Abstract:
A four-pole molded case circuit breaker is provided with connecting rods for simultaneously driving the contact arms in all four poles while at the same time allowing for a staggered contact depression in the fourth pole relative to the other three poles. A stabilizer clamp locks the connecting rods together to eliminate relative motion between the rods without interfering with the staggered contact depression. By staggering the contact depression in the fourth pole, a three-pole operating mechanism can effectively toggle a four-pole device since the load of the contact depression springs in all four poles is not seen by the operating mechanism at the same time.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to a clamping apparatus for locking together rods connecting rotary contact arms in a multi-pole molded case circuit breaker. More particularly, the present invention relates to a clamping apparatus for locking together rods connecting rotary contact arms in a multi-pole molded case circuit breaker while providing clearance between the connecting rods and the rotor in the outermost fourth pole of a four-pole molded case circuit breaker, thereby modifying the contact depression in the outermost pole for effective toggling on closure.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is generally well known in the art of multi-pole circuit breakers that rotary contact arms in each circuit breaker cassette are connected together with at least one rod (usually a drive rod and a support rod) to ensure their operation in unison. During quiescent operation, (i.e. when the circuit breaker contacts are closed to allow the flow of electrical current) the operating handle of an operating mechanism is in the “ON” position. To stop the current flow manually, the handle may be shifted to the “OFF” position thereby opening the electrical contacts. Upon attainment of a pre-determined condition (trip event), such as ground fault or overload, the operating mechanism of the circuit breaker will release the forces of the mechanism operating springs and release the operating handle to a tripped position between the “ON” position and the “OFF” position. Before the circuit breaker may be turned “ON”, the operating mechanism must be manually reset. This is accomplished by the operating handle placed beyond the “OFF” position against the bias of the operating mechanism springs, thereby locking the operating mechanism in position.  
           [0003]    The circuit breaker cassettes in a multi-pole molded case circuit breaker are preferably connected together with two rods interfacing a rotary contact arm in each circuit breaker cassette; a drive rod and a support rod. In a typical three-pole molded case circuit breaker, the operating mechanism is positioned upon a cassette located symmetrically between two of the circuit breaker cassettes. Stated alternatively, if the three cassettes of a three-cassette circuit breaker are counted from left to right the operating mechanism is located on the second cassette. It is known to be desirable for circuit breakers having multiple cassettes therein that all of the cassettes trip as closely in time to one another as possible. For this purpose it has been known to provide at least one and usually two rods that extend through all of the cassettes in a particular circuit breaker. The drive rod transmits the rotational movement within one of the cassettes, due to a trip, into an impetus for the other cassettes to also trip. Because of the mechanical nature of the connection through the rods, the first and third cassettes will change position almost immediately upon change of position of the second cassette. It is also the case that any two of the cassettes will react rapidly to any one of the cassettes experiencing a trip event. This is because the drive rod is actuated by the operating mechanism and since each cassette of the three-pole circuit breaker is immediately adjacent or in contact with the operating mechanism, no torque is lost. Since the first and third cassettes are immediately adjacent the second cassette, which is mechanically connected to the operating mechanism, there is little relative movement between the rods and they function well as intended.  
           [0004]    Four-pole circuit breakers present additional difficulties with respect to simultaneous operation of the four individual cassettes housed therein because conventionally the fourth circuit breaker cassette is added at one end of what would be the arrangement of a three-cassette circuit breaker. This is exclusive of any change in the operating mechanism. More particularly, the operating mechanism is still located on the second circuit breaker cassette. One of ordinary skill in the art thus appreciates that in a four-pole circuit breaker a single cassette is located on one side of the cassette to which the operating mechanism is attached, while two cassettes are located on the opposite side of the cassette to which the operating mechanism is attached. The rods that connect all of the cassettes in the breaker then extend further to reach the outer cassette on one side than they do on the other side. Because of relative movement between the rods and the length of the rods as it affects effective flexibility, the outer cassette may not react to movement of the operating mechanism as rapidly as would a cassette located closer to the operating mechanism. Since rapid movement of the rotor in the outer cassette is desirable, the art has sought means to speed the movement of the outer cassette.  
