US2502747A - Electric fuse - Google Patents

Description

April 1950 A. M. POPP 2,502,747

ELECTRIC FUSE Filed July 26 1946 Pm m4wm Patented Apr. 4, 1950 ELECTRIC FUSE Arthur M. Popp, Snyder, N. Y., assignor to Pierce Renewable Fuses, Inc., Buffalo, N. Y.

Application July 26, 1946, Serial No. 686,264

11 Claims.

This invention relates to electric fuses and fuse links formed to protect an electric circuit against overloads and constructed to provide a delayed action or time lag before the fuse link blows.

Fuses and fuse links have heretofore been constructed to provide a relatively long time lag at high overloads, such as 100 per cent overload and higher, so that the links will not blow at such overloads until a, certain time interval or lag has elapsed, but such prior fuses and links were not designed to provide sufficiently long time lags at lower overloads. It is obvious that if a circuit is overloaded, for example 30 per cent to 50 per cent, there is practically no danger of fire and very little danger of damage to motors or other equipment in the circuit controlled by the fuse, unless such overload continues for relatively long periods of time, and consequently, it is objectionable to have a fuse link blow on a relatively small overload after a short interval of time. The fact that a fuse link may be designed for a relatively long lag at high overloads, does not ensure that the link will also have the required longer time lag when the circuit is overloaded to a much smaller extent.

It is, consequently, an object of this invention to provide a fuse and a fuse link which is capable of providing a relatively long time lag at low overloads and at the same time, provide the desired time lag at high overloads.

Another object of this invention is to provide a fuse link of improved construction which is so formed as to provide better cooling of the link when the same is heated due to relatively low overloads, so as to provide an increased lag at such low overloads. A further object is to provide a fuse link having narrow slits or notches extending inwardly into the link at an inclination to the longitudinal edges of the link. Another object of this invention is to provide a fuse link having one or more portions thereof formed to provide a narrow neck of fusible material extending at an angle to the length of the link. Another object is to provide a fuse link having a section arranged between narrow necks of the fuse link and which section is providedwith diagonally extending slots by means of which the desired cooling effect is produced which delays the blowing of the fuse at low overloads until such low overloads have persisted for a relatively long period of time. A-further object of this invention is to provide a fuse link embodying these improvements and which is made of a single strip of metal of substantially uniform thickness 2 throughout its length. Other objects and advantages of this invention will appear from the following description and claims.

In the accompanying drawings:

Fig. 1 is a sectional elevation of a fuse housing or casing having a fuse link embodying this invention arranged therein.

Fig. 2 is a central sectional view thereof, on an enlarged scale, on line 2-2, Fig. 1.

Fig. 3 is a face view of a fuse link of modified construction removed from the casing.

In the accompanying drawings are shown fuse links embodying this invention arranged in fuse casings of the knife blade type, but it will be understood that the improved fuse links may be used in connection with fuse casings of other types. The fuse casing or housing shown includes an outer tubular enclosing casing or shell 6 of hard fiber or other suitable insulating material, an inner shell or frame I of similar material which may be open intermediate of its ends at one side thereof, that shown having the intermediate portion thereof of substantially semicylindrical form and the ends of cylindrical form. The removable fuse link 8 which will be hereinafter described more in detail may be inserted and removed from the frame or inner shell 1. 9 and I8 represent the usual blades of the fuse, which extend into the interior of the inner frame or shell 1 and the inner portions of these-blades form terminals H to which the ends of the fuse link 8 may be secured. The blades 9 and ID are suitably secured to the ends of the frame or inner shell 1 by any suitable means, such as pins l2 extending through the cylindrical end portions of the inner frame or shell I and also through a cupshaped member [4 arranged within each end of the frame or inner shell 1 of the fuse.

The outer shell of the fuse casing is provided at one end thereof with a ferrule or cap i6 rigidly secured thereto in any desired manner, for example, by means of a screw-threaded connection and indenting portions I! of the cap into the threaded portion of the shell 6, to lock the cap against unscrewing from the outer shell 6. This cap or ferrule'has at its end an inwardly extending'flange' I 8 having a hole therein large enough to permit the blade 9 to be rotated about its axis relatively-to the ferrule. Atthe other end of the outer housing 6 a similar ferrule or cap 20 is provided having an inwardly extending flange 2| which" is suitably connected rigidly with the blade Ill. This may, for example, be done by having the flange 2l' of the ferrule 20 extending inwardly to a greater extent than the flan e I a of the other ferrule, thus forming a hole in the end of the ferrule smaller in diameter than the blade I9 and forming notches in the flange at diametrically opposite portions thereof into which the edge portions of the blade l may extend. Any other mounting for the blade I0 and the ferrule may be provided so that there is no relative movement between these. parts. The cap or ferrule 20 has an internal screw thread i9 formed to mesh with an external thread formed on the end of the outer shell 6, as clearly shown in Figs. 1 and 2. Consequently, when the ferrule 20 is turned relatively to the ferrule I6 and shell 6; it will be screwed on or unscrewed from the outer shell 6, to enable the fuse casing to be. readily taken apart to afford access to the fuse link 8.

