Abstract:
A circuit breaker includes a trip unit and an electronic fault detection unit sharing a common trip latch for causing the circuit breaker to trip upon detection of a fault by either unit. The circuit breaker has an electromagnet for causing the circuit breaker to trip upon detection of a fault by an electronic fault detection unit. The electromagnet is oriented in the housing proximal the trip latch without any components interposed between them, and directly attracts the latch. Advantageously the electromagnet orientation does not impact operation or the range of motion of the latch or other trip unit components. Advantageously the circuit breaker of the present invention does not increase the trip latch mass, its bulk swept volume through its range of motion or require additional linkage components that potentially might increase trip cycle time. In some embodiments the electromagnet core is reciprocable.

Description:
CLAIM TO PRIORITY 
     This application claims the benefit of co-pending U.S. provisional patent application entitled “Electromagnet Assembly Directly Driving Latch of an Electronic Circuit Breaker” filed Sep. 22, 2008 and assigned Ser. No. 61/098,845, which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     1. Field of the Invention 
     The invention relates to circuit breaker circuit protection devices for electrical distribution systems. More particularly the present invention is directed to latch mechanisms for tripping the operating mechanism of a circuit breaker in response to an actual fault detection made by either a thermal-magnetic electromechanical or electronic trip unit (or other electronic monitoring device) that operate independently within a circuit breaker. Alternatively the operating mechanism may be tripped in response to simulated fault detection in the distribution system. 
     2. Description of the Prior Art 
     Circuit breakers are utilized in electrical distribution systems to interrupt power current flow upon detection of a potential fault in the system. Generally circuit breakers are interposed in a power distribution circuit between a line source of power and a downstream circuit load. A circuit breaker commonly includes one or more fixed and moving separable contact pairs that open and close the power distribution circuit. A trip unit (often thermal-magnetic electromechanical, analog electronic, digital electronic or combination) monitors circuit load and causes an operating mechanism to separate the contact pair (open the circuit) upon detection of a fault condition. Examples of distribution system faults include short circuit or thermal overheating overloads, ground faults and arc faults. 
     Circuit breakers incorporating both a thermal-magnetic electromechanical overload detection trip unit and an electronic fault interruption unit that operate independently within the circuit breaker are sold in the United States of America by Siemens Energy &amp; Automation, Inc. (“Siemens”) and other companies. An exemplary Siemens circuit breaker is shown in  FIGS. 1-3 . The Siemens circuit breaker incorporates a thermal-magnetic electromechanical trip unit for detection of short circuit and over current faults in electric power distribution circuits, and also an independently operating electronic fault interruption unit for detection of arc fault, ground fault or combination of both types of faults. Both the electromechanical trip unit and electronic fault interruption unit need to be able to activate the operating mechanism independently to open the circuit breaker contacts upon fault detection by either respective unit. 
     As shown in  FIG. 1 , the circuit breaker  10  is connected to a power source such as the line stab  11  of a power panel by sliding connection with the line terminal  12 . A power panel neutral terminal  13  is connected to the circuit breaker panel neutral wire  14 . The circuit breaker  10  load power terminal  15  is connected to load circuit power wire  16 . Correspondingly, the circuit breaker  10  load neutral terminal  17  is connected to the load circuit neutral wire  18 . 
     The circuit breaker  10  has a multi-component housing  20 , including a base  20 A, intermediate cover  20 B and top cover  20 C. The base  20 A and intermediate cover  20 B form a first compartment. The intermediate cover  20 B and top cover  20 C in turn form a second compartment. The circuit breaker handle  22  allows an operator to energize and de-energize the electrical distribution circuit, as well as reset the circuit breaker after fault condition trips the circuit breaker. The exemplary Siemens circuit breaker also has an electronic trip indicator light  24  and a test button  26  that is used to simulate a fault and confirm the breaker  10  operating condition. The fault circuit interrupter  27  is shown schematically and is of known design. The circuit breaker housing components  20 A,  20 B and  20 C are held together in tandem by a plurality of rivets  28 , one of which is shown. 