           [0005]    An additional consideration in a four-pole circuit breaker, relative to a three-pole circuit breaker, is the additional work that the operating mechanism must perform in order to toggle over the mechanism linkage to drive the contact arms of all four poles to full contact depression. One skilled in the art will recognize that a toggled over mechanism is one in which the linkage arrangement of the operating mechanism has reached its design detent position to establish full contact depression. Full contact depression is recognized by one skilled in the art to be that condition where the contact arms have been driven as far as the operating mechanism can drive them while compressing contact springs to establish the design contact force.  
           [0006]    Drive systems for four-pole devices are not limited to rotary circuit breakers, but can also be employed in such devices as conventional circuit breakers, current limiting circuit breakers, switches, and other multi-pole electrical disconnect devices. The applications that these devices are used in are vast, and include, but are not limited to, the utility, industrial, commercial, residential, and automotive industries, and may be employed in single device enclosures or multi-device electrical distribution panels.  
           [0007]    Four-pole circuit breaker solutions have been attempted, including the provision of additional assist mechanisms added to the outer cassette, or a wide operating mechanism which is symmetrically positioned about the rotary contact assemblies. While these alternatives do enhance movement of the rotor in the outer cassette, they also increase the manufacturing cost.  
           [0008]    Commonly assigned U.S. Pat. No. 5,287,077 (hereinafter the &#39;077 patent) entitled “Molded Case Circuit Breaker Multi-Pole Crossbar Assembly” describes a four-pole molded case circuit breaker arrangement wherein the separation distance between the movable and stationary contacts increases from the first pole to the fourth pole. Here, the elevation of each movable contact is controlled and incrementally increased across the four poles by specifically controlling the elevation of the stop surface on the unitary multi-pole crossbar. For unitary multi-pole crossbars, the teaching of the &#39;077 patent is applicable. However, for modular multi-cassette circuit breakers, it is desirable to have common parts with common dimensions.  
           [0009]    Commonly assigned U.S. patent application Ser. No. 09/517,934 entitled “Contact Depression Stabilizer For 4 Pole Molded Case Circuit Breaker” filed Mar. 3, 2000, describes a four-pole molded case rotary circuit breaker arrangement wherein a drive rod and a support rod are clamped together to ensure uniform operation across all four poles. Here, the clamping arrangement minimizes the lost motion present in an unclamped arrangement, thereby enhancing the uniformity of rotary action across all four poles. However, if the contact depression is not staggered across the four poles, the operating mechanism must be capable of driving all four poles to their full contact depression simultaneously. For modular multi-cassette circuit breaker arrangements encompassing both three-pole and four-pole configurations, it is desirable to have a common mechanism that is capable of driving a four-pole arrangement, while not exerting excessive load on the components of a three-pole arrangement.  
           [0010]    It would therefore be beneficial to provide a reliable and inexpensive clamping arrangement that eliminates the relative movement between the connecting rods and speeds the movement of the rotor in the outer cassette of an asymmetrically positioned four-pole molded case rotary circuit breaker, while at the same time providing a contact depression arrangement that is not uniform across all four poles for effective toggling of the operating mechanism on closure.  
         SUMMARY OF INVENTION  
         [0011]    In an exemplary embodiment of the invention, movement of contacts within individual cassettes of a multi-pole circuit breaker, occasioned by a trip event or operation of the operating mechanism thereof, is reliably and inexpensively effected by the addition of a clamp upon the connecting rods (drive rod and support rod) of the breaker, for example, between the third and fourth cassettes of the breaker. Clearance between the connecting rods and the rotor of the fourth cassette, and the absence of the same clearance in the first, second and third cassettes, produces reduced contact depression in the fourth pole, the neutral pole, and a staggered load on the operating mechanism during closure, thereby providing a three-pole operating mechanism with the ability to efficiently toggle a four-pole circuit breaker arrangement.  
           [0012]    The reduced contact depression in the fourth pole is chosen to be of sufficient value to meet the desired design performance for the device as a whole. A reduced electrical duty on the fourth pole, as compared to the other poles that carry primary current, provides the design option of reducing the contact depression in the fourth pole without a reduction in overall device performance. For example, in a theoretically balanced three-phase four-wire system, the first, second and third cassettes of a three-phase circuit breaker carry the primary current with a phase shift of 120-degrees between phases, and the fourth cassette for the neutral circuit carries no current in the neutral leg. However, in a typical application it is not uncommon for the neutral leg of the protected circuit to carry a fraction of the current present in one or more of the primary legs, resulting in the fourth pole cassette having a lesser electrical duty than the first, second or third cassettes. Since the electrical duty is of a lesser degree in the fourth pole as compared to the primary current poles, a lower contact depression may be employed in the fourth pole.  
