US3706062A - Remake proof time delay fuse - Google Patents

Abstract

PLUG FUSES OF "TYPE S" OR EDISON BASE VARIETIES IN WHICH THE FUSE LINK IS SO FORMED AND DISPOSED IN THE FUSE BODY THAT ONCE THE FUSE HAS BLOWN IT IS NOT POSSIBLE FOR THE REMAINING FUSE LINK PARTS TO MOVE WITHIN THE FUSE BODY SO AS TO CAUSE A RECONNECTION OF THESE REMAINING PARTS SUCH

AS WILL ALLOW ELECTRICAL CURRENT TO AGAIN FLOW THROUGH THE FUSE.

Description

Dec. 12, 1972 E. B. JUDD 3,706,062

REMAKE PROOF TIME DELAY FUSE Filed April 50, 1971 3 Sheets-Sneet 1 f4 Har/yay 12, 1972 I E. B. Juno 3,706,062

REMAKE PROOF TIME DELAY FUSE Filed April 30. 19'71 5 Sheets-smeet 2 By fda! i {far/1 ey De. 12, E B. JUDD REMAKE PROOF TIME DELAY FUSE 3 Sheets-Sneet 3 med April so. 1971 FIG. lO

FIG- 11 United States Patent O 3,706,062 REMAKE PROOF TIME DELAY FUSE Edwin B. Judd, East Greenwich, RJ., assigner to General Electric Company Filed Apr. 30, 1971, Ser. No. 138,989 Int. Cl. H01h 85/10, 85/20, 85/62 U.S. Cl. 337-159 1 Claim ABSTRACT F THE DISCLOSURE The present invention relates to improved plug fuses and particularly to plug fuses which can be operated with greater reliability. More specifically it relates to a fuse having a fuse link which essentially cannot be remade in the sense of regaining its capability to conduct electric power after it has once been blown.

Conventional plug fuses depend for their operation on the separation of a fuse link of a fuse into a least two parts when excessive electric power is passed therethrough. It can be very dangerous to have the portions of a fuse link recombine to permit electric power to pass again through a fuse link after the link has been subjected to excessive electric power. This danger of re-making of a blown fuse can be dangerous because severance of the link is a safety measure which prevents personal injury or property damage as due to the starting of an electrical lire or the like.

To improve probability of separation of the portions of a fuse link various schemes are employed including providing mechanically weakened portions in the link, placing certain bends and contours in the link, and providing certain accessories in the fuse link chamber. One such accessory and its operation is described in U.S. Pat. 3,042,- 777. In this fuse construction the accessory is a Weight to induce a great probability of movement of a severed portion of the link after excessive power passes through the link.

Also, accessories may be employed in connection with fuse links to impart other operating characteristics such as time delay characteristics as described in U.S. Pats. 2,557,926; 2,688,061; and 3,089,012.

In each of these described fuses the structure is shown in the drawings with the fuse in the position shown in FIG. 3 of the present application. Many tests of fuse reliability are also conducted with the fuse in the orientation shown in the patents and in FIG. 3 of this application, i.e., with the force of gravity operating parallel to the cylindrical axis of the fuse. However, in most households the fuse is inserted into a wall mounted fuse box so that the axis of the fuse is horizontal rather than vertical.

As will be evident from the figures of patents of the art where a fuse is mounted with its axis horizontal and a break occurs at only one location of the fuse link, it is possible for gravity to act on the remaining portions of the fuse link, particularly in a softened condition which accompanies a heating such as causes link severance, to re-align the remaining portions. Depending on the orientation of the remaining parts of the fuse link, which in turn depends on the turning of the fuse as it is screwed into place in a fuse box, it is possible for the remaining portions to be again brought into physical contact so that current can again ow through the fuse. This is what is meant in 3,706,062 Patented Dec. 12, 1972 this application by the terms re-making and by similar expressions.

It is accordingly an object of the present invention to provide a fuse structure having more reliable operation.

Another object is to provide a fuse structure having economy of construction.

A further object is to provide a fuse structure which cannot be re-made after blowing or which has such a low probability of re-making as to be for practical application non-remakable.

Other objects will be in part apparent and in part pointed out in the description which follows.

A better understanding of how these and other objects of the invention are achieved will be gained by reference to the accompanying drawing in which:

FIG. 1 is a top plan view of a fuse product of this invention showing the fuse link through a top window of the device.

FIG. 2 is a side elevation of the fuse of FIG. 1.

FIG. 3 is a vertical section of the fuse product of FIG. 1 taken along the line 3-3 of FIG. 1.

