The present invention relates generally to the field of circuit breakers, and more particularly to a wire lug/arc vent barrier for a molded case circuit breaker.
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.
Ratings of circuit breakers are continually increasing due to market driven requirements for space saving electrical equipment. As the ampere rating for a given circuit breaker frame size increases, space for wiring lugs within that circuit breaker becomes a premium. Lug size for attaching the various wires and cables is primarily driven by the wiring cable dimensions as defined in the National Electric Code or other country specific wiring standards or practices. Although this problem exists for all circuit breakers, it is especially acute for circuit breakers in the 100 amp to 125 amp range. In addition, the location of the wire lugs in the circuit breaker generally occupies the same relative space as the arc venting area near the main contacts. As the main contacts separate under an overload or short circuit condition, heat, gases, and arc by-products which are generated by the arcing in the arc chamber must vent out of the circuit breaker""s housing. Such out gassing typically envelopes the wire lug and cabling near the arc chamber of the circuit breaker. The close proximity of the wire lug, and the load and line terminals with the contact of the circuit breaker create additional space limitations because of insulation requirements. Prior arrangements to address such problems include providing larger housing for the circuit breaker to accommodate the thicker insulations and larger wire lugs and cables. Prior arrangements also included requiring additional gas venting deflectors. Such prior arrangements are more expensive and complex in relation to the benefits sought and not as effective or reliable.
Thus, there is a need for a molded case circuit breaker having a wire lug/arc vent barrier for protecting a wire lug in a circuit breaker utilizing a stacked pole construction. There is also a need for a wire lug/arc vent barrier that will direct arc gasses and by-products around the wire lug and wire binding screw. There is further need for a wire lug/arc vent barrier that incorporates the functions of a lug barrier, arc chamber venting and line end insulation system in a single integral molded piece. There is further need for a wire lug/arc vent barrier for a molded case circuit breaker that allows the ampere rating of the breaker to be increased without increasing the overall size of the circuit breaker. There is additional need for a wire lug/arc vent barrier for a molded case circuit breaker that provides for easy assembly and mounting within the circuit breaker housing.
The present invention provides a wire lug/arc vent barrier for protecting a wire lug in a circuit breaker, with the circuit breaker having a housing with a terminal for a load connection and a terminal for a line connection. The wire lug/arc vent barrier comprises a body having a first end including a tang, a second end including an elongated finger and a middle portion between the first end and the second end defining a concave space, with an opening at each end of the middle portion, wherein the body is mounted in the housing. Another embodiment of the wire lug/arc vent barrier provides the tang and elongated finger configured to engage the housing and the concave space is configured to receive the wire lug. The middle portion is configured to direct arc gases around and away from the wire lug. Another embodiment of the barrier provides that the first end, the second end and the middle portion are molded as a single, integral piece. Another embodiment provides that the body is composed of a dielectric material.
The present invention further provides a molded case circuit breaker comprising a molded case including a main cover, a first terminal and second terminal inserted in the case, a first contact electrically and mechanically coupled to the first terminal, and a second contact electrically and mechanically connected to the second terminal. An operating mechanism having a pivoting member movable between and ON position, an OFF position, and a TRIPPED position, wherein the pivoting member is coupled to the second contact. A trip unit coupled to the second contact and the second terminal with the trip unit in selective operative contact with the operating mechanism. An electric arc extinguishing apparatus is mounted in the housing and is positioned in confronting relation with the first and second contacts. A wire lug/arc vent barrier is coupled to the terminals. The barrier comprises a body having a first end including a tang, a second end including an elongated finger, and a middle portion between the first end and the second end defining a concave space, with an opening at each end of the middle portion, wherein the body is mounted in the housing. Another embodiment provides that the tang and elongated finger are configured to engage the housing and the concave spaces configured to receive a wire lug. Another embodiment provides that the middle portion is configured to direct arc gases around and away from the wire lug. Another embodiment provides wherein the first end, the second end and the middle portion are molded as a single, integral piece. Another embodiment provides wherein the body is composed of a dielectric material.
The present invention further provides a circuit breaker comprising a molded housing including a base. A means for connecting a load to the circuit breaker, mounted in the housing, a means for connecting an electrical line to the circuit breaker, and a means for coupling electrically to the means for connecting an electrical line. A movable means for contacting the means for connecting an electrical line to a means for operating mounted in the housing is coupled with the means for operating having a pivoting member movable between an ON position, an OFF position and a TRIPPED position. The pivoting member is coupled to the movable means for contacting and with the means for operating. A means for tripping is coupled to the movable means for contacting and the means for connecting the load with the means for operating. The means for tripping includes a means for releasing under a short circuit condition and a means for releasing under an overload condition. A means for extinguishing an electric arc is mounted in the housing with a movable means for contacting extended into the means for extinguishing. A means for shielding the means for connecting the load and line is mounted in the housing. Another embodiment provides that the means for shielding includes a tang and an elongated finger configured to engage the housing and a middle portion defining a concave space configured to receive a wire lug. Another embodiment provides where the middle portion is configured to direct arc gases around and away from the wire lug. It is also provided wherein the means for shielding is a single, integral piece of material. Another embodiment provides for the means of shielding to be a molded piece which can also be composed of a dielectric material.
The present invention further provides a method of assembling a wire lug/arc vent barrier system for a molded case circuit breaker having a housing with a load terminal, a line terminal, an operating mechanism connected to the line terminal, and a trip unit coupled to the operating mechanism and a load terminal. The method comprises the steps of providing a wire lug/arc vent barrier having a body, a first end including a tang, a second end including an elongated finger and a middle portion between the first end and the second end finding a concave space with an opening at each end of the middle portion. The method also includes providing a wire lug and installing the wire lug in the concave space. Then installing the wire lug/arc vent barrier and installed wire lug in the housing circuit breaker and securing the wire lug arc vent barrier and installed wire lug in the housing and one of the line terminal and load terminal.