Patent Publication Number: US-6222143-B1

Title: Positive off toggle mechanism

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of electrical circuit breakers, and more particularly to a circuit breaker which indicates an OFF condition only when contacts are separated. 
     BACKGROUND OF THE INVENTION 
     In general the function of a circuit breaker is to electrically engage and disengage a selected circuit from 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. 
     There are two modes 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. 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. 
     To engage the operating contacts of the circuit breaker, the circuit breaker operating handle is used to activate the operating mechanism such that the movable contact(s) engage the stationary contact(s). A motor coupled to the circuit breaker operating handle can also be used to engage or disengage the operating contacts. The motor can be remotely operated. 
     A typical industrial circuit breaker will have a continuous current rating ranging from as low as 15 amps to as high as several thousand amps. The tripping mechanism for the breaker usually consists of a thermal overload release and a magnetic short circuit release. The thermal overload release operates by means of a bi-metallic element, in which current flowing through the conducting path of a circuit breaker generates heat in the bi-metal element, which causes the bi-metal to deflect and trip the breaker. The heat generated in the bi-metal is a function of the amount of current flowing through the bi-metal as well as for the period of time that that current is flowing. For a given range of current ratings, the bi-metal cross-section and related elements are specifically selected for such current range resulting in a number of different circuit breakers for each current range. 
     On occasion, one or more movable contacts may be inadvertently welded to their respective stationary contacts due to, for example, excessive arcing or overcurrent. When this happens, it is desirable for the handle to not be positionable in the OFF position as to do so would mislead workers into believing that equipment and circuits connected to the load terminals of the circuit breaker were not electrically powered when, in fact, they would be. 
     Thus, there is a need for a circuit breaker to have a handle which is not positionable in an OFF position when contacts are welded together. There is also a need for a circuit breaker to have a positive “OFF” handle position to alert a worker that the contacts are welded together, or are otherwise inseparable. 
     SUMMARY OF THE INVENTION 
     The present invention provides a positive “OFF” toggle mechanism for a molded case circuit breaker having “ON”, “OFF”, and “TRIPPED” conditions and corresponding handle positions. The circuit breaker includes a pair of contacts, one of which is coupled to an operating mechanism having a pivoting member. The positive “OFF” toggle mechanism includes a lower toggle member having a first end operatively coupled to the contact coupled to the operating mechanism and a second end coupled to a toggle pivot pin; an upper toggle member having a first end coupled to the toggle pivot pin and a second end in operative contact with a toggle pin mounted on the operating mechanism. The positive “OFF” circuit breaker further includes a catch member mounted on the pivoting member of the operating mechanism, with the catch member arranged to engage the second end of the upper toggle when the circuit breaker is in the welded condition and the pair of contacts remain together. 
     The present invention also provides a positive “OFF” toggle mechanism for a circuit breaker having an operating mechanism including a handle and a moveable contact arm, a trip bar, a line terminal, a load terminal and a cover. The positive “OFF” toggle mechanism includes a lower toggle bar, having a first and a second end, with the first end pivotally coupled to the movable contact arm. The toggle mechanism further includes an upper toggle bar, having a first end and a second end, with the second end pivotally coupled to the second end of the lower toggle bar and with the first end of the upper toggle bar having a cam finger. A pivot pin is mounted on the operating mechanism and aligned to engage the first end of the upper toggle bar. The toggle mechanism further includes a handle arm associated with the handle, with the handle arm having a cam surface aligned to selectively engage the cam finger of the upper toggle bar when the operating mechanism is in a welded position and the movable contact arm has not moved, wherein the operating mechanism is prevented from being moved to an “OFF” position. 