FIG. 4 is a top plan view of a fuse link usable in a fuse product of this invention.

FIG. 5 is a fuse link as in FIG. 4 but having a heat sink crimped onto the link.

FIG. 6 is a cross-sectional View of the fuse link of FIG. 5 taken along the line 6 6 of FIG. 5.

FIG. 7 is an axial section of a fuse similar to that shown in FIG. 3 but with its axis horizontal.

FIG. 8 is an axial section of a fuse similar to that of FIG. 7 but omitting a heat sink.

FIG. 9 is an axial section of a porcelain Edison base plug fuse having the fuse link and related structure of this invention.

FIG. 10 is an axial section of the porcelain Edison base fuse of FIG. 9 with the crimped heat sink omitted.

FIG. 11 is a top plan view of a fuse of FIG. 10.

In one of its broader aspects the objects of the present invention are achieved by providing a fuse structure comprising a generally cylindrical insulating fuse housing, said housing having a window for viewing the body interior at one end and an external central contact extending into the fuse body at the other end, a second contact on the outer cylindrical surface communicating with the interior of said body, a fuse link within said housing extending between the central and side contact, a barrier wall section in said housing the top of which is disposed for viewing from the fuse exterior through said window, said link having a sector of reduced cross-section disposed over the top of said barrier in a position to be viewed through said window, said link having a longer and a shorter leg extending down from said sector of reduced cross-section, the upper portion of the longer leg touching the side of said barrier.

'I'he manner in which the objects of the invention may best be carried out is now described in greater detail.

Referring now rst to FIG. 1 and FIG. 2 a fuse product is shown having the form which is known in the trade a's a type S fuse. A porcelain fuse body 20 encloses a metal link 10 of a metal which fuses and severs when excessive electric power ows therethrough. The fuse link 10 is formed of a fusible metal and-a more fusible portion thereof is seen through a window 12 in the top of the device.

The fuse link 10 has mounted on it a crimped heat sink 40 also visible through window 12.

The window 12 is held in the frame 14. The frame y14 is an annular metal frame having an inwardly extending upper flange 17 and a crimped lower serated edge portion 18. The crimped portion extends under and into a recess 21 on the side of a porcelain body 20 as seen in FIG. 2. A ange 22 extends out below recess 21. Below the tlange 3 .Y 22, a threaded section 24 formed integrally with the body 20 provide's the threaded meansby which the device is inserted into a fuse receptacle. A lower contact 26 and an upper contact 28 are the two external electrical contacts of the fuse. The fuse link is mounted within the fuse \body to extend in electrical contact between the two contacts 26 and 28.

Referring now to FIG. 3 the arrangement of the fuse link within the body and its relation to the window and the external electrical contacts 26 and 28 is described. From the sectional view of FIG. 3 it will be noted that the electrical contact 26 is inserted from the bottom and upward through the ceramic housing 20 to provide a well 30 at the upper portion of the contact. The contact 26- is secured in place after insertion as by deforming the upper portion of the well. With reference to the fuse housing 20 this well is at the lower portion and within the chamber 32 in the interior of the housing 20. A mass of low melting metal such as 34 may be included in the well 30` and may be melted to effectively solder and bond the lower end 'segment 36 of the fuse link to the contact 26. The next upper segment 38 of the fuse link extends essentially in ia straight line between the well 30 and the heat 'sink 40. Heat sink 40 is crimped over a segment of the fuse link above 38. The segment of the link 42 which is beneath -the window 12 is the segment which may be seen best through the window. This segment 42 is designed to blow, that is, it is of such reduced cross-section that it is the segment heated to the highest temperature as a result of flow of excessive power through the link.

The segment 42 is located, pursuant to this invention, 'over the top of barrier 25 not only in order to gain the advantage of ready visibility through window 12, but al'so because the severance of a segment of this location results in a separation of the link into parts which essentially cannot recombine by movement of remaining portions of the link.

The next segment of the fuse link 44 is an end which is also embedded within a conducting metal body 46. Body 46 may be of solder-like soft conductive metal. It will also be noted that an inner portion of external contact 28 is embedded in this same mass 46 of conducting metal.

A form of a fuse link suitable for use in a fuse of the present invention is seen in FIG. 4 and the location and configuration of a heat sink mounted on such a fuse link is best seen in FIGS. and 6.

Referring first to FIG. 5 the link includes a first end segment 44 to be electrically connected to a rst external conductor as by embedding in the upper solder mass 46 as seen in FIG. 3.