When the fuse link 8 blows,. the products. of combustion resulting from the blowing. of the link.

together with particles of molten metal pass in opposite directions toward the ends of the fuse casing, and consequently, the cup members M are provided with a series of holes v24 therein and end plates 26, secured to theends of the inner shell I also have holes 25 therein by means of which the-fuse is vented. Suitable screening material 28 is preferablyprovided between these two series of holes so that any solid matter, such as lumps or molten metal as well as flame. will be prevented from passing outwardly beyond the ends of the fuse. These holes in the end plate 26 and in the cup members I' l also serve to ventilate the fuse while the same is in use in that heat developed in the fuse link will tend to cause an upward circulation of air in the fuse casing, cool outside air entering through the holes in the lower end plate 26*and the cup member M and heated airpassing out at the upper end of the fuse through corresponding holes. The screening material 28- maybe in the form of one or more layers of'finewiremesh, gauze or perforated metal. Fuse links may be clamped to the inner terminals H of the blades 0 and It in any suitable manner, for example, by means of screws 30 having a threaded engagement with nuts 3! which are suitably secured to the terminals l I".

The improved fuse links shown in the drawings are well suited for use in connection with fuse casings of the type described, but they may be used with fuse casings of other types and con structions. These links are made of flat sheets or strips of fusible metal by stamping and are preferably of uniform thickness throughout. The links have their ends formed to be clamped into contact with the terminals l i of the fuse casing. Two types of links are shown, the link shown in Fig. 1 being provided adjacent to the ends thereof with notches extending inwardly from opposite side edges of the link and toward each other to form narrow necks 36. During the use of the fuse, the fusible metal of the necks becomes heated when electric currents close to the rated capacity of the. link pass through the same from one fuse terminal H to the other. However, the fuse terminals and blades are quite large or bulky compared to the. fuse link 8, and consequently; heat developed in the necks of the fuselink is readily conducted through the end portions of the fuse link to the terminals H and the blades which are formed integral therewith. However, in the event that a sudden overload or excessive flow of current through the fuse link occurs, such for example as would result from a short circuit, the heating of, the-necks 35 of the fuse link; takes place much more rapidly than the 4 I conduction of heat from the link to the ter minals, so that the metal of the necks 36 will become fused or softened so that the link breaks or blows, thus breaking the circuit.

Between the two pairs of necks 36 at opposite end portions of the link, there is provided in the link shOWn in Fig. 1, a section 38 which is of considerably greater length than width, and in this section, slots or notches 40 are provided which extend substantially diagonally of this section of the link. These two notches which extend from opposite edges of the link have their inner ends spaced apart to form a neck 4| which, consequently, also extends diagonally of or at an acute angle to the length of the link. This neck is of considerably greater cross sectional area than the necks" 3,6 which have been described. These two inclined notches 40 are preferably in alinementwith each other as shown in Fig. 1, so thatthe neck M is located between the inner ends thereof, but any other arrangementof the-notches so as toform between them a neck of the desired cross sectional area and extending crosswise or diagonally of the link, may be provided. inclined notches divide: the section 38 ofthe fuse link into two" parts of substantial size which are capable of: absorbing and. dissipating considerable quantities of heat from the neck 4! which, of course, becomes heated if: overloads of electric current pass through. the. link. In the fuse link. shown in Fig. 1, in the event of. low over. loads, such for example" as approximately 35 per cent above the. rating of thef-use; thei neckportion H, which is designed to blow at approximately this overload, will be kept from. blowing or fusing for a considerable period of. time, for the reason that much of the heat developedin the neck 4! is readily transmitted to the two per tions of the section 38 of the fuselinkr The heat developed. in the necks 36 in low overloads is, of course, readily transmitted to the terminals, H and blades 9 and I llso that atlow overloads, the necks- 36 will not become fusedor. softened-to the extent. necessary to cause blowing. of. the fuse; If, however, this relatively low overload. persists for a considerable period of. time. so. as. to possibly endanger the circuit controlled by the. fuse or any apparatus inclined in. the. circuit, then eventually after the. two. parts of the sections38 have acquired a temperature at which. they can no longer absorb sufficient heat from the neck 4 l the neck 4| will become fused or softened to produce a break in the link, thus interrupting the flow of current through the fuse link- When the fuse link is subjected to higher overloads, the softening or melting of the neck 4| takes place in correspondingly shorter periods of time.

