element as it blew.

The various compartments within the fuse are filled with arc-quenching filler; and that filler is not only useful for its intended purpose of helping quench the arcs but it is also useful in helping to establish moderate pressures in the various compartments within the housing of the fuse. For example, if one of the compartments had no filler, and if the short fusible element in that compartment Was made heavy enough so it would not blow on most heavy overloads, there would be a relatively large air space in that compartment into which the gases and vapors from an adjacent compartment could pass; and the passage of those gases and vapors into the unfilled compartment might permit the pressure inthat adjacent compartment to fall to such a low value that the said pressure might not materially help in the quenching of the are formed in that adjacent compartment.

The various compartments within the housing of the fuse are defined by relatively massive metal walls; and those walls electrically interconnect, while physically spacing, the short fusible elements. The large thermal capacities of those walls enable those walls to tend to keep those fusible elements cool. In doing so, those walls make it possible to use fusible elements that have smaller than usual cross-sections; and such fusible elements will tend to blow more quickly on short circuit than would fusible elements of larger cross-section. The resultant quick blowing on short circuits limits the currents that can pass through the fuse prior to and during such blowing. Further, the reduced cross-sections of the short fusible elements reduce the total amount of metal that will be volatilized during the blowing of the fuse. It is therefore an object of the present invention to provide a fuse which has a number of relatively massive metal walls that subdivide the housing of the fuse into a number of compartments, and to mount fusible elements of reduced cross-section in those compartments.

Some of the materials of which the housings for fuses are made are subject to warping in the presence of moisture. Any such warping is very objectionable. The present invention minimizes Warping of the housing of the fuse by causing the various relatively massive metal Walls and the fusible elements between them to constitute a relatively rigid beam which extends through the housing of the fuse, and the metal Walls of that beam will contact that housing at points intermediate the ends of that housing. In contacting the interior of that housing, those metal walls will tend to physically resist any tendency of that housing to warp.

The provision of a series of short fusible elements that are connected in series relation between spaced metal walls within an elongated housing is additionally desirable Patented Oct. 30, 1962' because the possibility of the fusible elements sagging against the interior of the housing of the fuse is prevented. This possibility of sagging is prevented for several reasons; for example, the fusible elements are positively centered and spaced from the interior of the housing by being held at closely spaced points rather than by being held only at widely spaced points. Furthermore, the total overall expansion of each short fusible element is materially shorter than would be the total overall expansion of one elongated fusible element that extends from end to end of the housing of the fuse. Furthermore, the shorter fusible elements would, even if they did tend to expand and to bow toward the interior of the housing, be unable to experience the large deflection possible with elongated fusible elements; and hence those short fusible elements would be wholly unable to deflect far enough to engage the interior of the housing of the fuse.

The massive metal walls that subdivide the housing of the fuse into separate compartments also help cool the gases and vapors generated during blowing. in doing so, the metal walls help keep the pressures within the various compartments at moderate levels.

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, two 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 electric fuse that is made in accordance with the principles and teachings of the present invention,

FIG. 2 is a sectional view, on an enlarged scale, through the fuse of PEG. 1, and it is taken along the plane indi cated by the line 22. in FIG. 1,

FIG. 3 is a longitudinal section through another em bodiment of electric fuse that is made in accordance with the principles and teachings of the present invention, and

FIG. 4 is a sectional view, on an enlarged scale, through the fuse of FIG. 3, and it is taken along the plane indicated by the line 4-4 in FIG. 3.

Referring to the drawing in detail, the numeral 11 denotes a tubular housing that is made from a suitable insulating material. Preferably the housing lit is made of glass melamine, because glass melamine is strong and sturdy. That housing has openings d1 adjacent the ends thereof; and those openings are radially directed and they extend from the exterior of the housing It) to the interior of that housing.

