Abstract:
A parallel pole magnetohydraulic circuit breaker ( 10 ), having a single trip element ( 271 ) and a pair of trip mechanisms ( 101, 102 ), achieving an increased current carrying capacity with reduced nuisance trips. The tip mechanisms ( 101, 102 ) are contained within separate housings ( 14, 16 ), with electrical connections ( 30, 40 ) and multipole trip mechanism ( 101, 102 ) communicating through apertures in the common wall ( 14′ ). Preferably, the armature ( 260 ) of the trip element ( 271 ) acts on a single trip mechanism ( 101, 102 ), which multiplies the available force to trigger a trip of the other tip mechanism.

Description:
The present application is a 371 of PCT/US99/24468, filed Oct. 20, 1999, which is a continuation of U.S. patent application Ser. No. 09/176,169, filed Oct. 21, 1998, now U.S. Pat. No. 6,034,586, issued Mar. 7, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of circuit breakers, and more particularly to multipole circuit breakers in which contact sets are paralleled in order to increase breaker capacity rating. 
     BACKGROUND OF THE INVENTION 
     In the field of electrical circuit breakers, it is well known to tie the mechanisms of a plurality of electrical poles, or independent circuit paths, together. In this case, it is often desired to provide a single control lever and a trip mechanism which operates the electrical contacts in synchrony. See, U.S. Pat. Nos. 5,565,828; 5,557,082, 4,492,941, and 4,347,488, expressly incorporated herein by reference. 
     A single pole circuit breaker is a device that serves to interrupt electrical current flow in an electrical circuit path, upon the occurrence of an overcurrent in the circuit path. On the other hand, a multipole circuit breaker is a device which includes two or more interconnected, single pole circuit breakers which serve to substantially simultaneously interrupt current flow in two or more circuit paths upon the occurrence of an overcurrent in any one circuit path. 
     In a multipole circuit breaker, typically the poles switch independent phases of AC current. Thus, two-pole and three-pole breakers are well known. In these systems, each pole is provided with a current sensing element to generate a trip signal, so that an overload on any phase circuit is independently sensed. In the event that an overload occurs, all of the phase circuits are tripped simultaneously. A manual control lever is provided which operates the phase circuits synchronously as well. 
     Conventional multipole circuit breaker arrangements thus include a trip lever mechanism associated with each pole of the multipole circuit breaker. Each trip lever includes a portion for joining it to adjacent trip levers. If any pole is tripped open by an overcurrent, the breaker mechanism of that pole causes the trip lever to pivot about its mounting axis. The pivotal motion of one lever causes all the interconnected trip levers to similarly pivot. Each lever may include an arm for striking the armature or toggle mechanism of its respective pole, and causing each pole to be tripped open. 
     In order to increase the capacity of a circuit breaker system, it has been proposed to parallel a set of contacts, each of which might be insufficient alone to handle the composite load. Thus, by paralleling two single pole circuit breaker elements, a higher capacity circuit breaker may be achieved. However, the art teaches that, preferably, a single contact set is provided having a larger surface area and greater contact force in order to handle a larger load. These larger load-handling capacity devices are typically dimensionally larger than lower load carrying designs. This is because, in part, many elements within a circuit breaker scale in size in relation with current carrying capacity, including the lugs, trip elements, trip mechanism, contacts and breaker arm. 
     In designing a trip element or system, the type of load must be considered. There are two main classes of trip elements; thermal magnetic and magnetohydraulic. These differ in a number of characteristics, and typically have different application in the art. 
     However, where such contact parallelization is employed, the contact ratings of the breaker should be derated from the sum of current carrying capacity of each of the contact sets. This is because a contact set having a lower impedance than others will “hog” the current, and may thus see a significantly greater proportion of the total current than 50%, resulting in overheating, and possible failure. Therefore, the art typically teaches that a pair of paralleled contact sets are derated, by for example about 25%, to ensure that each component will operate within its safe design parameters. Further, the contact resistance of a switch may change significantly with each closure of the switch. In parallel contact systems, it is known to employ both unitary thermal magnetic and multiple parallel-operating trip elements in multipole breakers. Thus, it is possible to design a circuit breaker with a specially designed trip element that controls an entire breaker system, or to parallel two entire breaker circuits of a multipole arrangement. In the later case, in order to equalize the current as much as possible between the circuits, a current equalization bar has been proposed. However, this does not compensate for unequal contact resistance, and nuisance tripping of the circuit breaker results when the unequal division of the current has caused enough current to pass through one of the current sensing devices to cause it to trip its associated mechanism. 
