BACKGROUND OF THE INVENTION In general the function of a circuit breaker is to electrically engage and disengage a selected circuit from an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. The circuit breaker provides protection against persistent overcurrent conditions and against the very high currents produced by short circuits.

Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact.

A typical industrial circuit breaker will have a continuous current rating ranging from as low as 15 amps to as high as several thousand amps. The tripping mechanism for the breaker usually consists of a thermal overload release and a magnetic short circuit release. The thermal overload release operates by means of a bimetallic element, in which current flowing through the conducting path of a circuit breaker generates heat in the bi-metal element, which causes the bi-metal to deflect and trip the breaker.

The heat generated in the bi-metal is a function of the amount of current flowing through the bi-metal as well as the period of time that that current is flowing. For a given range of current ratings, the bi-metal cross-section and related elements are specifically selected for such current range resulting in a number of different current ranges for each circuit breaker. Electronic trip units are also used in some applications.

In the event of current levels above the normal operating level of the thermal overload release, it is desirable to trip the breaker without any intentional delay, as in the case of a short circuit in the protected circuit, therefore, an electromagnetic trip element is generally used. In a short circuit condition, the higher amount of current flowing through. the circuit breaker activates a magnetic release which trips the breaker in a much faster time than occurs with the bi-metal heating. It is desirable to tune the magnetic trip elements so that the magnetic trip unit trips at lower short circuit currents at a lower continuous current rating and trips at a higher short circuit current at a higher continuous current rating. This matches the current tripping performance of the breaker with the typical equipment present downstream of the breaker on the load side of the circuit breaker. Again, electronic trip units can also be used.

In an effort to improve the efficiency and response of the circuit breaker under short circuit conditions it has been known to include a second set of contacts in series with the main contacts of the breaker.

Such arrangement typically include an electromechanically operable means for opening the extra pair of contacts, a field magnet associated with the pair of additional contacts and in some instances, a resistor connected and parallel with the additional contact for purposes of shunting some of the short circuit current. Such arrangements typically require a larger circuit breaker housing to accommodate the additional contacts as well as their associated magnets, coils and resisters. Further such prior arrangements are more expensive and complex in relation to the benefit sought.

Thus, there is a need for a molded case circuit breaker having auxiliary contacts mounted in series with the main contacts of the circuit breaker that do not require an additional coil or magnet to operate efficiently. There is also a need for a molded case circuit breaker with an auxiliary contact apparatus that will fit in an existing molded case circuit breaker housing and requiring minimal modification to such housing. There is a further need for a molded case circuit breaker, the interrupting ratings of which can be increased while reducing the let-through energy in an inexpensive and simple manner.

SUMMARY OF THE INVENTION The present invention provides a circuit breaker with a line terminal and load terminal, having an operating mechanism with a main, movable contact arm coupled to a load terminal and an auxiliary contact apparatus coupled in series with the main movable contact arm. The auxiliary contact apparatus comprises an auxiliary stationary contact mounted on the load terminal, an auxiliary movable contact arm mounted for rotation in the circuit breaker and coupled to the main movable contact arm, an attraction plate mounted in the circuit breaker and aligned with the auxiliary movable contact arm wherein a magnetic flux induced in the metal plate attracts the auxiliary movable contact arm. The auxiliary contact apparatus can also be provided with a biasing member mounted in the circuit breaker and coupled to the auxiliary movable contact arm, wherein, the auxiliary movable contact arm is urged into a closed position with the auxiliary stationary contact. The auxiliary contact apparatus can also be provided with an arc chute structure mounted in the circuit breaker and aligned with the auxiliary movable contact arm, wherein the auxiliary movable contact arm moves through a channel defined in the arc chute structure.

The present invention further provides an auxiliary contact apparatus for a circuit breaker, with the circuit breaker having a primary contact apparatus and a load terminal. The auxiliary contact apparatus comprises an auxiliary stationary contact mounted on the load terminal and an auxiliary movable contact arm mounted for rotation in the circuit breaker and coupled to the primary contact apparatus. An attraction plate is mounted in the circuit breaker and aligned with the auxiliary movable contact arm wherein a magnetic flux induced in the attraction plate attracts the auxiliary movable contact arm. The auxiliary contact apparatuses can also be provided with a bias member mounted in the circuit breaker and coupled to the auxiliary movable contact arm wherein the auxiliary movable contact arm is urged into a closed position with the auxiliary stationary contact. The auxiliary contact apparatus can also include an arc chute structure mounted in the circuit breaker and aligned with the auxiliary movable contact arm, wherein the auxiliary movable contact arm moves through a channel defined in the arc chute structure. The auxiliary contact apparatus is connected in series with the primary contact apparatus of the circuit breaker.

