Patent Publication Number: US-7217895-B1

Title: Electrical switching apparatus contact assembly and movable contact arm therefor

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates generally to electrical switching apparatus and, more particularly, to contact assemblies for electrical switching apparatus, such as circuit breakers. The invention also relates to movable contact arms for circuit breaker contact assemblies. 
   2. Background Information 
   Electrical switching apparatus, such as circuit breakers, are employed in diverse capacities in power distribution systems such as, for example, to provide protection for electrical equipment from electrical fault conditions (e.g., without limitation, current overloads; short circuits; abnormal level voltage conditions). 
   As shown in  FIGS. 1 and 2 , a circuit breaker  2  ( FIG. 1 ) generally includes a housing  4  which encloses a line conductor  6 , a load conductor  8  ( FIG. 1 ), a fixed contact  10  and a movable contact  12 , with the movable contact  12  being movable into and out of electrical contact with the fixed contact  10 . This switches the contacts  10 ,  12  of the circuit breaker  2  between the OFF or open position shown in  FIG. 1 , and the ON or closed position (as best shown in  FIG. 3 ), or between the ON or closed position and a tripped or tripped off position (not shown). In the example shown, the fixed contact  10  is electrically connected to the line conductor  6  and the movable contact  12  is electrically connected to the load conductor  8  through a movable contact arm  16  by a suitable conductor, such as a flexible conductor (not shown). The circuit breaker  2  further includes an operating mechanism  14  ( FIG. 1 ) having the movable contact arm  16  upon which the movable contact  12  is disposed. The movable contact arm  16  and movable contact  12  disposed thereon move past and/or through an arc chute  18  which includes a plurality of arc plates  20  structured to attract and dissipate the resultant arc which is formed when the movable contact  12  initially separates from the fixed contact  10  in response to the trip condition. 
   The movable contact arms of many known circuit breakers, such as movable contact arm  16  of circuit breaker  2  ( FIG. 1 ) are made of solid copper or alloys of copper (e.g., silver bearing copper; a copper alloy with a relatively small percentage of silver), which are relatively good conductors of both electricity and heat, but which are not as strong as other materials. Hence, it is believed that relatively more copper than is necessary to handle the current (e.g., for thermal conductivity considerations) is typically employed in conventional movable contact arms  16  to handle the current and to provide the needed strength (e.g., rigidity). This undesirably adds weight, thus increasing the moment-of-inertia of the movable contact arm  16  and decreasing the performance of the circuit breaker  2 . More specifically, the movement-of-inertia of the movable contact arm  16  significantly affects the angular opening velocity of the movable contact arm  16 . It is known that the faster the movable contact arm  16  opening velocity is, the better the current-limiting capability of the circuit breaker  2 . Therefore, it is desirable to maximize the opening velocity of the movable contact arm  16  in order to improve the short-circuit interruption performance of the circuit breaker  2 . Previously, this has not been possible because material strength and thermal requirements have dictated the size and geometry of the movable contact arm  16 . 
   For example, the movable contact arm  16  shown in  FIGS. 1 ,  2 , and  3  is a single-piece arm  16  made from copper, as previously noted. In order to achieve the desired strength, the length  22  (i.e., the distance between the pivot point of the arm  16  and the end carrying the movable contact  12 ) ( FIGS. 1 and 2 ) of the movable contact arm  16  is required to be relatively short, and the width  24  ( FIGS. 2 and 3 ) of the movable contact arm  16  must be relatively wide. Specifically, it is believed that the ratio of the width  24  to length  22  is about 1:7.3, or more. The width  24  ( FIGS. 2 and 3 ) is also greater than desired with respect to the height  26  ( FIG. 3 ) of the movable contact arm  16 . Specifically, it is believed that the ratio of the width  24  to the height  26  is about 1:2, or more. The foregoing results in the weight and the movement-of-inertia of the movable contact arm  16  being greater than desired, and the aerodynamic efficiency of the movable contact arm  16  being less than desired, thus adversely affecting the angular opening velocity of the movable contact arm  16  and inhibiting the circuit interruption performance of the circuit breaker  2 . 
