Electric Circuit Breaker

Abstract

A movable contact-supporting arm comprising a relatively high conductivity low strength flat plate portion disposed with its major planar surface generally at right angles to the direction of movement of the contact arm and a relatively low conductivity high strength backing plate having its major planar surface disposed generally parallel to the direction of movement of said contact arm to form a generally T-shaped cross-sectional configuration, and a contact member mounted on the front surface of the high conductivity plate portion by suitable means, such as by welding.

Description

BACKGROUND OF THE INVENTION

Our invention relates generally to electric circuit control devices and more particularly is directed to new and improved contact arm assemblies for electric switches, circuit breakers and the like.

Heretofore movable electric contact arm assemblies for switches such as circuit breakers and the like have conventionally consisted essentially of a flat plate of relatively highly conductive material with a contact mounted on one edge thereof. The conductive plate was disposed generally perpendicular to the abutting surfaces of the contacts in the closed circuit position in order to best resist the high compressive forces exerted thereagainst during operation. Unfortunately such assemblies inherently possess the structural weaknesses associated with the use of high electrical conductivity materials. Accordingly it has been necessary to increase the cross-sectional area of such parts for purely structural purposes beyond the size required to carry the current of the switch or circuit breaker. This, of course, unnecessarily adds to the cost of the device, since the high conductivity materials (such as copper) are comparatively expensive.

In addition, such prior art contact arms presented a problem in that the mounting of the contact member on one edge portion of the contact arm member was difficult to accomplish. This is because the welding of contact members to supporting metallic members is best accomplished by an assembly which presents two opposed generally flat relatively wide planar surfaces which may be engaged by opposed electrodes of a welding machine, sandwich fashion, during the welding process. Contact arm assemblies of the type referred to of the prior art, however, present an edge portion of the support member as one of the two opposed surfaces which must be engaged by the welding electrodes. This makes the welding process more time consuming and also causes a higher number of defective welds to occur.

Furthermore, in addition to the above, the relatively small area of engagement between the edge portion of the supporting member and the generally planar back surface of the contact member of such prior art constructions does not provide a very good path for the conduction and dissipation of heat generated between the contacts in closed circuit position.

In addition to the above problems, the process of welding, as is well known, creates intense heat in the parts to be welded, with the result that the support member is softened or "annealed" by the welding. This weakens the support member at the precise point where strength is important, that is, at the point at which force is exerted thereon because of the engagement of the contacts in the closed position.

OBJECTS OF THE INVENTION

Accordingly, it is a general object of the present invention to provide a new and improved contact arm assembly for circuit control devices of the type described which uses a minimum of relatively expensive high electrical conductivity material.

It is another object of the invention to provide a supporting arm for a movable contact member including mounting means for the contact on the supporting arm which is readily adapted to standard welding processes and machines.

A further object of the invention is to provide a supporting arm for a movable contact member which also provides for good heat conductivity and dissipation of heat from the movable contact, and which furthermore nevertheless utilizes a minimum of relatively expensive high conductivity material.

It is another object of the present invention to provide a contact arm assembly for supporting a movable contact member of an electric switch or circuit breaker in which a minimum of relatively expensive high conductivity metallic material is required, but which nevertheless presents a contact supporting portion to which a contact may be welded, which is generally wide and flat in a direction parallel to the back surface of the contact member to be attached thereto, while yet providing required structural strength in the assembly.

It is a further object of the invention to provide a contact supporting arm construction of the type including a contact support member having a contact engaging portion of relatively high conductivity material, the contact being attached thereto by welding, the nature of the assembly being such that softening or weakening of the contact engaging portion of the assembly by said welding process does not detract from the required structural strength of the assembly.

A further general object of the present invention is to provide an improved contact arm assembly comprised of a composite metal construction exhibiting high strength, endurance and dependable operating characteristics.

A further object of the invention is to provide a switch or circuit breaker including a composite contact supporting arm comprising a minimum amount of relatively expensive high conductivity material combined with relatively inexpensive low conductivity high strength material in which the high conductivity portion is disposed and arranged to shield the main body of the low conductivity material from direct impingement by an arc drawn between the contacts.