           [0013]    The holding clamp for the connecting rods preferably includes surface features conducive to receiving and arresting the drive rod and the support rod relative to each other. By restricting relative movement between the drive rod and support rod, the outer cassette is provided with as much impetus to move due to actuation of the operating mechanism or a trip event as are the first or third cassettes, being immediately adjacent the second cassette upon which the operating mechanism is mounted. However, by allowing a degree of relative movement between the connecting rods and the rotor of the fourth cassette, the fourth cassette, now having a lower contact depression, will move with as much speed as the other cassettes, but with less toggling load on the operating mechanism.  
           [0014]    The clamp may be of a single piece of material such as metal or plastic with material removed therefrom to receive the rods, or may be of more than one piece wherein the separate pieces are attachable by various means with the desired result being that relative movement between the rods is minimized. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]    The present invention will now be described, by way of example, with reference to the accompanying drawings in which:  
         [0016]    [0016]FIG. 1 is a front perspective view of an electrical distribution panel;  
         [0017]    [0017]FIG. 2 is a front perspective view of a three-pole molded case circuit breaker;  
         [0018]    [0018]FIG. 3 is a front perspective view of the three-pole molded case circuit breaker of FIG. 2 with the cover removed;  
         [0019]    [0019]FIG. 4 is a side section view of a cassette of the molded case circuit breaker of FIG. 2 showing the internal components of the cassette;  
         [0020]    [0020]FIG. 5 is a perspective exploded view of a four-pole molded case circuit breaker similar to the three-pole circuit breaker of FIG. 2;  
         [0021]    [0021]FIG. 6 is a perspective exploded view of the stabilizer clamp and the drive rod and the support rod;  
         [0022]    [0022]FIG. 7 is a perspective view of stabilizer clamp assembled on the drive rod and the support rod;  
         [0023]    [0023]FIG. 8 is a perspective exploded view of an alternate embodiment of the clamp of FIG. 6; and  
         [0024]    [0024]FIG. 9 is a perspective view of the alternate clamp of FIG. 8 assembled on the drive rod and the support rod. 
     
    
     DETAILED DESCRIPTION  
       [0025]    Distribution Panel Generally  
         [0026]    A three phase electrical distribution panel is depicted generally in FIG. 1, is fully described in commonly assigned U.S. patent application Ser. No. 09/560,226 entitled “Electrical Distribution Panel With Split Neutral Bus” filed Apr. 28, 2000, functions generally to distribute protected power from a common main source to a plurality of branch circuits, and is described generally below.  
         [0027]    Referring to FIG. 1, a three phase electrical distribution panel  100  includes a panel base  102 , a panel cover  104  and an interior assembly  106 . The panel base  102  and panel cover  104  generally make up the panel housing  108  of distribution panel  100 . The interior assembly  106  is attached to panel base  102  by suitable fasteners, not shown, through mounting holes  110 . Upstanding supports  112  are integral to interior assembly  106  and provide attachment surfaces  114  for attachment of panel cover  104 , which is secured to the attachment surfaces  114  by suitable fasteners, not shown, through holes  116  in panel cover  104 .  
         [0028]    Interior assembly  106  includes main support  118  for mechanically supporting a main circuit device, such as but not limited to a circuit breaker  200  that is fully described below, at least one busbar  120  for connecting circuit breaker  200  to a plurality of branch circuit connections  122 , a ground connector  124  for providing an electrical ground connection within the distribution panel  100 , and a neutral connector  126  for providing an electrical neutral connection within the distribution panel  100 . Power distribution to a plurality of branch circuits, not shown, is made through the plurality of branch circuit connections  122 .  