       FIG. 2  shows a schematic plan view of the first compartment of the known Siemens circuit breaker  10 , showing exemplary components housed within the base  20 A of housing. Note that the intermediate cover  20 B is removed in this figure, so that the line terminal  12 , fixed contact  30 , moving contact  32  and moving contact arm  34  are visible. The operating mechanism  36  includes an engagement sear  42 , shown schematically as a dashed line. The operating mechanism  36  selectively opens and closes the circuit breaker contacts and interacts with the trip unit  50  by engagement of the sear  42  with the pivoting latch  52 . As is known to those skilled in the art, latch  52  pivots about a pivoting axis A, sweeping a pivotal motion volume. When the engagement sear  42  and latch  52  are engaged the circuit breaker contacts  30 ,  32  are maintained in the closed position. Conversely, the contacts are open when the latch  52  and engagement sear  42  are disengaged and the circuit breaker  10  does not enable current flow in the power distribution circuit. 
     The thermal-magnetic trip unit  50  shown in  FIG. 2  includes the latch  52  and latch extension tab  54  that projects laterally from the latch swept volume. As those skilled in the art are aware, the trip unit  50  is of the electromechanical thermal-magnetic type including over current bimetal and an armature assembly that generates a magnetic field attractive to the ferrous metal latch  52 . A high current flow through the armature assembly (for example caused by a short circuit in the electrical distribution system) creates a sufficiently dense magnetic flux to pivot the latch  52  in a counterclockwise direction to disengage the operating mechanism sear  42 . 
       FIG. 3A  shows the known Siemens circuit breaker  10  second compartment intermediate cover  20 B, with the top cover  20 C removed to show the fault circuit interrupter unit  27 . The intermediate cover  20 B defines an aperture  66  for passage of the latch extension tab  54  into the second compartment. The fault circuit interrupter unit  27  includes known fault detection electronics  67  (example: arc fault, ground fault or combination of both) shown schematically and solenoid energizing leads  68 . The known Siemens circuit breaker shown in  FIGS. 1-3  employs a solenoid  70  (see  FIG. 3B ) having a magnetically conductive metal solenoid housing  72  about which is wound a coil of conductive wire  74  that is connected to the solenoid energizing leads  68 . When the solenoid coil  74  is energized the solenoid  70  generates a torroidal magnetic field that expels metal plunger  76  to the right as shown by the arrow B, where it causes counterclockwise rotation of the latch extension tab  54 , thereby disengaging the latch  52  from the engagement sear  42  and causing the operating mechanism  36  to separate the circuit breaker contacts  30 ,  32 . Plunger reset spring  78  resets the plunger to its leftward stable position when the solenoid coil  74  is deenergized. 
     The known Siemens circuit breaker  10  design provides beneficial separation of the fault circuit interrupter electronics  67  from the compartment containing the moving contacts  30 ,  32 , so that arcs created during contact separation are less likely to contaminate the electronics. Use of the solenoid structure  70  on the left side of the extension tab  54  provides for positive pivoting disengagement of the latch  52  from the operating mechanism sear  42  and leaves open the right side of the extension tab. This is beneficial because trip unit  50  disengagement of latch  52  can be more forceful than that caused by the solenoid, so that the latch is caused to pivot with more counterclockwise rotation. Any components within the circuit breaker housing located to the right of the latch  52  should not impede the latch swept volume space occupied during all operational modes. 
     Despite the known benefits of the Siemens circuit breaker  10 , it is desirable to utilize a latch  52  tripping mechanism in the fault circuit interrupter unit  27  that is simpler and less expensive to manufacture than the prior solenoid  70  designs, yet provides for breaker tripping in a manner harmonious and compatible with the trip unit  50  operational modes. 