By arranging the slots or notches 4t and also the neck 4! at: an inclination to the length of the fuse link, the delayed fusing action of the neck 4'!" at low overloads is greatly improved. Numerous tests have demonstrated this superior action of this link with. low overloads and have demon-- strated the superiority of this link over other links having slots and necks formed in various different ways therein. It" has. even been shownby' tests that if" in place cf'the inclined or diagonally extending slots or notches and diagonally extending necks, two notchesof lengths equalto the lengths of the inclined notches are provided spaced apart and extendingtransversely' of" the length, that the links with the inclined slots and necks are greatly superior for low overload lag. For example, the lag in a link ofthe type shown in Fig. l of'the drawing; ra-ted at 30' amperes at 250 volts, after an overload of per cent in excess of the rated current of this fuse link was 16 minutes and 9 seconds, whereas the corresponding lag with a link of another manufacture of the same capacity or rating was 4 minutes and 19 seconds.

Fuse links of larger capacity for use in larger fuse casings may be constructed as shown in Fig. 3, in which the link is provided with two oppositely disposed notches adjacent each end thereof which terminate at necks 46. relatively small in size and will fuse or soften I'hese necks are so as to break the circuit through the link when the same is subjected to an extremely heavy overload, such as would be caused by a short circuit.

'This link has two sections 48 similar to the section 38 of the link shown in Fig. l, the sections 48 terminating in necks 49 connecting with a section 50, the two necks 49 being each produced by a pair of transversely extending slots or notches 5 i. The two sections 48' are provided with notches 53 extending at an acute angle to the length of the link and leaving relatively narrow diagonally extending necks 54 between the angugonally extending necks 54 at the angularly extending slots or notches are larger in cross section than the necks 49 and are not expected to become fused during normal operation of the fuse links. In the link shown in Fig. 3, the two sections 48 having the angularly extending notches therein are depended upon for dissipation of heat generated in the necks 49 during continued low overloads. Links of the type shown in Fig. 3 have been found equally effective in prolonging the lag on low overloads. For example, a ampere 250 volt link of this type tested on a 35 per cent overload, i. e., on amperes, blew 53 minutes and 4 seconds after application of the overload, whereas a link of another make not having the inclined notches therein and also rated 100 amperes at 250 volts, when carrying a current of 135 amperes blew in 36 minutes and 5 seconds after application of this load. Numerous other tests have clearly shown that the inclined notches and necks have a very pronounced effect upon the lag of links of this type at relatively low overloads.

Each notch extends in an approximately diagonal direction as shown in the drawings with reference to the section of the link in which the notch is located and the acute angle formed by the notch with the side edge of the fuse link is ap roximately from 30 to 60 degrees. The angle which provides the most desirable lag depends on many factors, including the size and thickness of the link, the current carrying capacity of the same, the voltage, the construction of the fuse housing and others.

The ends of the fuse links which are to be secured to the terminals of a fuse casing may be of any suitable or desired form, those shown in Figs. 1 and 3 being provided at one end with a longitudinal slot and at the other end with a transverse slot for cooperation with the screws 30, but the ends of the fuse links may be of any other suitable or desired form for connection with various types of terminals of fuse casings.

The reason for this improved action of fuse links with inclined notches and inclined necks is not deiintely known, but a greatly improved action results from the use of the inclined notches, regardless of whether the inclined notches form between them a neck which will blow at relatively low overloads, as in Fig. 1, or whether these necks are at one or both ends of sections of the fuse link in which the inclined notches are located, as in Fig. 3.

While the fuse links shown and described have particularly desirable low overload lag features, these fuses also provide approximately the same or slightly less lag than heretofore provided at higher overloads. This is desirable, since there is more danger to electrical apparatus or other devices on a circuit and more danger of fire from a heavily overloaded circuit. Tests have also shown that while the improved links herein disclosed produce a longer time lag at low overloads when the links are arranged in any type of casing, yet the best results are obtained when these links are used in ventilated casings, such as the one illustrated in Figs. 1 and 2.

I claim:

1. A fuse link for providing an extended time lag at low overloads, comprising a strip of fusible metal having means at its ends for connecting the link in an electric circuit, said link having a section which is connected with other portions of the link by relatively narrow necks, said section having substantially parallel sided notches extending into said section in a direction sub stantially diagonal with reference to said section.

2. A fuse link for providing an extended time lag at low overloads, comprising a strip of fusible metal having means at its ends for connecting the link in an electric circuit, said link having a section which is connected with other portions of the link by relatively narrow necks, said section having a relatively narrow notch formed therein and extending from an edge portion of said link into said section in a direction substantially dia gonal with reference to said edge portion, the edges of said notch extending substantially parallel to each other.