SUMMARY OF THE INVENTION

In accordance with the present invention these and related objects are attained by providing an electric circuit breaker of the type described with a new and improved movable contact arm assembly comprising an elongated contact carrier mounted for pivotal movement along a path between open and closed circuit positions and including a conductor blade disposed substantially perpendicular to a plane lying along the carrier's path. The contact carrier is a composite member comprising a platelike current conductor blade mounting the contact on its wide surface at one end thereof and a structural support member upstanding from the conductor at substantially a right angle thereto.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be better understood from the following detailed description taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 is a side elevation view of a circuit breaker, partly broken away and partly in section, illustrating one embodiment of the contact arm assembly of the present invention in its closed circuit position, its open circuit position being shown in phantom;

FIG. 2 is a fragmentary plan view illustrating only the movable contact arm assembly of FIG. 1;

FIG. 3 is an exploded isometric view of the contact arm assembly shown in FIG. 2;

FIG. 4 is a sectional view of the contact carrier of the assembly illustrating one manner of securing the backing member to the conductor blade; and

FIG. 5 is a side elevation view of another embodiment of a contact carrier of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to the drawing in greater detail, wherein like reference numerals indicate like parts throughout the several FIGS., the invention is shown in FIG. 1 as incorporated in a multipole electric circuit breaker having an insulating housing or casing comprised of a generally rectangular base member 10 and an overlying cover 12 mounted thereon. A manually operated ON/OFF button 14 protrudes through the cover 12 and is suitably connected through an operating mechanism, such as the spring driven overcenter toggle linkage 16 (shown in phantom), to each of the circuit breaker's contact arm assemblies, generally designated by the numeral 20. As illustrated in FIG. 1 the assembly 20 is mounted within the insulating casing for movement between its closed circuit position shown in full line and its phantom line open circuit position.

A terminal strap 22 associated with a line terminal of the circuit breaker is fixedly secured to the base member 10 of the casing and mounts a stationary contact 24 at one end thereof. As will be appreciated each of the movable contact arm assemblies 20 are operable in unison by the overcenter operating linkage 16 through a common contact cross arm 26 which extends transversely of the casing and provides a common pivot axis therefor. A flexible electric conductor or braid 28 is connected to each movable contact arm assembly 20 and is suitably associated with a load terminal on the opposite end of the breaker to complete the circuit thereacross.

Upon movement of the manually operated button 14 to its OFF position, the overcenter toggle linkage 16 moves the pivotal contact arm assembly 20 to the phantom line position shown in FIG. 1, opening the circuit and preventing the flow of electric current therethrough. Conversely, upon movement of the manually operated button 14 to its ON position illustrated in FIG. 1, the contact arm assembly is rapidly and effectively driven in a clockwise direction as viewed in FIG. 1 causing firm pressurized surface engagement between the movable contact 32 carried by the contact arm assembly 20 and the stationary contact 24 carried by the load terminal strap 22.

Upon the occurrence of an abnormally high current condition in the circuit controlled by the breaker, a suitable tripping mechanism, not shown, which may be of a thermal or magnetic character or a combination thereof, is activated to cause movement of the toggle linkage 16 a sufficient distance to permit operation of the overcenter mechanism and the resultant counterclockwise movement of the contact arm assembly 20 to its open circuit position. Upon correction of the condition resulting in the high current short circuit, the breaker may be manually reset by moving the manually operated button 14 to its OFF position.

In accordance with the present invention the pivotal contact arm assembly 20 comprises a contact operator 34 firmly mounted on the common cross arm 26 and a composite contact carrier including a current conducting blade 38 and support member 40 pivotally mounted on the contact operator 34 by means of an interconnecting pivot pin 42. The contact operator 34, best shown in FIG. 3, is a generally U-shaped member comprised of a substantially flat base portion 44 which rests against a flat surface 46 of the cross arm's square hub 48 and a pair of opposed sides 52 provided with aligned generally square openings 54 at their point of juncture with the base portion 44 for receiving the common cross arm 26 therethrough. As shown in FIGS. 1 and 2, the base portion 44 is held in secure fixed engagement with the common cross arm 26 by means of the fastener 56 whose tabs 58 extend through apertures 50 in the base portion 44 and bend over the outside surface thereof in locking engagement. The spaced generally parallel sides 52 of the contact operator are each provided with forwardly extending pinched-in journal tabs 60 spaced in substantial parallelism by a distance approximately equal to the width of the contact carrier's support member 40. In this manner the tabs 60, which are provided with aligned apertures 62 for receiving the pivot pin 42, securely mount the contact carrier therebetween for limited pivotal movement as discussed in greater detail hereinafter.

The current conducting blade 38 of the contact arm assembly is an elongated, generally rectangular strip or bar of copper or other suitable conductive material to which the movable contact 32 is affixed at one end thereof. It is an advantage of the present invention that the blade 38 is mounted in such a manner that the plane thereof is disposed at substantially a right angle to the assembly's path of travel between its open and closed circuit positions. More particularly the conductive blade 38 presents its wide bottom surface to the arcing area of the circuit breaker so that the blade's flat face portion 36 which mounts the contact 32 lies in confronting planar relationship to the terminal strap 22 and the stationary contact 24 mounted thereon. As mentioned, the blade 38 is preferably a flat copper strip or bar which provides excellent current conducting properties and is of sufficient length to provide for the secure attachment of the flexible conducting braid 28 which electrically interconnects the movable contact 32 with the load terminal of the circuit breaker.