The present invention also provides a circuit breaker with a primary contact apparatus and a load terminal and having an auxiliary contact apparatus coupled in series with the primary contact apparatus. The auxiliary contact apparatus comprises a first auxiliary means for contacting the load terminal and a second auxiliary means for contacting the primary contact apparatus. In one embodiment, the first auxiliary means for contacting is stationary and the second auxiliary means for contacting is movable. In another embodiment, the first auxiliary means for contacting is movable and the second auxiliary means for contacting is stationary. In either of the two embodiments, the first auxiliary means for contacting and the second auxiliary means for contacting are each jointly mounted in one of a vertical aspect and a horizontal aspect with respect to the load terminal of the circuit breaker.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side cut-away view of a molded case circuit breaker providing an exemplary embodiment of an auxiliary contact apparatus, with the auxiliary movable contact arm coupled to a main movable contact arm and mounted in a substantially horizontal aspect with respect to the load terminal of the circuit breaker.

Figure 2 illustrates the current path (by arrows) for the circuit breaker illustrated in Figure 1 with the main contacts and the auxiliary contacts in the"ON" (closed) position.

Figure 3 is a partial top exploded view of an auxiliary movable contact arm aligned in a channel defined in an arc chute structure and illustrating two arc plates included in the arc chute structure.

Figure 4 is a partial side cut-away view of a molded case circuit breaker providing an exemplary embodiment of an auxiliary contact apparatus, with the auxiliary movable contact arm coupled to a load terminal.

Figure 5 is a partial side cut-away view of a molded case circuit breaker providing an auxiliary contact apparatus mounted in a substantially vertical aspect with respect to the load terminal.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS Figure 1 generally illustrates single phase molded case circuit breaker 10 that includes an operating mechanism 20 having a handle 21. The operating mechanism 20 is mounted within a housing 18. The handle 21 is movable between an"ON"position, an"OFF"position and a"TRIPPED" position. The exemplary circuit breaker 10 is a single pole breaker however, it is contemplated that the several exemplary embodiments of the auxiliary contact apparatus 40 may be practiced in a three-phase or in other multi-phase circuit breakers. In such multi-phase breaker, each pole would be connected, in series, to a separate auxiliary contact apparatus 40.

The molded case circuit breaker 10 has a line terminal 12 and a load terminal 14 to which electrical wires or cables are attached when the circuit breaker 10 is installed in a selected circuit. The housing 18 encloses the components of the circuit breaker including an operating mechanism 20 to which a main movable contact arm 30 and a trip assembly 28 are coupled.

An auxiliary contact apparatus 40 is mounted within a suitable void in the housing 18 of the circuit breaker 10 and is coupled in series with the main movable contact arm 30. It is contemplated that an existing molded case circuit breaker will be minimally modified to accommodate the auxiliary contact apparatus 40. However, it is also contemplated that a new molded case circuit breaker design case initially incorporate the auxiliary contact apparatus 40.

The auxiliary contact apparatus 40 comprises an auxiliary stationary contact 42 mounted on a load terminal 14, an auxiliary movable contact arm 44 mounted for rotation in the circuit breaker 10 and coupled to the main movable contact arm 30 and an attraction plate 54 mounted in the circuit breaker 10. The attraction plate 54 is aligned with the auxiliary movable contact arm 44, wherein a magnetic flux is induced and the attraction plate attracts the auxiliary movable contact arm 44, as will be explained below. An auxiliary stationary contact pad 43 is mounted on the auxiliary stationary contact 42 with any suitable and satisfactory attachment method such as welding, riveting or brazing.

The auxiliary movable contact arm 44 has an auxiliary movable contact arm contact pad 45 mounted in a similar fashion. The auxiliary movable contact arm 44 is mounted for rotation in the circuit breaker 10 at a pivot 46 and held in place by a pivot clip 48. The pivot clip can be any suitable material such as metal or an engineered plastic with the preferred embodiment providing a nickel plated steel formed to engage and retain the auxiliary movable contact arm 44 within the housing 18 of the circuit breaker 10. One end of an auxiliary braid 52 is attached to one end of the auxiliary movable contact arm 44 with another end of the auxiliary braid 52 attached to the load bus 23.