         [0029]    Circuit Breaker Generally  
         [0030]    A three-pole circuit breaker  200  is depicted in the perspective view of FIG. 2 and the exploded view of FIG. 3. While reference is made to a three-pole circuit breaker  200  as depicted in FIGS.  1 - 3 , one skilled in the art will appreciate that this is for general descriptive purposes only and that the four-pole circuit breaker  200 ′ as depicted in FIG. 5 is more representative of the application of the present invention. Base  212  and midcover  214  captivate cassette  216 , trip unit  218  and operating mechanism  220  by fasteners, not shown, through holes  222 . For illustrative purposes, cassette  216 , shown in FIG. 3, will be referred to in the three-pole context, and cassettes  316 ,  318 ,  320 ,  322 , shown in FIG. 5, will be referred to in the four-pole context. However, one skilled in the art will appreciate that a three-pole cassette is interchangeable with a four-pole cassette. Cassette halves  216   a,b  are secured by fasteners, not shown, and are positionally located in pocket  224  of base  212 . Pushbutton  300  extends through opening  302  of top cover  304  and is described in more detail below. Top cover  304  is secured to midcover  214  by fasteners, not shown, through holes  306 .  
         [0031]    For simplicity and clarity, where more than one element of the same type is present, only one will be referenced, but the reader will readily recognize that the single reference pertains to more than one element of the same type. Here, for example, there are three cassettes  216  and three pockets  224 . Each cassette  216  is positionally located in an associated pocket  224 . Reference is made to a cassette  216  and a pocket  224 , but the reader will readily recognize that three cassettes  216  and three pockets  224  are present. Also for simplicity and clarity, reference will only be made to a three phase circuit breaker, but the reader will recognize that the present invention is equally applicable to single phase, two phase or multi-phase electrical switching devices of any kind.  
         [0032]    Extending through opening  226  of escutcheon  228  on topcover  304  is operating handle  230 , which is operatively connected to movable contact arm  232  by operating mechanism  220  and link  234 , best seen by referring to FIG. 4. Handle  230  enables the opening and closing of electrical contacts  236   a,b,c,d , best seen by referring to FIG. 4.  
         [0033]    An example of operating mechanism  220  is depicted generally in FIG. 3, is fully described in commonly assigned U.S. patent application Ser. No. 09/516,475 entitled “Circuit Interrupter Operating Mechanism” filed Mar. 1, 2000, and functions generally to open and close electrical contacts  236   a,b,c,d  by actuation of operating handle  230 .  
         [0034]    Trip unit  218  is of a type that is depicted generally in FIGS. 2 and 3. An example of such a trip unit is fully described in commonly assigned U.S. Pat. Nos. 4,589,052, 4,728,914, and 4,833,563, and functions generally to initiate a trip action within the actuator  264  after receiving a trip signal from current sensors  238 .  
         [0035]    Trip unit  218  is operatively connected to current sensors  238  by pins  240  and sockets  242 , and to operating mechanism  220  by actuator  264 , shown in phantom in FIG. 2, to effectuate the opening of contacts  236   a,b,c,d  upon the occurrence of an abnormal overcurrent condition.  
         [0036]    An example of an actuator  264  is shown generally in phantom in FIG. 2, is fully described in commonly assigned U.S. patent application Ser. No. 09/518,899 entitled “Fast Acting High Force Trip Actuator” filed Mar. 6, 2000, and functions generally to transfer the trip action to the operating mechanism  220  after receiving a trip signal from the trip unit  218 .  
         [0037]    Current sensor  238  is shown generally in FIGS. 3 and 4. A representative example of such a current sensor  238  is fully described in commonly assigned U.S. Pat. Nos. 4,589,052, 4,728,914, and 4,833,563, and functions generally to power up trip unit  218  and provide trip unit  218  with a signal representative of the circuit current in the protected circuit.  
         [0038]    Referring to FIG. 4, which depicts a cutaway side view of cassette  216  and current sensor  238  in base  212 , electrical connections between the protected circuit, not shown, and circuit breaker  200  are made through load terminal  244  on load side  246  of circuit breaker  200 . Electrical connections between the power source, not shown, and circuit breaker  200  are made through line terminal  248  on line side  250  of circuit breaker  200 .  