     Attempts have been made in thermal-type breakers to parallel the sets of contacts of a multipole breaker to achieve increased maximum current rating. In one case, exemplified by model QO12150 from Square-D Corp., a unitary thermal magnetic trip element was employed as a trip element for a set of two parallel contact sets, with a connecting member to trip both contact sets at the same time. In this case, the trip dynamics were defined by the thermal-magnetic trip element, and careful calibration of the thermal element was required. This design provided both contact sets within a common housing. Thus, while the internal parts were common with non-multipole arrangements, the housing itself was a special multipole breaker housing. The parallel breaker is housed in a shell that differs from single pole housings, with the parallel poles in a common space. 
     One typical known system is disclosed in U.S. Pat. No. 4,492,941, expressly incorporated herein by reference, provides electromagnetic sensing devices that are electrically connected at one of their ends to the load terminals. The load terminals are electrically connected in parallel with each other. A plurality of electromagnetic sensing devices are electrically connected at their other ends to each other and are electrically connected to all of the movable contacts which are themselves all electrically connected together. The stationary contacts are connected to line terminals that are also electrically connected in parallel with each other. Thus, the electromagnetic sensing devices are connected in parallel at both of their ends and the contact sets are also connected in parallel at both of their electrical ends, while the electromagnetic sensing devices, on the one hand, and the contact sets, on the other hand, are also in series with each other, thus seeking to equally divide the current among all of the electromagnetic sensing devices, even though the current may not be equally divided among all of the relatively movable contacts, because of varying contact resistances. 
     Another attempt to increase current carrying capability by paralleling contact sets using magnetohydraulic trip elements employed two parallel trip elements, each set for a desired derated value corresponding to half of the total desired current carrying capacity. For example, two 100 Amp breakers were paralleled (using a standard multipole trip bar) to yield a 150 Amp rated breaker, with 175% trip (about 250 Amps) rating, meeting UL 1077. The parallel set of breakers employed two side-by-side single breaker housings, with slight modifications, and thus did not require new tooling for housings and contact elements. 
     In this later case, it is difficult to comply with UL 489, which requires that the breaker trip at 135% maximum of rated capacity and 200% of rated capacity within 2 minutes, and that the breaker be capable of handling the specified loads without damage. For example, if the maximum expected deviation in contact resistance of the contact sets (which changes each time the contact is closed) could cause a current splitting ratio of 60%/40%, then in order to ensure reliable trip at 135% of total rated capacity, each trip element must be designed to trip at about 120% of rated capacity, which would lead to unreliability and nuisance trips because of insufficient margin. 
     Notwithstanding the foregoing attempts, it has heretofore been considered difficult to employ magnetohydraulic circuit breakers in parallel contact multipole breakers with relatively low overcurrent thresholds, such as that imposed by UL 489, especially for use in load environments with high peak to average load ratios, because the maximum expected currents would result in nuisance trips. 
     A main advantage of parallel contact circuit breakers is that these may employ many parts in common with lower current carrying single pole devices. It is thus often economically desirable to increase the current carrying capacity of circuit breakers by modifying as little as possible, existing circuit breakers. Toward this end, it has been proposed that the amount of current carrying capacity may be almost doubled by placing two single pole circuit breakers side-by-side (or almost tripled by using three side-by-side) and connecting the line terminals together and likewise connecting the load terminals together. 
     Commercial circuit breaker manufacturers generally manufacture a complete product line composed of a number of breaker sizes, each one covering a different (although sometimes overlapping) operating current range. Each breaker size typically has required its own component and case sizes. In general, each component and case size combination is useful in circuits having only a single current rating range. The need to have a different set of component and case sizes for each current rating has added to the overall cost of breakers of this general type. 
     As discussed above, there are two common types of trip elements for circuit breakers. A first type, called a thermal magnetic breaker, provides a thermal portion having a bimetallic element that responds to a heat generated by a current, as well as a solenoid to detect magnetic field due to current flow. Typically, the thermal element is designed to trigger a trip response at a maximum of 135% average of rated capacity, and the magnetic element responds quickly (within milliseconds) at 200% of rated capacity. The thermal portion of the breaker controls average current carrying capability, by means of thermal inertia, while the magnetic element controls dynamic response. This design seeks to provide adequate sensitivity while limiting nuisance trips. However, such thermal magnetic designs typically require calibration of the thermal trip mechanism for precision, and tuning of dynamic response is difficult. Further, the thermal element incurs a wattage loss. The operation of the thermal element is also sensitive to ambient temperature, since the heating of the bimetallic element by the current flow is relative to the ambient temperature. See, U.S. Pat. Nos. 3,943,316, 3,943,472, 3,943,473, 3,944,953, 3,946,346, 4,612,430, 4,618,751, 5,223,681, and 5,444,424. 