3. A fuse link for providing an extended time lag at low overloads, comprising a strip of fusible metal having means at its ends for connecting the link in an electric circuit, said link having a section which is connected with other portions of the link by relatively narrow necks, said section having a relatively narrow notch formed therein and extending from an edge portion of said link substantially diagonally into said section and dividing said section into two parts and terminating at the inner end thereof in a neck connecting said two parts of said section and extending at an inclination to the length of said link.

4. A fuse link for providing an extended time lag at low overloads, comprising a strip of fusible metal having means at its ends for connecting the link in an electric circuit, said link having a section which is connected with adjacent portions of the link by relatively narrow necks, said section having a pair of relatively narrow notches extending inwardly from the opposite side edges of said link and in a direction substantially diagonal with reference to said section and terminating adjacent to each other to form a neck in said section.

5. A fuse link for providing an extended time lag at low overloads, comprising a strip of fusible amen r7 metal: having means at its ends for connectin the link in an electric circuit, saidv link having a section which is connected with other portions ofthelink. by relatively narrow necks, said section, having a pair of relatively narrow notches extending inwardly from, the opposite edges of said link in a direction substantially diagonal of said section and terminating adjacent to each other tov form a neck in said section, said neck extending at an angle to the length of said link.

6. A fuse link for providing an extended time lag at. low overloads, comprising a strip of fusible metal having means at its ends for connecting the, link in an electric circuit, said link having a section which is connected with other portions of the link by relatively narrow necks, said section having a pair of parallel sided notches ex tending into the. same from opposite edges of said link ina direction substantially diagonal of said section and arranged substantially in alinement with each other, and spaced apart to form between the inner ends of said notches a relatively narrow neck.

7. A, fuse link for providing: an extended time terially greater length than width and having 3 notches formed, therein extending toward each other from opposite side edges of said link in a direction substantially. diagonal of said middle section, and. forming betweenthem a neck in said section, said neck being. of such cross section that it will become. softened by currents in ex cessof the rated capacity of said fuse link, the parts of said section at opposite sides of said last mentioned notches serving to. cool said last mentioned. neck to provide an extended time lag at low overloads.

8,, A fuse, link for providing an extended time lag at low overloads, comprising a strip of fusible. metal having means at its. ends. for connecting. thelink in an. electric circuit, and hav ing a pair of sections of materially greater length thanv width,,one of said sections being arranged adjacent to each. end of said link, said link having notches therein separating said ends from said sections, and a middle. section spaced from said first mentioned sections. by narrow necks, said first mentioned sections each having a notch therein. extending from an edge of said link in a direction. substantially diagonally thereof.

9. A fuse linkfor providing an extended time lag at low overloads, comprising a, strip of fusible, metal having means, at its. ends; for conconnecting, the link in; an. electric; circuit, and having a pair of. sections, of. materially greater length than width, one of. said sections being arranged adjacent to each end of said link, said link having notches therein separating said ends from said sections, and a middle section. spaced from said first mentioned sections by narrow necks, said first mentioned sections each, having apair of substantially parallel sided notches extending from the edge portions of said, link sub stantially diagonally with reference to said sec.- tions and dividing said sections into two portions separated by a neck.

10. A fuse. comprising a casing of substantially tubular form. and having openings at the opposite. ends thereof for ventilating said fuse casing, terminals extending into the. opposite: ends of said casing, and a fuse link of fusible meta-l formed to be connected to said; terminals, said link having narrow necks adjacent, to said terminals formed to blow at heavy, overloads,,-the sec tion of said link; between: said necks. havingv a relatively narrow notchformed therein, and ex;- tending, from an edge portion of said link into said section in a direction. substantially diagonally thereof, said notchterminating in a neck which is wider than: said first mentioned necks and formed to blow when said link. is. subjected to moderate. overloads for extended periods of time.

11. A fuse linkv comprising a stripv of fusible metal having its ends formedfor. connecting; the link in an electric circuit, said link having. a neck portion oi, materially less cross sectional area than other portions of the link, and, anotch arranged in said link and terminating at, one end at. said neck portion and arranged diagonally to the length of the link, said notch having substantially parallel sides. and, extending, at an. angle of not more than 60 degrees; to. the length of, said link.

ARTHUR M.. POPE.

REFERENCES CITED The following references are: of record in the file of this patent:

UNITED STATES PATENTS Number Name Date,

1,439,870 Conant Dec..2.6., 1922 2,028,720 La Mar Jan. 21, 19.36 2,181,825 Wood Nov. 28, 1939. 2,287,553 Floten June 23,1942

FOREIGN? PATENTS Number Country Date 395,038 Great Britain July 18,1933

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