   There is a need, therefore, to provide a movable contact arm  16  sized and shaped to optimize the angular opening velocity of the arm  16 , while exhibiting sufficiently high strength and thermal conductivity, and low electrical resistivity. 
   It is also desirable to maximize the space or gap  28  ( FIG. 1 ) between the movable and fixed contacts  10 , 12  in order to minimize the undesired continued flow of electrical current following the trip condition. Such current, commonly referred to as let-through current, must be minimized in order to protect electrical components from the harmful effects of over-current resulting from the trip condition. 
   There is, therefore, room for improvement in contact assemblies for electrical switching apparatus and in movable contact arms therefor. 
   SUMMARY OF THE INVENTION 
   These needs and others are met by embodiments of the invention which are directed to a movable contact arm for the contact assembly of an electrical switching apparatus, such as a circuit breaker. For example, through the use of lightweight, high-strength material(s), and by optimizing the size and shape of the movable contact arm to minimize the moment-of-inertia of the arm, the angular opening velocity of the arm is increased, thus improving the performance of the circuit breaker. The length of the arm may also be increased to increase the space or gap between the movable and fixed contacts of the contact assembly to further improve the circuit interruption performance of the electrical switching apparatus. 
   As one aspect of the invention, a movable contact arm is provided for a contact assembly of an electrical switching apparatus. The electrical switching apparatus includes a housing which encloses the contact assembly. The contact assembly includes a fixed contact and a movable contact separable from the fixed contact in response to a trip condition. The movable contact arm comprises: a first end structured to carry the movable contact of the contact assembly; a second end disposed distal from the first end; a pivot portion proximate the second end, the pivot portion having a first width; and a moving arm portion generally extending from the first end toward the pivot portion, the moving arm portion having a second width, wherein the movable contact arm has a moment-of-inertia and an angular opening velocity, and wherein the second width of the moving arm portion of the movable contact arm is less than the first width of the pivot portion of the movable contact arm, in order to minimize the moment-of-inertia of the movable contact arm, thereby increasing the angular opening velocity. 
   The moving arm portion may further comprise an upper edge, a lower edge, and a height defined by the distance between the upper edge and the lower edge, wherein the height of the moving arm portion is at least four times the second width of the moving arm portion. At least one of the upper edge of the moving arm portion and the lower edge of the moving arm portion may include at least one of a taper, a stepped portion, and a bevel in order to reduce the second width of the moving arm portion at the upper edge of the moving arm portion and/or the lower edge of the moving arm portion. The moving arm portion may also have a length, wherein the ratio of the second width of the moving arm portion to the length of the moving arm portion is about 1:9 to about 1:19. The pivot portion may comprise a number of spacers wherein each of the spacers has a width, and wherein the first width of the pivot portion of the movable contact arm includes the width of all of the spacers. 
   At least the moving arm portion of the movable contact arm may comprise a composite structure including at least two elongated members coupled together, side-by-side. Each of the elongated members may have a width wherein the width of a first one of the elongated members is different than the width of at least a second one of the elongated members, and wherein the second width of the moving arm portion of the movable contact arm comprises the combined width of all of the elongated members of the composite structure. A first one of the elongated members of the composite structure may be made from a different material than at least a second one of the elongated members of the composite structure. The elongated members of the composite structure may be coupled together without the use of separate mechanical fasteners. 
   The movable contact of the contact assembly may have a width which is greater than the second width of the moving arm portion of the movable contact arm. The movable contact arm may have a longitudinal axis, wherein the movable contact of the contact assembly is structured to be coupled to the movable contact arm at an angle with respect to the longitudinal axis of the movable contact arm in order that, when the movable contact arm is moved toward the closed position, the first end of the movable contact of the contact assembly engages the fixed contact of the contact assembly before the second end of the movable contact. 