     Other known circuit breakers have utilized electromagnets to trip circuit breakers upon detection of ground and arc fault conditions. As shown in  FIG. 4 , one other circuit breaker  80  utilizes a pivoting latch  82  that is coupled in series with a second hook  84  that pivots about hoop pivot  85 . The hook  84  has a downward projecting tab that abuts against the left side of the latch  82 . The hook  84  pivots counterclockwise and in turn pivots latch  82  counterclockwise to disengage the latch and corresponding engagement sear (not shown). Hook  84 , constructed of ferrous metal, is urged to pivot in a counterclockwise direction by an electromagnet  86  that attracts the hook upon energization of windings  87  about a bobbin having a ferromagnetic core  88 . The serially aligned pivoting latch  82  and hook  84  provide sufficient swept volume space for the latch  82  to be disengaged by the circuit breaker  80  trip unit during overcurrent (bimetal heating) or short circuit trip modes without the electromagnet  86  interfering with latch  82  counterclockwise pivoting motion to the right in the figure. However, utilization of the hook  84  adds an additional component to the circuit breaker design. Also, the need to pivot two serially abutting pivots (latch  82  and hook  84 ) increases system trip response time or the electromagnet current flux force necessary to move the hook  84  more quickly. 
     Another known latch mechanism employing an electromagnet is shown in  FIGS. 5A and 5B . Circuit breaker  90  has a trip unit  91  that occupies a defined volume within the housing during operational modes. The trip unit includes a known bimetal  92  for overcurrent detection that pivots latch  94  counter clockwise out of engagement with an operating mechanism sear (not shown). An electromagnet comprising a steel core  96  and an annular bobbin/winding  98  capturing the steel core therein provide for combined short circuit and electronic fault detection tripping. During short circuit, the steel core  96  through which the electrical distribution system current passes attracts the latch  94 , thereby rotating the latch out of engagement with the operating mechanism. When the electronic fault detection unit sends energizing current into the bobbin/winding  98 , the electromagnetic attraction of the armature  94  also causes the breaker to trip. Construction of latch  94  is shown more clearly in the cross sectional view of  FIG. 5B . The latch  94  has a generally C-shaped cross section when viewed along the pivot radius, so that it essentially wraps around the bimetal  92 . The latch  94  C-shaped cross section must be sufficiently deep left to right, so that the bimetal  92  is afforded its full range of operational deformation and it follows that the range of angular pivot motion of the latch  94  must increase in order to travel additional left-to-right clearance distance. This in turn increases the total occupied volume of the trip unit  91  and impacts the attractive magnetic force strength necessary to pivot the latch during short circuit and electronic fault detection unit trip operational modes. First, there being a limited, finite internal volumetric capacity of any circuit breaker housing, any increase of trip unit volume has adverse impact on other component volume. Second, the C-shaped cross section of the latch  94  increases its mass, thus requiring more current in-rush energy in the coil windings  98  during electronic trip operation or in the steel core  96  during short circuit trip operation to generate a greater magnetic attractive force. Third, the larger pivot angular distance that must be traversed by the latch  94  necessarily increases the distance from the attractive magnetic force of the core  96  and electromagnetic coil  98 . The increased distance requires generation of a higher intensity magnetic field in order to generate sufficient attractive force between the latch  94  and the magnetic source. 
     Thus, a need exists in the art for a trip latch actuator that has simpler construction than known solenoid designs, that does not add additional linkage components to move the trip latch, does not add mass to the trip latch, does not increase the circuit breaker case volume occupied by the trip unit and trip latch, and does not interfere with motion of other parallel-functioning thermal-magnetic trip unit components, such as short circuit armatures or bimetal elements. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the invention is to trip a circuit breaker upon detection of a fault by an electronic fault detection circuit with an electromagnet without interfering with operation of the independent, parallel operating electromechanical trip unit. The present invention is intended to operate without causing one or more of the following, separately or in any sub combination thereof: increasing significantly trip unit latch mass; increasing occupied swept volume of the trip unit components; addition of linkage components that might otherwise increase phase lag response of the trip operation; or interfering with the range of motion of the trip unit components during their modes of operation. 
