Abstract:
A stab assembly ( 41 ) in which a spring clip ( 24 ) and a conductor member ( 16 ) define a pair of engagement surfaces for engaging a stab blade ( 12 ). The conductor member ( 16 ) has an opening ( 34 ) to allow for the insertion of an extended surface of the spring clip ( 24 ). Once in position, the spring clip ( 24 ) and conductor member ( 16 ) are frictionally engaged and define a channel ( 126 ) that will accept and hold a stab blade ( 12 ). The stab assembly ( 14 ) is retained within a molded case circuit breaker ( 10 ) and provides electrical contact between a bus bar and the circuit breaker.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to electrical distribution equipment, and more particularly to a stab assembly for arc fault circuit breakers that are installed in load centers. 
     Arc fault circuit breakers are well known, and are used throughout electrical distribution systems to interrupt electrical power supplied to protected loads by electrical busway systems. These circuit breakers function as a manual switch, whereby the breakers disconnect or connect electrical power to the load equipment they are protecting when they are manually opened or closed. The circuit breakers are also equipped with a tripping unit that is capable of automatic interruption and isolation of the protected load from the bus upon the sensing of an electrical fault such as over current and arc-fault conditions. The circuit breaker enclosure, which is generally a molded plastic case, houses the tripping unit. The tripping unit monitors the circuit, and opens the circuit breaker if a fault condition occurs. 
     Circuit breakers are located in load centers, which contain a power bus and a plurality of cubicles, and which are designed to accept one or more circuit breakers. The cubicles in the load centers function to properly locate and structurally support the circuit breakers. When it is necessary to protect a new load, a circuit breaker is added to an available cubicle in a load center, and conductors are installed from the load to the circuit breaker. Circuit breakers may readily be removed and relocated within the load center as needed to properly supply the protected circuits with electrical current. Because of the diversity of power requirements and associated protection required by different loads, the size and configuration of each circuit breaker may vary. 
     Although the circuit breaker rating and configuration may vary among the loads connected to the circuit breakers in the load center, each circuit breaker must be configured so as to allow secure insertion into a cubicle in the load center. Proper insertion requires physical contact between the bus and the circuit breaker so that current can pass through the circuit breaker to the load. 
     Circuit breakers physically mate with stab blades that are electrically connected to the load center. The stab blades conduct the current from the load center to a fixed contact on the circuit breaker. These stab blades are short, stiff conducting metal bars that center the circuit breaker, provide physical support for the circuit breaker, and provide a conducting surface that allows current to flow from the load center to the circuit breaker. The circuit breaker requires a snug fit between the stab blade and the circuit breaker fixed contact in order to function properly. If the fit is not snug, hot spots can occur on the stab blade or fixed contact, and arcing between the stab blade and the fixed contact can result. Hot spots and arcing cause degradation of the circuit breaker, the stab, and/or the load center. 
     Typical stab assembly designs use a spring plug-in connection to a central stab blade to connect the circuit breaker to the load center. These designs do not lend themselves to be used except in either a right hand (the contact is located to the right of the stab blade), or a left hand configuration (the contact is located to the left of the stab blade). Two separate configurations require at least four separate parts: typically, a left contact, a left spring, a right contact, and a right spring. 
     Further, the assembly process precludes automated pre-assembly because the stab assembly falls apart unless assembled in the circuit breaker case where the parts are trapped. In addition, the prior art does not fully utilize economies to be gained from using common parts. 
     SUMMARY OF THE INVENTION 
     In an exemplary embodiment, the present invention comprises a circuit breaker stab assembly having a contact, the contact having a contact top portion and a conductor member angularly offset from the contact top portion. The contact top portion and the conductor member define an aperture. A spring clip in the stab assembly preferably has a spring clip top portion with a first surface and a second surface extending from the first surface. A first extension is preferably angularly offset from the first surface and a second extension angularly offset from the second surface, with the second extension extending through the aperture in the contact. Further, the second extension is preferably in intimate engagement with the conductor member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a circuit breaker, including a stab assembly embodying the present invention; 
     FIG. 2 is a perspective view of the stab assembly of FIG. 1; 
     FIG. 3 is a side elevational view of the stab assembly of one embodiment of the present invention, illustrating components in a disassembled condition; and 
     FIG. 4 is a side elevational view of the stab assembly of FIG. 3, illustrating components in an assembled condition. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, an exemplary embodiment of a circuit breaker prior to insertion into a load center is shown generally at  10  in relation to a stab blade  12 . The stab blade  12  is in a fixed location within a cubicle (not shown) of a load center. 