   As another aspect of the invention, a contact assembly is provided for an electrical switching apparatus including a housing, a line conductor and a load conductor both structured to be housed by the housing, and an operating mechanism. The contact assembly comprises: a fixed contact structured to be electrically connected to one of the line conductor and the load conductor; a movable contact structured to be electrically connected to the other of the line conductor and the load conductor; and a movable contact arm comprising: a first end, the movable contact of the contact assembly being mounted at or about the first end of the movable contact arm, a second end disposed distal from the first end of the movable contact arm, a pivot portion proximate the second end of the movable contact arm, the pivot portion of the movable contact arm having a first width, and a moving arm portion generally extending from the first end of the movable contact arm toward the pivot portion of the movable contact arm, the moving arm portion of the movable contact arm having a second width, an upper edge, a lower edge, and a height, the height being defined by the distance between the upper edge of the moving arm portion of the movable contact arm and the lower edge of the moving arm portion, wherein the movable contact arm is operable between a closed position in which the movable contact of the contact assembly is in electrical contact with the fixed contact of the contact assembly, and an open position in which the movable contact arm and the movable contact disposed thereon are spaced from the fixed contact of the contact assembly, wherein in response to a trip condition, the operating mechanism of the electrical switching apparatus separates the movable contact from the fixed contact and pivots the movable contact arm from the closed position toward the open position at an angular opening velocity, wherein the movable contact arm has a moment-of-inertia, and wherein the height of the moving arm portion of the movable contact arm is at least about four times the second width of the moving arm portion, in order to minimize the moment-of-inertia of the movable contact arm, thereby increasing the angular opening velocity. 
   The electrical switching apparatus may comprise a circuit breaker including an operating mechanism having a crossbar with an aperture, and the pivot portion of the movable contact arm may further comprise a number of spacers, wherein the pivot portion of the movable contact arm is structured to pivotably engage the aperture of the crossbar with the spacers being disposed within the aperture of the crossbar. Each of the spacers may have a width, wherein the first width of the pivot portion of the movable contact arm, including the width of all of the spacers, is greater than the second width of the moving arm portion of the movable contact arm. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
       FIG. 1  is a cross-sectional view of a molded case circuit breaker, and contact assembly and movable contact arm therefor; 
       FIG. 2  is a top plan view of the contact assembly and movable contact arm therefor of  FIG. 1 , modified to show the movable contact arm in the closed position; 
       FIG. 3  is a cross-sectional view taken along line  3 — 3  of  FIG. 2 , with the arc chute not being shown for simplicity of illustration; 
       FIG. 4  is a vertical elevational view of a contact assembly for a circuit breaker in accordance with an embodiment of the invention, with the movable contact arm shown in the closed position in solid line drawing and in the open position in phantom line drawing; 
       FIG. 5  is a top plan view of the contact assembly and movable contact therefor of  FIG. 4 , also showing an arc chute in simplified form; 
       FIG. 6  is a cross-sectional view taken along line  6 — 6  of  FIG. 5 , with the arc chute not being shown for simplicity of illustration; 
       FIG. 7A  is a cross-sectional view of a contact assembly and movable contact arm therefor, in accordance with another embodiment of the invention; 
       FIG. 7B  is a top plan view of the movable contact arm of  FIG. 7A , also showing the circuit breaker crossbar in simplified form; 
       FIG. 8A  is a cross-sectional view of a contact assembly and movable contact arm therefor, in accordance with another embodiment of the invention; 
       FIG. 8B  is a top plan view of the movable contact arm of  FIG. 7A , also showing the circuit breaker crossbar in simplified form; 
       FIGS. 9–11  are top plan views of laminate movable contact arms in accordance with embodiments of the invention; 
       FIG. 12A  is a top plan view of a movable contact arm having a coined portion in accordance with another embodiment of the invention; and 
       FIG. 12B  is an end elevational view of the movable contact arm of  FIG. 12A . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   For purposes of illustration, embodiments of the invention will be described as applied to the contact assemblies of molded case circuit breakers (MCCBs), although it will become apparent that they could be applied to the contact assembly or assemblies of a wide variety of other types of electrical switching apparatus (e.g., without limitation, circuit switching devices and other interrupters, such as contactors, motor starters, motor controllers and other load controllers). 
