Ionized gas deflector for a molded case circuit breaker

Information

  • Patent Grant
  • 6211759
  • Patent Number
    6,211,759
  • Date Filed
    Wednesday, January 12, 2000
    24 years ago
  • Date Issued
    Tuesday, April 3, 2001
    23 years ago
Abstract
A gas deflector for a line-in connector of a circuit breaker. The gas deflector is coupled to a collar with a top and a cavity, a threaded opening through the top, a screw threaded in the threaded opening. The collar is attached to the line-in for the circuit breaker. The gas deflector is an L-shaped shield with an integral screw sleeve and a slot sized to allow a terminal strap to pass therethrough. The terminal strap is connected to the collar. The shield device covers the collar top and the cavity and is held in place by the screw passing through the sleeve and by the terminal strap passing through the slot. The shield substantially reduces the amount of ionized gas infiltrating into the collar.
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'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.



Claims
  • 1. A gas deflecting terminal assembly for a circuit breaker comprising:a collar having a top, and a cavity; said cavity having an opposing first face and second face, each face having an opening to said cavity; a threaded opening through said collar top; a screw, threaded in said threaded opening; a shield device having a top plate and a perpendicular side plate; said top plate having an opening therethrough and an integral screw sleeve; a terminal strap; said terminal strap connected to said collar; said shield device coupled to said collar with said top plate covering said collar top, said side plate covering said first face and said first face cavity opening; and; wherein said shield device side plate has a slot passing therethrough and said terminal strap passes through said slot.
  • 2. The terminal assembly of claim 1, wherein said collar top includes an annular ridge disposed about said threaded opening and said shield device includes a recess disposed about said top plate opening, where said recess has a diameter larger than said annular ridge.
  • 3. The terminal assembly of claim 2, wherein;said collar has a bottom and two sides forming said cavity; said collar bottom having a detent protruding into said cavity; said collar sides each having a projection into said cavity; said terminal strap having a opening corresponding to said detent; wherein said terminal strap is frictionally held in said collar by said detent and said projections.
  • 4. A circuit breaker comprising;a circuit breaker housing having an arc chamber and an adjacent collar recess communicating with said arc chamber; a collar assembly comprising: a collar having a top and a cavity; said cavity having an opposing first face and second face, each face having an opening to said cavity; said collar seated in said collar assembly recess with said first face adjacent to said arc chamber; a threaded opening through said collar top; a screw threaded in said threaded opening; a shield device having a top plate and a perpendicular side plate; said top plate having an opening therethrough and an integral screw sleeve; a terminal strap coupled to said collar extending from said arc chamber into said cavity through said first face opening; said shield device coupled to said collar with said top plate covering said collar top, said side plate covering said first face and said first face cavity opening; and wherein said shield device side plate has a slot passing therethrough and said terminal strap passes through said slot.
  • 5. The circuit breaker of claim 4, wherein;said collar top includes an annular ridge disposed about said threaded opening and said shield device includes a recess disposed about said top plate opening, where said recess has a diameter larger than said annular ridge.
  • 6. The circuit breaker of claim 5, wherein said collar has a bottom and two sides forming said cavity;said collar bottom side having a detent protruding into said cavity; said collar sides each having a projection into said cavity; said terminal strap having a opening corresponding to said detent; wherein said terminal strap is frictionally held in said collar by said detent and said projections.
US Referenced Citations (5)
Number Name Date Kind
4181836 Miracle Jan 1980
4603376 Maier Jul 1986
4620076 Mrenna et al. Oct 1986
5753877 Hartzel et al. May 1998
5978208 Helms et al. Nov 1998