Low-voltage Fuse Having Molded Case

Abstract

An electric fuse has a substantially prismatic housing or casing formed by a pair of complementary hood-shaped half-shells. A terminal bar is affixed to each of the half-shells. Each terminal bar includes an external portion and an internal portion. The internal portions of the terminal bars include two sections, a first section and a second section. The first sections of the terminal bars extend in opposite directions each into one of said pair of half-shells. The second sections project substantially at right angles from the first sections and are conductively interconnected by fusible elements projecting from one of the pair of half-shells into the other of the pair of half-shells.

Description

BACKGROUND OF THE INVENTION

U.S. Pat. No. 2,837,614 to A.J.Fister, June 3,1958 for PROTECTORS FOR ELECTRIC CIRCUITS and U.S. Pat. No. 3,593,251 to James C.Wilson, July 13,1971 for FUSE DEVICE disclose so-called polyphase fuses which require special insulating spacers between the terminal bars thereof. The presence of such spacers increases the cost of production and reduces the space available for fusible conductor means and for pulverulent arc-quenching filler.

The patent applications of Frederick J.Kozacka, filed Dec.8,1970, Ser. No. 96,110 for COMPACT POLYPHASE FUSE, now U.S. Pat. No. 3,671,110; issued June 20,1971 of Kenneth W.Swain et al., filed Oct. 28,1971; Ser. No. 193,596 for POLYPHASE FUSE WITH BLOWN FUSE INDICATOR and of Richard Belcher et al., filed Aug. 24,1971; Ser. No. 174,455 for ELECTRIC LOW-VOLTAGE FUSE disclose polyphase fuses which have no and do not require any special insulating spacers between the terminal bars thereof. The present invention relates to a fuse structure different from those disclosed in the above referred-to copending patent applications and not requiring special insulating spacers between the terminal bars thereof.

The novel structure according to the present invention is more desirable in certain instances than the structures disclosed in the aforementioned copending patent applications. One particularly important feature of the novel structure according to the present invention consists in that it allows to use fusible elements of relatively great length, applicable in instances of relatively high circuit voltages.

SUMMARY OF THE INVENTION

Fuses according to the present invention include a housing formed by a pair of complementary half-shells of electric insulating material having juxtaposed edges and jointly defining a pair of complementary cavities. Such fuses further include a pair of terminal bars each having an external portion projecting away from said housing and each having an internal portion. Said internal portion of each of said pair of terminal bars includes two sections, i.e., a first section and a second section. The first sections of the pair of terminal bars project in opposite directions into one of said pair of complementary cavities and each of said first sections is affixed to one of said pair of half-shells. The second sections of the pair of terminal bars project substantially at right angles from the first sections thereof and are conductively interconnected by fusible means which extend from one of said pair of complementary cavities into the other of said pair of complementary cavities. There is a pulverulent arc-quenching filler inside of each of said pair of complementary cavities embedding the fusible means which are arranged therein. The aforementioned fusible means include ribbon fuse link means having one end connected to a point of said second section of one of said pair of terminal bars relatively close to said first section thereof and having another end connected to said second section of said pair of terminal bars relatively remote from said first section thereof. The aforementioned fusible means further include ribbon fuse link means having one end connected to a point of said second section of said one of said pair of terminal bars relatively remote from said first section thereof and having another end connected to a point of said second section of the other of said pair of terminal bars relatively close to said first section thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a fuse embodying the present invention;

FIG. 2 is a vertical section of the structure of FIG. 1, taken in substance along 2--2 of FIG. 1;

FIG. 3 is an isometric view of another fuse embodying the present invention;

FIG. 4 is a vertical section of the structure of FIG. 3 taken in substance along 4--4 of FIG. 3; and