   Directional phrases used herein, such as, for example, upper, lower and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein. 
   As employed herein, the statement that two or more parts are “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. Further, as employed herein, the statement that two or more parts are “attached”′ shall mean that the parts are joined together directly. 
   As employed herein, the term “let-through current” refers to the peak electrical current (measured in amperes) which passes through an overcurrent protective device, such as, for example and without limitation, a circuit breaker, during an interruption. In circuit breaker design, it is desirable to minimize the amount of let-through current and resulting let-through energy. Such current, commonly referred to as let-through current, must be minimized in order to protect electrical components from the harmful effects of over-current resulting from the fault condition. 
   As employed herein, the term “short circuit interruption rating” is the maximum available fault current which a circuit breaker is designed to interrupt. By way of example, and without limitation, an industrial circuit breaker typically has a circuit interruption rating of up to about 100,000 A, wherein the available fault current in a single-family home is rarely above about 10,000 A. 
   As employed herein, the term “threshold current” refers to the minimum current that causes the separable contacts to begin parting. 
   As employed herein, the term “contact gap” refers to the distance or measurement of the space between the separable contacts (i.e., the fixed contact and the movable contact) of the circuit breaker or other known or suitable electrical switching apparatus when the circuit breaker is open. 
   As employed herein, the term “number” means one or an integer greater than one (i.e., a plurality). 
   Among other improvements, the movable contact arms disclosed herein have been designed to reduce the moment-of-inertia of the arm as compared to known movable contact arm designs (e.g., without limitation, movable contact arm  16  of  FIGS. 1–3 ). As a result, a number of important parameters of circuit breaker performance have been improved, expressly including, without limitation, the angular opening velocity of the movable contact arm, the let-through current, the short circuit interruption rating, the threshold, and the contact gap. The following Examples disclose several ways of accomplishing these results. 
   In each example shown and described herein, like components are numbered similarly. For example, the various components of the contact assembly embodiment shown and described with respect to  FIGS. 4–6  below are numbered with 100 series reference numbers, whereas the embodiment of  FIGS. 7A and 7B  is numbered similarly but with 200 series reference numbers, the embodiment of  FIGS. 8A and 8B  is numbered similarly but with 300 series reference numbers, and so on. For simplicity of disclosure, similar features present in more than one embodiment of the invention are shown, but may not be repetitively discussed. 
   EXAMPLE 1 
     FIGS. 4 ,  5 , and  6  show a contact assembly  100  including a movable contact arm  116  as employed in a molded case circuit breaker (MCCB)  2 , partially shown in  FIG. 4 . It will be appreciated that, except for the contact assembly  100 , which will now be discussed, the MCCB  2 ′, ( FIG. 4 ) is, otherwise, substantially identical to the MCCB  2  shown and previously described with respect to  FIG. 1 . 
   The contact assembly  100  includes a fixed contact  110  which is coupled to the folded back line conductor  6  housed within the housing  4  ( FIG. 4 ) of the MCCB  2 ′ ( FIG. 4 ), and a movable contact  112  which is mounted on the movable contact arm  116 . Electrical connection of the movable contact arm  116  to the load conductor  8  (not shown) (see, for example,  FIG. 1 ) of the MCCB  2 ′ is provided in the same manner as movable contact arm  16  of  FIG. 1 . The movable contact arm  116  has a first end structured to carry the movable contact  112 , a second end  119  disposed distal from the first end  117 , a pivot portion  121  proximate the second end  119 , and a moving arm portion  123  which generally extends from the first end  117  toward the pivot portion  121 . 
   The pivot portion  121  has a first width  124 , and the moving arm portion  123  has a second width  125 , wherein the second width  125  of the moving arm portion  123  is less than the first width  124  of the pivot portion  121 . This reduces the amount of material required for the movable contact arm  16 , thus reducing the mass of the movable contact arm  16  and accomplishing the objective of minimizing the moment-of-inertia of the movable contact arm  116 . This, in turn, increases the angular opening velocity of the movable contact arm  116 . 