The support member 40 of the composite metal contact carrier is a flat, generally rectangular plate formed from rigid, high strength material, such as steel. The support member 40 is disposed at substantially a right angle to the conductor blade 38 so that its bottom longitudinal edge 64 rests on the broad top surface 66 of the blade imparting a generally T-shaped cross-sectional configuration to the contact carrier, as best seen in FIG. 4. A pair of depending securing lugs 68 extend downwardly from longitudinal edge 64 and interfit within central apertures 70 provided in conductor blade 38 to provide a secure interconnection therebetween when staked in the manner illustrated in FIG. 4. The support member 40 is further provided with a central aperture 72 for receiving the pivot pin 42 and facilitating pivotal interconnection with the operator 34 of the contact arm assembly. Thus, the upright support member 40 provides a strong, durable support backing for the current conducting blade 38 in the form of a beam capable of imparting to the assembly the strength and durability necessary for prolonged trouble-free operation.

Although the contact carrier is pivotally mounted on its contact operator 34, the pivotal movement thereof is substantially limited. For example, when the circuit breaker is fully assembled with the contact arm assembly 20 mounted on the common cross arm 26, the clockwise rotation of the contact carrier assembly when the parts are in the open circuit position is limited by the interfering engagement of a tapered tail portion 74 of the support member 40 with the fastener 56. Additionally, rotation in a counterclockwise direction as viewed in FIG. 1 is resisted by a wire spring 76 held by the operator 34 and pivot pin 42 for engagement with the top longitudinal edge 78 of the support member 40. As shown in FIG. 1 the spring 76 passes beneath pivot pin 42 and rests within its locking grooves 82 while the spring's free ends 80 are held within the side apertures 84 of the operator 34. Thus, it will be appreciated that as the snap action of the overcenter mechanism drives the contact arm assembly 20 in a clockwise direction toward the closed circuit position and brings movable contact 32 into surface engagement with stationary contact 24, the spring 76 permits only limited counterclockwise rotation of the current conducting blade 38 and support member 40. Consequently, clockwise rotational movement of the common contact cross arm 26 beyond that necessary for engagement between the contacts will load spring 76 and assure full pressurized engagement between the contacts at their closed circuit position and a minimum electrical contact resistance.

The support member 40 of the assembly is also provided with a forwardly protruding nose portion 86 which advantageously provides a terminal point 88 suitable for operation as an arc runner for the movable contact arm assembly. As shown in FIG. 5 an alternative embodiment of the nose portion is depicted. In the latter embodiment the nose portion 90 extends below the flat face portion 36 of the blade's bottom surface toward the terminal strap 22.

As will be seen from the foregoing detailed description, the present invention provides a new and improved composite metal contact arm assembly which exhibits improved interruption characteristics on high current short circuits. The assembly is comprised of a current conducting blade oriented so as to dispose its broad flat surface toward the arcing area of the circuit breaker and a structural backing member capable of imparting increased rigidity and durability to the assembly. The T-shaped cross-sectional configuration of the contact arm assembly not only provides the desirable strength and electrical conductivity characteristics required for circuit breaker operation but also appears to provide a beneficial heat dissipating effect over the large conductive surface presented to the arc during the circuit breaking operation. In addition, an important advantage of the T-shaped cross-sectional configuration disclosed is that the wide dimension of the highly conductive blade 38 shields the support member 40, which is desirably of a higher strength but lower conductivity material, from the action of an arc drawn between the contacts. Thus as previously noted, the blade portion 38 is preferably constructed of copper or a copper alloy, while the portion 40 is preferably constructed of steel or a steel allow. In the form of FIG. 5, the portion 40 is extended to provide an arc runner portion 90, but damage to this portion, such as by erosion due to effects of arcing, will not adversely affect the function of the part 40 as a strength beam or reinforcing member.

As will be apparent to persons skilled in the art, various modifications and adaptations of the structure above-described will become readily apparent without departure from the spirit and scope of the invention.

Certain aspects of the structure disclosed herein, particularly relating to the spring means for biasing the contact carrier assembly with respect to the contact operator 34, are disclosed and claimed in our copending application Ser. No. 4,836 filed 1-22-70and assigned to the same assignee as the present invention.

