Abstract:
An apparatus and method for restricting auxiliary latch movement within a tripped circuit breaker. An auxiliary latch is held in a closed state and is biased into an open state. When the trip bar is activated in response to an overload condition, it releases the auxiliary latch which pivots to the open state. The cradle is released and pivots to disengage the breaker contact. Tabs on the cradle and auxiliary latch cooperatively interlock to limit auxiliary latch movement until the latch is properly reset.

Description:
RELATED APPLICATION INFORMATION 
       [0001]    This application claims priority to provisional application Ser. No. 61/029,588 filed on Feb. 19, 2008 the contents of which are incorporated herein by reference thereto. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    This disclosure relates generally to the field of electrical circuit breakers and more particularly to a mechanical interlock feature that engages upon circuit breaker tripping. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, circuit breakers are employed to selectively engage a branch circuit to an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. The circuit breaker provides protection against persistent overcurrent conditions and against the very high currents produced by short circuits. Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact. 
         [0006]    There are several ways by which the operating mechanism for the circuit breaker can disengage the operating contacts: the circuit breaker operating handle can be used to activate the operating mechanism; or a tripping mechanism, responsive to unacceptable levels of current carried by the circuit breaker, can be used to activate the operating mechanism; or auxiliary devices can be used to trip the circuit breaker thereby move the movable contact. For many circuit breakers, the operating handle is coupled to the operating mechanism such that when the tripping mechanism activates the operating mechanism to separate the contacts, the operating handle moves to a fault or tripped position. 
         [0007]    When an overload condition occurs, the trip bar is rotated away allowing the trip bar latch to disengage the auxiliary latch. With the auxiliary latch free, the cradle is able to pivot thereby disengaging the breaker contacts. This sequence of event is referred to as the breaker tripping. In order for the breaker to be safely reset, the auxiliary latch must be held open until the cradle is first reset. According to the prior art, a variety of heavy springs and dampers are used to keep the auxiliary latch from resetting prematurely. In addition a push to trip button could be used to trip the mechanism again. 
         [0008]    The disadvantage of the prior art systems are that there is no guarantee that the auxiliary latch will not reset after the breaker is tripped. In addition, using some type of damper will add extra cost to the mechanism. Using a heavier torsion spring could make the auxiliary latch rebound thereby allowing itself to reset with the trip bar latch. The cradle could not be reset in this case as it would strike the top of the auxiliary latch. 
         [0009]    Accordingly, there is a need for a secure feature that will prevent the auxiliary latch from resetting prematurely. 
       SUMMARY OF THE INVENTION 
       [0010]    An apparatus for restricting auxiliary latch movement within a tripped circuit breaker having an auxiliary latch held in a closed state and being biased into an open state. A cradle disengages the breaker contact when the auxiliary latch moves into the open state. An interlock limits the auxiliary latch from exiting the open state until the cradle is properly reset. The interlock comprises complementary interfering parts on the auxiliary latch and the cradle which physically prevent the auxiliary latch from exiting the open state when the cradle is disengaged. One interfering part is an auxiliary latch tab which is disposed on said auxiliary latch. Another interfering part is a cradle tab which is disposed on said cradle. 
         [0011]    The cradle pivots to a disengaged position where the cradle tab is disposed at a radial distance R from the auxiliary latch axis, corresponding to the radial location of the auxiliary latch tab, thereby preventing the auxiliary latch from pivoting out of its open state. The cradle synchronously pivots with an auxiliary latch surface for selective meshing and unmeshing, with the auxiliary latch tab and the cradle tab cooperatively interlocking in the unmeshed state to maintain said auxiliary latch in proper rotational alignment for subsequent meshing upon cradle resetting. A trip bar latch holds said auxiliary latch in a closed state until the breaker trips. The interlock restricts said auxiliary latch from pivoting back into the closed state thereby avoiding accidental trip bar reset. 
         [0012]    Another embodiment of the invention includes a method of restricting auxiliary latch movement within a tripped circuit breaker, including selectively meshing an auxiliary latch with a cradle via synchronous pivoting on respective parallel axes. Next, the auxiliary latch pivots out of mesh with the cradle allowing it to disengage the breaker contact. The auxiliary latch and the cradle are interlocked to prevent the auxiliary latch from exiting the open state until the cradle is reset. 
