Abstract:
An improved arc chute wrapper for an arc chute of a circuit breaker includes left and right halves that form a conjoined two-part member and that carry a plurality of spaced arc plates thereon. The left and right halves of the wrapper are formed with a plurality of left and right grooves, respectively, in confronting relation when the left and right halves are assembled together. The left and right grooves extend at most only partially into the arc chute wrapper, such that the arc chute wrapper is free of holes extending therethrough in the vicinity of the arc plates. The arc plates are free of spinning tabs extending outwardly therefrom, and rather are securely mounted in the left and right grooves of the wrapper. The arc chute wrapper is manufactured by molding or other appropriate method. The arc chute employing the wrapper of the present invention is more reliable, less expensive, and easier to produce than arc chutes employing wrappers and arc plates of the type heretofore known.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to circuit breakers and, more particularly, to an improved arc chute for a circuit breaker. Specifically, the invention is related to an arc chute having arc plates that are mounted in grooves formed in the arc chute wrapper. 
     2. Description of the Related Art 
     Numerous types of circuit breakers are known and understood in the relevant art. One of the purposes for which circuit breakers are provided is to interrupt an electrical circuit on command or according to certain criteria. Circuit breakers thus typically include a set of stationary electrical contacts and a set of moveable electrical contacts. The stationary and moveable contacts are in physical contact with one another when it is desired that the circuit breaker provide electricity therethrough to a load. When it is desired to interrupt the circuit, however, the moveable contacts are moved away from the stationary contacts, thus removing the moveable contacts from physical contact with the stationary contacts, creating a space therebetween, and interrupting the circuit. 
     As is understood in the relevant art, however, the movement of the moveable contacts away from the stationary contacts results in the formation of an electrical arc in the space between the moveable and stationary contacts beginning at the time the moveable and stationary contacts are initially separated. Such an arc is undesirable for a number of reasons. For example, the arc evidences current flowing through the circuit breaker to the load when it is desired that no such current should flow thereto. Additionally, an arc extending between the stationary and moveable contacts often results in vaporization or sublimation of the contact material itself, eventually resulting in destruction or pitting of the moveable and stationary contacts. It is thus desired to eliminate any such arcs as soon as possible upon their propagation. 
     As is understood in the relevant art, the moveable contacts typically are mounted on pivoting arms that pivot the moveable contacts away from the stationary contacts. An arc chute is provided along the path of each arm to break up and dissipate such arcs. Such arc chutes typically include a plurality of spaced apart arc plates mounted in a wrapper, the arc plates being aligned with the axis about which the arm pivots. As the moveable contact is moved away from the stationary contact, the moveable contact moves past the ends of the arc plates, with the arc being magnetically urged toward and between the arc plates. The arc plates are electrically insulated from one another such that the arc is broken up and extinguished by the arc plates. 
     Such arc chutes are not, however, without limitation. For instance, arc chutes of the type known and understood in the relevant art have heretofore been manufactured using arc plates formed with spinning tabs extending outwardly therefrom and extending through holes formed in the wrapper. Such spinning tabs and holes are indicated generally at the numerals  27 A and  47 A, respectively, in FIG. 6 of U.S. Pat. No. 4,963,849 to Kowalczyk et al. The spinning tabs are then compressed to retain the arc plates in fixed relation to the wrapper. The outer surface of the wrapper is then coated with a layer of ceramic paint to eliminate shorts between the compressed spinning tabs of adjacent arc plates. Such shorting can occur when an arc travels through a hole formed in the wrapper to the exterior of the wrapper and thence to another arc plate or to the circuit breaker housing. The aforementioned manufacturing process is less than fully reliable in eliminating shorts. 
     It is thus desired to provide an arc chute wrapper that overcomes the problems of arc chute wrappers heretofore known in the art and that is relatively simple and inexpensive to manufacture. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, an arc chute wrapper in accordance with the present invention is a two-piece conjoined member formed with a plurality of grooves, the grooves being structured to receive a plurality of spaced apart arc plates. The arc chute wrapper is free of holes extending therethrough, and the arc plates are free of spinning tabs. 
     An aspect of the present invention is to provide a circuit breaker incorporating an arc chute, the general nature of which can be stated as including a wrapper, the wrapper having an inner surface and an outer surface, the wrapper being formed with a plurality of grooves extending into the wrapper from the inner surface, and a plurality of arc plates, the arc plates being mounted in the grooves. 
     Another aspect of the present invention is to provide an arc chute wrapper that is structured to extend at least partially around a plurality of arc plates, the general nature of which can be stated as including a generally U-shaped body formed with a plurality of grooves, the grooves being structured to at least partially receive arc plates therein. 
