Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Reexamination Certificate
2000-01-25
2001-09-04
Tso, Edward H. (Department: 2838)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
Reexamination Certificate
active
06285534
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to circuit breakers provided with both ground fault and arc fault trip circuits, and more particularly, to a common test button for actuating selectively a ground fault test circuit and an arc fault test circuit.
BACKGROUND INFORMATION
Circuit breakers provide overcurrent and short circuit protection for electric power systems. In the small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. Such a device includes a bimetal which is heated and bends in response to a persistent overcurrent condition thereby unlatching a spring powered operating mechanism which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system. An armature attracted by the sizable magnetic forces generated by a short circuit also unlatches, or trips, the operating mechanism.
In many applications, the miniature circuit breaker also provides ground fault protection. An electronic circuit detects leakage of current to ground and generates a ground fault trip signal. This signal energizes a shunt trip solenoid which unlatches the operating mechanism, typically through actuation of the thermal-magnetic trip device.
Recently, there has been considerable interest in also providing protection against arcing faults. Arcing faults are intermittent high impedance faults which can be caused for instance by worn insulation, loose connections, broken conductors, and the like. Because of their intermittent and high impedance nature, arcing faults do not generate currents of sufficient instantaneous magnitude or sufficient average current to trigger the thermal-magnetic trip device. Consequently, separate electrical circuits have been developed for responding to arcing faults.
Ground fault protection circuits and arc fault protection circuits typically include test circuits for affirming their continued operability. These tests must be performed independently to assure operation of both functions. The simplest approach is to provide separate test switches, each with its own test button, for performing the ground fault and arc fault tests. However, the molded cases of the miniature circuit breakers have been standardized for interchangeable use in load centers. There is limited space available in the standardized miniature circuit breakers for all of the additional circuitry required for ground fault and arc fault protection, let alone the test circuits.
Commonly owned U.S. patent application Ser. No. 069,355 filed on Apr. 29, 1998 discloses an arrangement in which a common test button selectively actuates either the ground fault test circuit or the arc fault test circuit. The arc fault test switch and ground fault test switch comprise cantilevered electrically conductive flat springs straddling but spaced from a common flat spring. The free ends of all three of these flat springs are in parallel planes. The common test button is a rocker button rotatable in one direction from a neutral position to deflect the flat spring of the arc fault test switch into contact with the common flat spring to actuate the arc fault test circuit. When the rocker button is rotated in the other direction from the neutral position, the flat spring of the ground fault test switch is rotated into engagement with the common flat spring. One or more leaf springs secured in slots in the rocker button bias it to the neutral position. While this common rocker button separately actuates the two test circuits, its reliability is dependent upon tight manufacturing tolerances. Also, the biasing springs add additional labor and cost to manufacture of the circuit breaker.
There is a need, therefore, for an improved arrangement for selectively actuating an arc fault test circuit and a ground fault test circuit in a circuit breaker, and especially in a miniature circuit breaker.
There is a further need for such a circuit breaker which is easy to use, is inexpensive to manufacture, and does not require the holding of tight manufacturing tolerances.
SUMMARY OF THE INVENTION
These needs and others are satisfied by the invention which is directed to a circuit breaker which incorporates an electronic trip circuit which includes two test circuits each having their own test switch, such as for instance, for testing a ground fault protection circuit and an arc fault protection circuit. These test switches include separate first and second test contacts and a common contact. These first and second test contacts comprise cantilevered electrically conductive elongated springs selectively deflectable in generally orthogonal planes into engagement with the common contact. The circuit breaker further includes a common actuator moveable to a first position to deflect only the first test contact into engagement with the common contact to actuate only the first test circuit, and moveable to a second position to deflect only the second test contact into engagement with the common contact to actuate only the second test switch. The common actuator has a neutral position in which neither switch is actuated.
Preferably, the first and second test switch contacts and the common contact are flat electrically conductive elongated cantilevered springs having free ends. The free ends of the first switch contact and the common contact extend in parallel planes while the free end of the second switch contact extends in a plane substantially perpendicular to these parallel planes. The free end of the first flat switch contact is deflectable into flat surface contact with the common contact. The free end of the second flat switch contact is deflectable with a flat surface thereof engaging an edge of the common contact. The common actuator is moveable in a first direction from the neutral position to a first position in which the first switch is actuated, and is moveable in a second direction opposite the first direction from the neutral position to a second position to actuate the second switch. In the preferred embodiment, the common actuator is a rocker button mounted for rotation about a pivot axis which is parallel to the planes of the free ends of all three of the contact springs.
When the electronic trip means is provided on a printed circuit board, the cantilevered flat springs have fixed ends which are fixed to the printed circuit board with all of the fixed ends extending in parallel planes. The second switch contact is then bent between the fixed end and the free end so that the free end is substantially perpendicular to the plane of the fixed end.
Preferably, the rocker button has fingers which engage the flat springs of the first switch contact and second switch contact and are spaced apart so that a preload is applied to the first and second switch contacts to bias the rocker button to the neutral position.
REFERENCES:
patent: 4686600 (1987-08-01), Morris et al.
patent: 4823225 (1989-04-01), Foster et al.
patent: 4851951 (1989-07-01), Foster, Jr.
patent: 5260676 (1993-11-01), Patel et al.
patent: 5293522 (1994-03-01), Fello et al.
patent: 5546266 (1996-08-01), Mackenzie et al.
Gibson Jeffrey Scott
Whipple Michael Jerome
Eaton Corporation
Moran Martin J.
Tso Edward H.
LandOfFree
Circuit breaker with common test button for separate testing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Circuit breaker with common test button for separate testing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Circuit breaker with common test button for separate testing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2525732