Patent Publication Number: US-6211759-B1

Title: Ionized gas deflector for a molded case circuit breaker

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a circuit breaker and, more specifically, to a shield structure which directs ionized gases, created by separation of the circuit breaker&#39;s contacts, away from a collar assembly coupled to the line side of a circuit breaker. 
     2. Description of the Prior Art 
     Molded case circuit breakers are generally known in the art. Such circuit breakers are used to protect electrical circuits from damage due to an overload, a short circuit or both. Circuit breakers typically have a molded plastic housing enclosing at least one pair of separable contacts including a fixed contact and a moveable contact. During an overload or a short circuit, the circuit breaker will trip causing the contacts to separate thereby opening the circuit. Additionally, the circuit breaker may be tripped manually should the need arise. 
     When the electrical contacts within a circuit breaker separate, an electrical arc may form between the contacts creating hot ionized gases. The ionized gases formed by an electrical arc are conductive. If these ionized gases collect in the vicinity of the line terminals of the circuit breaker, they may establish a conduction path between the terminals connected to different phases of the line current, or between the terminals and an electrical ground. Such a connection can lead to electrical faults on the line side of the circuit breaker and damage the equipment. Circuit breakers typically include vents to allow the ionized gases to quickly escape as well as a shield to protect a collar assembly which connects the line to the terminal strap or contact. 
     A collar assembly will generally have a four sided collar defining a cavity. The collar is attached to the terminal strap which incorporates the fixed contact of the circuit breaker. The collar will also have a screw, or other such device, which may be used to clamp the line end against the terminal strap. The collar and the line end are in close proximity to the contact point of the circuit breaker and, when the circuit is broken, ionized gases are in the immediate vicinity of the line end and collar assembly. To deflect the ionized gasses away from the collar assembly and towards a vent, most collar assemblies include a gas deflector. 
     Prior art gas deflection devices include a generally L-shaped paper shield mounted on top of the collar which overlays the contact side of the collar, as well as a separate plastic sleeve disposed about the screw and passing through the paper shield. This design has several disadvantages. For example, because the paper shield device is not coupled to the collar assembly, it can easily be accidentally removed. Also, because the paper shield is not fixed, it may move within the circuit breaker housing, allowing a path for ionized gases to reach the collar assembly and line. Because the screw sleeve is not integral to the paper shield, another path for ionized gases to contact the collar assembly could exist through the screw sleeve hole in the paper shield. Additionally, because the paper shield and screw sleeve are separate components, there is an additional cost associated with assembling the device. 
     There is a need for a gas deflection device to isolate the line end terminals of a circuit breaker from each other and areas adjacent to the circuit breaker to substantially reduce the amount of ionized gases infiltrating into those spaces. 
     There is a further need for a gas deflection device which is compatible with collar assemblies presently used on circuit breakers. 
     There is a further need for a gas deflection device which is inexpensive and may be conveniently installed within a circuit breaker. 
     SUMMARY OF THE INVENTION 
     The present invention satisfies the above referenced needs by providing a one piece shield which protects the collar assembly from ionized gases. The shield has an integral sleeve which provides access for the mounting screw. Additionally, the shield is provided with a slot allowing the terminal strap to pass therethrough. The shield is made of a rigid material, such as plastic. The shield is held in place at one end by the sleeve and at the other end by the terminal strap passing through the shield. Thus, the shield is less likely to be subject to deflection than a paper shield. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of the gas deflection device and collar assembly mounted within a circuit breaker housing. 
     FIG. 2 shows a perspective view as in FIG. 1, with the top portion of the circuit breaker housing removed. 
     FIG. 3 is an exploded view of a terminal assembly. 
     FIG. 4 is a cross sectional view of the shield. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A shield device  10  according to the present in invention is shown disposed within a circuit breaker housing  20  in FIGS. 1 and 2. The circuit breaker housing  20  includes a top portion  22  and a bottom portion  24  forming an arc chamber  26 , an movable contact chamber  28 , a collar assembly recess  30  and separation ribs  32 ,  34 . A terminal assembly  40  fits mainly within the collar assembly recess  30 , with a terminal strap  80  extending between separation ribs  32 ,  34  and into the arc chamber  26 . Within the arc chamber  26  is a fastener hole  36 . A fastener  38  passes through a fastener hole  90  on a terminal strap  80  into fastener hole  36  thereby attaching the terminal assembly  40  to the circuit breaker housing bottom portion  24 . 