   As best shown in  FIG. 6 , the moving arm portion  123  of the movable contact arm  16  has an upper edge  128 , a lower edge  130 , and a height  126  defined by the distance between the upper edge  128  and the lower edge  130 . The height  126  of the moving arm portion  123  of the example movable contact arm  116  is at least about four times the second width  125  of the moving arm portion  123 . Thus, the ratio of second width  125  to height  126  is about 1:4. which is substantially less than the width-to-height ratio of known movable contact arms, such as movable contact arm  16  of  FIGS. 1–3 , which has only one arm width  24  and a ratio of width  24  to height  26  of about 1:2 (best shown in  FIG. 3 ). It will be appreciated that the exact dimensions of the various portions of the movable contact arm (e.g., pivot portion  121 ; moving arm portion  123 ; upper edge  128 ; lower edge  130 ) are not meant to be limiting upon the scope of the invention. Specifically, the particular electrical application in which the movable contact arm  116  will be employed will dictate what arm dimensions are necessary to achieve the predetermined circuit breaker parameters (e.g., without limitation, let-through current; short circuit interruption rating; threshold; contact gap) of the application. Accordingly, it will be appreciated, for example, that in other embodiments of the invention the height  126  of the moving arm portion  123  may be slightly less than four times (e.g., without limitation, 3.7 times) the second width  125  of the moving arm portion  123 . 
   At least one of the upper edge  128  and the lower edge  130  of the moving arm portion  123  can include at least one taper  132  and/or a bevel  134 , in order to reduce the second width  125  of the moving arm portion  123  of at least one of the upper edge  128  and the lower edge  130  of the moving arm portion  123 . The example movable contact arm  116  of  FIGS. 4–6  has an upper edge  128  which includes two side tapers  132  comprising a bevel  134  (best shown in the cross-sectional view of  FIG. 6 ). It will, however, be appreciated that the movable contact arm  116  could have a taper  132  and/or bevel  134  and/or any other suitable geometry at on or both of upper edge  128  and the lower edge  130  of the moving arm portion  123 . For example and without limitation, as will be discussed in connection with  FIGS. 12A and 12B  hereinbelow, the moving arm portion  723  could include a stepped portion (see, for example, stepped portion  732  of moving arm portion  723  of movable contact arm  716  of  FIG. 12B ). 
   Reducing the second width  125  at the upper edge  128  further improves the angular opening velocity of the movable contact arm  16 , not only by further weight reduction of the arm  116 , but also by providing relatively less material at the upper edge  128  for current to flow through, thereby forcing current down toward the lower edge  130 . This results in the electric current which is flowing in opposite directions in the folded back line conductor  6  and the movable contact arm  16 , being closer to each other, thereby advantageously creating an increased repulsion force on the movable contact arm  116  to propel it open. 
   Another significant aspect of embodiments of the invention relates to the length  122  ( FIGS. 4 and 5 ) of the movable contact arm  116 . Specifically, in the example of  FIGS. 4–6 , the ratio of the second width  125  of the moving arm portion  123  of the movable contact arm  116  to the length  122  of the moving arm portion  123  is preferably about 1:9 to about 1:19. It was previously believed that such a width-to-length ratio was not possible, for example, in view of limitations of the strength and conductive properties of known materials commonly used for movable contact arms. Accordingly, this is a significant increase over known movable contact arm designs. For example, as previously discussed, movable contact arm  16  of  FIGS. 1–3  has a width  24  to length  22  ratio of about 1:7.3. One advantageous result of this ratio difference is an increase in the contact gap  127  ( FIG. 4 ). In other words, the separation distance between the movable contact  112  and the fixed contact  110  when the movable contact arm  116  is in the open position, shown in phantom line drawing in  FIG. 4 , is increased with respect to known movable contact arms (see, for example, contact gap  28  of movable contact arm  16  of  FIG. 1 ). Among other advantages, this reduces the amount of let-through current of the circuit breaker. 