     These and other objects are achieved in accordance with the present invention by use of an electromagnet that attracts the latch. The electromagnet structure employs a reciprocating ferromagnetic core oriented proximal the latch, such as proximal a latch extension. Close proximity of the ferromagnetic core and latch enables efficient magnetic attraction of the latch to the electromagnet when the circuit breaker is tripped by the electronic fault detection circuit. However, the reciprocating core can be pushed by the latch or latch extension when the latch is pivoted by the electromechanical trip unit during detection and interruption of overcurrent or short circuit faults. Alternatively, the electromagnet may be constructed with a fixed core. In this alternative embodiment of the present invention, the electromagnet is oriented outside the swept volume of the latch. In another alternative embodiment of the present invention the electromagnet is oriented outside the swept volume of the latch and may be oriented radially tangential to a face of the latch extension. As the latch pivots about its pivot axis, the latch extension face sweeps an arc. The electromagnet is oriented laterally spaced away from the latch extension pivoting arc. In this configuration the electromagnet attracts the latch extension when energized by the electronic fault detection unit. However, when tripped by the electromechanical trip unit, the latch extension pivots laterally past the electromagnet. 
     The present invention features a circuit breaker including a housing. The housing includes therein a pair of separable contacts for selectively opening and closing an electrical power distribution circuit current flow when the contacts are in respective opened and closed positions. An operating mechanism is coupled to the contacts for selectively opening and closing the contacts. The housing also has therein an overload trip unit, occupying a volume within the housing, for detecting overload conditions in an electrical power distribution circuit. The overload trip unit has a moveable latch, the latch engageable with the operating mechanism, wherein the contacts are maintained in the closed position when the latch is engaged with the operating mechanism and the contacts are open when the latch is disengaged from the operating mechanism. The trip unit disengages the latch upon detection of an overload condition. The housing also includes an electromagnet unit having windings, oriented in the housing proximal the latch, without any components interposed between them. The electromagnet directly attracts the latch and disengages the latch when the windings are energized. A fault interruption unit for detecting fault conditions in an electrical power distribution circuit is also within the housing and electrically coupled to the electromagnet windings. The interruption unit energizes the electromagnet unit upon detection of a fault condition. 
     The present invention is also directed to a circuit breaker for electrical power distribution circuits, having a housing that includes therein a pair of separable contacts for selectively opening and closing an electrical power distribution circuit current flow when the contacts are in respective opened and closed positions. An operating mechanism is coupled to the contacts for selectively opening and closing the contacts. An overload trip unit for detecting overload conditions in an electrical power distribution circuit is also in the housing, and has a pivotal latch sweeping a pivotal motion volume and a latch extension coupled to the latch projecting outside of the pivotal motion volume. The latch is engageable with the operating mechanism, wherein the contacts are maintained in the closed position when the latch is engaged with the operating mechanism and the contacts are open when the latch is disengaged from the operating mechanism. The trip unit disengages the latch upon detection of an overload condition. The circuit breaker also has an electromagnet unit having windings, oriented in the housing laterally to the latch swept volume proximal the latch extension without any component between them. The electromagnet directly attracts the latch extension and disengages the latch when the windings are energized. The circuit breaker also has a fault interruption unit for detecting fault conditions in an electrical power distribution circuit, electrically coupled to the electromagnet windings. The interruption unit energizes the electromagnet unit upon detection of a fault condition. 