The numeral 12 denotes a massive wall of metal that is dimensioned to have a sung fit with the interior of the housing it and that wall has a generally rectangular terminal 14 connected to it. That terminal may be made cast integrally with the wall I12, or it may be permanently integrated with it by silver solder or the like. The terminal 14 can be suitably bolted or otherwise connected to a bus bar or other electrical conductor. The wall 12 has a threaded passageway 16 through it, and a threaded plug 1-8 is normally disposed within that passageway to close it. However, whenever it is desirable to do so, the plug 18 can be removed from the threaded passageway 16. The wall 12 has a number of radially-directed recesses at the periphery thereof, and those recesses are alined with the openings 11 at the right-hand end of the housing The recesses in the wall 12 and the openings 1.1 in the housing 10 will accommodate pins 38; and those pins can be pressed into position to permanently secure the wall '12 to the housing It The numeral 20 denotes a massive wall of metal that is so dimensioned to fit snugly within the interior of the lefthand end of the housing '10. That wall has a number of radially-directed recesses at the periphery thereof, and

those recesses can be alined with the openings 11 at the left-hand end of the housing 10. Pins 38 are forced into the openings 1-1 and into the recesses in the wall 20 to permanently secure the wall 20 to the housing 10. A terminal 22 can be cast integrally with or permanently integrated with the wall 26', as by silver solder or the like. That terminal can be bolted or otherwise secured to a bus bar or other electrical conductor. A threaded passageway 24- is provided in the Wall 2t and a threaded plug 26 will normally occupy and fill that passageway. However, when it is desirable to do so, the plug 26 can be removed from that passageway.

The numeral 28 denotes a massive metal wall which is dimensioned to fit snugly within the housing 10. That Wall has a small passageway 34 through it; and that passageway is smaller than either of the passageways 16 or 24 A generally similar wall 3d, and a generally similar wall 32 are also provided for the fuse of FIG. 1. Each of those walls has a small passageway 34 through it; and the walls 23, 3t} and 32 will be set so the passageways 3.4 therethrough are in alinement with each other and with the passageways 16 and 24- in the walls 12 and 29, respectively.

The various

massive metal walls

12, 32, 3d, 28 and 2t? will be spaced apart to define a number of compartments or chambers within the housing 10. Pusible elements 36 will extend between and will be suitably secured to the confronting faces of the

walls

12, 32, 30, 28 and 20, as by solder or the like. Each of the fusible elements 36 will have a portion of reduced cross section; and that reduced cross section is easily attained by forming an opening 37 in that fusible element.

As indicated particularly by FIG. 2, there will usually be a number of fusible elements 35 in each of the compartments or chambers defined by the various metal walls. in the particular embodiment shown, there are six fusible elements 356 in each of those compartments or chambers. However, more or fewer fusible elements could be provided in each compartment or chamber. When the fusible elements 36 are soldered to the various walls, they will coact with those walls to constitute a fabricated metal beam. That beam will have considerable rigidity even though each of the individual fusible elements 36 is of small cross section and is thus not very strong. When that beam is telescoped within the housing 10, the exteriors of the spaced

metal Walls

12, 32, 3t), 28 and 20 will bear snugly against correspondingly spaced portions of the interior of housing 10; and will thus tend to stiffen that housing. The resultant stiffening of the housing 10. is desirable because it minimizes any warping of that housing.

The compartments or chambers defined by the housing it and the various metal Walls '12, 32, 3t 23 and 20 will be filled with arc-quenching filler. In the particular embodiment shown, the compartments or chambers defined by the

walls

12 and 32, 32 and 3d, and 3t) and 28 will be wholly filled with sand; whereas only part of the compartment or chamber defined by the walls 23 and 20 will be filled with sand. Specifically, the right-hand portion of the latter compartment or chamber will be filled with sand, but the left-hand portion of that compartmen or chamber will be filled with a coarsely ground filler material such as anhydrous calcium sulphate. The sand is denoted by the numeral 40, and the anhydrous calcium sulphate is denoted by the numeral 42. The two arcquenching fillers 4t] and 42 are preferably introduced into the various compartments or chambers after the fabricated metal beam has been telescoped within the housing It) and the pins 38 have been pressed home. At such time the plug 1 8 will be seated solidly within the threaded passageway 16 in the wall 12, and the housing 10* will be set on end. The threaded plug 26 will be removed from the threaded passageway 24, and then sand will be introduced through that passageway and caused to pass downwardly through the passageways 34 in the

walls

28, 30

and 32 until the bottom three compartments or chambers are completely filled. Thereafter, further sand will be introduced to' fill approximately three quarters of the uppermost compartment or chamber. At such time, the anhydrous calcium sulphate will be introduced through the passageway 24. The sand 4a is thus caused to fill substantially all of the free space in the interior of the fuse with the exception of the space occupied by the anhydrous calcium sulphate 42. As a result, there are no large voids or spaces, in the fuse provided by the present invention, into which vapors or gases could pass and expand during the blowing of the fuse.