     The present invention further provides a molded case circuit breaker including a molded housing provided with a removable breaker cover, a first terminal and a second terminal mounted in the case, a contact electrically coupled to the first terminal, a moveable contact electrically coupled to the second terminal, and an operating mechanism having a pivoting member moveable between an “ON” position, an “OFF” position and a “TRIPPED” position, wherein the pivoting member is coupled to the moveable contact. The circuit breaker also includes an intermediate latching mechanism mounted in the housing and coupled to the operating mechanism, a trip unit having a trip bar and coupled to the moveable contact and the second terminal with the trip unit in selective operative contact with the intermediate latching mechanism; and an accessory socket formed in the removable breaker cover on either side of an opening for the pivoting member; with the accessory socket in communication with the housing and configured to accept a plurality of different types of accessories. The circuit breaker further includes an accessory cover sized to cover the accessory mounted in the accessory socket, and a positive “OFF” toggle mechanism. The positive “OFF” toggle mechanism includes a lower toggle bar having a first and a second end, with the first end pivotally coupled to the movable contact arm; an upper toggle bar, having a first end and a second end, with the second end pivotally coupled to the second end of the lower toggle bar and with the first end of the upper toggle bar having a cam finger; a pivot pin mounted on the operating mechanism with the pivot pin aligned to engage the first end of the upper toggle bar; and a handle arm associated with the handle. The handle arm is provided a cam surface aligned to selectively engage the cam finger of the upper toggle bar when the operating mechanism is in a tripped position and the movable contact arm has not moved, wherein the operating mechanism is prevented from being reset. 
     The present invention still further provides a circuit breaker including a molded housing including a base and a cover, a means for connecting a load to the circuit breaker, mounted in the housing; a means for connecting an electrical line to the circuit breaker; and a means for coupling electrically to the means for connecting an electrical line. The circuit breaker also includes a movable means for contacting the means for connecting an electrical line to a means for operating mounted in the housing coupled with the means for operating having a pivoting member movable between an “ON” position, an “OFF” position, and a “TRIPPED” position, with the pivoting member coupled to the movable means for contacting and with the means for operating coupled to an intermediate means for latching the means for operating. The circuit breaker further includes a means for tripping coupled to the movable means for contacting and the means for connecting a load with the intermediate means for latching, wherein the means for tripping includes a means for releasing under a short circuit condition and a means for releasing under an overload condition; and a means for preventing the pivoting member from moving to the “OFF” or a reset position when the movable means for contacting has not moved and the means for operating is in the “TRIPPED” position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric drawing of a molded case circuit breaker which includes an embodiment of the present positive “OFF” toggle mechanism. 
     FIG. 2 is a section view of the circuit breaker shown in FIG. 1 along the lines  2 — 2  and is used to describe the operation of the circuit breaker. 
     FIG. 3 is an exploded isometric drawing of the operating mechanism, contact structure, and bi-metal trip unit of the circuit breaker shown in FIG.  1 . 
     FIG. 4 is an illustration of the circuit breaker cover for the circuit breaker shown in FIG.  1 . 
     FIG. 5 is a side elevation of the circuit breaker shown in FIG. 1, wherein the contacts are operatively in an “ON” position. 
     FIG. 6 is a side elevation of the circuit breaker shown in FIG. 1, wherein the contacts are welded in an “ON” position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 generally illustrates a three phase molded case circuit breaker  10  of the type which includes an operating mechanism  40  having a pivoting member  13  with a handle  14 . The pivoting member  13  and handle  14  are moveable between an “ON” position, an “OFF” position, and a “TRIPPED” position. The exemplary circuit breaker  10  is a three pole breaker having three sets of contacts for interrupting current in each of the three respective electrical transmission phases. In the exemplary embodiment of the invention, each phase includes separate breaker contacts and a separate trip mechanism. The center pole circuit breaker includes an operating mechanism which controls the switching of all three poles of the breaker. Although an embodiment of the present invention is described in the context of the three phase circuit breaker, it is contemplated that it may be practiced in a single phase circuit breaker or in other multi-phase circuit breakers. 
     Circuit breaker  10  includes a positive “OFF” toggle mechanism  402 , described below, which prevents handle  14  from being repositioned to an “OFF” position when the operating mechanism  40  has responded to a “TRIP” condition but, due to arcing and/or overcurrent, a movable contact  42  has inadvertently been welded to a fixed contact  44  and circuit breaker  10  therefore remains “ON.” 