     The present invention includes a circuit breaker for electrical power distribution circuits having a housing including therein at least a pair of first and second compartments defining an inter-compartment aperture there between. The first compartment includes therein a pair of separable contacts for selectively opening and closing an electrical power distribution circuit current flow when the contacts are in respective opened and closed positions. An operating mechanism is coupled to the contacts for selectively opening and closing the contacts. An overload trip unit for detecting overload conditions in an electrical power distribution circuit is in the first compartment and has a moveable latch and a latch extension coupled to the latch. The latch is engageable with the operating mechanism, wherein the contacts are maintained in the closed position when the latch is engaged with the operating mechanism and the contacts are open when the latch is disengaged from the operating mechanism. The trip unit disengages the latch upon detection of an overload condition. The second compartment includes therein an electromagnet unit having windings, oriented proximal the latch extension. The electromagnet attracts the latch extension and disengages the latch when the windings are energized. A fault interruption unit for detecting fault conditions in an electrical power distribution circuit is electrically coupled to the electromagnet windings. The interruption unit energizes the electromagnet unit upon detection of a fault condition. 
     The present invention is also directed to a circuit breaker for electrical power distribution circuits having a housing including therein a pair of separable contacts for selectively opening and closing an electrical power distribution circuit current flow when the contacts are in respective opened and closed positions. An operating mechanism is coupled to the contacts for selectively opening and closing the contacts. An overload trip unit for detecting overload conditions in an electrical power distribution circuit is in the housing and has a pivotal latch defining a pivot axis and radius. The latch sweeps a pivotal motion volume. A latch extension is attached to the latch and projects outside of the pivotal motion volume. At least a portion of the latch extension projects generally tangentially to the pivot radius. The latch is engageable with the operating mechanism, wherein the contacts are maintained in the closed position when the latched is engaged with the operating mechanism and the contacts are open when the latch is disengaged from the operating mechanism. The trip unit disengages the latch upon detection of an overload condition. An electromagnet unit having windings is oriented in the housing laterally to the latch swept volume proximal to and laterally spaced away from the tangential portion of the latch extension. The electromagnet directly attracts the tangential portion of the latch extension and disengaging the latch when the windings are energized. A fault interruption unit for detecting fault conditions in an electrical power distribution circuit is electrically coupled to the electromagnet windings. The interruption unit energizes the electromagnet unit upon detection of a fault condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic perspective view of a prior art circuit breaker; 
         FIG. 2  is a schematic plan view of the prior art circuit breaker of  FIG. 1  showing a first compartment of the circuit breaker; 
         FIGS. 3A and 3B  are respectively a schematic plan view of the prior art circuit breaker of  FIG. 1  showing a second compartment of the circuit breaker and an axial cross section of a solenoid in that compartment; 
         FIG. 4  is a schematic plan view of a second prior art circuit breaker; 
         FIGS. 5A and 5B  are respectively schematic plan and cross sectional views of a third prior art circuit breaker; 
         FIG. 6  is a perspective view of a first compartment of a circuit breaker of the present invention; 
         FIG. 7  is a perspective view of a second compartment of a circuit breaker of the present invention; 
         FIG. 8  is a partial cross-sectional plan view of an embodiment of an electromagnet of the present invention; 
         FIGS. 9 and 10  show schematically interaction of the electromagnet of  FIG. 8  and latch extension during electromagnet-induced trip initiated by the electronic fault detector unit and overcurrent trip initiated by the electromechanical trip unit, respectively; 
         FIG. 11  is a perspective plan view of another embodiment of the electromagnet and latch extension of the present invention; 
         FIGS. 12 and 13  are schematic views of the electromagnet and latch extension embodiment of  FIG. 11 , showing the range of motion of the latch extension during electromagnet induced trip initiated by the electronic fault detector unit and overload trip initiated by the electromechanical trip unit; 
         FIG. 14  is a plan view of another embodiment of the electromagnet and latch extension of the present invention, wherein those components are oriented below the trip unit; 
         FIG. 15  is a perspective elevation schematic view of the electromagnet and latch extension of  FIG. 14  without the surrounding components of the circuit breaker; 
         FIG. 16  is a schematic elevation view of an molded case circuit breaker (MCCB) with separate plug-in trip unit incorporating the electromagnet and latch extension of the present invention; and 
         FIG. 17  is a schematic elevation view of an MCCB similar to that of  FIG. 16 , showing a different embodiment of the electromagnet and latch extension of the present invention. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical or substantially similar elements that are common to the figures. 