FIG. 5 is a top-plan view of a polyphase version of the structure shown in FIGS. 1 and 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, housing 1a,1b is formed by a pair of complementary half-shells 1a and 1b of electric insulating material having juxtaposed edges 2a and 2b and jointly defining a pair of complementary cavities 3a and 3b. Reference characters 4a and 5a have been applied to indicate the external portions of a pair of terminal bars. Each terminal bar includes in addition to an external portion 4a and 5a, respectively, projecting away from housing 1a, 1b an internal portion 4b,4c and 5b,5c. Internal portion 4b,4c comprises a first section 4b affixed to half-shell 1a and a second section 4c projecting at right angles from section 4b. In the same fashion internal portion 5b,5c comprises a first section 5b affixed to half-shell 1b and a second section 5c projecting at right angles from section 5b. Sections 4b,5b project in opposite directions into half-shells 1a,1b and are arranged inside of grooves 18a,18b and may be cemented to half-shells 1a,1b by an epoxy cement. Sections 4c,5c are provided with grooves 19a,19b extending in a direction longitudinally thereof. Ribbon fuse link means 6 whose ends are inserted into grooves 19a,19b conductively interconnect sections 4c,5c of the internal portions of the pair of terminal bars 4a,4b,4c and 5a,5b,5c and extend from one of the pair of complementary cavities 3a into the other of said pair of complementary cavities 3b. This imparts a relatively great length to fuse link means 6 tending to yield a relatively high arc-voltage incident to blowing of the fuse by major fault currents. Cavities 3a,3b are filled with a pulverulent arc-quenching filler 7 (only indicated in part) embedding fuse link means 6.

In the structure of FIGS. 1 and 2 the half-shells 1a,1b have a different geometry, one of them being provided with a hollow projection 8 for receiving a spring-biased blown fuse indicator 9 and the other being provided with a filling aperture 10 for arc-quenching filler 7 which aperture is closed by a plug 11 upon completion of the assembly process of the fuse structure. The blown fuse indicator 9 is normally held in position by a V-shaped restraining wire 12 whose ends are affixed by means of screws 13 to the external portions 4a,5a of terminal bars 4a,4b,4c and 5a,5b,5c. Section 5c of terminal bar 5a,5b,5c is provided with a bore 20 for the passage of restraining wire 12 which is lined with an electric insulating material to insulate the converging portion of wire 12 from part 5c.

In the structure of FIGS. 3 and 4, both half-shells 1a', 1b' are congruent and engage along edges 2a'; 2b' .

In all embodiments of the invention shown half-shells 1a,1b and 1a',1b', respectively, are joined together by studs 17, 17' and 17", respectively.

In the structure of FIGS. 1 and 2 the external portions 4a,5a of terminal bars 4a,4b,4c and 5a,5b,5c are arranged substantially in the plane defined by the juxtaposed edges 2a,2b of half-shells 1a,1b.

In FIGS. 3 and 4 the same reference characters have been applied as in FIGS. 1 and 2 to indicate like parts, except that a prime has been added to all reference characters appearing in FIGS. 3 and 4.

According to FIGS. 3 and 4 each of juxtaposed walls 14a', 14b' of half-shells 1a',1b' is provided with one of a pair of perforations 15a',15b'. The external portions 4a',5a' of each pair of terminal bars 4a',4b',4c' and 5a',5b',5c' project through perforations 15a',15b' from the inside of the housing formed by half-shells 1a',1b' to the outside thereof. The plane generally defined by the juxtaposed edges 2a',2b' of half-shells 1a',1b' is positioned substantially at right angles to the plane defined by external portions 4a',5a' of terminal bars 4a',4b',4c' and 5a',5b',5c'. Each half-shell 1a',1b' has a semi-cylindrical aperture 10a' and 10b', respectively, jointly defining a cylindrical passageway closed by a plug 11'. The complementary cavities 3a',3b' formed by half-shells 1a',1b' are filled with pulverulent arc-quenching filler 7'. The sections 4c',5c' of terminal bars 4a',4b',4c' and 5a',5b',5c' are conductively interconnected by ribbon fuse links 6' of silver submersed in arc-quenching filler 7' and extending from cavity 3a' into cavity 3b' across the plane defined by shell edges 2a',2b'. Each hood-shaped half-shell 1a',1b' is provided with a hollow projection 8' in the form of one-half of a solid of revolution. Projections 8' are complementary and form a housing for blown fuse indicator 9'. The axially inner end of blown fuse indicator housing 8' has a perforation for the passage of restraining wire 12' whose ends are affixed by means of screws 13' to the external portions 4a',5a' of terminal bars 4a',4b'4c' and 5a', 5b',5c' .

The structure shown in FIG. 5 is substantially the same as that shown in FIGS. 1 and 2 but involves three integral phase units rather than one single such unit. FIG. 5 shows below three external portions 4a" of terminal bars and above three external portions 5a" of three terminal bars. The upper half-shell 1a" abuts against a lower half-shell both being tied together by studs 17". Both half-shells form jointly three separate compartments of which each has a filling hole 10" closed by a plug 11". Reference character 13" has been applied to indicate screws for affixing the ends of restraining wires of blown fuse indicators (not shown in FIG. 5) to parts 4a" and 5a", respectively.