A bi-metal/magnetic trip assembly 66 is mounted in the housing 18 of the circuit breaker 10 and couples the load bus 23 to the main movable contact arm 30 via a main braid 26. The bi-metal assembly includes the bi-metal element 70 fixed at one end to the load bus 23 at a joint 73 formed by the load bus 23 and the bi-metal 70. The joint 73 is created by suitable weld or braze. A magnetic armature 68 and a magnetic yoke 72 form a part of the bi-metal assembly 66. The response characteristics of the bi- metal/magnetic trip assembly 66 is controlled by a calibrating screw 74 mounted in the load bus 23 and by the physical attributes of the trip assembly.

In operation, with the circuit breaker 10 in the ON position, the main movable contact arm 30 and main stationary contact 32 are closed. The auxiliary stationary contact 42 and auxiliary movable contact arm 44 of the auxiliary contact apparatus 40 are also closed, as shown in Figure 2. In such condition, the current flows through the line terminal 12 into the line bus 22 and through the main stationary contact 32 into the main movable contact arm 30 of the primary contact apparatus 29. The current then flows through the main braid 26 into the bi-metal/magnetic trip assembly 66 and then through the load bus 23 and into the auxiliary contact apparatus 40. From the load bus 23 current flows through the auxiliary braid 52 into the auxiliary movable contact arm 44 and into the auxiliary movable contact arm contact pad 45 to the auxiliary stationary contact pad 43. The current then flows through the auxiliary stationary contact 42 through the load terminal 14 and onto the load (not shown).

Under a short circuit condition, the circuit breaker 10 having the auxiliary contact apparatus 40 will experience high current flowing through the circuit described above. Such high current will cause the magnetic yoke 72 and the magnetic armature 68 in the bi- metal/magnetic trip assembly 66 to activate the trip assembly 28 of the circuit breaker 10. However, prior to the response of the magnetic armature, the auxiliary contact apparatus 40 will respond to the high current flowing through the auxiliary contact pads 43,45 with a force that varies in relation to the square of the current flowing through such contact pads. Such constriction force at the contact pads will tend to blow the contacts apart since the current concentration at the area of contact between the contact pads 43,45 is considerably higher than the current concentration in the bi-metal/magnetic trip assembly 66 and magnetic armature 68. In addition, as seen in Figure 2, the current flow to and from the contact pads 43,45 of the auxiliary contact apparatus 40 are in opposite directions which also creates a repulsive force which assists in pushing the auxiliary movable contact arm 44 away from the auxiliary stationary contact 42. The force generated by these mechanisms overcome the bias force exerted by a bias member 50 coupled to the auxiliary movable contact arm 44.

The auxiliary movable contact arm 44 is urged into a closed position with the auxiliary stationary contact 42 by such bias member 50. The bias member can be a compression or clip spring and preferably a torsion spring as shown in Figures 1,4 and 5.

The current flowing through the auxiliary movable contact arm 44 also induces a magnetic flux in the movable contact arm 44 and an attraction plate 54 mounted in the circuit breaker 10. The magnetic flux induced in the auxiliary movable contact arm 44 and the attraction plate 54 assists in keeping the auxiliary movable contact arm 44 in an opened position during the current interruption operation of the circuit breaker 10. Although only one attraction plate 54 is illustrated, multiple plates can be used in each pole of the circuit breaker 10, as selected during the manufacture of the circuit breaker.

The electrical arc typically created during the opening of the auxiliary contact apparatus 40 under short circuit conditions, is drawn into an arc chute structure 56 which extends and cools the arc to assist in the current interruption operation of the circuit breaker. The main movable contact on arm 30 and the main stationary contact 32 are blown apart by the magnetic force generated under the short circuit condition. The operating mechanism 20, trip assembly 28 and the bi-metal assembly 66 of the circuit breaker 10 also operates to hold the main movable contact arm 30 in its TRIPPED and OPENED position. With the circuit opened, the main movable contact arm 30 remains in an open position until the handle 21 of the circuit breaker 10 is reset and placed in the on position. This can be done manually by an operator or can be done by a motor coupled to the circuit breaker or by a stored energy device coupled to the circuit breaker. With the circuit open and no current flowing through the circuit breaker, the auxiliary movable contact arm 44 is urged back to the closed position by the bias member 50. With no current flowing through the circuit breaker, there is no magnetic flux induced in the movable contact arm 44 or the attraction plate 54 as described above.

