Cassette assembly with rejection features

A cassette assembly for rotary contact circuit breakers utilizing a first electrically insulative cassette half piece and a second electrically insulative cassette half piece which are arranged to mate with each other to form an enclosure. The electrically insulative cassette half pieces include improper installation rejection features for both the rotor and arc chute assemblies. The inner surface of a electrically insulative cassette half piece including a groove and recesses formed therein. A rotor is properly positioned within the electrically insulative cassette half piece by inserting a pin on the face of the rotor into the groove. An arc chute assembly is properly positioned within the electrically insulative cassette half piece by inserting a tab located on a side member of the arc chute assembly into a corresponding recess located in the electrically insulative cassette half piece.

BACKGROUND OF THE INVENTION
 This invention relates generally to a circuit breaker, and, more
 particularly, to a circuit breaker cassette assembly.
 Circuit breakers are one of a variety of overcurrent protective devices
 used for circuit breaker protection and isolation. The basic function of a
 circuit breaker is to provide electrical system protection whenever an
 electrical abnormality occurs in any part of the system. In a rotary
 contact circuit breaker, current enters the system from a power line. The
 current passes through a load strap to a stationary contact fixed on the
 strap and then to a moveable contact. The moveable contact is fixedly
 attached to an arm, and the arm is mounted to a rotor that in turn is
 rotatably mounted in a cassette. As long as the fixed contacts are in
 physical contact with the moveable contacts, the current passes from the
 fixed contacts to the moveable contacts and out of the circuit breaker to
 downline electrical devices.
 In the event of an overcurrent condition (e.g. a short circuit), extremely
 high electro-magnetic forces are generated. These electro-magnetic forces
 repel the movable contact away from the stationary contact. Because the
 moveable contact is fixedly attached to a rotating arm, the arm pivots and
 physically separates the stationary and moveable contacts, thus tripping
 the unit. When the contacts are rapidly opened as is the case during a
 trip caused by a short circuit event, an arc is produced. Swift extinction
 of the arc usually entails the resort to electromagnetic or pneumatic
 means for motivating the arc so as to increase its path length, promote
 removal of the arc from the breaker contacts, and facilitate cooling and
 splitting of the arc; all contributing to increasing the arc voltage to a
 value in excess of the system driving voltage. When the arc voltage
 surpasses the source voltage, it becomes difficult for the arc voltage to
 maintain the arc voltage so that the arc is extinguished. Accordingly,
 there occurs a voltage corresponding to the source voltage between the
 stationary contact and the moveable contact, thereby carrying out the
 circuit breaker operation. It is common practice to employ an arc chute
 assembly to extinguish this resultant arc.
 Such arc chute assemblies consist of a plurality of metallic chute plates
 that are held in stacked, spaced-apart relationship by side panels that
 are fabricated from electrically non-conductive material. Retention of the
 chute plates between the side panels is usually achieved by providing the
 plates with small protrusions that are slipped into a series of radiused
 notches in the side panels.
 Circuit breaker design, and more particularly, cassette design should
 enable the efficient and proper positioning of the various components,
 such as the rotor and arc chute assemblies, into the cassette. For
 example, improper installation of a rotor into a cassette can result in
 the two cassette half pieces not mating correctly together. Also, care
 must be taken to ensure that an arc chute assembly is conectly positioned
 into the cassette. This ensures proper rotation of the moveable contact
 arm as well as the proper spacing between the moveable contact and the
 plate closest to the moveable contact. Improper installation of either a
 rotor or an arc chute assembly into a cassette half piece will require
 disassembly and reassembly of the cassette. Such disassembly and
 reassembly is time consuming and can increase the production cost of the
 circuit breaker.
 BRIEF SUMMARY OF THE PRESENT INVENTION
 In an exemplary embodiment of the invention, a cassette assembly suitable
 for use with a rotary contact circuit breaker includes a first
 electrically insulative cassette half piece having an inner surface with a
 first recess and a groove formed therein and a second electrically
 insulative cassette half piece having an inner surface with a third recess
 formed therein. The second electrically insulative cassette half piece is
 arranged for mating with the first electrically insulative cassette half
 piece.