     The circuit breaker  10  provides an electrical current path from an electrical bus via stab blade  12 , to a protected load when a movable contact arm  17  is in a closed position. The movable contact arm  17  can be manually set to the closed position, and will move to an open position if a current fault is detected in the circuit. The movable contact arm  17  may also be manually switched to the open position. 
     A movable contact  19  is disposed on movable contact arm  17 , and is controlled either by electronic controls located within the circuit breaker housing  13  of the circuit breaker  10 , or a manual switch  11  protruding from the circuit breaker housing  13 . A stab assembly  14  is located inside the circuit breaker housing  13  approximate an upper end  15 , and is disposed between the movable contact  19  and the stab blade  12 . Stab assembly  14  provides an electrical connection between movable contact and stab blade  12 , when movable contact arm  17  is in the closed position. 
     Referring now to both FIG.  1  and FIG. 2, an exemplary embodiment of an assembled stab assembly is shown generally at  14 . The stab assembly comprises a contact  18  and a spring clip  24  that are disposed in intimate and secure contact by friction. The stab assembly  14  is positioned within the housing of the circuit breaker  10  with the spring clip  24  and the contact  18  accessible through a centrally located opening in the circuit breaker upper end  15 . The opening in the circuit breaker  10  allows the stab blade  12  to enter a channel  26  between the spring clip  24  and the contact  18 . Stab blade  12  is frictionally engaged within channel  26 , thereby providing the electrical connection between stab blade  12  and stab assembly  14 . 
     Contact  18  comprises a contact top portion  20 , a contact arm  22 , and the conductor member  16 , which is adapted to receive the spring clip  24 . When assembled, the conductor member  16  and the spring clip  24  define the channel  26  for accepting the stab blade  12 . 
     The contact arm  22  extends downward from the contact top portion  20 , and is further aligned generally perpendicular to the conductor member  16 . The contact top portion  20  is disposed between the conductor member  16  and contact arm  22 , with both the conductor member  16  and the contact arm  22  depending from the contact top portion  20 . A tang  72  extends from an end  74  of the contact top portion  20  approximate the contact arm  22 . A generally cylindrical contact protrusion  40  is attached to an outer surface  42  of the contact arm  22  proximate to a distal end  76  of the contact arm  22 . Contact protrusion  40  contacts movable contact  19  when movable contact arm  17  is in the closed position, thereby creating the electrical connection between stab assembly  14  and movable contact  19 . 
     The conductor member  16 , which has an outer surface  28 , extends generally perpendicularly downward from the contact top portion  20 . The conductor member  16  steps outwardly at the outer surface  28  from which it then extends further downward and forms a channel wall  30 . An inward extension  32  of the conductor member  16  at an entrance  64  to the channel  26  provides a chamfered surface for guiding the stab blade  12  into the channel  26 . 
     An aperture  34  is defined at the boundary between the contact top portion  20  and the conductor member  16 . The aperture  34  is sized to allow the spring clip  24  to enter the aperture  34  in order to position the spring clip  24  in locking relationship with the contact  18 . A knee channel  36  is defined in the inner surface  70  of the conductor member  16 . The knee channel  36  is preferably rectangular or a similar geometry and is laterally positioned on the opposite side of the conductor member  16  from the channel wall  30 , extending along the inner surface  70 . The knee channel  36  has a predetermined width and depth that allow the knee channel to engage a knee  38  (see FIG. 3) of the spring clip  24 . 
     Referring now to FIGS. 3 and 4, the spring clip  24  consists of a unitary conducting material shaped to cooperate with the conductor member  16  of the contact  18  to form the channel  26  when assembled with the contact  18 . The spring clip  24  comprises a spring clip top portion  44 , a first extension  50  and a second extension  52 . 
     The spring clip top portion  44  of the spring clip  24  comprises a rectangular planar first surface  54  and a narrow rectangular planar second surface  56  extending therefrom. The second surface  56  is a predetermined size to pass through the aperture  34  of the contact  18 . The first surface  54  includes a downward bend  48  located at the boundary between the first surface  54  and second surface  56 . A first surface  58  of the bend  48  faces toward the outer surface  28  of the conductor member  16 , providing a detent which both supports and positions the spring clip  24  in contact with the conductor member  16 . 
     The first extension  50  of the spring clip  24  having a first surface  60  extends generally perpendicularly downward from the first surface  54  of the spring clip top portion  44  opposite the second surface  46  of bend  48 . The first extension  50  depends angularly inward at the first surface  60 , and then extends further downward forming a channel wall  62 . A spring tab  66  extending from the first extension  50  at the entrance  64  of channel  26  provides a chamfered surface extending outward for guiding the stab blade  12  into the channel  26 . The first extension  50  of the spring clip  24  is generally the same width as the conductor member  16  of the contact  18 . 
