Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Reexamination Certificate
2001-12-18
2003-08-26
Huynh, Kim (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
C361S049000, C340S650000
Reexamination Certificate
active
06611406
ABSTRACT:
BACKGROUND OF THE INVENTION
Ground Fault Circuit Interrupters (GFCI) are electrical devices in wide spread use today. They are designed to protect users against shock hazards by detecting very low levels of ground fault current. GFCIs are widely employed in both commercial and residential environments. A typical GFCI incorporating a duplex receptacle provides protection for devices plugged into itself and all devices located downstream of the GFCI device. Typically GFCIs are four terminal devices, two hot or AC leads for connection to AC electrical power and two LOAD leads for connection to downstream devices. Properly wired, a GFCI provides ground fault protection to downstream devices connected to its LOAD leads and to devices plugged into the GFCI receptacle itself. However, if the GFCI is reverse wired or improperly wired then downstream devices are still protected if there is a ground fault but the duplex receptacle on the GFCI itself is not.
In spite of detailed instructions that come packaged with most GFCIs and identification of AC and LOAD terminals, GFCIs are sometimes miswired. One possible reason for this miswiring is that in a new home there may not be any power coming into the distribution panel, making it difficult to identify which wires are the AC and which are the LOAD. The problem is compounded when it is considered that most GFCIs have a test button that will trip and shut off the power when pushed to verify operation of internal functions in the GFCI. However, use of the test button does not indicate whether the built in duplex receptacle is protected. Typical users may not be aware of this. Users simply test the device after installation and verify that the unit trips upon pressing the test button by way of an audible click, for example. This gives the user a false sense that all is well. What is actually happening is that the GFCI disconnects power from and protects everything downstream, but does not protect the receptacle contacts of the GFCI itself. The device will trip depending on the condition of internal components and irrespective of the how the GFCI was wired. It does not matter that the GFCI was reverse wired when it is tested.
One way for a user to verify that the GFCI is properly wired is to plug an electrical device or test lamp into the receptacle contacts of a GFCI and monitor it going off and on when pressing the test followed by the reset buttons. However, this is time consuming and labor intensive. Moreover, even when explained clearly in instructions provided with the GFCI, some users do not always follow them.
Therefore, it is quite apparent that there is a strong need for an automatic way to sense when a GFCI is miswired and to indicate to the user by visual (i.e. blinking light) or audible (i.e., loud buzzer) indications. In addition, when the GFCI is improperly wired the user needs to be alerted with alarms that cannot be stopped until the electricity is disconnected and the GFCI is correctly wired.
Although the prior art has attempted to solve this problem, the so called solutions have their own disadvantages and drawbacks. For example, one approach utilizes a GFCI with reverse line polarity lamp indicator to indicate proper installation of the GFCI. However, a push button needs to be manually pressed in order to detect whether the GFCI is miswired. An apparent drawback with this scheme is that the test is never self initiating, i.e., automatic, since the user must always remember to actually press a button to test the GFCI. In addition, no audible signal is generated to alert the user of a miswiring condition.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a system capable of automatically indicating when a GPCI is miswired or not properly electrically connected to its source of electrical power and to subsequently generate an alarm indicating to the user that a potentially unsafe condition exists.
Another object of the present invention is to provide a reliable miswiring indicating function irrespective of how the GFCI is connected to the electrical wiring. This is achieved whether the AC and LOAD terminals are simply reversed or if they are cross reversed, meaning the AC hot and neutral are connected not to the AC or LOAD side but to either the AC-hot and LOAD-hot terminals or the AC-neutral and LOAD-neutral terminals.
Yet another object of the present invention is to have the alarm remain in the on state once generated, until the user corrects the miswiring problem. More specifically, once the alarm is generated it is latched and cannot be shut off without removing the device and installing it properly.
Still yet another object of the present invention is to provide both a visual alarm and an audible alarm in the event a miswiring condition is detected. The visual alarm might be in the form of a blinking light. The audible alarm might be in the form of a buzzing or high tone sound that could beep on and off at a suitable rate.
REFERENCES:
patent: 4084203 (1978-04-01), Dietz et al.
patent: 4447844 (1984-05-01), Schossow et al.
patent: 5051732 (1991-09-01), Robitaille
patent: 5625285 (1997-04-01), Virgilio
patent: 5729417 (1998-03-01), Neiger et al.
Gershen Bernard
Neiger Benjamin
Rosenbaum Saul
Huynh Kim
Leviton Manufacturing Co. Inc.
Sutton Paul J.
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