Thenext segment 42 of the link is the longer narrow section of the link. Because of its longer length and narrower width it is least able to dissipate heat proandv narrower width it i's least able to dissipate heat produced by electrical overloads and is accordingly the segment at which a blow or vaporization or fusion of metal to sever the link into the electrically isolated parts is most likely to occur. In comparison to segment 39, which, as is evident from FIG. 5, is also of reduced cross-section, the segment 42 will blow first because it is the longest segment of reduced cross-section.

-In other words segment 42 will blow first where its cross-section is the 'same as that of segment 39 because heat can be dissipated from the mid-portion of segment 42 at a slower rate than from any other portion of the link. In its preferred mode the longer segment 42. is of smaller cross-section, by perhaps 20%, than that of segment 39 so that the dissipation of heat from its mid-portion is reduced even further.

A mid-'segment 41 of link 10 is the segment onto which the heat sink 40' is crimped in the link of FIG. 5. The link of FIG. 5 corre'sponds to that shown in the fuse structure of FIG. 3.

Y Thin segment 39 may also be severed by a strong surge of excessive current thus separating the mid-segment 41 and heat sink 40y entirely from the remainder of the link. On the other hand when the current llow through the link is strong enough to fuse segment 42 and sever it, it is frequently strong enough to soften segment 39` and permit the mid-segment 41 and heat sink 40 to move in chamber 32 under the inuence of gravity.

It will be apparent that any movement of the end of segment 41 can, because of the unique combination of features of the fuse structure taught herein, only increase the distance between segment 41 and segment 44. Similarly if fusion or blowing of a portion only of fuse segment 42 occurs (i.e., less than the entire length of 'segment 42 is vaporized or otherwise separated from the remainder of the link), any movement of the remaining portions of the fuse link can only result in an increase in the separation of the remaining portions. This means that the distances between the remaining portions of segment 42 will increase, i.e., a further 'separation of that portion remaining attached to segment 44 from that portion remaining attached to segment 41 will occur.

Considering this movement of the fuse link parts further reference is now made to the illustration of FIG. 7 wherein a type S fuse is shown with a horizontal axis corresponding to the position of the fuse in the conventional fuse box of a residence or other building.

In order to illustrate the principle of the pre'sent invention the fuse is shown as having been disposed in a conventional fuse box in a position which might permit the longer leg of the fuse to be pulled by gravity toward the shorter leg after the fuse is once blown. As is evident the fuse link is essentially as shown in FIG. 3.

It will be understood that the fuse of this invention has the non-remakable feature whether the fuse is disposed with its axis vertical or horizontal or at any other angle and also that the feature is present when a fuse link is present having the heat sink in place or when it is absent.

In the fuse of FIG. 7 when a portion of the thin segment 42 is blown or when the entire segment is blown the remaining segments 38, 39, 41 of the link as well as a portion of segment 42 may remain. Further these remaining segments and portion may be in a position to be pulled by gravity toward the segment 44 or toward a portion of segment 42 remaining attachedv to segment 44. However, because the link is mounted in the fuse body to extend along essentially the shortest path between the 'contact 26 and contact 28, and because it touches the side of barrier 27 it is not possible for the segments or portions to reach each other again in such manner as to cause ow of i11- terrupted current to resume.

An important point here concerns the disposition of link 42. Link 42 should not be in contact with the top 25 of the barrier 27 as it would in this case yield too much heat to the barrier and not be as subject to fusion and failure within this segment as it is when disposed above the top 25 of barrier V27 as shown in FIG. 3 or 7 for example. This is particularly important because it is the severance of segment 42 on which the operation of the fuse as a current interrupter depends and it is highly preferable that when the fuse blows an appreciable portion of the segment be evaporated or melted or otherwise removed. This is preferable because it reduces the possibility that the remaining portions of the segment will be able to reach each other to allow current to pass again through the link. This possibility is further-reduced by the fact that the segment 42 is designed to blow under many overload or power surge conditions in such manner that an appreciable portion of metal is removed at the time it blows.

Further the portions of segment 42 which remain are quite light in weight and gravity is less likely to cause them to move even in a softened condition than if` they are attached to a larger segment which is free to move and particularly a larger segment to which a weight is crimped or otherwise appended.

In addition, the arched segment 42 is disposed in such a position that gravity is less likely to act on the remaining portions of the segment to recombine them than if the fuse were used in a vertical axis position. The residual segments of the blown arch 42 falling toward barrier surface 25, which might possibly occur if the axis were vertical, is far less likely to result in recombination if the axis is horizontal as in most use situations for fuses, then if the axis is vertical because gravity will pull at least one remaining portion of segment away from the surface 25.