     The second extension  52  of the spring clip  24  depends perpendicularly downward from the second surface  56  of the spring clip top portion  44  opposite the first surface  58  of bend  48 . The second extension  52  of the spring clip  24  is generally the same width as the second surface  56  of the spring clip top portion  44  of the spring clip  24 , both being sized to pass into and through the aperture  34 . The second extension  52  includes an inward knee  38  distally located from the spring clip top portion  44 . 
     Referring now to FIG. 3, before attachment, the spring clip  24  is in its unstrained configuration. With the spring clip  24  in its unstrained configuration, the entrance  64 ′ at the channel wall  62  of the first extension  50  is positioned at a sufficient offset (e.g. about 5° or another angle appropriate with the particular geometry) from the entrance  64  of the channel  26  after it is assembled. The knee  38  is similarly sufficiently offset (e.g. by approximately 5°) for being accepted into the aperture  34  in the contact top portion  20  and for further acceptance into the knee channel  36 . 
     With the 5° offset, for example, the surface  58  of the bend  48  contacts the outer surface  28  of the conductor member  16  with the knee  38  snapping into the knee channel  36  thereby forming channel  26 , which has generally parallel walls  30 ,  62 . The magnitude of the frictional force of the stab channel  26  on the stab blade  12  is proportional to the displacement of the spring tab  66  by the stab blade  12 . The size and specific geometry of channel  26  can change according to size and geometry of stab blade  12 , with a typical size being about 0.03 inches to about 0.09 inches thick and about 0.2 to about 0.4 inches deep. 
     An exemplary embodiment of the assembled stab assembly is shown in FIG.  4 . Knee channel  36  is positioned to engage the knee  38  when the stab assembly  14  is fully assembled. The surface  58  of the bend  48  is in contact with the outer surface  28  of the conductor member  16 , while the knee  38  snaps into the knee channel  36  and is retained in the knee channel  36  after the spring clip  24  and the contact  18  are assembled. 
     A channel wall  62  of the first extension  50  defines a stab channel  26  with the channel wall  30  of the conductor member  16 . Stab channel  26  comprises a gap “G” serving as a lead-in for the stab blade  12  when the stab assembly  14  is assembled. The width of the stab channel  26  is less than the thickness of the stab blade  12 , and the stab channel  26  frictionally engages the stab blade  12 . The strength of the frictional engagement is proportional to the displacement of the first extension  50  of the spring clip  24  upon inserting the stab blade  12 . The strength of the frictional engagement and the size of the gap is thereby determined by the position of the knee  38 , the location of the surface  58  of the bend  48 , the location of the channel wall  62  of the first extension  50  of the spring clip  24 , and the length of the stab channel  26 . 
     The contact  18  is constructed from hard, rigid, conductive material to provide a bearing surface when the stab blade  12  is urged against the conductor member  16  by the spring tension. The material also provides structural support for a contact protrusion  40  disposed on the contact arm  22 . Possible contact materials include metals such as copper and others, as well as alloys and composites thereof. Possible spring clip materials include metals such as steel, ferrous materials, and alloys and composites thereof, with spring steel and spring bronze preferred. 
     It is to be appreciated that, when assembled, the second extension  52  of the spring clip  24  is elastically deformed, which results in a tensile force. The tensile force seats the knee  38  in the knee channel  36 . With the knee  38  seated in the knee channel  36 , the surface  58  of the bend  48  is urged against the outer surface  28  of the conductor member  16 , thus retaining the spring clip  24  in locking engagement with the contact  18 . The frictional engagement within the stab channel  26  provides the structural support required for firmly attaching the circuit breaker in its cubicle within the load center, and results in a sure electrical contact. 
     The stab assembly is illustrated in the “right” configuration in FIGS. 1 and 2, i.e., the contact arm  22  is located to the right of the conductor member  16 , and in the “left” configuration in FIGS. 3 and 4, so that the second extension  52  may be viewed in FIGS. 3 and 4. 
     An advantage of the present stab assembly is that only three separate parts are required: a right contact, a left contact and a common spring clip  24 . The right contact and the left contact are mirror-image versions of the contact  18 , while the spring clip is the described spring clip  24  in both cases. A further advantage is the economy gained by using a common spring clip. The present invention allows the stab assembly to be assembled using automated means, since the press fit simply requires an insertion of spring clip  24  through the aperture  34  in the contact and since the parts are frictionally bound, thus enabling insertion into the circuit breaker housing without separating. 
     While the preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit sand scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.