It is necessary or desirable to seal half-shells 1a,1b and 1a',1b' along the edges 2a,2b and 2a',2b', respectively. It is further necessary or desirable to seal the points where terminal bars 4a,4b,4c and 5a,5b,5c and 4a',4b',4c' and 5a',5b',5c' project from the inside to the outside of the casing 1a,1b and 1a',1b', respectively. This can best be achieved without use of gaskets by the application of self-curing silicone rubber in paste-form.

It will be noted that half-shells 1a,1b and 1a',1b' are the only means for positioning and spacing terminal bars 4a,4b,4c;5a,5b,5c and 4a',4b',4c' and 5a',5b',5c'. The complementary cavities 3a,3b; 3a',3b' are unencumbered by spacing posts of insulating material extending between the sections 4c,5c; 4c',5c' of terminal bars 4a,4b,4c; 5a,5b,5c;4a',4b',4c'; 5a',5b',5c' .

Referring to FIG. 2, it will be apparent that sections 4c,5c of terminal bars 4a,4b,4c and 5a,5b,5c are conductively interconnected by four ribbon fuse links 6. Considering the ends of ribbon fuse link 6 to the left of FIG. 2 it is apparent that the upper end thereof is connected to a point of section 4c relatively close to section 4b while the lower end thereof is connected to a point of section 5c relatively remote from section 5b. Considering the ends of ribbon fuse link 6 to the right of FIG. 2 it is apparent that the upper end thereof is connected to a point of section 4c relatively remote from section 4b while the lower end thereof is connected to a point of section 5c relatively remote from section 5b. As a result of this geometry, the current path from section 4a to section 5a is of equal length through either of the two fuse links at the extreme left and the extreme right which have been considered above, and the same is also true in regard to the two intermediate ribbon fuse links 6. Equality of the length of the current paths of all ribbon fuse links 6 results in equality of the ohmic resistance thereof. It will also be apparent from FIG. 2 that all ribbon fuse links 6 are arranged at right angles to the plane defined by juxtaposed engaging edges 2a,2b of half-shells 1a,1b.

The assembly of the structure of FIGS. 1 and 2 can be effected as follows: The lower ends of ribbon fuse links 6 are inserted into grooves 19b provided in the section 5c of terminal bar 5a,5b,5c and connected with section 5c by solder joints. Thereupon terminal bar 5a,5b,5c with the fuse links 6 affixed to it may be inserted into and secured to half-shell 1b. Now the upper ends of fuse links 6 are inserted into the grooves 19a in section 4c of terminal bar 4a,4b,4c and connected to it by solder joints. Then terminal bar 4a,4b,4c is inserted into, and affixed to, upper half-shell 1a which is positioned to engage with its edge 2a the edge 2b of lower half-shell 1b. Inserting terminal bar 4a,4b,4c into half-shell 1a and affixing the former to the latter is a single step operation if the terminal bar 4a,4b,4c is cemented to half-shell 1a. The step of cementing terminal bars 4a,4b,4c; 5a,5b,5c to half-shells 1a,1b is greatly facilitated if half-shells 1a,1b are provided with the aforementioned grooves 18a,18b into which the internal sections 4b,5b of the terminal bars can be fitted readily.

The structure of FIGS. 3 and 4 can be assembled in substantially the same way as that of FIGS. 1 and 2.

The fuses disclosed above are intended to back-up other switching equipment such as, for instance, molded case circuit breakers or motor starters. Major fault currents result in fusion of fusible elements 6 or 6' in periods of time less than a quarter cycle of a current wave. Thus an arc-voltage is formed between the sections 4c,5c or 4c',5c' of the terminal bars. This causes fusion of restraining wires 7 or 7', respectively, and activation of blown fuse indicators 9 or 9', respectively.

It will be apparent from the above that terminal bars 4a,4b,4c;5a,5b,5c; 4a',4b',4c';5a',5b',5c' are substantially Z-shaped and that the internal sections 4c,5c,4c',5c' are substantially parallel to the external portions 4a,5a,4a',5a' .