     DETAILED DESCRIPTION 
     After considering the following description, those skilled in the art will clearly realize that the teachings of the present invention can be readily utilized in circuit breaker trip units. 
     The general construction of the circuit breaker internal components shown in  FIG. 6  are substantially similar to those of the prior art Siemens circuit breaker first compartment described with respect to  FIGS. 1 and 2 . As will be described in further detail herein, some embodiments of the latch  52  and latch extension  54 , as well as the second compartment components of the circuit breaker of the present invention are different than those of the prior art second compartment embodiment shown in  FIG. 3 . While some of the exemplary circuit breaker embodiments described herein have two separate compartments, it is possible to package the internal components in a single compartment. 
       FIG. 6  is a perspective plan view of the first compartment of a circuit breaker  10  of the present invention, showing exemplary components housed within the base  20 A of housing  20 . Note that the intermediate cover  20 B is removed in this figure, so that the line terminal  12 , fixed contact  30 , moving contact  32  and moving contact arm  34  are visible. The operating mechanism  36  includes cradle  38 , operating spring  42  and engagement sear  42 . The operating mechanism  36  selectively opens and closes the circuit breaker contacts and interacts with the trip unit  52  by engagement of the sear  42  with the pivoting latch  52 . As is known to those skilled in the art, latch  52  pivots about a pivoting axis, sweeping a pivotal motion volume. When the engagement sear  42  and latch  52  are engaged the circuit breaker contacts  30 ,  32  are maintained in the closed position. Conversely, the contacts are open when the latch  52  and engagement sear  42  are disengaged and the circuit breaker  10  does not enable current flow in the power distribution circuit. 
     The trip unit  50  shown in  FIG. 6  includes the latch  52  and latch extension tab  54  that projects laterally from the latch swept volume. As those skilled in the art are aware, the trip unit  50  is of the electromechanical type including overcurrent bimetal  56  that deforms when heated and pivots the latch  52  in counterclockwise fashion to disengage it from the disengagement sear  42 . The trip unit also includes an armature assembly  58  that generates a magnetic field attractive to the ferrous metal latch  52 . A high current flow through the armature assembly  58  (for example caused by a short circuit in the electrical distribution system) creates a sufficiently dense magnetic flux to pivot the latch  52  in a counterclockwise direction to disengage the operating mechanism sear  42 . Calibration screw  60  is used to calibrate the bimetal  56 . Braid  62  enables electrical continuity from the trip unit  50  to the moving contact arm  34 . 
       FIG. 7  is a plan view of the second compartment of the circuit breaker  10  of the present invention showing the intermediate cover  20 B; the top cover  20 C is removed. Similar to  FIG. 2 , the latch extension  54  projects from the first compartment into the second compartment through the aperture  66  formed within the intermediate cover  20 B. The fault circuit interrupter unit  27  includes the fault detection electronics (examples: arc fault, ground fault or combination of both, parallel overcurrent fault detection, or a remote communication device implementing a command to trip the circuit breaker by way of a communications network coupled to the fault detection electronics), energizing leads  68  and an electromagnet unit  100 . The leads  68  are schematically illustrative and as a matter of design choice may constitute wires, bus bars, printed circuit board conductive pathways or any other known structure necessary to transfer power to the electromagnet  100  in this or in any other embodiments of the invention that are described herein. The electromagnet unit  100  attracts (pulls) the latch extension  54  when energized by the fault detection electronics  67 , rotating the latch extension counterclockwise and to the right in the figure. This differs significantly from the prior art Siemens circuit breaker design of  FIG. 3  that oriented a solenoid  70  on the left side of the latch extension  54  and “pushed” the latch extension to the right. In the prior art design of  FIG. 3  the solenoid  70  was clear of the right side of the latch extension  54 , giving the latter full freedom of motion to be tripped by the electromechanical trip unit  50 . In this manner the electromechanical trip unit  50  and the fault detection electronics  27 /electromagnet unit  100  act on a common trip latch  52 , yet they operate independently. 