   Another unique aspect of embodiments of the invention is best shown in  FIG. 4 . Specifically, the movable contact  112  has a first end  114  and a second end  115 , and the movable contact arm  116  has a longitudinal axis  139 . The movable contact  112  is coupled to the movable contact arm  116  such that it forms an angle  141  with respect to the longitudinal axis  139 , as shown. This results in the first end  114  of the movable contact  112  engaging the fixed contact  110  of the contact assembly  100  before the second end  115  of the movable contact, when the movable contact arm  116  is pivoted to the closed position, shown in solid line drawing in  FIG. 4 . The exact dimension of the angle  141  is not meant to limit the scope of the invention. 
   As shown in  FIG. 5 , the movable contact arm  116  of the example contact assembly  100  pivots through an arc chute  118  having suitable narrow-channel arc plates  120 . In other words, the arc plates  120  are shaped and configured to provide a relatively narrow channel through which the movable contact  112  and the first end  114  of the movable contact arm  116  travel in response to a trip condition. This shape (e.g., without limitation, generally U-shape) and configuration (e.g., without limitation, narrow channel for receiving the contact arm  116 ) function to attract the arc (not shown) which is formed in response to the trip condition, in order that it is retained in the arc chute  118  and is extinguished. 
   EXAMPLE 2 
   As a non-limiting example, the moving arm portion  123  of the movable contact arm  116  of  FIGS. 4–6  has a length  122  of about 1.168 inches, a second width  125  of about 0.062 inches, and a height  126  of about 0.250 inches. 
   EXAMPLE 3 
     FIGS. 7A and 7B  show cross-sectional and top plan views, respectively, of a contact assembly  200  having a movable contact arm  216  substantially similar to movable contact arm  116  previously discussed in connection with  FIGS. 4–6 , but having a pivot portion  221  which comprises a number of spacers  236 , 238 . Specifically, the example pivot portion  221  includes a pair of spacers  236 , 238  disposed on opposite sides of the moving arm portion  223  of the movable contact arm  216  proximate the second end  219  of the movable contact arm. Each of the spacers  236 , 238  has a width  240 , wherein the first width  224  of the pivot portion  221  of the movable contact arm  216  includes the combined width  240  of all of the spacers (e.g., spacers  236 , 238 ), along with the second width  225  of the moving arm portion  223 . 
   The pivot portion  221  pivotably couples the movable contact arm  216  to the crossbar  203  (shown in simplified form in  FIG. 7B ) of the circuit breaker operating mechanism  14  ( FIG. 1 ). As shown in simplified form in  FIG. 7B , the crossbar  203  includes an aperture  205 . The spacers  236 , 238  are disposed within the aperture  205  of the crossbar  203  in order to account for the reduced width of the movable contact arm  216  while permitting the arm  216  to be used without requiring modification to the crossbar  203 . In other words, the spacers  236 , 238  occupy any excess space within the aperture  205  of the crossbar  203  and provide for proper alignment of the movable contact arm  216  pivotably coupled thereto. 
   EXAMPLE 4 
   It will be appreciated that the spacers  236 , 238  could be made from any known or suitable material. For example and without limitation, the spacers  236 . 238  could comprise Belleville washers (not shown). It will also be appreciated that any suitable number and configuration of spacers (e.g.,  236 , 238 ) could be employed within the aperture  205  of the crossbar  203 , without departing from the scope of the invention. 
   EXAMPLE 5 
   For example, as shown in  FIGS. 8A and 8B , the pivot portion  321  of the movable contact arm  316  could alternatively comprise a single spacer  336  having a width  340  which is greater than the widths  240  of the individual spacers  236 , 238  of  FIGS. 7A and 7B , previously discussed. The first width  324  of the pivot portion  321  of the movable contact arm  316  includes, in part, width  340  of the spacer  336  such that the pivot portion  321  fits securely within the aperture  305  of the circuit breaker crossbar  303 , and is properly aligned, as shown in  FIG. 8B . 