The fuse of FIGS. 1 and 2 will carry the current for which it is rated; and it will carry that current indefinitely. That fuse will also carry low overloads for a time, be cause the heat generated by the passage of low overload currents through the fusible elements 36 will be largely conducted to, and absorbed by, the

massive metal walls

12, 32, 30, 28 and 20. Some of that heat will then be conducted by those walls to the housing 10, and that housing will be able to radiate part of that heat. As a reseult, the fusible elements 36 will be able to remain relatively cool. Specifically, the fusible elements 36 will remain much cooler than would one long fusible element that extended from the Wall 12 to the wall 20. The heat absorbing action of the massive metal walls is so great that the fusible elements 36 actually remain cooler than would such an elongated fusible element; even though the total cross sections of the fusible elements 36 in any compartment or chamber are smaller than the cross section of such an elongated fusible element and, therefore, those fusible elements will generate more heat than would such an elongated fusible element.

The fact that the fusible elements 36 are so small in cross section is desirable because it reduces the amount of metal that can be volatilized during the opening of the circuit by the fuse. Such a reduction in the amount of metal that can be volatilized is helpful in keeping the generated pressures within moderate limits.

If all of the fusible elements 36 in the four compartments of the housing of FIGS. 1 and 2 were to blow at the same time, the voltage across the fusible elements in any one of those compartments would be considerably less than the total voltage across the fuse. Consequently, the fusible elements 36 in each compartment would be able to blow while generating only moderate pressures. Such pressures are easily withstood by the housing 10.

In the event the fusible elements 36 in just some of the four compartments of the fuse of FIGS. 1 and 2 were to blow, the pressures generated in those compartments in which the fusible elements did blow would be greater than they would have been if the fusible elements 36 in all of the compartments had blown. However, the resultant increased pressures can not cause the housing 10 to burst, because those increased pressures will be reduced by the escape of vapors and gases from those compartments into the compartment or compartments in which the fusible elements 36 did not blow. That escape is made possible by the small passageways 34 in the

walls

28, 30 and 32.

The passageways 34 are made small so they will not permit a sudden dissipation of the pressure in the compartment or compartments in which the fusible elements 36 have blown. Such sudden dissipation of pressure would tend to cause the loss of the beneficial results obtained by having moderate pressures generated within the compartments where the actual blows occur. Yet, the passageways 34 must be large enough to pass vapors and gases to enable heavy pressures in the compartments in which the blowing actually occurs to be reduced by the flow of the gases and vapors into the compartment or compartments in which the blows did not occur. Preferably, the diameters of the passageways 34 will be such that the area of a passageway 34 is less than five percent of the area of the metal wall in which it is located.

The reduced cross sections of the fusible elements 36 also make it possible for the fuse to interrupt heavy overload currents and short circuit currents before those currents reach the high values which they could reach if the fuse had elongated fusible elements that extended from the metal wall 12 to the metal wall 20. This is very desirable because it means that the overall pressures which can be generated within the housing during the blowing of the fuse will be materially smaller than they could be if elongated fusible elements were used. The overall result is quiet and explosion-free operation of the fuse.

The reduced pressures that will be generated within the housing, because of the use of the reduced cross section fusible elements 36, make it possible to make the fuse ventless. For example, it will be noted that a tight, vent-free engagement is provided between the peripheries of the walls 12 and 2t and the interior of the housing 10, and further that the threaded plugs 18 and 26 are tightly seated in the

passageways

16 and 24, respectively. As a result, gases and vapors will be unable to escape from the fuse.

The

metal walls

28, 39 and 32 act to center the fusible elements at three points intermediate the ends of the housing 10. If elongated fusible elements were to be extended between the

end walls

12 and 20 of the housing 10, those fusible elements could tend to sag or deflect into engagement with the interior of that housing; and the tendency to sag or deflect would increase as those elongated elements became heated by the passage of current through them. However, with the short fusible elements 36, made possible by the present invention, such sagging or deflecting is obviated. This desirable result is due, in part, to the fact that the fusible elements 36 are kept cooler than would elongated elements which extended between the

end walls

12 and 20 of the fuse; and it is due, in part, to the fact that the fusible elements 36 are supported at three points intermediate the ends of the fuse housing. Because the short fusible elements 36 provided by the present invention will not sag or deflect into engagement with the interior of the housing 10, that housing will be protected from charring and from the other undesirable results that would ensue from any engagement of the heated fusible elements 36 with the interior of that housing.