     As shown in FIG. 3, the terminal assembly  40  for a circuit breaker includes a collar assembly  50 , a shield device  10  and a terminal strap  80 . The collar assembly has a four-sided collar  52  defining a cavity  54  with openings on the opposing first face  60  and second face  62 . As used herein, the first face  60  refers to the face of the collar  52  that will be adjacent to the arc chamber  26  when the terminal assembly  40  is installed in circuit breaker housing  20 . Conversely, the second face  62  of the collar  52  will be adjacent to the line-in when the terminal assembly  40  is installed in circuit breaker housing  20 . The collar  52  also includes a top  56 , a bottom  58 , and two sides  64 ,  66 . The collar top  56  has a threaded opening therethrough with an annular ridge  68  disposed about the threaded opening. A screw  70  is engaged with the threaded opening and passes through the collar top  56  into the cavity  54 . The screw  70  may be adjusted vertically through the collar top  56 . The collar bottom  58  has a detent  72  which protrudes into cavity  54 . Each collar side  64 ,  66  has a projection  74 ,  76  into cavity  54 . The projections  74 ,  76  are located proximal to the collar bottom  58 . 
     The shield device  10  is a member having a top plate  12  and a perpendicular side plate  14 . The top plate  12  is sized to cover the collar top  56 , while the side plate  14  is sized to cover the collar first face  60  and cavity  54 . The top plate  12  further includes an opening  11 , a screw sleeve  16  disposed about opening  11  which is sized to fit about screw  70 . As shown on FIG. 4, the lower side  13  of the top plate  12  has a circular recess  15  which has a diameter slightly larger than the annular ridge  68 . The side plate  14  includes a slot  18  at its distal end. The slot  18  is sized to allow the terminal strap  80  to pass therethrough. The shield device  10  is preferably made from a dielectric material. 
     As shown on FIG. 3, the terminal strap  80  includes a line-in tab  82  and a contact tab  84  connected by a medial portion  86 . The line-in tab  82  and the contact tab  84  are approximately in parallel planes while the medial portion  86  is perpendicular to such planes. As such, the terminal strap  80  has a Z-shape. The line-in tab  82  includes an opening  88  therethrough which is sized to fit about the detent  72  located on the collar bottom  58 . The contact tab  84  includes a fastener opening  90  and the stationary contact point  92 . In operation, the contact point  92  would touch the movable contact of the load side of the circuit breaker. 
     When assembled, the shield device  10  covers the collar top  52  and the first face  60  and the cavity  54 . The screw sleeve  16  fits over the screw  70  and the recess  15  encircles the annular ridge  68 . The terminal strap  80  passes through the terminal strap slot  18 . When assembled, the terminal strap is partially secured by detent  72  on housing bottom  58  which is disposed in opening  88 . Additionally, the terminal strap  80  is held by projections  74 ,  76 . 
     As noted above, and as shown in FIG. 1, a circuit breaker housing top portion  22  is attached to the circuit breaker housing bottom portion  24 . The circuit breaker housing top portion  22  has chambers corresponding to the arc chamber  26 , the movable contact chamber  28 , the collar assembly recess  30  as well as has a screw access hole  21  positioned over screw  70 . The line side cable (not shown) fits within cavity  54  of the collar assembly  50 . The cable is secured within the collar assembly  50  by tightening screw  70  thereby clamping the cable against line-in tab  82  of terminal strap  80 . The load side of the circuit breaker is coupled to the moveable contact assembly (not shown) which is mounted adjacent to the movable contact chamber  28  and which has a contact passing into the arc chamber  26  which touches contact point  92  of terminal strap  80  when the circuit breaker is in the closed position. 
     In operation, the contacts will be closed. When a current interruption occurs in the circuit breaker, or when the circuit breaker is intentionally tripped, the electrical contacts separate and may form an electric arc therebetween. The electrical arc may create ionized gases which can conduct electricity. These gases are initially in the arc chamber  26  but may travel to the collar assembly chamber  40 . A substantial amount of these gases, however, are prevented from reaching the collar assembly  50  by shield device  10 . Because the shield device  10  substantially covers the collar assembly  50 , the gases will pass over the shield device  10  and exit the circuit breaker housing  20  through the back of the collar recess  30 . 
     While specific embodiments of the invention have 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 arrangement disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breath of the appended claims and any and all equivalence thereof.