     Referring to FIG. 2, handle  14  is operable between the “ON” and “OFF” positions to enable a contact operating mechanism  40  to engage and disengage a moveable contact  42  and a stationary contact  44  for each of the three phases, such that the line terminal  18  and load terminal  16  of each phase can be electrically connected. The circuit breaker housing  12  includes three portions which are molded from an insulating material. These portions include a circuit breaker base  12   a , a circuit breaker cover  20  and an accessory cover  28  with breaker cover  20  and the accessory cover  28  having an opening  29  for the handle  14  of the pivoting member  13 . The pivoting member  13  and handle  14  move within the opening  29  during the several operations of the circuit breaker  10 . FIG. 2 is a cut away view of the circuit breaker  10  along the lines  2 — 2  shown in FIG.  1 . As shown in FIG. 2, the main components of the circuit breaker are a fixed line contact arm  46  and a moveable load contact arm  45 . It should be noted that another embodiment of the circuit breaker  10  has a movable line contact arm to facilitate a faster current interruption action. The load contact arms for each of the three phases of the exemplary breaker are mechanically connected together by an insulating cross bar member  55 . This cross bar member  55 , in turn, is mechanically coupled to the operating mechanism  40  so that, by moving the handle  14  from left to right, the cross bar  55  rotates in a clockwise direction and all three load contact arms  45  are concurrently moved to engage their corresponding line contact arms  46 , thereby making electrical contact between moveable contact pad  42  and stationary contact pad  44 . A trip device or trip unit  60  is mounted in the circuit breaker,  10  and coupled to the load terminal  16  and the movable contact arm  45  (see FIG.  2 ). The trip unit  60  includes a short circuit and thermal overload release. The short circuit release is facilitated by a magnetic element  64 . The thermal overload release is facilitated by a bimetallic element  62 . Further discussion of the operation of these elements is described below. 
     The operating mechanism  40  includes a cradle  41  which engages an intermediate latch  52  to hold the contacts of the circuit breaker in a closed position unless and until an over current condition occurs, which causes the circuit breaker to trip. A portion of the moveable contact arm  45  and the stationary contact bus  46  are contained in an arc chamber  56 . Each pole of the circuit breaker  10  is provided with an arc chamber  56  which is molded from an insulating material and is part of the circuit breaker  10  housing  12 . A plurality of arc plates  58  is maintained in the arc chamber  56 . The arc plates facilitate the extension and cooling of the arc formed when the circuit breaker  10  is opened while under a load and drawing current. The arc chamber  56  and arc plates  58  direct the arc away from the operating mechanism  40 . 
     The exemplary intermediate latch  52  is generally Z-shaped having an upper leg which includes a latch surface that engages the cradle  41  and a lower leg having a latch surface which engages a trip bar  54 . The center portion of the Z-shaped intermediate latch element  52  is angled with respect to the upper and lower legs and includes two tabs which provide a pivot edge for the intermediate latch  52  when it is inserted into the mechanical frame  51 . As shown in FIG. 2, the intermediate latch  52  is coupled to a torsion spring  53  which is retained in the mechanical frame  51  by the mounting tabs of the intermediate latch  52 . The torsion spring  53  biases the upper latch surface of the intermediate latch  52  toward the cradle  41  while at the same time biasing the trip bar  54  into a position which engages the lower latch surface of the intermediate latch  52 . The trip bar  54  pivots in a counter clockwise direction about an axis  54   a , responsive to a force exerted by a bimetallic element  62 , during, for example, a long duration overcurrent condition. As the trip bar  54  rotates, in a counter clockwise direction, the latch surface on the upper portion of the trip bar disengages the latch surface on the lower portion of the intermediate latch  52 . When this latch surface of the intermediate latch  52  is disengaged, the intermediate latch  52  rotates in a counter clockwise direction under the force of the operating mechanism  40 , exerted through a cradle  41 . In the exemplary circuit breaker, this force is provided by a tension spring  50 . Tension is applied to the spring when the breaker toggle handle  14  is moved from the open position to the closed position. More than one tension spring  50  may be utilized. 
     As the intermediate latch  52  rotates responsive to the upward force exerted by the cradle  41 , it releases the latch on the operating mechanism  40 , allowing the cradle  41  to rotate in a clockwise direction. When the cradle  41  rotates, the operating mechanism  40  is released and the cross bar  55  rotates in a counter clockwise direction to move the load contact arms  45  away from the line contact arms  46 . 