In the very unlikely event that the edges of the remaining portions of Segment 42 do touch there is likely to be only a very momentary flow of current and reblowing of the segment because the only portions which can possibly touch are parts of segment 42 and this is the segment of smallest cross-section of any segment of the link. This is in contrast with the situation in fuses of the art where segments of larger cross-Section can move in the fuse chamber and contact each other and establish current paths capable of carrying higher power than the power which can be carried by the unblown fuse link.

In other words the novel fuse construction of this invention is not at all remakable to have a higher power handling capacity than the unblown fuse and is essentially unremakable for passing any level of power for the reasons stated above. By essentially unremakable is meant that the fuse has such a low probability of remaking in comparison to prior art fuses that no instance of remaking will be found in a test of a number of these fuses which is much larger than the number of prior art fuses which are blown in normal houshold use circumstances before a remake of a blown prior art fuse occurs.

FIG. 8 is an axial section of a type S fuse similar to that of FIG. 7 with the exception that the fuse link is essentially the link of FIG. 4 with the heat sink omitted rather than the link of FIG. 5 as seen in FIG. 7.

Similarly numbered parts perform functions corresponding to the parts bearing the same numbers in FIG. 3. Generally the parts of the link correspond to those of FIG. 4 so that the thinner longer sector 52 of link 60 of FIG. 4 performs essentially the same function as thinner longer sector 42 of link 10. Note that thin sector 52 loops up and over the top 25 of barrier 27 and out of contact with the top of barrier 27.

No heat sink is on mid-sector 54 similar to the heat sink 40 on mid-sector 41 of line 49 of FIG. 5. Accordingly the link of FIG. 4 has less capability to serve the time delay function performed by link as in permitting a momentary overload as a motor is being started.

FIG. 9 shows an Edison base plug fuse having a fuse link aligned in the unremakable configuration of the type S fuse structures discussed above.

In the structure of this figure the parts numbered as seen in FIGS. 3 and 7 are in essence the same and perform essentially the same functions as performed by similarly numbered parts of the devices of FIGS. 3 and 7.

A principal difference is that the external contact 128 6 is a screw shell. The screw shell contact is electrically connected to solder body 46. The screw shell has a set of threads different from the set of threads of the type S fuse, each having threads to match a threaded fuse socket into which it is to be screwed.

FIG. 9 shows an Edison base plug fuse having a fuse link having a heat sink crimped on a mid-segment thereof. The performance of this product is similar in essentially all respects to that described with reference to the device of FIG. 7.

Referring specifically to FIG. 4 there is shown a fuse link having no heat sink crimped to it but having one end sector 50 for connection to one electrode and another end sector 58 for attachment to the other electrode. Its sector 52 of smallest cross-section is adjacent to end sector 50 and a mid-sector 54. A sector S6 of reduced cross-section separates mid-sector 54 from end sector 58.

Similarly FIG. 10 is a fuse device similar to that of FIG. 9 with the exception that the time delay heat sink is absent and the fuse performs in a fashion similar to the fuse of FIG. 8. Similar parts bearing numbers the same as those of the parts of FIG. 8 have essentially the same function as described with reference to FIG. 8.

FIG. ll is a top plan view of the fuse of FIG. 10 showing the fuse link over a wall barrier top portion as it may be seen by the user of such a fuse in use.

What is claimed is:

1. A. fuse structure comprising a generally cylindrical insulating fuse housing, said housing having a window for viewing the body interior at one end and an external central contact extending into the fuse body at the other end, a second contact on the outer cylindrical surface communicating with the interior of said body, a fuse link within said housing extending between the central and side contact, a barrier wall section in said housing the top of which is disposed for viewing from the fuse exterior through said window, said link having a sector of lowest heat dissipating capacity disposed over the top of said barrier in a position to be viewed through said window, said link having a longer leg extending from said sector of lowest heat dissipation into contact with said central contact, the upper portion of the longer leg touching the side of said barrier and said link having a shorter leg extending from said sector of lowest heat dissipation into contact with said side contact.

References Cited UNITED STATES PATENTS 1,385,285 7/1921 Thomas 337-260 3,042,777 7/1962 Pertici 337-260 XR ROY N. ENVALL, JR., Primary Examiner D. M. MORGAN, Assistant Examiner 1U.S. Cl. X.R. 337-262

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