Abstract:
A shunt wire spacer provides for proper spacing between the shunt wires extending from the movable arm to the bimetal within a circuit breaker, thereby ensuring that the shunt wires do not come together during over-current conditions within the circuit breaker, and preventing the shunt wires from interfering with the movement of the trip bar.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to circuit breakers. More specifically, the present invention provides a spacer for the shunt wires within the circuit breaker. 
     2. Description of the Related Art 
     A typical circuit breaker includes both a thermal trip mechanism and a magnetic trip mechanism for moving the arm having the movable contact away from the fixed contact when an over-current is present. The trip unit includes a bimetal connected at its fixed end to the load terminal, and at its free end to a shunt, which is connected to the contact arm. A trip bar mounted adjacent to the bimetal includes a thermal trip arm and a magnetic trip armature. The trip bar engages a latch on the operating mechanism for tripping the circuit breaker. 
     In use, current will flow from the line terminal, through the fixed contact, through the movable contact and arm, through the shunt, through the bimetal, and then through the load terminal. When a persistent low level over-current occurs, the heating of the bimetal will cause it to bend until it strikes the thermal trip arm of the trip bar, thereby tripping the circuit breaker. A larger over-current will cause the magnetic trip armature to be attracted toward the bimetal by a magnetic field generated by a short circuit current flowing through the bimetal, again rotating the trip bar and tripping the circuit breaker. 
     During a high interruption capacity test, it is possible for magnetic attraction caused by current flow in the same direction to cause the shunt wires to come together, thereby causing mechanical interference preventing movement of the thermal trip arm, thereby preventing tripping of the circuit breaker. Accordingly, there is a need for a means for maintaining proper spacing between the shunt wires to maintain proper function of the circuit breaker. 
     SUMMARY OF THE INVENTION 
     The present invention provides a shunt wire spacer for maintaining the proper distance between the shunt wires within a circuit breaker. The shunt wire spacer includes a pair of wire-receiving ends connected by a spacer portion. The shunt wire spacer may be made of any suitable material, such as metal or plastic. Because current in both shunt wires is flowing in the same direction, from the same origin destination, the conductive or insulative properties of the shunt wire spacer are not critical. 
     In use, the shunt wire spacer is inserted between the shunt wires, with each shunt wire within one of the two shunt wire receiving ends. With the shunt wire spacer in place, the shunt wires are held the proper distance apart to permit proper movement of the circuit breaker&#39;s thermal trip arm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cut-away isometric view of a circuit breaker for which the present invention will be used. 
     FIG. 2 is a cut-away side view of a circuit breaker with which the invention will be used. 
     FIG. 3 is an isometric view of three contact arm carriers and their associated contact arms, shunt wires, bimetals, and shunt wire spacer, according to the present invention. 
     FIG. 4 is a front view of a shunt wire spacer according to the present invention. 
     FIG. 5 is a front view of another embodiment of a shunt wire spacer according to the present invention. 
     FIG. 6 is a front view of an alternative embodiment of a shunt wire spacer according to the present invention. 
     FIG. 7 is an isometric view of a movable contact arm, bimetal, connecting shunt wires, and shunt wire spacer according to the present invention. 
    
    
     Like reference numbers denote like elements throughout the drawings. 
     DETAILED DESCRIPTION 
     The present invention provides a spacer for use with the shunt wires of a circuit breaker, thereby maintaining the proper distance between these wires to permit proper tripping of the circuit breaker. 
     FIGS. 1-3 illustrate a circuit breaker  10  with which a shunt wire spacer of the present invention may be used. The circuit breaker  10  includes a housing  12  having a front face  14 . The face  14  defines an opening  16 , permitting the operating handle  18  to move therein between its open and closed positions. 
     The interior of the housing  12  includes three identical trip mechanisms, one of which will be described herein. Each trip mechanism includes an arc chamber  20  having a plurality of substantially parallel, spaced apart plates  22 . A fixed electrical contact  24  is located at one end of the arc chamber  20 , and is in electrical connection with the line terminal  26 . A movable contact  28  is secured to the free end  30  of the arm  32 . The pivoting end  34  of the arm  32  is housed within a contact arm carrier  36 , which also includes a spring therein for holding the fixed  24  and movable  28  contacts together against the magnetic forces generated by the current flowing in opposite directions through these contacts. The operating handle  18  is operatively connected to the contact arm carrier  36 , so that pivoting of the contact arm carrier  36  between the open position of the movable contact  28  (illustrated in FIG. 1) and the closed position of the movable contact  28  (illustrated in FIG. 2) may be controlled using the operating handle  18 . 