         [0039]    Referring to FIGS. 2, 3 and  4 , circuit breaker  200  includes operating handle  230  for driving operating mechanism  220  to manually open and close electrical contacts  236   a,b,c,d . Contact  236   a  is carried by elongated fixed contact arm  252 , contacts  236   b,c  are carried by elongated movable contact arm  232 , and contact  236   d  is carried by elongated fixed contact arm  254 . FIG. 4 also shows movable contact arm  232   a , depicted in phantom, following an opening action by trip unit  218  and operating mechanism  220 . Fixed contact arm  252  extends through opening  256  of cassette  216  to terminate in line terminal  248 , which is accessible through an opening, not shown, in line side  250  of base  212 . Obviously, each phase of the multi-phase circuit breaker would have separate conductors per phase, not shown. Operating mechanism  220  is operatively connected to contact arm  232  by connecting pin  260 , link  234 , bell crank pin  266 , bell crank  268 , drive rod  402 , rotor  258 , and rotor pivot  259 . Connecting pin  260  connects link  234  to operating mechanism  220 , bell crank pin  266  connects link  234  to bell crank  268 , drive rod  402  connects bell crank  268  to rotor  258 , and bell crank  268  operatively pivots about rotor pivot  259 .  
         [0040]    The current path through circuit breaker  200  in the closed position is best seen by referring to FIG. 4. Under quiescent operating conditions, the current from the power source enters circuit breaker  200  through line terminal  248  (and other line terminals on adjacent phases not shown), and exits through load terminal  244  (and other load terminals on adjacent phases not shown). Between line terminal  248 , and load terminal  244 , the current path consists of; fixed contact arm  252 , electrical contacts  236   a  and b, movable contact arm  232 , electrical contacts  236   c  and d, fixed contact arm  254 , and sensor strap  262 . Sensor strap  262  passes through and provides primary current signal to current sensor  238 , which is operatively connected to trip unit  218  by pins  240  and sockets  242 . Fixed contact arm  254  is mechanically and electrically connected to sensor strap  262  by a fastener, not shown. Sensor strap  262  passes through current sensor  238  to terminate in load terminal  244 , which is accessible through an opening, not shown, in load side  246  of base  212 .  
         [0041]    Arc chute, or arc extinguishing assembly  270 , is removably captivated within cassette  216  by molded detail  272  that is integral to cassette  216 . Arc plates  274 , are typically, but not necessarily, arranged substantially parallel to one another, have tabs  276  that are captivated in corresponding slots in plate supports  278 . Exhaust baffle  280  is removably captivated within cassette  216  by molded slot, not shown, that is integral to cassette  216 . Holes in exhaust baffle  280 , not shown, provide for the passage of arc effluent generated from a short circuit interruption condition. The arc effluent passing through exhaust baffle  280  on line side  250  of circuit breaker  200  will exit base  212  through terminal chamber  282 . The arc effluent passing through exhaust baffle  280  on load side  246  of circuit breaker  200  will exit base  212  through vent channel  284 , shown in phantom in FIG. 4.  
         [0042]    Vent channels  284  are shown generally in phantom in FIG. 4, are fully described in commonly assigned U.S. patent application Ser. No. 09/366,473 entitled “Bottom Vented Circuit Breaker Capable of Top Down Assembly Onto Equipment” filed Aug. 3, 1999, and function generally to provide a passage for the arc effluent to travel from the inside of cassette  216  to the outside of circuit breaker  200  during an abnormal overcurrent condition.  
         [0043]    Drive Rod Assembly  
         [0044]    [0044]FIG. 5 depicts several subassemblies of the circuit breaker of FIG. 2 in an exploded perspective view. First, second, third and fourth cassettes  316 ,  318 ,  320  and  322  are depicted in an exploded assembly arrangement with operating mechanism  220  arranged on second cassette  318 , and with drive rod assembly  400  shown between third and fourth cassettes  320  and  322 . First and fourth cassettes  316 ,  322  are generally known as outboard cassettes, and second and third cassettes  318 ,  320  are generally known as inboard cassettes.  
         [0045]    The rotor and movable contact arm within the first cassette  316 , on one side of the operating mechanism  220 , and the rotor and movable contact arm within the third and fourth cassettes  320  and  322 , on the opposite side of the operating mechanism  220 , are coupled together with the drive rod  402  and the support rod  404 , and move in unison under the action of the operating mechanism  220  thereby providing a complete multi-pole circuit interruption.  