     During normal operation of the circuit breaker, current flows from the line terminal  18  through the line contact arm  46  and its stationary contact pad  44  to the load contact arm  45  through its contact pad  42 . From the load contact arm  45 , the current flows through a flexible braid  48  to the bimetallic element  62  and from the bimetallic element  62  to the load terminal  16 . (See FIG. 3) When the current flowing through the circuit breaker exceeds the rated current for the breaker, it heats the bimetallic element  62 , causing the element  62  to bend towards the trip bar  54 . If the over current condition persists, the bimetallic element  62  bends sufficiently to engage the trip bar surface. As the bimetallic element engages the trip bar surface and continues to bend, it causes the trip bar  54  to rotate in a counter clockwise direction releasing the intermediate latch  52  and thus unlatching the operating mechanism  40  of the circuit breaker. 
     FIG. 3 is an exploded isometric drawing which illustrates the construction of a portion of the circuit breaker shown in FIG.  2 . In FIG. 3 only the load contact arm  45  of the center pole of the circuit breaker is shown. This load contact arm  45  as well as the contact arms for the other two poles, are fixed in position in the cross bar element  55 . As mentioned above, additional poles, such as a four pole molded case circuit breaker can utilize the same construction as described herein, with the fourth pole allocated to a neutral. The load contact arm  45  is coupled to the bimetallic element  62  by a flexible conductor  48  (e.g. braided copper strand). As shown in FIG. 3, current flows from the flexible conductor  48  through the bimetallic element  62  to a connection at the top of the bimetallic element  62  which couples the current to the load terminal  16  through the load bus  61 . The load bus  61  is supported by a load bus support  63 . It should be noted that more than one flexible conductor  48  may be utilized. 
     In the exemplary circuit breaker  10 , the cross bar  55  is coupled to the operating mechanism  40 , which is held in place in the base or housing  12  of the molded case circuit breaker  10  by a mechanical frame  51 . The key element of the operating mechanism  40  is the cradle  41 . As shown in FIG. 3, the cradle  41  includes a latch surface  41   a  which engages the upper latch surface in the intermediate latch  52 . The intermediate latch  52  is held in place by its mounting tabs which extend through the respective openings  51   a  on either side of the mechanical frame  51 . In the exemplary embodiment of the circuit breaker, the two side members of the mechanical frame  51  support the operating mechanism  40  of the circuit breaker  10  and retain the operating mechanism  40  in the base  12   a  of the circuit breaker  10 . 
     FIG. 4 illustrates the breaker cover  20 . The breaker cover  20 , in the preferred embodiment, has two accessory sockets  22  formed in the cover  20 , with one accessory socket  22  on either side of the opening  29  for the pivoting member  13  and handle  14 . The breaker cover  20  with the accessory sockets  22  or compartments can be formed, usually by well known molding techniques, as an integral unit. The accessory socket  22  can also be fabricated separately and attached to the breaker cover  20  by any suitable method such as with fasteners or adhesives. The breaker cover  20  is sized to cover the operating mechanism  40 , the moveable contact  42  and the stationary contact  44 , as well as the trip mechanism  60  of the circuit breaker  10 . The breaker cover has an opening  29  to accommodate the handle  14 . 
     Each accessory socket or compartment  22  is provided with a plurality of openings  24 . The accessory socket openings  24  are positioned in the socket  22  to facilitate coupling of an accessory  80  with the operating mechanism  40  mounted in the housing  12 . The accessory socket openings  24  also facilitate simultaneous coupling of an accessory  80  with different parts of the operating mechanism  40 . Various accessories  80  can be mounted in the accessory compartment  22  to perform various functions. Some accessories, such as a shunt trip, will trip the circuit breaker  10 , upon receiving a remote signal, by pushing the trip bar  54 , causing release of the mechanism latch  52  of the operating mechanism  40 . The shunt trip has a member protruding through one of the openings in the accessory socket  22  and engages the operating mechanism  40 , via the trip bar  54 . Another accessory, such as an auxiliary switch, provides a signal indicating the status of the circuit breaker  10 , e.g. “on” or “off”. When the auxiliary switch is nested in the accessory socket  22 , a member on the switch assembly protrudes through one of the openings  24  in the socket  22  and is in engagement with the operating mechanism  40 , typically the cross bar  55 . Multiple switches can be nested in one accessory socket  22  and each switch can engage the operating mechanism through a different opening  24  in the socket  22 . 
     FIG. 5 shows positive “OFF” toggle mechanism  402  in an “ON” condition of operation. Movable load contact  42  abuts fixed line contact  44 , and electricity is thereby conducted from line terminal  18  through contact arm  45  and crossbar  55  to load terminal  16 . Other devices included in circuit breaker  10  (e.g., bimetallic element  62  and braid  48 , shown in FIG. 2) are deleted from FIG. 5 for clarity. 