     A second type of trip element is called a magnetohydrodynamic or magnetohydraulic breaker. See, U.S. Pat. Nos. 4,062,052 and 5,343,178. In this element, the current passes through a solenoid coil wound around a plastic bobbin, acting on static pole piece and a movable armature. Within the solenoid coil is a moveable magnetically permeable core, which is held away from the pole piece in a damping fluid, e.g., a viscous oil, by a spring. As a static current through the coil increases, the core is drawn toward the pole piece through the viscous fluid, resulting in a nonlinear increase in force on the armature, which lies beyond the pole piece, as the moveable core nears contact with the pole piece. Thus, as the moveable core is pulled toward the pole piece, the magnetic force on the armature suddenly increases and the armature rapidly moves. In this case, it is primarily the spring constant of the spring which controls the precision of the trip element, and thus a final calibration is often unnecessary given the ease of obtaining precision springs. In the event of a dynamic current surge, the core is damped by the fluid, and thus does not rapidly move toward the pole piece, resulting in a dynamic overload capability, determined by the viscosity of the damping fluid, and thus avoiding nuisance trips. The armature is typically counterbalanced and may be intentionally provided with an inertial mass to provide further resistance to nuisance trips. 
     Nuisance tripping is a problem in applications where current surges are part of the normal operation of a load, such as during motor start-up or the like. For example, starting up of motors, particularly single phase, AC induction types, may result in high current surges. Motor starting in-rush pulses are usually less than six times the steady state motor current and may typically last about one second, but may be 10 or more times the steady state current. In the later case, a breaker may revert to an instantaneous trip characteristic, because the magnetic flux acting on the armature is high enough to trip the breaker without any movement of the delay tube core or heating of the thermal element, depending on the design. One way to address this problem is by increasing the distance between the coil and armature. 
     A second type of short duration, high current surge, commonly referred to as a pulse, is encountered in circuits containing transformers, capacitors, and tungsten lamp loads. These surges may exceed the steady state current by ten to thirty times, and usually last for between two to eight milliseconds. Surges of this type will cause nuisance tripping in conventional delay tube type electromagnetic circuit breakers. This problem may be addressed by increasing the inertia of the trip element or by other means. See, U.S. Pat. Nos. 4,117,285, 3,959,755, 3,517,357, and 3,497,838, expressly incorporated herein by reference. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     The applicants have found that a single magnetohydraulic trip element can advantageously be used to provide desired trip dynamics in a circuit breaker by passing all current from a set of parallel contact sets through a unitary trip element, and providing a multipole trip arm triggered by the unitary trip element which trips the parallel contact sets simultaneously. 
     The preferred design employs parallel circuit breaker poles each having a trip mechanism, switch contacts and a housing, which share most components in common with a single pole circuit breaker in the same “family”, thus reducing required number of inventoried parts and engineering costs. The trip element of the preferred design, however, differs from single pole designs, being configured for the desired ratings and dynamic response, and portions of the housing between adjacent poles are modified for common access to electrical terminals to bridge the load and to provide a standard type multipole trip bar. The magnetohydraulic trip element, which is preferably a 150 Amp element with desired dynamic trip characteristics, sits asymmetrically in one of the pole housings within a standard frame, in the normal trip element position, and actuating a standard armature. 
     The external lugs of each poles are made electrically parallel by placing a conductive bar therebetween. This also serves the visual function of alerting the installer as to the electrical function of the breaker, which is similar to a multipole breaker that is not paralleled. Internally, one set of lugs are connected together with conductive straps to one end of the magnetic coil. The other end of the magnetic coil is connected with conductive straps to each of the contact arms. In order to provide physical access for these connections, a portion of each of the common walls of the breaker pole housings are machined to form an aperture or portal therebetween. 
     The modifications to the standard single pole housing are minimized; other than the portal in the common wall between the poles, the only other modifications are, for example, an arcuate slot for a common trip mechanism, and an arcuate slot for an internal linkage of the manual switch handles. In the preferred embodiment, however, the handles are linked externally by a crossbar, which fits between the handles and causes them to move in unison. In this way, the standard mountings for the handle, pivot axis of the moveable contact bar, stationary contact, and arc chute and slot motor are unaffected. Further, the safety factors of the design remain relatively intact. 