         [0046]    In the case of an asymmetrical arrangement of cassettes, that is, where there are more cassettes on one side of the operating mechanism than the other, the farther the drive rod  402  and support rod  404  extend from the operating mechanism  220 , the more relative movement there will be between the two rods. In a four-pole molded case circuit breaker, the relative movement between the drive rod  402  and the support rod  404  connecting to the fourth cassette causes a torque loss from the operating mechanism  220  to the movable contact arm in the fourth cassette  322 . A stabilizer clamp  406  reduces the relative movement between the drive rod  402  and the support rod  404  and thereby allows the rods to deliver maximum torque to the movable contact arm of the fourth cassette  322 . To provide for effective toggling of the operating mechanism  220  on closure, clearance is provided between the drive and support rods  402 ,  404 , and the rotor of the fourth cassette  322 . Since it is desirable to have one cassette construction for each of the four cassettes in a four-pole circuit breaker, the clearance is best provided by the construction of the drive and support rods  402 , 404 , as is best seen by now referring to FIGS. 6 and 7.  
         [0047]    Drive Rod and Support Rod  
         [0048]    Referring to FIGS. 6 and 7, a drive rod  402 , support rod  404  and stabilizer clamp  406  are illustrated apart from other components of the circuit breaker. First ends  402   a ,  404   a  of drive and support rods  402 , 404 , have a larger dimension, or cross-sectional area, than second ends  402   b ,  404   b . The first ends  402   a ,  404   a , are arranged to couple with the first, second and third cassettes  316 ,  318 ,  320 , and the second ends  402   b ,  404   b , are arranged to couple with the fourth cassette  322 . Since the openings in the rotor  258 , shown generally at  402 ,  404  in FIG. 4, are preferably the same across all four poles, the smaller dimension of second ends  402   b ,  404   b , will result in a clearance condition between drive and support rods  402 ,  404 , and the rotor of the fourth cassette  322 , thereby resulting in a loosely coupled arrangement between rods  402 ,  404  and the fourth cassette  322 . The staggered contact depression resulting from this loosely coupled arrangement will thereby enable effective toggling of the operating mechanism on closure.  
         [0049]    One embodiment of the stabilizer clamp  406  is preferably constructed from a single piece of material. The material may be of any type capable of providing stability to the two rods. Preferred materials include but are not limited to metal and plastic. Openings  408  formed in clamp  406  are dimensioned to conform to the shape of second ends  402   b ,  404   b  of drive and support rods  402 ,  404 . However, one skilled in the art will also appreciate that openings  408  may alternatively be dimensioned to conform to the shape of first ends  402   a ,  404   a  of drive and support rods  402 ,  404 . The choice of which end of drive and support rods  402 ,  404  the openings  408  conform to is a matter of design choice, provided that the desired effect of a staggered contact depression is achieved.  
         [0050]    With the clamp  406  positioned within the circuit breaker, drive rod  402  is positioned through opening  408 , and support rod  404  is positioned through the other opening  408 . It is preferable that the rods be affixed in the desired position to the clamp, which can be effected in several ways. A preferred arrangement for affixing the clamp is to provide the stabilizer clamp  406  with a slot  410  extending from one opening  408  to the other opening  408 . The slot  410  and openings  408  result in bifurcating a top portion  412  and a bottom portion  414  of clamp  406 , which allows for some resilient movement between the top portion  412  and the bottom portion  414 . By urging top portion  412  toward bottom portion  414 , openings  408  are affected. The affect is to reduce the dimension measured from top portion  412  to bottom portion  414 . Reducing this dimension in each of the openings  408  causes the rods to be pinched by the clamp within each opening. The pinching action, when orchestrated to a sufficient degree, will reliably retain the rods and reduce relative movement therebetween. However, since second ends  402   b ,  404   b  have a smaller dimension than first ends  402   a ,  404   a  of drive and support rods  402 ,  404 , the reduced relative movement between the rods will not negatively impact the desired staggered contact depression between the fourth pole and the other three poles.  