Referring to FIGS. 3 and 4, the numeral 46 denotes a housing which is preferably made from a material such as glass melamine. A massive Wall 48 of metal is dimensioned to fit snugly within the interior of that housing. That wall is provided with a terminal 50; and that terminal can be cast integrally with, or can be permanently integrated with, the wall 48, as by silver solder or the like. The wall 48 has a threaded passageway 52 through it, and a threaded plug 54 normally closes that passageway. The housing 46 has radailly-directed openings 74 adjacent the opposite ends thereof, and the wall 48 has radially-directed recesses at the periphery thereof. The openings 74 in the housing 46 can be set in register with the recesses in the wall 48, and then pins 75 can be pressed into those openings and into those recesses. Those pins will permanently secure the Wall 48 to the housing 46.

A wall 56, generally comparable to the wall 48, is dimensioned to have a snug fit with the interior of the other end of the housing 46. The wall 56 has a threaded passageway 60 through it, and a threaded plug 62 isnorma-lly disposed within and normally closes that passageway. The wall 56 has radially-directed recesses at its periphery; and those recesses can be set in register with the radially-directed openings 74 at the left-hand end of the housing 46. Thereupon, pins 75 can be pressed into those openings and seated in those recesses; and those pins will permanently secure the wall 56 to the housing 46. The wall 56 has a terminal 58; and that terminal can be cast integrally with, or permanently integrated with, the wall 56, as by silver solder or the like. The terminal 58 is not as large in cross section as is the terminal 50, and it has a relatively narrow neck 58.

A massive wall 64 of metal is disposed within the housing 46, and it is located between the walls 48 and 56. That wall is dimensioned to have a snug fit with the interior of the housing 46. A plurality of short fusible elements 68 of small cross section are suitably secured to the confronting faces of the walls 48 and 64- and 64 and 56, as by solder or the like. Those fusible elements hold the

walls

48, 64 and 56 in spaced relation while physically and electrically connecting them together. The fusible elements 68 coact with the

walls

48, 64 and 56 to constitute a fabricated metal beam; and that beam will have considerable resistance to bending even though each of the individual fusible elements 68 is not very strong. Each of the fusible elements 68 has a portion 69 of reduced cross section; and those portions are conveniently formed by punching an opening in each of those fusible elements.

The wall 64 can, as shown by FIG. 3, be provided with a number of radially-directed recesses at the periphery thereof. Those recesses will be in register with centrally-located, radially-directed openings 74 in the housing 46; and pins 75 can be pressed into those openings and into those recesses to fixedly hold the wall 64 relative to the housing 46. The wall 64 has a small passageway 66 through it; and that passageway is alined with the

passageways

52 and 68 in the walls 48 and 56, respectively.

The compartments or chambers defined by the

Walls

48 and 64 and 64 and 56 will be filled with arcquenching filler. Specifically, the compartment defined by the

walls

48 and 64 will be filled with sand, and the compartment defined by the walls 64 and 56 will be dominantly filled with sand but will have its left-hand end filled with anhydrous calcium sulphate. The sand is denoted by the numeral 78 and the anhydrous calcium sulphate is denoted by the numeral '72.

The housing 46, the

walls

48, 64 and 56, and the fusible elements 68 will be assembled; and then the free spaces in that housing will be filled with the fillers 7t) and 72. The fillers will preferably be introduced by closing the passageway 52 by seating the threaded plug 54 within that passageway, by setting the housing 46 on end, and by removing the plug 62 from the passageway 68. The sand 78 will be introduced first; and then subsequently the anhydrous calcium sulphate 72 will be introduced. Thereafter, the plug 62 will be solidly seated Within the passageway 60. The housing 46 and its components will generally resemble the fuse of FIGS. 1 and 2, with the exception that it will have just two compartments whereas the fuse of FIGS. 1 and 2 has four compartments. The engagement between the housing 46 and the walls 48 and 56 is quite snug; and that engagement coacts with tight seating of the

plugs

54 and 62 in the threaded

passageways

52 and 68, respectively, to render the housing 46 ventless.