     The circuit breaker includes a thermal-magnetic trip unit  38  for separating the contacts  24 ,  28  in response to an overcurrent. The thermal-magnetic trip unit  38  includes a bimetal  40  having a fixed end  42 , and a free end  44 . A pair of shunt wires  46  provide for electrical connection between the pivoting end  34  of the arm  32 , and the free end  44  of the bimetal  40 . The fixed end  42  of the bimetal  40  is electrically connected to the load terminal  48 . When the circuit breaker  10  is closed, current may thereby flow through the line terminal  26 , fixed contact  24 , movable contact  28 , arm  32 , shunt wires  46 , bimetal  40 , and load terminal  48 . A pivotally mounted trip bar  50  is also within the thermal magnetic trip unit  38 , adjacent to the bimetal  40 . The trip bar  50  includes a thermal trip arm  52 , depending substantially perpendicular to the trip bar  50 , and substantially parallel to the bimetal, and a magnetic trip armature  54 , which in many preferred embodiments will be substantially parallel to the thermal trip arm  52 . Both the thermal trip arm  52  and magnetic trip armature  54  are positioned adjacent to the bimetal  40 . A persistent low level overcurrent within the bimetal  40  will cause the bimetal  40  to bend until it engages the thermal trip arm  52 . A larger overcurrent will cause a magnetic attraction between the bimetal and the magnetic trip armature  54 , thereby instantly rotating the trip bar  50  to bring the armature  54  toward the bimetal  40 . It is well known in the art of circuit breakers that rotation of the trip bar  50  will release a latch that will permit the arm  32  and carrier  36  to be instantly spring-biased away from the fixed contact  24 , thereby opening the circuit breaker. Additionally, the current flow in the fixed contact  24  and movable contact  28 , being in opposite directions, will generate opposing magnetic forces sufficiently strong to overcome the spring within the carrier  36 , causing the arm  32  to pivot with respect to the carrier  36 , possibly before the pivoting of the carrier  36  would open the circuit breaker. 
     During a high interruption capacity test, it is possible for magnetic attraction caused by current flow in the same direction to cause the shunt wires to come together, thereby causing mechanical interference preventing movement of the thermal trip arm  52 , thereby preventing proper tripping of the circuit breaker. Accordingly, the present invention provides a spacer  56  for the shunt wires  46 . Some preferred embodiments of the shunt wire spacer  56  are illustrated in FIGS. 4-6. In describing these embodiments, a reference number utilized without a letter, will refer to all embodiments, a reference number followed by an A will refer to the embodiments of FIG. 4, a reference number followed by the letter B will refer to FIG. 5, and a reference number followed by the letter C will refer to FIG.  6 . 
     The shunt wire spacer  56  includes a pair of ends  58 , having a shunt wire receiving portion, and being connected by a connection portion  60  that is sufficiently rigid to hold the shunt wires  46  apart against the magnetic forces they generate. In the illustrated examples, the end portions  58 A take the form of open-ended loops that partially encircle the shunt wires  46 . The end portions  58 B take the form of closed loops, completely circling the shunt wires  46 . The example of FIG. 5 includes end portions  58 C, defining a pair of prongs  62 C,  64 C, defining a shunt wire receiving channel  66 C therebetween. 
     Referring to FIGS. 2,  3 , and  7 , the shunt wire spacer  56 A is illustrated holding the shunt wires  46  in the proper position. When current is passed through the wires, causing magnetic attraction between them, they will therefore not tend to be drawn together, as they would without the shunt wire spacer  56 . Therefore, the shunt wires  46  will not interfere with the movement of the thermal trip arm  52 . 
     The shunt wire spacer  56  may be made out of any material that is sufficiently rigid to keep the shunt wires  46  spaced a proper distance apart. Examples of preferred materials include metal, such as metal wire, and various plastics. Because current in both shunt wires  46  has the same potential, the shunt wire spacer  56  may be made out of an electrically conductive material without any danger of shorting the shunt wires  46 . A preferred method of installing the shunt wire spacer  56 A is to begin with the straight wire, and then bend the end portions of the wire  56 A to encircle the shunt wires  46 . 
     While a specific embodiment of the invention has been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.