         [0051]    With respect to urging top portion  412  and bottom portion  414  toward one another, one preferred tightening means is a screw  416 . Alternate tightening means include, but are not limited to, a thread-forming screw, a nut and bolt, and a rivet. In an embodiment where a screw is used, the screw is passed through the top portion  412  via a clearance opening  418  and threaded into the bottom portion  414  via a threaded opening  420 . Tightening the screw  416  urges the top portion  412  and the bottom portion  414  together and allows the openings to embrace the rods tightly as stated above, thereby locking them together. FIG. 7 illustrates a drive rod assembly  400  where stabilizer clamp  406  is mounted on drive and support rods  402 ,  404 , using screw  416  to securely lock the rods together.  
         [0052]    Alternative Embodiment for Drive Rod Assembly  
         [0053]    [0053]FIGS. 8 and 9 illustrate an exploded and assembled view, respectively, of an alternate drive rod assembly of the invention. In FIGS. 8 and 9, like numerals have been employed for like elements discussed in connection with FIGS. 6 and 7. Elements of FIGS. 8 and 9 that are similar to elements of FIGS. 6 and 7 but not identical thereto are discussed briefly below. However, one of ordinary skill in the art will clearly understand the alternative embodiment from a review of the drawings and reference to the foregoing discussion.  
         [0054]    Stabilizer clamp  426  includes upper portion  428  and lower portion  430  with segmented openings  432 . Clearance opening  434  and threaded opening  436  accept the screw  416  as discussed above to securely tighten the upper and lower portions of the stabilizer clamp and lock the rods together.  
         [0055]    Additional Alternative Embodiment for Drive Rod Assembly  
         [0056]    The aforementioned drive rod assembly  400  and fourth pole cassette  322  are coupled together by second ends  402   b ,  404   b  of drive and support rods  402 ,  404  engaging rotor openings, generally depicted at  402 ,  404  in FIG. 4, of rotor  258 . In the aforementioned embodiment, it was considered desirable to use a standard construction rotor  258  across all three poles, wherein the rotor openings for accepting drive and support rods  402 ,  404  were sized to accept both first and second ends  402   a ,  402   b ,  404   a ,  404   b  of drive and support rods  402 ,  404 . As described above, use of a smaller dimension for second ends  402   b ,  404   b  than for first ends  402   a ,  404   a , resulted in a loosely coupled arrangement between drive rod assembly  400  and fourth cassette  322 .  
         [0057]    Alternatively, a loosely coupled arrangement between drive rod assembly  400  and fourth cassette  322  may be achieved by using drive and support rods  402 ,  404  where first and second ends  402   a ,  404   a ,  402   b ,  404   b  are of the same size, but where the rod-accepting openings in the fourth pole rotor in the fourth cassette  322  are larger in size than the respective openings in the first, second and third cassettes  316 ,  318 ,  320 .  
         [0058]    Thus, a loosely coupled arrangement between drive rod assembly  400  and fourth cassette  322  may be achieved by using a standard cassette arrangement for all four cassettes and a drive rod assembly with dissimilar rod end dimensions, or by using a non-standard cassette arrangement for the fourth cassette and a drive rod assembly with similar rod end dimensions.  
         [0059]    Operation of Invention Generally  
         [0060]    Under quiescent operating conditions with the circuit breaker  200  in the closed state, drive and support rods  402 ,  404  interact with rotor  258  to hold contacts  236   a,b,c,d  in the closed position under the influence of the operating mechanism  220 . As described previously, first ends  402   a ,  404   a  of drive and support rods  402 ,  404  are arranged to couple with the first, second and third cassettes  316 ,  318 ,  320 , and second ends  402   b ,  404   b  are arranged to couple with the fourth cassette  322 , thereby providing a fourth pole arrangement with slightly less contact depression than the other three poles, but with sufficient contact depression for the desired performance of the circuit breaker as a whole.  
         [0061]    Under a dynamic closing condition, drive and support rods  402 ,  404  urge movable contact arm  232  in each of the four cassettes  316 ,  318 ,  320 ,  322  toward the closed position. Since first ends  402   a ,  404   a  of drive and support rods  402 ,  404  have a larger dimension than second ends  402   b ,  404   b , the contacts  236   a,b,c,d  in the first, second and third cassettes  316 ,  318 ,  320  will make contact before the contacts in the fourth cassette, thereby resulting in a staggered load as seen by the operating mechanism  220 . Completion of the closing action results in a fully toggled operating mechanism and all four poles being at their respective full contact depression.  
         [0062]    While this invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.