The housing-46 Will be telescoped within a larger diameter tubular housing 73; and the latter housing Will preferablyv be made of a less-expensive insulating material, such as fiber. A disc 76 of insulating material is telescoped within the housing 73, and it has a large notch in the bottom thereof to accommodate and fit neck 59. A hook 80 is secured to and supported by the disc 76. A disc 78 also is telescoped within the housing 73, and thatdisc has a rectangular opening therein to accommodate the left-hand end of the terminal 58 on the wall 56'. That disc also has a smaller opening to accommodate the righthand end of a heater 86. That right-hand end of that heater is spaced a short distance above the terminal 58; but it is normally connected to it by a conmotor 88 that is soldered to the terminal 58 and to the right-hand end of the heater 86. That connector is of the type shown and described in my co-pending application Serial No. 793,415 which was filed February 16, 1959, for Protectors For Electric Circuits. Low-melting point solder is used to secure the connector 88 to the heater 86 and to the terminal 58, and that solder Will soften when the terminal 58 reaches a predetermined temperature. At such time a helical extension spring 90, which is integrally secured to the connector 88 and which has its right-hand end set over the hook 8-9, will pull the connector 88 to the right and open the circuit between the heater 86 and the terminal 58.

The left-hand end of the heater 86 is riveted or otherwise secured to a terminal 82. That terminal has an opening through it and that opening accommodates and holds a pin That pin is rectangular in horizontal section; and it has a length that is greater than the inner diameter of the housing '73 but that is smaller than the outer diameter of that housing. One of the flat faces of that pin abuts the left-hand end of the housing 73; and that flat face limits movement of the terminal 82 inwardly of the housing 73 while helping hold that terminal coaxial with the axis of the housing 73. A cup-like closure 92 for the left-hand end of the housing 73 has an opening which telescopes over the terminal 82; and fasteners 96 extend through openings at the periphery of that closure 92 and seat in openings in the lefthand end in the housing 73. That closure holds the pin 84 solidly against the left-hand end of the housing 73, and it thereby helps hold the terminal 82 solidly in position adjacent the left-hand end of that housing.

A cup-like closure 94 has an opening that telescopes over the terminal of the wall 48, and that closure telescopes over the right-hand end of the housing 73. Fasteners 96 pass through openings in the periphery of the closure 84 and then seat in openings in the right-hand end of the housing 73 to permanently secure that closure to that housing. The closure 94 abuts the right-hand face of the Wall 48 and thereby limits movement of the housing 46 to the right.

The fuse of FIGS. 3 and 4 is a dual element fuse; because the low-melting point solder can melt on long continued low overloads to release the connector 88' and thereby open the circuit, and the fusible elements 68 can blow on heavy overloads and on short circuits to open the circuit. The heater 86 will supply part of the heat to the low-melting point solder 88, but that heater will be made so it will not blow. The fuse of FIGS. 3 and 4 will carry its rated current indefinitely, its connector 88 will move to open the circuit on low overloads after a predetermined time delay, and the fusible elements will blow to open the circuit on heavy overloads and on short circuits.

The fusible elements 68 within the housing 46 will be of small cross section, and they will thus provide quick blowing at overload currents approaching short circuit values. in blowing quickly, those fusible elements minimize the pressures that can be generated within the compartments of the housing 46. The passageway 66 those compartments at a time when the fusible elements in the other compartment do not blow. The passage of those vapors and gases will keep the pressures in the compartment where the fusible elements did blow from' being excessiveand from causing the casing 46 to burst.

If desired, the fusible elements 36 in one of the compartments or chambers of the fuse of FIGS. 1 and 2 could be equipped with small masses of alloying material of the type shown and described in said co-pending application. Such masses would foster blowing of those fusible elements on long continued low overloads, and would thus further minimize pressure generation within the housing 10.