         [0013]    These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]    This disclosure will present in detail the following description of preferred embodiments with reference to the following figures wherein: 
           [0015]      FIG. 1  is a side schematic view of a circuit breaker interlock feature in accordance with one illustrative embodiment; 
           [0016]      FIG. 2  is an isometric view of the auxiliary latch tab in accordance with one illustrative embodiment; and 
           [0017]      FIGS. 3A ,  3 B and  3 C are a series of side schematic views of a circuit breaker in a tripped condition in accordance with one illustrative embodiment. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0018]    The present invention provides devices and methods relating to an interlock feature which prevents the auxiliary latch from improperly reengaging the trip bar latch. It is used in a breaker mechanism to restrict the auxiliary latch from reengaging after the breaker has been tripped, i.e. to prevent a nuisance relatch. If the auxiliary latch is reengaged before the cradle is in place, then the breaker cannot be reset. In  FIG. 1 , the circuit breaker  148  is set in the on position. When an overload condition occurs a series of actions lead to the tripped condition shown in  FIG. 3A . More particularly, when trip bar  140  is tripped, the trip bar latch  142  releases auxiliary latch  100  which pivots to the open position wherein cradle  160  is free to move into the disengaged state. Movement of the auxiliary latch  100  back into the closed position should be initiated when the cradle  160  is reset to the engaged position  180 . However, auxiliary latch rebound could follow a breaker trip, whereby trip bar  140  gets reset prematurely, i.e. before the latch is reengaged, as shown in  FIG. 3C . The interlock  130  of  FIG. 3B  restricts the movement of auxiliary latch in the tripped condition, until the cradle is reset. 
         [0019]    The present principles will be described in terms of single pole circuit breakers employed for residential applications. However, the embodiments described are not limited to the illustrative example and may be employed in other configurations for other applications. For example, the present principles are equally applicable to two or more pole mechanisms, breakers that include push to test features, any size breakers, multiple breaker systems in a single housing, etc. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. For example, reference to clockwise and counter clockwise are provided for explanatory purposes and are non-limiting. The alternate or opposite directions are intended to be included within the concepts and mechanisms described herein. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure). 
         [0020]    Thus, for example, it will be appreciated by those skilled in the art that the drawings presented herein represent conceptual views of illustrative system components embodying the principles of the invention. Referring now in specific detail to the drawings in which like reference numerals identify similar or identical elements throughout the several views, and initially to  FIG. 1 , there is shown a schematic internal view of an auxiliary latch  100 , a trip bar  140  and a cradle  160  of a circuit breaker  148  set in the on position. When an overload condition occurs a trip bar initiates a sequence of movements that shut off power through the breaker and place it in a tripped condition. The final tripped condition is shown in  FIG. 3A . A problem with certain prior art designs can lead to auxiliary latch rebound, where the trip bar gets reset before the cradle is reengaged, as shown in  FIG. 3C . The interlock feature  130 , according to an embodiment of the invention, keeps the auxiliary latch in its open position until the cradle initiates movement of the auxiliary latch back to the closed position. 
         [0021]    In general, all breakers have mechanisms that engage and disengage the electrical contacts when operated by the handle. In addition to those two functions, the mechanism must be able to trip automatically when an overload condition occurs. The part called the cradle engages with the auxiliary latch. The auxiliary latch in turn engages a trip bar latch. When the trip bar is rotated in a first direction the trip bar latch disengages the auxiliary latch allowing the cradle to push the auxiliary latch in a second direction and disengage the breaker contacts. This action is referred to as the breaker tripping. 
         [0022]    When the breaker is reset after being tripped the operator moves the handle which is attached to the cradle. The cradle than engages the auxiliary latch moving it in the first direction to the reset position allowing the trip bar latch to engage the auxiliary latch thus locking the cradle in place. Once the cradle is locked in place the breaker can be turned to the on position reengaging the electrical contacts. The function of the invention is to keep the auxiliary latch from resetting against the trip bar latch before the cradle is reset. 
         [0023]    If the auxiliary latch is reset before the cradle is reset then the cradle will run into the auxiliary latch, and the breaker will not be able to be reset. In prior art devices, a variety of heavy springs and dampers are used to keep the auxiliary latch from resetting. In addition a push to trip button could be used to trip the mechanism again. The disadvantages of the prior art systems are that there is no guarantee that the auxiliary latch will not reset after the breaker is tripped. In addition using some type of damper will add extra cost to the mechanism. Using a heavier spring could make the auxiliary latch rebound thereby allowing itself to reset with the trip bar latch. The cradle could not be reset in this case as it would strike the top of the auxiliary latch. 
         [0024]    The advantage of the invention is that there is no physical way the auxiliary latch can reset while the breaker is tripped. The tab on the auxiliary latch engages a tab on the cradle. The cradle has to be reset before it is possible for the auxiliary latch to be reset. In addition to preventing reset, the tab on the auxiliary latch is bent with a radius which improves the trip characteristics of the mechanism by removing the sharp edge off of the auxiliary latch. 