 First and second arc chute assemblies are arranged between the first and
 second electrically insulative cassette half pieces. A first arc chute
 assembly includes a first side member, a second side member, a tab, and a
 plurality of plates disposed between the first and second side members and
 arranged in a stacked spaced-apart relationship. The tab extends from the
 first side member and through the first recess for properly positioning
 the first arc chute assembly in the first electrically insulative cassette
 half piece. A second arc chute assembly includes a third side member, a
 fourth side member, a tab and a plurality of plates disposed between the
 third and fourth side member and arranged in a spaced apart relationship.
 The tab extends from the third side member and through the third recess
 for properly positioning the second arc chute assembly in the first
 electrically insulative cassette half piece.
 In one embodiment of a circuit breaker cassette assembly, a rotor defining
 first and second opposing sides thereon includes a pin formed on a first
 side. The rotor is then properly assembled within the first electrically
 insulative cassette half piece by placing the pin within the groove. Thus,
 the rotor is permitted to travel within the groove as required when the
 circuit breaker is tripped.

DETAILED DESCRIPTION OF THE INVENTION
 Referring to FIG. 1, a rotary contact assembly 12 in a circuit breaker
 cassette assembly 10 is shown in an electrically insulative cassette half
 piece (second electrically insulative cassette half piece) 60,
 intermediate a line-side contact strap 16, load-side contact strap 18 and
 associated arc chutes 20, 22. Line-side contact strap 16 is electrically
 connected to line-side wiring (not shown) in an electrical distribution
 circuit, and load-side contact strap 18 is electrically connected to
 load-side wiring (not shown) via a lug (not shown) or some device such as
 a bimetallic element or current sensor (not shown). Electrically
 insulative shields 24, 26 separate load-side contact strap 18 and
 line-side contact strap 16 from the associated arc chute assemblies 20, 22
 respectively. Although a single rotary contact assembly 12 is shown, it is
 understood that a separate rotary contact assembly 12 is employed within
 each pole of a multi-pole circuit breaker and operate in a similar manner.
 Electrical transport through the circuit breaker interior proceeds from the
 line-side contact strap 16 to associated first fixed and first moveable
 contacts 28, 30 at one end of a movable contact arm 32, to first fixed and
 first movable contacts 34, 36 at the opposite end thereof, to the
 associated load-side contact strap 18. The movable contact arm 32 is
 arranged between two halves of a circular rotor 37. Moveable contact arm
 32 moves in unison with the rotor 37 upon manual articulation of the
 circuit breaker operating mechanism (not shown) to drive the first and
 second movable contacts 30, 36 between CLOSED (depicted in FIG. 1) and
 OPEN positions. A first contact spring 38 extends between a pair of spring
 pins 40, 42 within the contact spring slot 48 formed within one side of
 the rotor 37 and a second contact spring (not shown) extends between pins
 40, 42 in a similar manner on the opposite side of rotor 37.
 The arc chute assemblies 20, 22 are positioned in the electrically
 insulative cassette half piece 60 adjacent the respective pairs of first
 fixed and first moveable contacts 28, 30 and second fixed and second
 moveable contacts 34, 36. The first and second movable contacts 30, 36 and
 moveable contact arm 32 move through a passageway provided by the arc
 chute assemblies 20, 22 in order to engage and disengage the respective
 first and second fixed contacts 28, 34. Each arc chute assembly 20, 22 is
 adapted to interrupt and extinguish the arc which forms when a circuit
 breaker is tripped and the first and second moveable contacts 30, 36 are
 suddenly separated from the first and second fixed contacts 28, 34.
 Referring to FIG. 2, a first electrically insulative cassette half piece 14
 is shown. First electrically insulative cassette half piece 14 has an
 inner surface 52 having a first recess 56 and second recess 54 formed
 therein. The first recess 56 having a first portion 96 and a second
 portion 98. The second recess 54 having a third portion 100 and a fourth
 portion 102. A groove 58 is also formed on the inner surface 52 of the
 first electrically insulative cassette half piece 14. A rotor recess 86 is
 also formed on the inner surface 52. Chute recesses 88, 90 are formed on
 the inner surface 52 on opposite ends of the rotor recess 86. Load-side
 and line-side contact strap recesses 92, 94 are also formed on the inner
 surface 52 proximate the arc chute recesses 88, 90.
