Circuit breaker with a single test button mechanism

Details Circuit breaker with a single test button mechanism Circuit breaker with a single test button mechanism

2001-11-26

2003-03-25

Sircus, Brian (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

Ground fault protection

C361S044000

Reexamination Certificate

active

06538862

ABSTRACT:

BACKGROUND OF INVENTION
Conventional residential, light industrial and commercial circuit breakers typically have a thermal trip mechanism which responds to persistent overcurrents of moderate magnitude to provide a delayed trip in the breaker. Also included in the circuit breaker is a magnetic trip mechanism which responds instantaneously to overcurrent conditions of greater magnitudes. It is becoming more common for these circuit breakers to further include a ground fault trip mechanism as one of the active mechanisms. The ground fault trip mechanism includes a trip unit which detects faults between the line conductor and ground and the neutral conductor and ground. Line to ground faults are commonly detected by the use of a differential transformer. The line and neutral conductors are passed through the coil so that in the absence of a line to ground fault, the currents are equal and opposite and no signal is generated. However, when a line to ground fault exists, it creates a sizeable imbalance between the two currents in the two conductors which can be level detected. As is known, a neutral to ground fault may be detected by injecting a signal onto the neutral conductor which will produce an oscillation if feedback is provided.
In addition, conventional circuit breakers include mechanisms designed to protect against arc faults. For example, an arc fault may occur in the device when bare or stripped conductors come into contact with one another and the current caused by such a fault produces magnetic repulsion forces which push the conductors apart, thereby striking an arc. The arc that is caused by these faults can damage the conductors by melting the copper therein and this is especially true for stranded wire conductors such as extension cords, which can ignite surrounding materials.
Typically, the circuit breaker includes contacts that open upon sensing arcing from line to ground and/or from line to neutral. Arc fault circuit breakers typically use a differential transformer to measure arcing from line to ground. Detecting arcing from line to neutral is accomplished by detecting rapid changes in load current by measuring voltage drop across a relatively constant resistance, usually a bi-metal resistor.
Unfortunately, many conventional circuit breakers, including residential circuit breakers, do not permit the user to test both the arc fault circuit interrupter (AFCI) and ground fault circuit interrupter (GFCI) circuits in the device. On the other hand, if these circuit breakers allow the user to test both the AFCI and GFCI circuits, these circuit breakers necessitate the use of an opto-coupler to pass the trip signal while electrically isolating the two line phases from the detection circuitry. In addition, the prior art requires using two test switches, one switch for each phase, testing both ground fault and arc fault. Furthermore, the ability to test both of these detection circuits is very important for customer safety and because a vast amount of individuals do not understand the implications of a circuit failure, it is important to best educate these individuals about these implications and what systems are available to minimize the likelihood that such a circuit failure occurs.
SUMMARY OF INVENTION
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a single test mechanism for use in a circuit breaker. More specifically, the single test mechanism includes a dual test button which comprises a single switch for testing both the AFCI and GFCI circuits of the breaker. The test mechanism includes a circuit board, which forms a part of the circuit breaker, and a test button assembly which includes a test button and signaling components which are electrically connected to the circuit board.
The test button has a first position and a second position, wherein positioning the test button in the first position produces a first signal and positioning the test button in the second position produces a second signal. A trip mechanism is included in the circuit breaker and includes a pair of separable contacts, wherein the trip mechanism is electrically connected to the circuit board so that in response to receiving one of the first and second signals, the circuit board generates a trip signal which directs the trip mechanism to separate the pair of separable contacts. In an exemplary embodiment, the first position comprises a test position for the AFCI circuit associated with one pole and the second position comprises a test position for the AFCI circuit associated with another pole. In either the first or second position, AFCI circuitry initiates a trip by generating a current imbalance causing the GFCI circuitry to generate a trip signal for tripping the circuit breaker. Thus, the present disclosure permits the customer to test both the AFCI and GFCI circuits by positioning a single test button accordingly in either the first or second test button positions.
The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.


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