Circuit breaker with shunt

Details Circuit breaker with shunt Circuit breaker with shunt

2001-05-21

2004-04-27

Sircus, Brian (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

Ground fault protection

C361S042000

Reexamination Certificate

active

06728085

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to circuit breakers and, more particularly, to a circuit breaker having a bus bar extending through at least a first current transformer, in which a shunt extends from the bus bar.
2. Description of the Related Art
Numerous types of circuit breakers are known and understood in the relevant art. Among the purposes for which circuit breakers are provided is to interrupt current on demand or under certain defined circumstances.
One type of circuit breaker that is typically used in relatively lower-current domestic applications is known as a “miniature” circuit breaker. Such miniature circuit breakers often are single pole breakers and are configured to be installed in a cabinet that houses a plurality of such miniature circuit breakers.
In their most simple form, miniature circuit breakers include a line terminal that is connectable with a power source and a load terminal that is connectable with an electrical load. Such a miniature circuit breaker typically includes a thermal trip mechanism in the form of a bimetal strip that triggers an operating mechanism to separate a pair of separable electrical contacts to interrupt the flow of current therethrough during an overcurrent condition of a sustained duration. Such circuit breakers typically additionally include a magnetic trip mechanism that triggers the operating mechanism in the event of a sudden increase in the current flowing through the circuit breaker.
A relatively more advanced miniature circuit breaker additionally includes a ground fault detection system that is operatively connected with the operating mechanism to open the contacts in the event of a line-to-ground fault or a neutral-to-ground fault. Such circuit breakers typically are referred to as ground fault circuit breakers.
The ground fault detection system of the ground fault circuit breaker typically includes a pair of spaced current transformers and a circuit board. The primaries of the current transformers are conductors that pass the current traveling through the circuit breaker through the central bores of the toroidal current transformers forming the secondary windings. The secondary windings of the current transformers are connected with the circuit board. As is set forth in U.S. Pat. No. 5,293,142 to Fello et al., the circuit breaker can include relatively rigid bus bars that are connected with the conductors and extend between the current transformers.
Such ground fault circuit breakers include a line terminal connectable with a power source, a load terminal connectable with an electrical load, a neutral terminal for connecting the electrical load with a neutral conductor of the circuit breaker, and a pigtail extending from the neutral conductor of the circuit breaker and connected to the distribution system neutral conductor.
A still more sophisticated type of ground fault circuit breaker can additionally detect the existence of an arc fault between a wire connected with the line terminal and a wire connected with the neutral terminal. Such circuit breakers are typically known as arc fault circuit breakers, one of which is described generally in U.S. Pat. No. 5,224,006, and a preferred one of which is described generally in U.S. Pat. No. 5,691,869.
Such arc fault circuit breakers typically sense the current traveling through the circuit breaker and analyze a waveform derived therefrom to detect an arc fault. In previously known circuit breakers, the current was sensed by connecting a pair of sensing leads to opposite ends of the bimetal strip and detecting the voltage drop along the bimetal strip between the leads to sense current.
While such arc fault circuit breakers have been generally effective at achieving their intended goals, such arc fault circuit breakers have not, however, been without limitation. For instance, in circumstances where the voltage drop along the bimetal strip is measured in order to sense current flowing through circuit breaker, the leads that are connected with the bimetal strip are attached thereto by welding. Such welding has a deleterious effect on the sensitive material of the bimetal strip. Additionally, leads that are attached to the bimetal strip have a tendency to resist the natural flexing motion of the bimetal strip in response to a prolonged overcurrent condition and thus interfere with the desirable current interruption features of the circuit breaker. While it has been known to provide an additional conductor extending from the free end of the bimetal strip toward the fixed end thereof in order to avoid having to connect a lead directly to the free end of the bimetal strip, such a methodology still does not avoid the need to weld at least one lead onto the bimetal strip.
Another shortcoming of such known arc fault circuit breakers involves a separating wall disposed within the circuit breaker. Such a separating wall is advantageously provided both for structural reasons as well as to separate the mechanical components of the circuit breaker from the circuit board. Such separation is desirable in order to resist contamination of the circuit with vaporized metal and carbon that results during interruption of the circuit. In known circuit breakers in which leads are connected directly with the bimetal strip, the leads must be passed through a passageway in the separating wall for connection with the circuit board. Such extension of the leads through the separating wall increases the complexity and cost of the circuit breaker, both in terms of materials and labor.
It is thus desired to provide an improved arc fault circuit breaker in which sensing leads are not welded to a bimetal strip and do not pass through the separating wall of the circuit breaker. Such a circuit breaker preferably will be configured such that the sensing leads are connected with another conductive component on the same side of the separating wall as the circuit board.
SUMMARY OF THE INVENTION
In view of the foregoing, a circuit breaker that is capable of detecting ground faults as well as arc faults includes a at least a first current transformer, a line conductor extending through the current transformers, a circuit board, and a pair of sensing leads extending between the line conductor and the circuit board. In a first embodiment the line conductor is a relatively rigid line bus bar, and in a second embodiment the line conductor is a relatively flexible line shunt. The circuit board is disposed adjacent a first side of a separating wall within the circuit breaker, and the line conductor extends along the first side such that the sensing leads that extend between the line conductor and the circuit board do not pass through a plane defined by the separating wall. The circuit breaker includes a bimetal strip that is free of sensing leads that extend between the bimetal strip and the circuit board.
An aspect of the present invention is to provide a circuit breaker that is free of sensing leads welded to a bimetal strip thereof.
Another aspect of the present invention is to provide a circuit breaker having a pair of current transformers and a line conductor extending between the current transformers, in which a pair of sensing leads are connected at spaced locations with the line bus bar and extend to a circuit board within the circuit breaker.
Another aspect of the present invention is to provide a circuit breaker having a separating wall that separates a plurality of mechanical components of the circuit breaker from a circuit board of the circuit breaker, in which sensing leads that are connected with the circuit board do not pass through a plane defined by the separating wall.
Another aspect of the present invention is to provide a circuit breaker having an arc fault detection capability in which sensing leads extend between a circuit board and a substantially rigid line bus bar.
Another aspect of the present invention is to provide a circuit breaker having an are fault detection capability in which sensing leads extend between a circuit board and a re

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