 Referring to FIG. 3, the second electrically insulative cassette half piece
 60 is shown prior to attaching with the first electrically insulative
 cassette half piece 14 (FIG. 2) to form a complete enclosure. Second
 electrically insulative cassette half piece 60 has an inner surface 62.
 Inner surface 62 has a third recess 64 and a fourth recess 66 formed
 therein. Second electrically insulative cassette half piece 60 is attached
 to the first electrically insulative cassette half piece 14 (FIG. 2) by
 suitable mechanical fastening means. A rotor recess 86 is also formed on
 the inner surface 62. Chute recesses 88, 90 are formed on the inner
 surface 62 on opposite ends of the rotor recess 86. Load-side and
 line-side contact strap recesses 92, 94 are also formed on the inner
 surface 62 proximate the arc chute recesses 88, 90.
 Referring to FIG. 4, a circular rotor 37 is shown prior to being positioned
 in first electrically insulative cassette half piece 14 (FIG. 2). Rotor 37
 is rotatably supported by a shaft (not shown) rotatably and axially
 mounted inside first electrically insulative cassette half piece 14 (FIG.
 2). One or more rotor springs (not shown) are positioned in grooves 33 on
 face 19. Grooves 33 contain slots 39 disposed lengthwise along grooves 33
 for accommodating pins (not shown) to which springs (not shown) arc
 mounted. A pivot pin 25 extends from a central portion of the moveable
 contact arm 32 to a central portion of the rotor 37 for allowing rotation
 of the moveable contact arm 32 with respect to the rotor 37. A molded pin
 114 extends from the face 19 of rotor 37.
 Referring to FIGS. 2 and 4, the rotor 37 is assembled into first
 electrically insulative cassette half piece 14 by positioning pin 114 into
 groove 58. The pin 114 permits travel of the rotor 37 within the groove
 58. If the pin 114 is not properly set into groove 58 upon assembly of the
 rotor 37 into the first electrically insulative cassette half piece 14,
 then the second electrically insulative cassette half piece 60 will not
 properly mate with the first electrically insulative cassette half piece
 14. Thus, the improper completion of the enclosure will be prevented.
 Referring to FIG. 5 the arc chute assembly 22 for a circuit breaker is
 shown. The arc chute assembly 22 includes a plurality of plates 68, a
 first side member 70 and a second side member 72. Typically, the plates 68
 are metallic so as to induce magnetism thereby promoting removal of the
 arc generated by a short circuit trip in the circuit breaker. Each plate
 68 has a first edge 90, a second edge 92 opposing the first edge 90, a
 third edge 94 and a fourth edge 96 opposing the third edge 94. The first
 edge 90 and the second edge 92 are positioned between the third and fourth
 edges 94, 96, as shown in FIG. 5. Each plate 68 has a protrusion 74
 extending from the third edge 94 and the fourth edge 96. Each plate 68
 also includes a radiused notch 78 formed on the first edge 90. The
 radiused notch 78 provides clearance for the contact arm 32 when the arc
 chute assembly 22 is mounted within the electrically insulative cassette
 half pieces 14, 60 (FIGS. 2 and 3).
 Referring to FIGS. 5 and 6, first and second side members 70, 72 have a
 plurality of slots 76 formed therethrough. The protrusions 74 of the
 plates 68 are respectively inserted into a corresponding one of the slots
 76 formed in the first and second side members 70, 72. The plates 68 are
 disposed in this manner between the first and second side members 70, 72
 and are arranged in a stacked, spaced-apart relationship to each other.
 Second side member 72 is identical to first side member 70. The first and
 second side members 70, 72 are assembled so as to be opposedly oriented to
 each other. First and second side members 70, 72 each include a first end
 98 and an opposing second end 100. First side member 70 has a tab 80
 centrally located on the second end 100 opposite to the radiused notch 78.
 A tab 80 is similarly located along second side member 72.
 A second arc chute assembly 20 comprises a plurality of plates 68 and third
 and fourth side members 82, 84. Third and fourth side members 82, 84 are
 identical to first and second side members 70, 72. Third and fourth side
 members 82, 84 are assembled so as to be opposedly oriented to each other.
 Third side member 82 has a tab 80 centrally located on an end opposite to
 the radiused notch 78 of the plate 68. A tab 80 is similarly located along
 the fourth side member 84.