If the fusible elements 36 in the various compartments of the housing 10 all had the same current-carrying capacity, the fusible elements 36 in the two central compartments of that housing would blow on low overloads before the fusible elements 36 in the end-most compartments of that housing could blow. This is due to the fact that the bus bars or other electrical conductors, to which the terminals 14 and 22 are secured, will absorb and conduct away a good deal of heat from the fusible elements 36 in those end-most compartments. Where it is desired to have all of the fusible elements blow simultaneously on low overloads, the fusible elements 36 in the two central compartments will be made so they have larger current-carrying capacities than do the fusible elements in the end-most compartments. This can be done by increasing the cross sections of the central fusible elements, by making those fusible elements of metal having higher fusing points, by making the openings 37 in those fusible elements small, by placing the openings 3'7 closer to the

walls

28, 30 or 32, or by any of a number of other ways. Where this is done, the voltage across the fuse will be divided equally between the four compartments, and the voltage across each fusible element 36 will be just one quarter of the total voltage across the fuse.

The heat absobed by the Walls 12, 2t), 2%, 30' and 32 delays the blowing of the fusible elements 36 on low overloads. This delay is desirable because it enables the fuse to avoid blowing when the circuit is subjected to harmless transient overloads. lay can be controlled by properly selecting the thicknesses for the

walls

12, 2d, 28, 30 and 32; and this delay can be varied Without unduly varying the rating of the fuse, Specifically, where a longer time delay is desired, the thicknesses of the Walls 12., 20, 28, 30 and 32 will be increased; but where a shorter time delay is desired, the thicknesses of those walls will be decreased.

Whereas the drawing and accompanying description have shown and described two 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. An electric fuse that comprises a housing of insulation material, said housing being hollow and being tubular, a plurality of massive metal walls disposed within said housing and subdividing the interior of said housing into a number of separate but contiguous compartments, a plurality of fusible elements disposed in each of said compartments, said fusible elements being secured to and extending between said metal walls, said fusible elements and said walls constituting a fabricated metal beam, the peripheries of said metal walls snugly engaging the interior of said housing to minimize warping of said housing, said metal walls absorbing heat from said fusible elements and transferring some of said heat to said housing for radiation from said housing to delay the blowing of said fusible elements on low overloads, the fusible elements adjacent the longitudinal center of said housing having larger current-carrying capacities than do the fusible elements in the end-most compartments of said housing whereby all of said fusible elements blow substantially simultaneously on low overloads, and arc-quenching filler in said compartments, said arc-quenching filler substantially filling the spaces in said compartments whereby there are no large spaces or voids in said housing into which gases and vapors can expand, the end-most of said metal walls substantially closing and sealing the ends of said housing and thereby rendering said fuse ventless, the intermediate metal walls having small cross section passageways therethrough to permit some of the gases and vapors generated during the blowing of the fusible elements in one of said compartments to pass into adjacent The amount of this decompartments if the pressures in said adjacent compartments are below the level of the pressure generated in said one compartment and thereby keep the pressure in said one compartment from becoming excessive, said passageways having cross sections less than five percent of the sections of said metal walls, the engagements between the peripheries of said intermediate metal walls and said interior of said housing limiting communication between said compartments to said small passageways, said metal walls holding said fusible elements out of engagement with said interior of said housing and preventing deflection of any portions of said fusible elements into engagement with said interior of said housing.

2. An electric fuse that comprises a housing, said housing being hollow and being tubular, a plurality of massive metal walls disposed within said housing and subdividing the interior of said housing into a number of separate but contiguous compartments, fusible elements disposed in said compartments, said fusible elements being secured to and extending between said metal walls, said fusible elements and said walls constituting a fabricated metal beam, the peripheries of said metal walls snugly engaging the interior of said housing to minimize warping of said housing, said metal walls absorbing heat from said fusible elements and transferring some of said heat to said housing for radiation from said housing to delay the blowing of said fusible elements on low overloads, the fusible elements adjacent the longitudinal center of said housing having larger current-carrying capacities than do the fusible elements in the end-most compartments of said housing, and arc-quenching filler in said compartments, said arc-quenching filler substantially filling the spaces in said compartments whereby there are no large spaces or voids in said housing into which gases and vapors can expand, the end-most of said metal walls substantially closing and sealing the ends of said housing and thereby rendering said fuse ventless, the intermediate metal walls having small cross section passageways therethrough to permit some of the gases and vapors generated during the blowing of the fusible elements in one of said compartments to pass into adjacent compartments if the pressures in said adjacent compartments are below the level of the pressure generated in said one compartment and thereby keep the pressure in said one compartment from becoming excessive.