     A preferred design provides two parallel switch poles with a design rating of 100 Amps each, in a housing 2.5 inches long, 0.75 inches wide, and 2 inches deep, with electrical contact bolts on 2 inch centers. The resulting parallel multipole design with a rating of 150 Amps therefore fits within a form factor of 2.5 by 1.5 by 2 inches, a substantial improvement over prior 150 Amp rating circuit breakers. 
     It should be seen that the form factor may be varied according to the present invention, for example other standard size circuit breakers which may be formed as multipole parallel contact breakers are, for example, 2 inches long, by 0.75 inches wide, by 1.75 inches deep (e.g., 50 Amp rating) and 7.25 inches long by 1.5 inches wide by 3 inches deep (e.g., 250 Amp rating). 
     The present invention may incorporate other known circuit breaker features, such as a mid-trip stop for the manual control lever or other trip indicators, and indeed may be formed into a traditional multipole design with parallel sets of contacts for each of multiple switch poles. 
     It is also seen that, while the preferred embodiments employ housing parts which are common in essential design with single pole designs, that this is not a limitation on the operability of the inventive design. 
     It is therefore an object of the invention to provide a magnetohydrodynamic circuit breaker which has a low average overcurrent trip capability with good nuisance trip immunity. 
     It is also an object of the present invention to provide a circuit breaker having a high current rating and a small form factor. 
     It is a further object of the invention to provide a circuit breaker having a set of parallel contacts, driven by a trip mechanism, wherein all of the contact sets are tripped by a common magnetohydrodynamic trip element. 
     These and other objects will be apparent from an understanding of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and further objects and advantages of the invention will be more apparent upon reference to the following specification, claims and appended drawings wherein: 
     FIG. 1 is a side view of a single pole breaker mechanism having a housing half removed; 
     FIGS. 2A and 2B are detail views of a known breaker toggle mechanism; 
     FIG. 3A is an exploded view of a parallel pole master/slave circuit breaker of a slightly different base design than FIG.  1 . FIG. 3B shows a cutaway view of a delay tube shown in FIG. 3A; 
     FIGS. 4A and 4B shown, respectively, an exploded view of a housing structure, and a side view of an inner case half, for the master/slave circuit breaker according to FIG.  3 A. 
     FIG. 4C shows a partial assembly drawing of exploded view  4 A, with a gap between the master housing and slave housing, revealing the electrical and mechanical connections between interconnecting the respective housings. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments will no be described by way of example, in which like reference numerals indicate like elements. 
     EXAMPLE 
     Components of a conventional type single pole circuit breaker are depicted in FIGS. 1,  2 A and  2 B. See, U.S. Pat. No. 5,293,016, expressly incorporated herein by reference. As shown, the single pole circuit breaker 10 includes an electrically insulating casing  20  which houses, among other things, stationary mounted terminals  30  and  40 . In use, these terminals are electrically connected to the ends of the electrical circuit that is to be protected against overcurrents. 
     As its major internal components, a circuit breaker includes a fixed electrical contact, a movable electrical contact, an electrical arc chute, a slot motor, and an operating mechanism. The arc chute is used to divide a single electrical arc formed between separating electrical contacts upon a fault condition into a series of electrical arcs, increasing the total arc voltage and resulting in a limiting of the magnitude of the fault current. See, e.g., U.S. Pat. No. 5,463,199, expressly incorporated herein by reference. The slot motor, consisting either of a series of generally U-shaped steel laminations encased in electrical insulation or of a generally U-shaped, electrically insulated, solid steel bar, is disposed about the contacts to concentrate the magnetic field generated upon a high level short circuit or fault current condition, thereby greatly increasing the magnetic repulsion forces between the separating electrical contacts to rapidly accelerate separation, which results in a relatively high arc resistance to limit the magnitude of the fault current. See, e.g., U.S. Pat. No. 3,815,059, incorporated herein by reference. 
     The trip mechanism includes a contact bar, carrying a movable contact of the circuit breaker, which is spring loaded by a multi-coil torsion spring to provide a force repelling the fixed contact. In the closed position, a hinged linkage between the manual control toggle is held in an extended position and provides a force significantly greater than the countering spring force, to apply a contact pressure between the moveable contact and the fixed contact. The hinged linkage includes a trigger element which, when displaced against a small spring and frictional force, causes the hinged linkage to rapidly collapse, allowing the torsion spring to open the contacts by quickly displacing the moveable contact away from the fixed contact. The trigger element is linked to the trip element. 