     Movable contact arm  45  is pivotally secured to crossbar  55  at a pivot  43 , for being repositioned between “ON,” “OFF,” and “TRIPPED” positions. Contact arm  45  may be placed in the “ON” position by use of handle  14 , in which event an upper toggle bar  410  and a lower toggle bar  404  will be disposed in the positions shown in FIG.  5 . Upper pivot  416  (which rotationally couples a first end  412  of upper bar  410  to cradle  41  of operating mechanism  40 ) is aligned with an intermediate pivot  418  (which rotationally couples a second end  414  of upper bar  410  to a second end  408  of lower bar  404 ) and with a lower pivot  420  (which rotationally couples a first end  406  of lower bar  404  to contact arm  45 ). The lower end of spring  50  (shown in FIG. 2) is secured to intermediate pivot  418 , and biases intermediate pivot  418  against a stop (not shown) to maintain toggle mechanism  402  in stable disposition as shown. A second lower toggle bar and a second upper toggle bar configured and operated identically as the upper toggle bar  410  and the lower toggle bar  404  as described above, can be mounted on the other side of the handle  14 . The symmetry of the multiple toggle bar sets on each side of the handle  14  equalizes the forces on the handle  14 . 
     When moving contact arm to the “OFF” position by moving handle  14  to the left, spring  50  changes its angle with respect to upper bar  410  and lower bar  404  and “bends” the pair toward the left at intermediate pivot  418 . Because contact arm  45  is also changing position at the same time, toggle mechanism  402  “folds” quickly and readily. 
     When circuit breaker  10  encounters a condition requiring breaking of the circuit (e.g., overcurrent) and trips, or is intentionally tripped by use of an accessory  80 , operation of toggle mechanism  402  is essentially as described above. Handle  14  is moved to the left, contact arm  45  is moved upward and counterclockwise, and toggle mechanism  402  is folded quickly and readily. 
     In an overcurrent, or other circuit breaking condition, a trip device  60  repositions trip bar  54  and unlatches cradle  41 . Spring  50  (shown in FIG. 2) causes cradle  41  to pivot upward. A pivot pin  416   a  of pivot  416  is affixed to cradle  41  at a notch  416   b  of first end  412  of upper bar  410 , and this pulls pivot pin  416   a  out of notch  416   b , disconnecting toggle mechanism  402  from operating mechanism  40  and handle  14 . Handle  14  is moved by operating mechanism  40  to its “TRIPPED” position. 
     When, however, handle  14  is actuated toward the OFF position and movable contact  42  has been welded to fixed contact  44 , contact arm  45  will be held in the closed position by the weld and will not open the circuit. It is highly desirable that, in that event, handle  14  not go to the “OFF” position, as the welded contacts prevent it being truly “off” but its visual “OFF” position could dangerously mislead a worker to expect power to be removed from equipment and circuits connected to load terminals  16 . 
     Therefore, upper bar  410  is provided a projecting cam finger  422  and handle  14  is provided an arm  14   a  having a cam surface  424 . As shown in FIG. 6, when handle  14  is repositioned toward its “OFF” position but contact arm  45  does not rise or rotate about pivot  43  of crossbar  55 , toggle mechanism  402  does not fold as quickly or completely as it otherwise would. This causes cam finger  422  to encounter and abut cam surface  424 , and effectively interferes with, thereby preventing, additional travel of handle  14  toward its “OFF” position. In the preferred embodiment, pivoting member  13 , handle  14 , and handle arm  14   a  are one piece. 
     While the embodiments illustrated in the figures and described above are presently preferred, it should be understood that these embodiments are offered by way of example only. Invention is not intended to be limited to any particular embodiment, but it is intended to extend to various modifications that nevertheless fall within the scope of the intended claims. For example, it is also contemplated that the trip mechanism having a bi-metal trip unit or an electronic trip unit with a load terminal be housed in a separate housing capable of mechanically and electrically connecting to another housing containing the operating mechanism and line terminal, thereby providing for a quick and easy change of current rating for an application of the circuit breaker contemplated herein. Modifications will be evident to those with ordinary skill in the art.