3. An electric fuse that comprises a housing, said housing being hollow, a plurality of massive walls disposed within said housing and subdividing the interior of said housing into a number of separate but contiguous compartments, fusible elements disposed in said compartments, said fusible elements being secured to and extending between said metal walls, said metal walls absorbing heat from said fusible elements and transferring some of said heat to said housing for radiation from said housing to delay the blowing of said fusible elements on low overloads, the fusible elements adjacent the longitudinal center of said housing having larger current-cariying capacities than do the fusible elements in the end-most compartments of said housing whereby all of said fusible elements blow substantially simultaneously on low overloads, and arc-quenching filler in said compartments, said arc-quenching filler substantially filling the spaces in said compartments whereby there are no large spaces or voids in said housing into which gases and vapors can expand, the end-most of said metal walls substantially closing and sealing the ends of said housing and thereby rendering said fuse substantially ventless, the intermediate metal Walls having small cross section passageways therethrough to permit some interchange between adjacent compartments of the gases and vapors generated during the blowing of the fusible elements, said passageways having cross sections less than five percent of the cross sections of said metal walls, the engagements between the peripheries of said intermediate metal walls and said interior of said housing substantially limiting 1 1 communication between said compartments to said small passageways, said fusible elements providing an interruptible circuit that normally interconnects the metal walls adjacent the ends of said housing, the voltagefacross each of said fusible elements being less than the voltage across said fuse.

4. An electric fuse that comprises a housing, said housing being hollow, a plurality of massive metal walls disposed within said housing and subdividing the interior of said housing into a number of separate but contiguous compartments, fusible elements disposed in each of said contiguous compartments, said fusible elements being secured to and extending between said metal walls, said metal walls absorbing heat from said fusible elements and transferring some of said heat to said housing for radiation from said housing to delay the blowing of said fusible elements in said contiguous compartments on low over-loads, and arc-quenching filler in said compartments, said arc-quenching filler substantially filling the spaces in said compartments whereby there are no large spaces or voids in said housing into which gases and vapors can expand, the endmost of said metal walls substantially closing and sealing the ends of said housing and thereby rendering said fuse substantially ventless, tie intermediate metal walls having small cross section passageways therethrough to permit some of the gases and vapors generated during the blowing of the fusible elements in one of said contiguous compartments to pass into adjacent compartments, said passageways being dimensioned so sufiicient gases and vapors can pass therethrough to avoid bursting of said housing but not to permit a sudden dissipation of the pressure in said one compartment, the engagements between the peripheries of said intermediate metal walls and said interior of said housing substantially limiting communication between said contiguous compartments to said small passageways, said fusible elements providing an interruptible circuit that normally interconnects the metal walls adjacent the ends of said housing.

5. An electric fuse that comprises a housing, said housing being hollow, a plurality of massive metal walls disposed within said housing and subdividing the interior of said housing into a number of separate but contiguous compartments, fusible elements disposed in said contiguous compartments, said fusible elements being secured to and extending between said metal walls, and arcquenching filler in said compartments, said arc-quenching filler substantially filling the spaces in said compartments whereby there are no large spaces or voids in said housing into which gases and vapors can expand, the end-most of said metal walls substantially closing and sealing the ends of said housing and thereby rendering said fuse ventless, the intermediate metal walls having small cross section passageways therethrough to permit some of the gases and vapors generated during the blowing of the fusible elements in one of said contiguous compartments to pass into adjacent compartments if the pressures in said adjacent compartments are below the level of the pressure generated in said one compartment and thereby keep the pressure in said one compartment from becoming excessive.

6. An electric fuse that comprises a housing, a plurality of metal walls disposed within said housing and subdividing the interior of said housing into a number of separate but contiguous compartments, fusible elements disposed in said contiguous compartments, said fusible elements being secured to and extending between said metal walls, and arc-quenching filler in said compartments, said arc-quenching filler substantially filling the spaces in,said compartments whereby there are no large spaces or voids in said housing into which gases and vapors can expand, the intermediate metal walls having small cross section passageways therethrough to permit some of the gases and vapors generated during the blowing of the fusible elements in one of said contiguous Compartments to pass into adjacent compartments if the i2 pressures in said adjacent compartments are below the level of the pressure generated in said one compartment and thereby keep the pressure in said one compartment from becoming excessive.