     As is known, the casing  20  also houses a stationary electrical contact  50  mounted on the terminal  40  and an electrical contact  60  mounted on a contact bar  70 . Significantly, the contact bar  70  is pivotally connected via a pivot pin  80  to a stationary mounted frame  100 . A helical spring  85 , which encircles the pivot pin  80 , pivotally biases the contact bar  70  toward the frame  100  in the counterclockwise direction per FIG. 1. A contact bar stop pin  90  or contact bar stop mounted on the contact bar  70  (or optionally other stop, such as a surface which contacts the frame), limits the pivotal motion of the contact bar  70  relative to the frame  100  in the non-contacting position (contact bar  70  rotated about pin  80  in the counterclockwise direction to separate contacts  50  and  60 , not shown in FIG.  1 ). By virtue of the pivotal motion of the contact bar  70 , the contact  60  is readily moved into and out of electrical contact with the stationary contact  50 . In the contacting position (shown in FIG.  1 ), the stationary contact  50  limits the motion of the contact  60 , thus limiting the angular rotation of the contact bar  70  about pin  80 . The pivot pin  80  sits in a conforming aperture in the frame, while a slot  81  is provided in the contact bar  70  to allow a small amount of vertical displacement. Thus, in the contacting position, the contact bar  70  may be displaced vertically by the pressure of the toggle linkage composed of cam link  190  and link housing  200  in the aligned relative orientation (shown in FIG.  1 ), against a force exerted by the helical spring  85 . 
     An electrical coil  110 , which encircles a magnetic core  120  topped by a pole piece  130 , is positioned adjacent the frame  100 . An extension  140  of the coil material, typically a solid copper wire, or an electrical braid, serves to electrically connect the terminal  30  to one end of the coil  110 . An electrical braid  150  connects the opposite end of the coil  110  to the contact bar  70 . Thus, when the contact bar  70  is pivoted in the clockwise direction (as viewed in FIG.  1 ), against the biasing force exerted by the spring  85 , to bring the contact  60  into electrical contact with the contact  50 , a continuous electrical path extends between the terminals  30  and  40 . 
     Magnetic core  120  includes a delay tube. By way of example only, the coil and delay tube assembly may be of the type shown and described in U.S. Pat. No. 4,062,052, expressly incorporated herein by reference. 
     Magnetic core  120  has at an upper position thereof, a pole piece  130 . Adjacent pole piece  130  is an armature  260  pivotally mounted on a pin  261  secured to frame  100 . Armature  260  is rotatably biased in a clockwise direction (relative to FIG. 3) by a spring (not shown), and comprises an arm  265  and a counterweight  266 . Counterweight  266  comprises an enlarged extension of armature  260 , and may include a slot  267  for receiving a pin of an inertia wheel rotatably mounted on frame  100 , not shown. See, U.S. Pat. Nos. 3,497,838, 3,959,755, 4,062,052, and 4,117,285, expressly incorporated herein by reference. 
     The delay tube of the magnetic core  120  is a typical design, which is disclosed, for example, in U.S. Pat. No. 4,062,052, expressly incorporated herein by reference. In this design, an outer tube  122  of the magnetic core  120  is supported in the frame  100  by a bobbin  121 , about which the coil  110  is wound. The outer tube is a drawn single piece shell, sealed at its open end by the pole piece  130 . The interior of the delay tube is conventionally filled with a viscous fluid  123  such as oil. Typically, the viscosity of the oil is selected to provide a desired damping within a standard delay tube design, although mechanical modifications, most notably with respect to the clearance around a magnetic delay core  124  (not shown in FIG. 1) or slug in the outer tube  122 , will also influence the damping or delay of the system. The construction materials of the magnetic delay core or slug and pole piece  130  may also alter the force induced by the coil  110 . The delay core or slug is biased away from the pole piece  130  by a helical spring  125  provided within the outer shell  122 . For example, the delay core has an enlarged lower end and a reduced diameter upper end around which a portion of spring passes and defining an annular shoulder against which the lower end of spring bears. In conventional circuit breaker delay tubes, the distance from the bottom of the core to the plane containing the bottom of the coil  110 , is customarily chosen to be about one-third of the overall interior distance of the delay tube, namely from the bottom of the core to the underside of the pole piece  130 . Customarily, the coil  110  surrounds the upper two-thirds of the delay tube outer shell  122 . This conventional construction optimizes the delay function of the tube while, at the same time, maintaining the overall length of the tube within reasonable bounds. 