     Another aspect of the present invention is to provide a method of manufacturing a wrapper for an arc chute of a circuit breaker, the general nature of which can be stated as including the steps of shaping the wrapper into a general U-shape and forming a plurality of grooves in the wrapper. 
     These and other aspects and advantages of the present invention will be more readily understood from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is top plan view of an arc chute wrapper in accordance with the present invention; 
     FIG. 2 is a sectional view as taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a sectional view as taken along line  3 — 3  of FIG. 1; 
     FIG. 4 is a top plan view of an arc plate in accordance with the present invention; 
     FIG. 5 is a top plan view of an arc chute in accordance with the present invention; 
     FIG. 6 is a side elevational view of an arc chute in accordance with the present invention; and 
     FIG. 7 is a sectional view as taken along line  7 — 7  of FIG.  6 . 
    
    
     Similar numerals refer to similar parts throughout the specification. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An arc chute wrapper  2  in accordance with the present invention is indicated generally in FIGS. 1-7. The wrapper  2  is a component of an arc chute  6  that includes the wrapper  2  and a plurality of spaced apart arc plates  10 . The arc chute  6  is incorporated into a circuit breaker  14  (FIG. 5) and helps to break up and dissipate arcs forming during separation of the moveable contacts from the stationary contacts of the circuit breaker  14 . 
     The wrapper  2  is advantageously a conjoined two-part member including a left half  18  and a right half  22  that are attachable or conjoinable to one another. The left and right halves  18  and  22  are each generally L-shaped, although the left and right halves  18  and  22  can have other combinations of shapes without departing from the spirit of the present invention. 
     The wrapper  2  is preferably manufactured out of a strong, lightweight material that is electrically insulative or is resistive to the flow of electricity. The material is also preferably capable of being formed by molding, cutting, or other working, and preferably includes a substantial glass component, either in the nature of fibers or granules. While any of a wide variety of appropriate materials may be used, the wrapper is preferably manufactured out of an electrically insulative material that is suited to withstand the elevated temperatures typically experienced in an arc chute application. Such a material would include a compound in accordance with standard GPO-3 as established by the National Electrical Manufacturers Association (NEMA), which is a higher temperature, rigid fiberglass-reinforced polyester thermoset material. Such a material is manufactured by Glastic Corporation of Cleveland, Ohio, 44121 USA. Other appropriate materials may, of course, be used without departing from the concept of the present invention. 
     The left half  18  includes a left base  26 , a left leg  30 , and a left tab  34 . The left base  26  and left leg  30  are generally planar members that are oriented substantially perpendicular to one another and are connected with one another along an arcuate left transition  36 . The left tab  34  protrudes outwardly from the end of the left base  26  opposite the left transition  36 . 
     The left base  26 , the left leg  30 , and the concave surface of the left transition  36  together define a left inner surface  38 . A left outer surface  42  is defined on the left half  18  opposite the left inner surface  38 . The left inner surface  38  also extends along the left tab  34 , with the left tab  34  including a substantially planar left joining surface  44  that is aligned parallel with and disposed approximately midway between the left inner and outer surfaces  38  and  42  as defined along the left base  26 . 
     The right half  22  includes a right base  46 , a right leg  50 , and a right tab  54 . The right base  46  and right leg  50  are generally planar members that are oriented substantially perpendicular to one another and are attached to one another along an arcuate right transition  56 . A right inner surface  58  extends along the right base  46  and right leg  50  and includes the concave surface of the right transition  56 . A right outer surface  62  is defined on the right half  22  opposite the right inner surface  58 . 
     The right tab  54  extends outwardly from the end of the right base  46  opposite the right transition  56 . The right outer surface  62  extends along the right tab  54 , with the right tab  54  including a right joining surface  66 , which is a substantially planar surface that is oriented substantially parallel with and disposed approximately midway between the right inner and outer surfaces  58  and  62  as defined along the right base  46 . 
     As can be seen in FIG. 2, a plurality of left grooves  70  are formed in the left half  18 . Specifically, the left grooves  70  extend into the left leg  30  from the left inner surface  38 . The left grooves  70  are sized to accommodate and at least partially receive the arc plates  10  therein with minimal clearance. The left grooves  70  each extend along the left leg  30  and terminate at a left retention ledge  72  that is formed in the left leg  30  and is spaced from the outermost end of the left leg  30 . The left grooves  70  also terminate at or prior to the left transition  36  and thus do not extend along the left base  26 . It is understood, however, that in alternative embodiments the left grooves  70  may be formed along the left transition  36  or additionally along the left base  26  without departing from the spirit of the present invention. 