7. A11 electric fuse that comprises a housing, a said housing being hollow and being tubular, a plurality of metal walls disposed within said housing and subdividing the interior of said housing into a number of separate but contiguous compartments, fusible elements disposed in said contiguous compartments, said fusible elements being secured to and extending between said metal walls, and arc-quenching filler in said compartments, said arequenching filler substantially filling the spaces in said compartments whereby there are no longer spaces or voids in said housing into which gases and vapors can expand, the end-most of said metal walls substantially closing and sealing the ends of said housing and thereby rendering said fuse substantially ventless, the intermediate metal walls having small cross section passageways therethrough to permit some interchange between adjacent compartments of the gases and vapors generated during the blowing of the fusible elements, the engagements between the peripheries of said intermediate metal walls and said interior of said housing limiting communication between said compartments to said small passageways, said metal walls holding said fusible elements out of engagement with said interior of said housing and preventing deflection of any portions of said fusible elements into engagement with said interior of said housing, said fusible elements providing an interruptible circuit that normally interconnects the metal walls adjacent the ends of said housing.

8. An electric fuse that comprises a housing, said housing being hollow and being tubular, a plurality of metal walls disposed within said housing and subdividing the interior of said housing into a number of separate but contiguous compartments, a plurality of fusible elements disposed in each of said contiguous compartments, said fusible elements being secured to and extending between said metal walls, said fusible elements and said walls constituting a fabricated metal beam, the peripheries of said metal walls snugly engaging the interior of said housing to minimize warping of said housing, and arc-quenching filler in said compartments, said arc-quenching filler substantially stilling the spaces in said compartments whereby there are no large spaces or voids in said housing into which gases and vapors can expand, the end-most of said metal =walls substantially closing and sealing the ends of said housing and thereby rendering said fuse ventless, the intermediate metal walls having small cross section passageways therethrough to permit some of the gases and vapors generated during the blowing of the fusible elements in one of said compartments to pass into adjacent compartments if the pressures in said adjacent compartments are below the level of the pressure genera-ted in said one compartment and thereby keep the pressure in said one compartment from becoming excessive, the engagements between the peripheries of said intermediate metal walls and said interior of said housing limiting communication between said compartments to said small passageways.

9. An electric fuse that comprises a housing, said housing being hollow, a plurality of metal walls disposed within said housing and subdividing the interior of said housing into a number of separate but contiguous compartments, fusible elements disposed in said contiguous compartments, said fusible elements being secured to and extending between said metal walls, and arc-quenching filler in said compartments, said arc-quenching filler substantially filling the spaces in said compartments whereby there are no large spaces or voids in said housing into which gases and vapors can expand, the intermediate metal walls having small cross section passageways therethrough to permit some interchange between adjacent compartments of the gases and vapors generated during the blowing of the fusible elements, the engagements between the peripheries of said intermediate metal walls and said interior of said housing substantially limiting communication between said compartments to said small passageways, said fusible elements providing an interrupti-ble circuit that normally interconnects the metal walls adjacent the ends of said housing, the voltage across each of said fusible elements being less than the voltage across said fuse.

10. An electric fuse that comprises a housing, said housing being hollow, a plurality of metal walls disposed within said housing and subdividing the interior of said housing into a number of separate but contiguous compartments, fusible elements disposed in said contiguous compartments, said fusible elements being secured to and extending between said metal Walls, and arc-quenching filler substantially filling the spaces in said compartments whereby there are no large spaces or voids in said housing into which gases and vapors can expand, the end-most of said metal walls substantially closing and sealing the ends of said housing and thereby rendering said fuse substantially ventless, the intermediate metal walls having small cross section passageways therethrough to permit some of the gases and vapors generated during the blowing of the fusible elements in one of said compartments to pass into adjacent compartment-s, the engagements between the peripheries of said intermediate metal walls and said interior of said housing substantially limiting communication between said compartments to said small passageways, said fusible elements providing an interruptible circuit that normally interconnects the metal walls adjacent the ends of said housing.

References Cited in the file of this patent UNITED STATES PATENTS 569,373 Downes Oct. 13, 1896 1,959,770 Slepian May 22, 1934 2,605,371 Fahnoe July 29, 1952 2,665,348 Kozacka Jan. 5, 1954 2,866,040 Skeats Dec. 23, 1958 2,871,314 Swain et al. Jan. 27, 1959 2,892,060 Gaskill June 23, 1959