   EXAMPLE 6 
   As shown in  FIGS. 5–6 ,  7 B,  8 B,  9 ,  10 ,  11 , and  12 A– 12 B, respectively, the movable contact  112 , 212 , 312 , 412 , 512 , 612 , 712  has a width  113 , 213 , 313 , 413 , 513 , 613 , 713  which can be greater than the second width  125 , 225 , 325 , 425 , 525 , 625 , 725  of the moving arm portion  123 , 223 , 323 , 423 , 523 , 623 , 723  of the movable contact arm  116 , 216 , 316 , 416 , 516 , 616 , 716 . 
   EXAMPLE 7 
   At least the moving arm portion  423 , 523 , 623 , 723  of the movable contact arm  416 , 516 , 616 , 716  may comprise a composite structure  450 , 550 , 650 , 750  including at least two elongated members  452 , 545 , 552 , 554 , 652 , 654 , 752 , 754  coupled together side-by-side. It will be appreciated that each of the elongated members  452 , 545 , 552 , 554 , 652 , 654 , 752 , 754  of the composite structure  450 , 550 , 650 , 750  may be made from the same or different materials. 
   EXAMPLE 8 
   The elongated members  452 , 545 , 552 , 554 , 652 , 654 , 752 , 754  of the composite structure  450 , 550 , 650 , 750  are preferably coupled together without the use of mechanical fasteners. It will be appreciated that this may be accomplished using any known or suitable fastening process or mechanism, such as, for example and without limitation, soldering, brazing or welding, such as cold welding, ultrasonic welding, or resistance welding. 
   EXAMPLE 9 
     FIG. 9  shows a movable contact arm  416  wherein the composite structure  450  includes two elongated members  452 , 454  suitably coupled side-by-side, and wherein the first elongated member  452  has a first width  458  and the second elongated member  454  has a second width  460 . The second width  460  of second elongated member  454  is different (e.g., greater) than the first width  458  of the first elongated member  452 . In this manner, two different materials could be employed to form the composite structure  450  having the desired strength and conductive properties, while maintaining the desired second width  425  of the moving arm portion  423  and length  422 , for example, of the movable contact arm  416 . 
   The pivot portion  421  of the example movable contact arm  416  includes two spacers  436 , 438  adjacent the first and second elongated members  452 , 454  of the composite structure  450 , respectively. The spacers  436 , 438  have the same width  440 , and function to properly align the movable contact arm  416  within the aperture  405  of the circuit breaker crossbar  403  (shown in simplified form). 
   EXAMPLE 10 
     FIG. 10  shows a movable contact arm  516  wherein the composite structure  550  includes two elongated members  552 , 554  suitably coupled side-by-side, and having first and second widths  558 , 560 , which are the same. 
   Like pivot portion  421  of movable contact arm  416  of  FIG. 9 , the pivot portion  521  of movable contact arm  516  includes two spacers  536 , 538  disposed adjacent the first and second elongated members  552 , 554 , respectively, and having the same width  540  to properly align the movable contact arm  56  within the aperture  505  of the circuit breaker crossbar  503  (shown in simplified form). It will, however, be appreciated that in other embodiments of the invention the widths could be different. 
   EXAMPLE 11 
     FIG. 11  shows a movable contact arm  616  wherein the composite structure  650 , like composite structure  450  of  FIG. 9 , includes two elongated members  652 , 654  suitably coupled side-by-side, and having different first and second widths  658 , 660 . However, the pivot portion  621 , unlike pivot portion  421  of movable contact arm  416  of  FIG. 9 , includes only one spacer  636 , which is disposed adjacent the first elongated member  654 . The spacer has the appropriate width  640  to properly align the movable contact arm  616  within the aperture  605  of the circuit breaker crossbar  603  (shown in simplified form). 
   EXAMPLE 12 
     FIGS. 12A and 12B  show a movable contact arm  716  wherein the composite structure  750  comprises a first elongated member  752  having a first height  727  ( FIG. 12B ), a second elongated member  754  having a second height  726  ( FIG. 12B ), and a third elongated member  756  having a third height  731 . The composite structure  750  also includes a cross-section ( FIG. 12B ) having an upper edge  728 , a lower edge  730 , and an intermediate portion  729  ( FIG. 12B ). 