Claims

We claim:

1. A movable contact arm assembly for an electric circuit breaker comprising a contact; an elongated composite contact carrier including a generally rectangular platelike current conducting blade having a bottom surface including a substantially flat face portion mounting said contact adjacent one end of the blade; an elongated structural support member having a longitudinal edge mounted in direct contact with the top surface of said blade, said support member being secured to the blade intermediate the ends thereof and including a pointed nose portion extending beyond the end of said blade mounting said contact; a contact operator pivotally mounting said carrier and including means for limiting pivotal movement of said carrier in a first pivotal direction and biasing means mounted on said operator for urging said carrier in said first pivotal direction to provide releasable engagement between said carrier and said limiting means.

2. In an electric switching device comprising a casing, a first contact mounted in said casing, a second contact in said casing having a surface adapted to engage a surface of said first contact, a movable contact arm assembly mounting said second contact for movement into and out of surface engagement with said first contact, and drive means moving said contact arm assembly toward and away from said first contact, the combination wherein the contact arm assembly includes a composite contact carrier comprising a platelike current conducting blade and a backing member for the blade in intimate supporting engagement therewith, said blade having a face portion disposed in confronting relationship to the first contact during surface engagement between said contacts; said blade being a generally rectangular strip having a bottom surface including said face portion, said second contact mounted on said face portion adjacent one end of said blade, the backing member having a longitudinal edge mounted in secured abutting relationship to said blade, and said backing member including an arc runner portion mounted adjacent said second contact.

3. A movable contact arm assembly for an electric circuit breaker comprising a contact, an elongated contact carrier including a platelike current conducting blade having a face portion mounting said contact and a structural support member secured to the blade, a contact operator mounting said carrier for limited movement in a first direction and biasing means operable against said support member for urging said carrier in said first direction, said blade being a generally rectangular strip having a bottom surface including said face portion, said contact mounted on said face portion adjacent one end of the blade, the support member having a longitudinal edge mounted in secured abutting relationship to said blade, the contact arm assembly including a contact operator mounting the carrier for limited movement in a first direction and biasing means associated with said operator for urging said carrier in said first direction.

4. In an electric switching device of the type comprising a casing, a normally stationary contact supported in said casing, a movable contact arm assembly supported in said casing and including a movable contact portion movable along a predetermined path into and out of engagement with said stationary contact, the combination wherein said movable contact arm assembly comprises:

a. an elongated relatively wide, thin, flat current conducting member;

b. a movable contact member rigidly and conductively mounted on a first wide surface of said current conducting member adjacent one end thereof;

c. a backing member of relatively high strength material rigidly affixed to said current conducting member at a second wide surface thereof opposite said first wide surface, said backing member comprising a relatively wide, thin, flat member having its wide surfaces extending generally perpendicular to said wide surfaces of said current conducting member and having a longitudinal edge portion mounted in abutting relationship to said second wide surface of said current conducting member; and

d. said contact arm assembly disposed in said casing with said first and second wide surfaces of said current conducting member extending substantially perpendicular to said predetermined path of movement of said movable contact member.

5. The combination as set forth in claim 13 wherein:

a. said current conducting member comprises a relatively high electrical conductivity metallic material;

b. said backing member comprises a metallic material having an electrical conductivity substantially lower than that of said current conducting member; and

c. said backing member further being composed of a material having a mechanical strength greater than that of said current conducting member.

6. The combination as set forth in claim 4 wherein:

a. said current conducting member comprises copper; and

b. said backing member comprises steel.

7. The combination as set forth in claim 4 wherein said backing member is disposed substantially along the longitudinal center line of said current conducting member and is attached thereto by means of integral lug portions which extend through corresponding holes in said current conducting member.

8. The combination as set forth in claim 4 wherein said one end of said current conducting member is offset from the general plane of said current conducting member in a direction toward said first wide surface, and said backing member has its said longitudinal edge portion conforming to the contour of said offset at the portion abutting thereagainst.

9. The combination as set forth in claim 4 wherein said backing member has a nose portion extending beyond said current conducting member at said one end thereof and having a depending portion extending in the direction of said contact, said nose portion having a longitudinal edge portion extending substantially flush with the contacting face of said contact to provide an arc runner capable of readily accepting transfer of an arc from said contacting face of said contact.

10. The combination as set forth in claim 4 wherein said combination also comprises means supporting said contact arm assembly for pivotal movement in said casing between open and closed circuit positions with respect to said stationary contact, and flexible conductor means connected directly to said current conducting member of said contact arm assembly adjacent the end thereof opposite said one end whereby all current entering said current conducting member enters directly and without having to first pass through any portion of said backing member.