     When the latch  52  of the present invention circuit breaker is tripped by the electromechanical trip unit  50 , it is caused to rotate counterclockwise (i.e., swing toward the right of  FIG. 7 ). The number of degrees of latch  52 /latch extension  54  pivotal arcuate swing may vary as a function of whether the trip is initiated by the bimetal  56  or the armature  58  or the intensity of the overload condition. It is desirable to allow latitude of range of free motion to the latch  52 . As was noted with respect to the prior art electromagnet designs shown in  FIGS. 4 and 5 , increasing free space between the electromagnet and the latch requires a stronger magnet to generate sufficient attractive force to trip the latch, or, alternatively, additional linkage components must be added to the latch. Both are undesirable design tradeoffs that are obviated by the circuit breaker design of the present invention. 
     Referring to  FIGS. 7-10 , the circuit breaker of the present invention facilitates close lateral spacing of the electromagnet  100  and the latch extension tab  54 , yet allows the latch extension  54  to have sufficient free sweeping movement space in all operational modes and conditions of the electromechanical trip unit  50 . The electromagnet  100  has a bobbin  102  that is affixed to the intermediate cover  20 B, and coil windings  104  for generation of a magnetic field upon energization of the windings through the leads  68  that are coupled thereto. A ferromagnetic core  106  is reciprocable within a bore defined by the bobbin  102 . As is shown in  FIG. 9 , the core  106  is closely laterally spaced away from the latch extension  54 , thereby minimizing the gap to be bridged by the electromagnetic field that is generated by the electromagnet  100 . When the latch  52  and latch extension  54  are tripped by the electromechanical trip unit  50 , as shown in  FIG. 10 , the core  106  is pushed to the right as is necessary to enable sufficient free travel of the latch extension, without potentially damaging the latch or electromagnet  100 . 
     As shown in  FIGS. 7-10 , the ferromagnetic core  106  may be repositioned back to its initial state proximal the latch extension  54  with a biasing spring  108 . The spring  108  is anchored to the circuit breaker intermediate cover  20 B by a stop  110 , shown schematically. In order to limit reciprocation of the core  106  to the left, it may be constructed with an annular core flange  112  that abuts against an annular face  114  of the bobbin  102 . Alternatively, one skilled in the art may choose to construct the ferromagnetic core  106  without the flange  112 , instead relying on abutting contact of the core and latch extension  54  to reposition the core back to its initial state. 
     An alternate embodiment of the present invention is shown in  FIGS. 11-13 , wherein the latch extension  54  includes bent tab  55  that is aligned generally tangential to the radius of the latch  52  pivoting axis. Electromagnet  120  is oriented outboard of and laterally proximate to the bent tab  55 , so that the ferromagnetic core  106  is aligned to attract the latch  52  upon energization of the coil windings  104  by the fault detection electronic unit  67  via the leads  68 , as previously described with the embodiment shown in  FIG. 7 . As shown in  FIGS. 12 and 13 , when the latch is tripped by the electromechanical overload trip unit, the extension bent tab  55  has sufficient angular (Δθ) and lateral left-to-right (ΔX) clearance to pivot past the ferromagnetic core  106  without interference or impact. In this embodiment the electromagnet  120  may have a fixed ferromagnetic core  106 , because it is oriented to remain clear of the latch tab  55  through the full range of the latter&#39;s pivotal motion in all modes of operation. 