     When a prolonged overcurrent passes through coil  110 , delay core moves upwardly in the outer shell  122 , with motion damped by the viscous oil, to compress spring until the upper end of delay core engages pole piece  130 , causing an increased magnetic flux in the gap between the pole piece  130  and armature  260 , so that the armature  260  is attracted to the pole piece  130  and rotates about its pivot  261  to engage the sear striker bar  240  to result in collapse of the toggle mechanism, separating the electrical contacts and opening the circuit in response to the overcurrent, as will become apparent below. 
     The circuit breaker  10  also includes a handle  160 , which is pivotally connected to the frame  100  via a pin  170 . Handle  160  includes a pair of ears  162  with apertures for receiving a pin  180 , which connects handle  160  to a cam link  190 . In addition, a toggle mechanism is provided, which connects the handle  160  to the contact bar  70 . The handle  160  is provided with a helical spring  161 , which applies a counterclockwise force on the handle  160  about pin  170  with respect to frame  100 . A significant feature of the cam link  190 , shown in expanded view in FIG. 2B, is the presence of a step, formed by the intersection of non-parallel surfaces  194  and  198 , in the outer profile of the cam link  190 . Cam link  190  is pivotally connected by a rivet or pin  210  to a housing link  200 . 
     With further reference to FIGS. 2A and 2B, the toggle mechanism of the circuit breaker  10  also includes a link housing  200 , which is further connected a projecting arm  205 . The link housing is pivotally connected to the cam link  190  by a pin or rivet  210  and pivotally connected to the contact bar  70  by a rivet  220 . 
     The toggle mechanism further includes a sear assembly, including a sear pin  230  which extends through an aperture in the link housing  200  generally corresponding to a location of an outer edge  195  of the cam link  190 . This sear pin  230  includes a circularly curved surface  232  (see FIG. 2B) which is intersected by a substantially planar surface  233 . The sear assembly also includes a leg  235  (see FIG.  2 A), connected to the sear pin  230 , and a sear striker bar  240 , which is connected to the leg  235  and projects into the plane of the paper, as viewed in FIG. 2A. A helical spring  250 , which encircles the sear pin  230 , pivotally biases the leg  235  of the sear assembly clockwise, into contact with the leg  205  of the link housing  200 , and biasing the planar surface  233  of the sear pin  230  into substantial contact with the bottom surface  198  of the step in the cam link  190 . A force exerted against the sear striker bar  240  is transmitted to the leg  235 , and acts as a torque on the sear pin  230  to angularly displace the substantially planar surface  233  of the sear pin  230  from coplanarity the surface  198  of the cam link  190 , thus raising the leading edge  234  of the substantially planar surface  233  of the sear pin  230  above the top edge of the surface  194 . This rotation results in elimination of a holding force for the contact bar  70  in the contacting position, generated by the helical spring  85  acting on the contact arm  70 , through the rivet  220  and link housing  200  and sear pin  230  leading edge  234 , against the surface  194  of the cam link  190 , acting on the pin  180 , ears  162  of handle  160 , held in place by pin  170  with respect to the casing  20  and frame  100 . 
     The initial clockwise rotation of the cam link  190  is limited by a hook  199  in the outer profile of the cam link  190 , at a distance from the step, which partially encircles, and is capable of frictionally engaging, the sear pin  230 . In addition, the distance from the step to the hook  199  is slightly larger than the cross-sectional dimension, e.g., the diameter, of the sear pin  230 . This dimensional difference determines the amount of clockwise rotation the cam link  190  undergoes before this rotation is stopped by frictional engagement between the hook  199  and the sear pin  230 . 
     As a consequence, the sear pin  230  engages the step in the cam link  190 , i.e., a portion of the surface  194  of the cam link  190  overlaps and contacts a leading portion of the curved surface  232  of the sear pin  230 . Thus, it is by virtue of this engagement that the toggle mechanism is locked and thus capable of opposing and counteracting the pivotal biasing force exerted by the spring  85  on the contact bar  70 , thereby maintaining the electrical connection between the contacts  50  and  60 . 