         [0025]    By way of comparison there is shown schematically several components that interact when a breaker transitions from the on or reset position to the tripped position. The “on” position is shown in  FIG. 1  wherein trip bar  140  is in the reset condition  152 ; the auxiliary latch  100  is in the closed state  122 ; and the cradle  160  is in the engaged position  180 . The “tripped” position is shown in  FIG. 3A  wherein trip bar  140  is in the tripped condition  150 ; auxiliary latch  100  is in the open state  120 ; and cradle  160  is in the disengaged position  182 . 
         [0026]    Typically, a reset occurs by manual movement of a handle which is connected to cradle  160  and extends outside of the circuit breaker  148  housing. Starting from the orientation of  FIG. 3A , cradle  160  is pivoted about its axis, formed as an axle  162 , clockwise toward the engaged position  180 . The free end of the cradle contacts the lower plate  114  of the auxiliary latch  100  which is mounted for pivoting movement about its axis, formed as an axle  102 . Auxiliary latch  100  will pivot counterclockwise to the closed state  122  where trip bar latch  142  will hold the mechanism in the reset condition  152 . Trip bar latch  142  holds auxiliary latch in a closed state  122  against the force of spring  104  which is biasing auxiliary latch toward the open state  120 . While a torsion spring is shown, various types of springs like coil springs and other suitable devices may be used to provide a bias of appropriate force. 
         [0027]    Since axles  162  and  102  are parallel, the respectively mounted cradle  160  and auxiliary latch  100  interact via synchronous meshing, like gears. The free end of cradle  160  functions like one gear tooth, while auxiliary latch tab  110  and lower plate  114  function like two gear teeth. The teeth-like portions of the cradle and the auxiliary latch will selectively mesh ( FIG. 1 ) and unmesh ( FIG. 2A ). When the components are unmeshed, they must remain in a certain orientation ( FIG. 3A ) to accommodate resetting of the latch. Sometimes, during a breaker trip, the biasing force  104  causes the auxiliary latch to rebound to an extent that trip bar latch  142  is reengaged, as shown in  FIG. 3C . A problem arises because the cradle cannot be reset. The cradle tooth, is out of sync with the teeth on the auxiliary latch. Instead of meshing within auxiliary latch, the free end of the cradle is boxed out. 
         [0028]    The interlock  130  according to an embodiment of the invention is shown in  FIG. 3B . The interlock is a combination of interfering tabs formed on the auxiliary latch and the cradle to restrict the movement of the auxiliary latch under a tripped condition. An auxiliary latch tab  110  is shown contacting a cradle tab  170 . When cradle  160  is in the disengaged position  182 , the cradle tab  160  resides in a path of auxiliary latch tab  110  to prevent it from pivoting in to the problematic orientation shown in  FIG. 3C . By limiting rotation of auxiliary latch  100 , the trip bar latch is prevented from accidentally resetting. 
         [0029]    An exemplary, cross-sectional view of the back half of auxiliary latch  100  is shown in  FIG. 2 . Auxiliary latch is a open box-like device which wraps around four sides, with three of those sides being shown in the illustration. Starting at the bottom, a lower plate  114  is shown which wraps upwardly to a first side wall  116   a  in which the axle  102  is mounted. First side wall  116   a  the wraps around to the top which includes a lip  108 . In the prior art devices, lip  108  extends across the entire top before wrapping downwardly into the second side wall (not shown for the sake of clarity). The second side wall includes a second axle  102  mounting aperture. 
         [0030]    The disadvantage of lip  108  is clearly shown in  FIG. 3C . When auxiliary latch becomes unmeshed from cradle  160  it is susceptible to over rotation in the counter-clockwise direction. Lip  108  can catch underneath the free end of cradle  170 . According to one embodiment of the invention, the top side of auxiliary latch is provided with a radius surface  112  that extends smoothly into an auxiliary latch tab  110 . Auxiliary latch tab extends in a generally radial direction outwardly from axis  102 . A further aspect of the invention is the addition of cradle tab  170 . 
         [0031]    As can be seen in  FIG. 3B , tabs  110  and  170  interlock against each other to restrict auxiliary latch  100  from pivoting into engagement with trip bar latch  142 . Upon reset, the breaker handle is able to pivot cradle  160  past tab  110  into its meshed position within the box of the auxiliary latch. Cradle tab  170  will then contact lower plate  114 , pivoting the auxiliary latch to the closed state  122 , as shown in  FIG. 1 . During an overload condition, the radius surface  112  improves trip characteristics by eliminating the sharp edge of lip which was previously present. 
         [0032]    Having described preferred embodiments for cradle and auxiliary latch interlocks for circuit breakers (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as outlined by the appended claims. Having thus described the invention with the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.