     Similarly, and as is depicted generally in FIG. 3, a plurality of right grooves  74  are formed in the right half  22 . The right grooves  74  extend into the right leg  50  from the right inner surface  58 . The right grooves  74  each extend along the right leg  50  and terminate at a right retention ledge  76  that is formed in the right leg  50  and is spaced from the outermost end of the right leg  50 . While the right grooves  74  extend along the right leg  50  and terminate at or prior to the right transition  56 , it is understood that in alternative embodiments the right grooves  74  may extend along the right transition  56 , and may additionally extend along the right base  46  depending upon the specific needs of the particular application. 
     The inclusion of the left and right retention ledges  72  and  76  makes the left and right grooves  70  and  74  blind grooves, meaning that the left and right grooves  70  and  74  do not terminate at the edges of the left and right legs  30  and  50 , but rather terminate prior thereto at the left and right retention ledges  72  and  76 . The left and right retention ledges  72  and  76  are retention structures that help to retain the arc plates  10  captured within the left and right grooves  70  and  74  when the left and right halves  18  and  22  are brought together. By providing blind grooves with the left and right retention ledges  72  and  76 , the arc plates  10  can be captured between the left and right halves  18  and  22  when brought together without the need for additional retention structures, adhesives, compressive forces on the arc plates  10 , and the like, although the use of such would not depart from the spirit of the present invention. 
     The left and right retention ledges  72  and  76  are preferably integrally formed with and are unitary with the left and right halves  18  and  22 . The left and right retention ledges  72  and  76  advantageously retain the arc plates  10  within the left and right grooves  70  and  74  without the need to attach or mount additional structures to the left and right halves  18  and  22  to retain the arc plates  10  thereon, which advantageously reduces expense and the cost of assembly. 
     The arc plate  10  depicted generally in FIG. 4 includes a pair of parallel and spaced apart sides  78  that are connected by a head  80  disposed therebetween. The arc plates  10  are generally planar pieces of sheet steel that are, by way of example, 0.062 inches in thickness, although other thicknesses for the arc plates  10  are appropriate depending upon the specific needs of the particular application. The arc plates  10  are preferably plated with chromium to resist corrosion, although other corrosion-resistance methodologies may be employed without departing from the spirit of the present invention. 
     In assembling the arc chute  6 , the arc plates  10  are positioned with respect to one another in a fashion that will enable the ends of the arc plates  10  to be received in the left and right grooves  70  and  74 . The left and right halves  18  and  22  are then brought together to capture the arc plates  10  between the left and right halves  18  and  22  and within the left and right grooves  70  and  74 . The caption of the arc plates  10  between the left and right halves  18  and within the left and right grooves  70  and  74  secures the arc plates in fixed relation with respect to one another and with respect to the wrapper  2 , and additionally obviates any need for additional structures to extend from the arc plates  10  to the left and/or right outer surfaces  42  and  62 . 
     The assembled arc chute  6  is indicated generally in FIG.  5 . The left half  18  is attachable to the right half  22  by adhering the left tab  34  to the right tab  54 . In such position, the left and right tabs  34  and  54  at least partially overlie one another to form a lap joint therebetween. The left and right tabs  34  and  54  are adhered to one another with the left joining surface  44  and the right joining surface  66  in a face-to-face opposed relationship. The left and right tabs  34  and  54  are adhered with an appropriate adhesive of sufficient strength and resilience appropriate to the lo application such as Super Bonder 496 manufactured by Loctite Corporation, North American Group, located at Rocky Hill, Conn. 06067, USA. It is understood, however, that alternate appropriate adhesives may be used without departing from the spirit of the present invention. 
     When the left and right halves  18  and  22  are conjoined in the aforementioned fashion, the left and right grooves  70  and  74  are in confronting relation with one another such that each left groove  70  has a corresponding right groove  74  aligned therewith. The left and right grooves  70  and  74  are sized to accommodate the sides  78  of the arc plates  20  therein with minimal clearance therebetween. The arc chute  6  is thus assembled by positioning arc plates  10  with the sides  78  thereof disposed in confronting pairs of left and right grooves  70  and  74  such that arc plates  10  occupy all of the left and right grooves  70  and  74 . In such position, the heads  80  of the arc plates  10  are disposed against the left and right inner surfaces  38  and  58  of the left and right bases  26  and  46 , respectively. In such a configuration, the depths of the left and right grooves  70  and  74  preferably smoothly change from their nominal depths along the left and right legs  30  and  50  to a point of zero depth located generally at the junctures between the left leg and base  30  and  26  and the right leg and base  50  and  46 . The depths of the left and right grooves  70  and  74  alternatively may remain constant without the aforementioned change in depth without departing from the spirit of the present invention. The left and right grooves  70  and  74  are blind also in that they terminate at the left and right bases  26  and  46 . 