     By manually pivoting the handle  160  in the counterclockwise direction (as viewed in FIG.  1 ), the toggle mechanism, while remaining locked, is translated and rotated out of alignment with the pivotal biasing force exerted by the spring  85  on the contact bar  70 . This biasing force then pivots the contact bar  70  in the counterclockwise direction, toward the frame  100 , resulting in the electrical connection between the contacts  50  and  60  being broken, thus assuming a noncontacting position. When in the full counterclockwise position, the handle  160  applies a slight tension or no force on the cam link  190 , resulting in a full extension of the cam link  190  with respect to the link housing  200 . In this position, the leading edge of the surface  232  of the sear pin  230  engages the surface  194 , and thus the toggle mechanism is in its locked position. Therefore, manually pivoting the handle  160  from the left to right, i.e., in the clockwise direction, then serves to reverse the process to close the contacts  50 ,  60 , since a force against the action of spring  85  is transmitted by clockwise rotation of the handle to the contact bar  70 . 
     As shown in FIG. 1, the armature  260 , pivotally connected to the frame  100 , includes a leg  265  which is positioned adjacent the sear striker bar  240 . In the event of an overcurrent in the circuit to be protected, this overcurrent will necessarily also flow through the coil  110 , producing a magnetic force which induces the armature  260  to pivot toward the pole piece  130 . As a consequence, the armature leg  265  will strike the sear striker bar  240 , pivoting the sear pin  230  out of engagement with the step (intersection of surfaces  194 ,  198 ) in the cam link  190 , thereby allowing the force of spring  85  to collapse the toggle mechanism. In the absence of the opposing force exerted by the toggle mechanism, the biasing force exerted by the spring  85  on the contact bar  70  will pivot the contact bar  70  in the counterclockwise direction, toward the frame  100 , resulting in the electrical connection between the contacts  50  and  60  being broken. 
     As a safety precaution, the operating mechanism is configured to retain a manually engageable operating handle  160  in its ON or an intermediate, tripped position, if the electrical contacts  50 ,  60  are welded together. Thus, the handle  160  will not assume the OFF position if the contacts are held together. In addition, if the manually engageable operating handle  160  is physically restricted or obstructed in its ON position, the operating mechanism is configured to enable the electrical contacts  50 ,  60  to separate upon a trip, e.g., due to an overload condition or upon a short circuit or fault current condition. See, U.S. Pat. No. 4,528,531, expressly incorporated herein by reference. 
     Two or more single pole circuit breakers  10  are readily interconnected to form a multipole circuit breaker. In this configuration, each such single pole circuit breaker  10  further includes, as depicted in FIG. 1, a trip lever  270  (shown in dotted line) which is pivotally connected to the frame  100  by pin  261 , which also is the pin about which the armature  260  pivots. The trip lever  270  is generally U-shaped and includes arms  280  (shown in FIG. 1) and  290  (not shown in FIG. 1) which at least partially enfold the frame  100 . A helical spring  330 , positioned between the frame  100  and the arm  280  and encircling the pin  162 , pivotally biases the trip lever toward the frame  100 . A projection  300  of the trip lever  270 , which, as viewed in FIG. 1, projects out of the plane of the paper, is intended for insertion into a corresponding aperture  301  in the trip lever of an adjacent single pole circuit breaker. Thus, any pivotal motion imparted to the trip lever  270 , in opposition to the biasing force exerted by the spring  330 , is transmitted to the adjacent trip lever, and vice versa. The projection  300  and aperture of a trip lever of an adjacent breaker, are preferably tapered, to ensure a secure fit therebetween. When the toggle link collapses, a protrusion  291  (not shown in FIG. 1) from the contact bar  70  displaces a cam surface  292  of the arm  290 , thus rotating the trip lever about pin  261 , and displacing the projection  300 . The projection  300  thus moves in an arc about the pin  261 , and thus an arcuate slot is provided in a housing half of housing  20  to transmit forces through the projection  300 . A portion of arm  280  acts directly on the sear striker bar  240 , to trip the associated toggle mechanism of an adjacent switch pole. A protrusion from the frame, for example a stop, limits the motion of arm  290  of the trip lever  270 , in response to a bias spring about the pivot axis. Thus, Since the trip lever  270  is not operated directly by the armature  260 , the trip dynamics of the circuit breaker are unaffected. The drag on the trip mechanism from the trip lever  270  is insignificant. 