       FIGS. 14-15  show another alternate embodiment of the present invention, wherein the latch  52  latch extension  54  extends below the trip unit  50  (shown schematically). The electromagnet  120  is oriented below the trip unit outside the pivotal sweep range of the latch extension  54  (clockwise and to the left of the figure), so that the two components do not impact each other during any of the circuit overload trip modes. In this embodiment the latch  52  engages a yoke  37  that is part of the operating mechanism  36  (shown schematically), the interaction of the yoke and the rest of the operating mechanism being understood by those skilled in the art. Other previously described circuit breaker components including the operating handle  22 , circuit breaker housing  20 ,  20 A, fixed contact  30 , moving contact  32  and moving contact arm  34  are shown schematically. 
     The present invention can also be applied to various types of circuit breakers that incorporate trip latches.  FIGS. 16 and 17  depict schematically application of the present invention within an industrial-type molded case circuit breaker (MCCB) of the type shown and described in U.S. Pat. No. 6,274,833. The MCCB Includes a circuit breaker frame housing  200  that is coupled to a separable trip unit housing  210  so that trip units having different functional capabilities can be interchanged while the MCCB frame housing remains installed in its operating environment, such as a panel board, motor control center or other switchgear. The frame housing  200  includes at least one fixed contact  230 , one moving contact  232  and corresponding moving contact arm  234 . Pivotal operation of the moving contact arm  234  to control opening and closing of the contacts is performed by the operating mechanism  236 . As is known in the art, industrial circuit breakers such as MCCBs often are of multi-phase construction and typically have three phases with three sets of contacts coupled by a common cross bar (not shown) that is coupled to the operating mechanism. Handle  222  can be utilized to open and close the respective contacts  230 ,  232  as well as reset the circuit breaker after a fault trip. A generally S- or bell crank-shaped trip bar  270  that pivots about axis  270 A is an intermediate linkage member in the trip mechanism. In this exemplary MCCB embodiment, counter clockwise pivoting of the trip bar  270  causes the operating mechanism to release the contact arm(s)  234  to a contacts open position. 
     The removable trip unit housing  210  includes an short circuit/over current trip unit  250  that pivots the latch  252  about its pivoting axis  252 A that in turns pivots the trip bar  270  upon detection of a fault condition. The trip unit  250  may be electromechanical with thermal magnetic trip mechanisms previously discussed or it may be a purely electronic trip unit. The latch  252  includes a latch extension  254  that is attracted by electromagnet  220  when the electromagnet is energized by an electronic fault detector  267  through energizing leads  268 . The fault detector  267  as previously described may detect faults such as ground faults or arc faults. The electromagnet  220  is oriented outside the full range of pivoting motion of the latch  252  and its extension  254 , so as to assure that those respective components do not impact during any trip mode of circuit breaker operation. The electromagnet may have a fixed core construction of the type shown and described with reference to  FIG. 10  or a reciprocating core construction of the type shown and described with respect to  FIGS. 8-10 . As shown in  FIG. 17 , the latch extension  254  includes bent tab  255  that is aligned generally tangential to the radius of the latch  252  pivoting axis. Electromagnet  220  is oriented outboard of and laterally proximate to the bent tab  255 , so that the ferromagnetic core  206  is aligned to attract the latch  252  upon energization of the coil windings by the fault detection electronic unit  267  via the leads  268 , as previously described with the embodiment shown in  FIG. 7 . The electromagnet  220  may have a fixed ferromagnetic core  206 , because it is oriented to remain clear of the latch tab  255  through the full range of the latter&#39;s pivotal motion in all modes of operation. 
     In summary, the circuit breaker of the present invention utilizes parallel electronic fault detection and electromechanical fault detection through actuation of a common latch mechanism interface with the circuit breaker contacts operating mechanism. The latch interface for the electronic fault detector is an electromagnet that directly attracts the latch. 
     Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.