     In this regard, it is understood that if the left and right grooves  70  and  74  are configured to extend along the left and right transitions  36  and  56 , or still additionally along the left and right bases  26  and  46 , the arc plates  10  are appropriately disposed therein. Still alternatively, it may be preferable depending upon the specific needs of the particular application to provide a small space between the heads  80  of the arc plates  10  and the left and right inner surfaces  38  and  58  of the left and right bases  26  and  46 . 
     The uppermost arc plate  10  preferably additionally includes an arc horn  82  extending upwardly therefrom for purposes that are understood in the relevant art. The presence or absence of the arc horn  82  does not affect the functionality of the present invention. As is understood in the relevant art, the arc horn  82  is typically attached to the uppermost arc plate  10  by known methods such as spot welding, with the arc plate  10  and arc horn  82  then together being chrome plated and installed into the arc chute  6  along with the other arc plates  10 . 
     When the left and right halves  18  and  22  are conjoined, the wrapper  2  is thus a generally U-shaped member or body that captures the arc plates  10  within the left and right grooves  70  and  74  formed thereon. The wrapper  2  is sufficiently rigid and strong to resist the magnetic forces experienced by the arc plates  10  during propagation, disruption, and dispersion of the arc formed between the movable and stationary contacts of the circuit breaker  14 . 
     In this regard, the left and right halves  18  and  22  are preferably formed by molding such that the glass contents of the wrapper  2  are molded around the left and right grooves  70  and  74 . As is understood in the relevant art, formation of the left and right halves  18  and  22  by a molding process facilitates molding of the glass contents of the wrapper  2  along and around the left and right grooves  70  and  74  for the greatest strength. It is understood, however, that the left and right grooves  70  and  74  can be formed in the left and right halves  18  and  22  by other methodologies, such as by cutting, grinding, milling, and the like, depending upon the specific needs of the particular application, and without departing from the spirit of the present invention. 
     It is also understood that the configuration of the wrapper  2  with the left and right halves  18  and  22  may be varied as needed, depending upon the specific needs of the particular application. For instance, the wrapper  2  may be configured as a single unit that is molded around the arc plates  10  that are held in a given position by a fixture. It is additionally understood that the joining of the left and right halves  18  and  22  by lapping and adhering the left and right tabs  34  and  54  can be accomplished in other fashions, such as by heat welding and other appropriate attachment methodologies. 
     With the arc chute  6  assembled as such, the arc plates  10  are electrically insulated from one another and additionally are insulated from the left and right outer surfaces  42  and  62 . Such electrical insulation and isolation results from spacing the arc plates  10  away from one another and by configuring the left and right grooves  70  and  74  to extend at most only partially into the left and right halves  18  and  22 , respectively. In this regard, it can be seen that the left and right halves  18  and  22  are free of holes extending therethrough between the inner and outer surfaces thereof. More specifically, the left and right halves  18  and  22  are free of holes extending between the left inner and outer surfaces  38  and  42  and between the right inner and outer surfaces  58  and  62  in the vicinity of the arc plates  10 . The absence of any such holes facilitates and enhances the electrical insulation and isolation of the arc plates  10  from one another. 
     In this regard, the arc chute  6  need not be painted with ceramic paint after assembly of the arc plates  10  in the wrapper  2 . The arc chute wrapper  2  being free of ceramic paint thus advantageously simplifies assembly of the arc chute  6  and reduces the cost thereof. 
     The configuration of the wrapper  2  without holes extending therethrough for receiving spinning tabs simplifies the configuration of the wrapper  2  and increases the strength thereof. Additionally, the configuration of the arc plates  10  without spinning tabs extending outwardly therefrom simplifies the tooling used to stamp the arc plates  10  out of stock material and increases the life of such tooling inasmuch as failures of such tooling most often occur at the spinning tab portions. The configuration of the wrapper  2  with the left and right grooves  70  and  74  thus reduces tooling costs by reducing tooling complexity and by increasing tool life. 
     The arc chute wrapper  2  of the present invention thus increases the simplicity of the arc chute  6 , reduces the cost thereof, and increases the overall strength and reliability thereof. The enchanced reliability of the arc chute  6  increases the overall reliability of the circuit breaker  14 , which is highly beneficial in applications requiring the circuit breaker  14  to operate reliably under overload and other conditions. 
     While particular embodiments of the present invention have been described herein, it is understood that various changes, additions, modifications, and adaptations may be made without departing from the scope of the present invention, as set forth in the following claims.