Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Reexamination Certificate
2000-11-28
2004-10-19
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
C361S044000, C361S045000
Reexamination Certificate
active
06807035
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a fault interrupter, particularly but not necessarily a ground fault circuit interrupter (GFCI), which utilizes a microprocessor to sense faults and to automatically test for proper function of the interrupter on a periodic basis, without the need for external intervention, and to disable the load circuit if an unsafe condition exists.
BACKGROUND OF THE INVENTION
Conventional GFCI devices are designed to trip in response to the detection of a ground fault condition at an AC load. Generally, the ground fault condition results when a person comes into contact with the hot side of the AC load and an earth ground at the same time, a situation which can result in serious injury. The GFCI device detects this condition by using a sensing transformer to detect an imbalance between the currents flowing in the hot and neutral conductors of the AC supply, as will occur when some of the current on the hot side is being diverted to ground. When such an imbalance is detected, a circuit breaker relay within the GFCI device is immediately tripped to an open condition, thereby opening both the hot and neutral sides of the AC line and removing all power from the load. Many types of GFCI devices are capable of being tripped not only by contact between the hot side of the AC load and ground, but also by a connection between the neutral side of the AC load and ground. The latter type of connection, which may result from a defective load or from improper wiring is potentially dangerous because it can prevent a conventional GFCI device from tripping at the intended threshold level of differential current when a line-to-ground fault occurs.
GFCI devices need to undergo periodic testing. Most GFCI devices can be manually tested for proper operation by means of a test further which, when depressed, simulates an actual ground fault by creating a momentary imbalance between the currents flowing in the hot and neutral conductors of the AC power supply. However, most users will use the manual test button occasionally or not at all. Therefore, proposals have been made for GFCI devices which carry out automatic self-tests on a periodic basis, without the need for user-intervention. However, the self-testing GFCI devices proposed so far do not have the ability to directly test for proper operation of the circuit breaker or relay contacts that are intended to remove power from the load in the event of a fault. If the contacts malfunction, power may continue to be available to the load although the GFCI device has taken the necessary steps to create an open circuit condition.
U.S. Pat. No. 5,600,524 discloses a ground fault circuit interrupter which incorporates a self test that attempts to check the state of the contacts. The self test involves briefly applying a small amount of current to the contacts through the trip coil. If this small amount of current is measured at the trip coil, the device assume that the trip coil and thus the contacts will function properly. However, a significant disadvantage to this type of indirect testing is that the current is not measured at the contacts themselves. Accordingly, there may still be current flowing through the contacts after a fault if they are welded closed, and the load will still be drawing power, resulting in a dangerous condition. This is despite the fact that the GFCI device has properly detected the fault and has attempted to create an open circuit condition at the load. Thus, a need exists for a means of directly testing the circuit breaker or relay contacts of a GFCI device to determine if they have opened and disabled power to the load.
In addition, U.S. Pat. No. 5,600,524 discloses complex circuitry to achieve self-testing, fault generation and fault testing. A need exists for less complicated circuitry, thus producing a more efficient and less costly method for ground fault circuit interruption.
SUMMARY OF THE INVENTION
In accordance with the present invention, a fault interrupter, such as a ground fault circuit interrupter (GFCI), an arc fault circuit interrupter (AFCI) or a combined GFCI/AFCI device, is provided that can automatically test its internal circuitry on a periodic basis, such as on a monthly, weekly, daily or even hourly basis.
Another aspect of the present invention is to provide a fault interrupter that detects actual imbalances in the load current using a microcontroller.
Another aspect of the present invention is to provide a fault interrupter which operations when a ground fault signal occurs, the load is opened substantially coincident with a zero-crossing of the AC power source.
Another aspect of the present invention is to provide a fault interrupter in which manual testing is accomplished by pushing a manual test button, thus initiating a driver circuit which generates a fault. The fault is sensed by a sense transformer that has an input into the microcontroller, which activates a load relay to an open condition.
An additional aspect of the present invention is to provide a fault interrupter in which the manual test button is a direct input to a microcontroller. When the microcontroller receives such an input, it generates an imbalance in the load current and activates the load relay to an open condition.
Yet another aspect of the present invention is to provide a fault interrupter with the ability to detect when it has been incorrectly wired, that is, when line and load connections have been reversed. Upon detection of a miswiring condition, a visual and/or audible alarm is triggered to alert the user, and the load contacts are opened removing power from downstream electrical devices.
In accordance with yet another aspect of the present invention, a periodic test reminder signal is provided to alert the user to manually test the fault interrupter. A visual and/or audible alert signal can be generated 30 days after power was initially applied or 30 days after the last manual test was performed. A daylight detector can be included to silence the test reminder signal during evening and nighttime hours.
In accordance with another aspect of the present invention, the microcontroller creates a closed circuit condition if the load circuit becomes open through some eternal shock or vibration.
The foregoing aspects are substantially achieved by a circuit interrupter apparatus for detecting faults connected to a line monitoring device and a line interrupter circuit. The circuit interrupter apparatus is comprised of a microcontroller connected to a line monitoring device and to a line interrupter circuit, the microcontroller being programmable to receive and process inputs from the line monitoring device to determine the occurrence of a fault in the load, and to operate the line interrupter circuit when a fault is detected.
Another aspect is substantially achieved by a circuit interrupter apparatus for detecting faults in a load connected to a line monitoring device and a line interrupter circuit, wherein the circuit interrupter apparatus comprises a microcontroller and a manual test device. The microcontroller is connected to the line monitoring device and to the line interrupter circuit and the microcontroller is programmable to receive and process inputs from the line monitoring device to determine the occurrence of a fault in the load and to operate the line interrupter circuit when a fault is detected. The manual test device comprises a manual test switch connected to a driver circuit, the driver circuit being connected to the line monitoring device and being operable in response to activation of the manual test switch to induce a fault condition that is detected by the line monitoring device and indicated to the microcontroller by the inputs.
Another aspect of the present invention is substantially achieved by a circuit interrupter apparatus for detecting faults in a load connected to a line monitoring device and a line interrupter circuit wherein the circuit interrupter apparatus comprises a microcontroller and a manual test switch. The microcontroller is connected t
Baldwin John Richard
Batko Thomas James
Ellison David Francis
McDonald Thomas Michael
'Hubbell Incorporated
Goodman Alfred N.
Jackson Stephen W.
Longanecker Stacey J.
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