   The second elongated member  754  is disposed between, and suitably coupled to, the first and third elongated members  752 , 756 . The first height  727  of the first elongated member  752  and the third height  731  of the third elongated member  756  are substantially the same, and are less than the second height  726  of the second elongated member  754 , as best shown in  FIG. 12B . In this manner, the upper edge  728  of the composite structure  750  includes a stepped portion  732  so that the width  760  of the upper edge  728  of the cross-section is less than the combined widths  758 , 760 , 762  of the intermediate portion  729  of the cross-section. This stepped portion  732  affords the same advantages (e.g., magnetic propulsion) as those previously discussed with respect to tapers  132  and bevel  134  of movable contact arm  116  of  FIGS. 4–6 . 
   EXAMPLE 13 
   It will be appreciated that the stepped portion  732  of the composite structure  750  may alternatively be produced by, for example, coining the composite structure  750  at the moving arm portion  723  thereof, in order to reduce the respective heights  727 , 726  and/or widths  758 , 762  of at least the first and third elongated members  752 , 756  of the composite structure. In this manner, the pivot portion  721  of the movable contact arm  716  may have the effect of spacers, such as spacers  536 , 538  of movable contact arm  516  of  FIG. 10 , previously discussed, without requiring a separate spacer component. In other words, the portions of the first and third elongated members  752 , 756 , which have not been coined or otherwise suitably reduced in width and/or height, comprise the first width  724  of the pivot portion  721 , which is greater than the second width  725  of the moving arm portion  723  of the movable contact arm  716  that has been coined or otherwise suitably reduced in width and/or height. 
   EXAMPLE 14 
   A wide range of other suitable contact arm geometries, other than those shown and described herein, could be employed without departing from the scope of the invention. 
   EXAMPLE 15 
   A wide range of suitable movable contact arm materials may be employed. For example, a suitable relatively good conductive material (e.g., without limitation, copper) may be used side-by-side in combination with a suitably high-strength material with reasonably good thermal properties (e.g., without limitation, aluminum), in order to reinforce the relatively good conductive material. 
   EXAMPLE 16 
   Furthermore, there are a wide range of suitable alloys of these materials that work with various suitable tempers and hardnesses. For example, suitable example copper alloys include C11000, C17510, C15725, C17200, C17000, C17500, C17460, and C17410, although it will be appreciated that other suitable light-weight, high-strength alloys and other suitable metallic and/or non-metallic materials (e.g., without limitation, suitable aluminum alloys) could be employed in any known or suitable configuration. 
   EXAMPLE 17 
   An intermediate layer (e.g., brass) (not shown) may be advantageously employed to bridge the difference in the coefficient of thermal expansion (CTE) between the two different movable contact arm materials of the composite structure to prevent, for example, delamination or cracking of the interface therebetween, especially if welding or brazing is employed to join the different materials. Furthermore, one or more of the materials may also be plated (e.g., nickel plated), in order to improve bonding characteristics. 
   The disclosed contact assemblies  100 , 200 , 300 , 400 , 500 , 600 , 700  provide movable contact arms  116 , 216 , 316 , 416 , 516 , 616 , 716  which improve circuit breaker performance by, among other things, increasing the angular opening velocity of the movable contact arm. This is achieved through use of a suitable relatively lightweight, yet relatively strong, current-carrying material, in an optimized configuration (e.g., size; shape; orientation), in order to reduce the moment-of-inertia of the arm. The design may also focus the magnetic field with respect to the movable contact arm, in order to propel it open, and it may provide a relatively longer arm than is known, in order to increase the available gap (i.e., space) between the fixed and movable contacts, when they are separated. A composite structure employing two or more elongated members side-by-side may also be employed, and the disclosed movable contact arm designs may also be readily incorporated into existing circuit breakers without any changes to existing moldings or to the operating mechanisms. For example, one or more spacers may be employed at the pivot portion of the movable contact arm to provide proper alignment within the existing crossbar of the circuit breaker operating mechanism. Accordingly, the disclosed movable contact arm designs allow for low-cost, mass production quantities suitable for MCCBs while still maintaining desirable current carrying, thermal, and interruption properties. 
   While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.