     Side  280  has a cam surface  285 , having a bend of about 45 degrees, which engages the sear striker bar  240  at about the position of the bend. Side  290  has a bend  293 , forming cam surface  292 , which is perpendicular with the portion of the side  290 . Protrusion  291  extends from the side of the moveable contact bar  70 , which contacts the surface  292  midway through the travel of the contact bar  70 . When the contact bar  70  is displaced, the protrusion  291  pushes against the surface  292 , causing a rotation about the pin  261 , causing the surface  285  of side  280  to displace the sear striker bar  240 . It is clear that in operation, rotation of trip lever  270  about pin  261  will result in tripping of the toggle mechanism, and tripping of the toggle mechanism will result in rotation of the trip lever about the pin  261 . See, e.g., U.S. Pat. Nos. 5,557,082, 5,214,402, 5,162,765, 5,117,208, 5,066,935, and 4,912,441, and also U.S. Pat. Nos. 4,492,941, 4,437,488, 4,276,526, and 3,786,380, expressly incorporated herein by reference. 
     In addition to the above-described “master” pole, adjacent thereto is provided a “slave” pole. This “slave” pole is identical to the “master” pole with the exception that it lacks the coil  110 , magnetic core  120 , pole piece  130 , and armature  260 . The projection  300  passes through aligned arcuate slots in the respective case walls between the adjacent “master” and “slave” switch pole housings  20 . The trip lever  271  in the “slave” pole, like the trip lever  270  of the “master” pole, receives a torque with respect to its frame from the tapered projection  300 , extending laterally from the “master” pole housing  20  into the “slave” pole housing  20 , into a tapered recess of the trip lever  271  of the “slave” pole. As the trip lever  271  in the “slave” pole rotates, it applies a force to the “slave” pole sear striker bar  240 , which in turn rotates the “slave” pole sear pin  230  about its axis, resulting in collapse of the “slave” pole toggle mechanism  102 . Thus, when the “master” mechanism  101  trips or is manually switched OFF, the “slave” mechanism  102  trips slightly thereafter. A dual ended rod  302  connects the handle  160  of the master and slave circuit breakers so that they move in unison. 
     As shown in FIG. 3, an electrical braided wire  141  serves to connect the terminal  30  in the “master” pole and an electrical braid  142  serves to electrically connect the terminal  31  in the “slave” pole to one end of the coil  110 . Electrical braids  150 ,  152  connect the opposite end of the coil  110  to the contact bars  70 ,  71  of the “master” and “slave” poles, respectively. Electrical braid  151  passes through a rectangular portal formed in both adjacent case halves. The end of the coil  110  extends through the portal, so that electrical braid  142  does not have to pass through the portal, and indeed, to facilitate connection, the braid  141  may partially or completely pass through the portal to join the end of coil  110 . Conductive plates  43 ,  42  are provided for bridging the lug connections  30 ,  31  and  40 ,  41 , respectively, to ensure low impedance between the “master” and “slave” mechanisms. 
     To extinguish arcing caused by opening of the contacts  50  and  60 , a stacked array of metal plates  73  (shown in FIG. 3) are supported within and by the two half cases  14  and  16  of the circuit breaker housing  20  around the moveable contact arm  70 . 
     Each housing casing half  14 ,  16  includes the following features: An upper boss (half) for the toggle handle  21 ; a lower access port  22 ; a set of four rivet holes for assembly  23 ; a pair of half-recesses for a mounting nut  24 ; a first pivot recess for the handle pin  25 ; a second pivot recess for the contact arm pin  26 ; a pair of half-recesses for electrical contact lugs  27 ; a set of indentations for supporting the arc chute members  28 ; and a number of side port halves  29 . In addition, each respective inner case half  16 ,  14 ′ of the “master” and “slave” housing, respectively, has a number of apertures. First, a generally rectangular portal  31  is provided for paralleling the electrical connections from the pair of lug contacts  30 ,  31  and the movable contact bars  70 ,  71 . Second, an arcuate aperture  32  is provided for the projection  300  of the trip lever  270 . Optionally, an arcuate slot  33  is provided for an internal pin connecting the manual operation handles, causing them to operate synchronously. A cover  34  is provided to close each of the lower access ports. Each of the “master” and “slave” housings  20  are about 2.5 inches long, 0.75 inches wide, and 2 inches deep, with electrical contact bolts on 2 inch centers, each being individually rated at about 100 Amps. The resulting parallel multipole design with a rating of 150 Amps therefore fits within a form factor of 2.5 by 1.5 by 2 inches, 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are, therefore, intended to be embraced therein. The term “comprising”, as used herein, shall be interpreted as including, but not limited to inclusion of other elements not inconsistent with the structures and/or functions of the other elements recited.