The auxiliary movable contact arm 44 is mounted for rotation in the housing 18 of the circuit breaker 10 as can be seen in Figures 1 and 3. The bias member 50 is also mounted in the circuit breaker and coupled to the auxiliary movable contact arm 44. The bias member 50 urges the auxiliary movable contact arm 44 into a closed position with the auxiliary stationary contact 42. In one embodiment, the bias member 50 pushes against the auxiliary movable contact arm 44 from underneath the arm as shown in Figures 1 and 3.

In another embodiment, the bias member 50 pushes against the auxiliary movable contact arm 44 from above as shown in Figure 4. Figure 5 shows another embodiment of the auxiliary contact apparatus 40 aligned in a vertical aspect with respect to the load terminal 14. In that embodiment, the bias member 50 pushes the auxiliary movable contact arm 44 from behind the arm into a closed position with the auxiliary stationary contact 42. In all embodiments, the bias member 50 biases the auxiliary movable contact arm 44 to a closed position. The electromagnetic forces generated in the auxiliary contact apparatus 40 in a short circuit condition overcomes the bias force exerted by the bias member 50 to open the contacts 43,45 of the auxiliary contact apparatus 40. The bias member 50 can be a compression spring, a clip spring or a torsion spring. The preferred embodiment provides a steel torsion spring as illustrated in the figures.

Another feature of an auxiliary contact apparatus 40 includes an arc chute structure 56. Two arch chute side panels 62 having a plurality of slots 63 (see Fig. 2) support a plurality of arc plates 60 (See Figs. 1,3 and 5).

The arc plates, as best seen in Fig. 3, are generally U- shaped and are stacked between the two side plates 60. The arc plates 60 can be provided with tabs 61 which engage the slots 63 to form the arc chute structure 56. In the stacked position, as shown in the figures, an arc channel 58 is formed between the two legs of each arc plate 60. When inserted into the housing 18 of the circuit breaker 10, the arc chute structure 56 is aligned with the auxiliary movable contact arm 44 of the auxiliary contact apparatus 40. The auxiliary movable contact arm 44 moves through the channel 58 of the arc chute structure 56 as the auxiliary movable contact arm 44 moves from one position to another position.

During a short circuit condition, as the movable contact arm 44 opens an electrical arc is drawn between the contact pads 43,45 of the auxiliary contact apparatus 40. Such electric arc extends into the arc chute structure 56 which lengthens and cools the arc as the arc voltage increases until the current ceases to flow in the circuit. An arc runner 64 can also be provided on the auxiliary movable contact arm 44 to facilitate the extension, into the arc channel 58, of the arc generated during a short circuit condition. The arc runner 64 can be integrally formed with the auxiliary movable contact arm 44 during the manufacture of the auxiliary contact apparatus 40.

Figures 1,2,4 show the auxiliary contact apparatus 40 in a substantially horizontal aspect 47 with respect to the load terminal 14. Figure 5 illustrates the auxiliary contact apparatus 40 in a substantially vertical aspect 41 with respect to the load terminal 14. Other embodiments of the auxiliary contact apparatus 40 provide for the auxiliary movable contact arm 44 to pivot while attached to one of the load terminal 14 (See Figs. 4 and 5) or the load bus 23 (See Fig. 1) coupled to the main movable contact arm 30 of the circuit breaker 10.

Thus, there is provided a circuit breaker with a line terminal and a load terminal, having an operating mechanism with a main movable contact arm coupled to a load terminal and an auxiliary contact apparatus coupled in series with the main movable contact arm. While the embodiments illustrated in the figures and described above are presently preferred, it should be understood that these embodiments are offered by way of example only. The invention is not intended to be limited to any particular embodiment, but is intended to extend to various modifications that nevertheless fall within the scope of the appended claims. For example, it is also contemplated that the trip mechanism can be an electronic trip mechanism or that the load terminal and auxiliary contact apparatus be housed in a separate housing capable of mechanically and electrically connecting to another housing containing the operating mechanism and line terminal thereby providing for a quick and easy change of current rating for an application of the circuit breaker contemplated herein. It is also contemplated that the auxiliary contact apparatus 40 can be included in a circuit breaker having a main movable contact arm and a main movable line contact. It is also contemplated that the auxiliary contact apparatus 40 can be provided in a multi-phase molded case circuit breaker wherein a separate auxiliary contact apparatus 40 is provided in series with each pole of the multi-pole circuit breaker. Additional modifications will be evident to those with ordinary skill in the art.