 Referring to FIGS. 2 and 5, the first arc chute assembly 22 is correctly
 positioned into the first electrically insulative cassette half piece 14
 by placing the tab 80 of the first side member 70 into the first recess 56
 of first electrically insulative cassette half piece 14. Similarly, the
 second arc chute assembly 20 is correctly positioned into the first
 electrically insulative cassette half piece 14 by placing tab 80 of the
 third side member 82 into the second recess 54 of first electrically
 insulative cassette half piece 14.
 If a cassette assembly does not include tabs 80 and recesses 56, 54 to
 correctly position the arc chute assemblies 22, 20 for example, then the
 radiused notches 78 in the plates 68 might be incorrectly positioned to
 face opposite the first and second moveable contacts 30, 36 and the first
 and second fixed 28, 34 contacts. If this were to occur, the moveable
 contact arm 32 would not be permitted proper operation when the circuit
 breaker is tripped due to a short circuit event. Also, the arc chute
 assembly 22 could be placed upside down with respect to the first
 electrically insulative cassette half piece 14. If this were to occur,
 there can be insufficient air space between the plate 68 that is closest
 to the first moveable contact 30 and the line-side contact strap 16. The
 loss of a conducting plate in the arc chute assembly 22 can result in an
 insufficient amount of electromagnetic force to quench the arc. Thus, tabs
 80 ensure the correct positioning of the arc chute assemblies 22, 20
 within the recesses 56, 54.
 Referring now to FIGS. 2, 3, 4 and 5, after the first and second arc chute
 assemblies 22, 20 are properly assembled into the first electrically
 insulative cassette half piece 14, the second electrically insulative
 cassette half piece 60 is placed over the first electrically insulative
 cassette half piece 14 to form a complete enclosure. As a result, tab 80
 of the second side member 72 will be inserted into the third recess 64 of
 the second electrically insulative cassette half piece 60. Tab 80 of the
 fourth side member 84 will likewise be inserted into the fourth recess 66
 of the second electrically insulative cassette half piece 60. Thus, the
 first and second arc chute assemblies 22, 20 will be correctly positioned
 into the first and second electrically insulative cassette half pieces 14,
 60. Proper operation of the rotary contact arm assembly is achieved.
 The first, second, third and fourth side members 70, 72, 82, 84 have been
 heretofore described with tabs 80 that are centrally located. The
 advantage to this arrangement of the tabs 80 along the respective ends of
 the side members 70, 72, 82, 84 is the cost savings attributed to forming
 one mold pattern that can be used for all side members 70, 72, 82, 84 for
 both the first and second arc chute assemblies 22, 20.
 Since the first and second arc chute assemblies 22, 20 are assembled prior
 to placement within the first electrically insulative cassette half piece
 14, correct positioning of the first and second arc chute assemblies 22,
 20 can also be achieved by using tabs 80 on only the first and third side
 members 70, 82. In this alternative embodiment, the second and fourth side
 members 72, 84 would have no tabs 80. However, this would require the
 manufacture of two structurally different side members. Further, tabs 80
 on the first and third side members 70, 82 can be located generally offset
 as opposed to centrally located along the edges of the respective side
 members. However, this would further require the manufacture of a third
 type of side member to accommodate the offset tab arrangement.
 As described herein, a cassette assembly for rotary contact circuit
 breakers utilizing a first electrically insulative cassette half piece 14
 and a second electrically insulative cassette half piece 60 are arranged
 to mate with each other to form an enclosure. The electrically insulative
 cassette half pieces 14, 60 include improper installation rejection
 features for both the rotor 37 and the arc chute assemblies 22, 20.
 Therefore, the cassette assembly, as described herein, prevents such
 disassembly and reassembly that can be time consuming and increase the
 production cost of the circuit breaker.
 While this invention has been described with reference to a preferred
 embodiment, it will be understood by those skilled in the art that various
 changes may be made and equivalents may be substituted for elements
 thereof without departing from the scope of the invention. In addition,
 many modifications may be made to adapt a particular situation or material
 to the teachings of the invention without departing from the essential
 scope thereof. Therefore, it is intended that the invention not be limited
 to the particular embodiment disclosed as the best mode contemplated for
 carrying out this invention, but rather that the invention will include
 all embodiments falling within the scope of the appended claims.