The distance between the surface of the casing 1a,1b or 1a',1b' where the blown fuse indicator 9 or 9' is located and the surface of the casing 1a,1b or 1a',1b' where plug 11,11' is located may be referred to, and is generally referred to, as the length of the casing. The length of a casing is generally its largest dimension. The length of fuse links may be maximized if they extend parallel to the length of the casing or in a direction longitudinally thereof. Thus the geometry shown in FIGS. 2 and 4 allows to maximize the length of fuse links 6,6'. This can readily be achieved by increasing the length of section 4b,4b' of terminal bar 4a,4b,4c; 4a',4b',4c', thus locating section 4c,4c' closer to plug 11,11' than shown in FIGS. 2 and 4. This, in turn, tends to greatly increase the potential interrupting capacity of fuses according to this invention over and above comparable prior art fuses.

Claims

I claim as my invention:

1. An electric fuse including

a. a housing formed by a pair of complementary half-shells of electric insulating material having juxtaposed engaging edges and jointly defining a pair of complementary cavities;

b. a pair of terminal bars each including an external portion projecting away from said housing and each including an internal portion affixed to one of said pair of half-shells, said internal portion of each of said pair of terminal bars including a first section immediately adjacent said first portion thereof, said first section of said internal portion of each of said pair of terminal bars projecting in opposite directions into one of said pair of complementary cavities, and said internal portion of each of said pair of terminal bars further including a second section projecting substantially at right angles from said first section thereof;

c. fusible means conductively interconnecting said second section of said internal portion of each of said pair of terminal bars, said fusible means including ribbon fuse link means having one end connected to a point of said second section of one of said pair of terminal bars relatively close to said first section thereof and having another end connected to a point of said second section of the other of said pair of terminal bars relatively remote from said first section thereof, and said fusible means further including ribbon fuse link means having one end connected to a point of said second section of said one of said pair of terminal bars relatively remote from said first section thereof and having another end connected to a point of said second section of said other of said pair of terminal bars relatively close to said first section thereof; and

d. a pulverulent arc-quenching filler inside each of said pair of complementary cavities embedding said fusible means.

2. An electric fuse as specified in claim 1 wherein said complementary half-shells are substantially congruent.

3. An electric fuse as specified in claim 1 wherein said pair of half-shells is the only means positioning and spacing said pair of terminal bars, said pair of complementary cavities being unencumbered by spacing posts of insulating material extending between said internal portion of each of said pair of terminal bars.

4. An electric fuse as specified in claim 1 wherein said external portion of each of said pair of terminal bars is arranged substantially in a plane defined by said juxtaposed engaging edges of said pair of half-shells and wherein said fusible means project substantially at right angles through said plane.

5. An electric fuse as specified in claim 1 wherein juxtaposed walls of each of said pair of half-shells are provided with one of a pair of perforations, said external portion of each of said pair of terminal bars projecting through one of said pair of perforations from the inside of said housing to the outside thereof, and wherein the plane generally defined by said juxtaposed edges of said pair of half-shells is positioned substantially at right angles to the plane defined by said external portion of each of said pair of terminal bars.

6. An electric low voltage fuse including

a. a pair of complementary substantially hood-shaped half-shells of electric insulating material arranged to abut with juxtaposed edges thereof and jointly defining a cavity having a predetermined length substantially exceeding the other dimensions of said cavity;

b. a pulverulent arc-quenching filler inside said cavity;

c. a pair of substantially Z-shaped terminal bars each affixed to one of said pair of half-shells and each having an external portion projecting away from said pair of half-shells and each having a pair of internal sections enclosing substantially right angles, one of said internal sections of each of said pair of terminal bars being substantially parallel to the external section thereof; and

d. fusible means submersed in said pulverulent arc-quenching filler extending in a direction substantially longitudinally of said cavity and conductively interconnecting said one of said internal sections of said pair of terminal bars, said fusible means including ribbon fuse link means having one end connected to a point of said one of said internal sections of one of said pair of terminal bars relatively close to the other of said internal sections thereof and having another end connected to a point of said one of said internal sections of the other of said pair of terminal bars relatively remote from the other of the internal sections thereof, and said fusible means further including ribbon fuse link means having one end connected to a point of said one of said internal sections of said one of said pair of terminal bars relatively remote from the other of said internal sections thereof and another end connected to a point of said one of said internal sections of said other of said pair of terminal bars relatively close to the other of said internal sections thereof.