U.S. patent application number 11/467814 was filed with the patent office on 2006-12-21 for ground fault circuit interrupter incorporating miswiring prevention circuitry.
Invention is credited to Benjamin Neiger.
Application Number | 20060285262 11/467814 |
Document ID | / |
Family ID | 22215963 |
Filed Date | 2006-12-21 |
United States Patent
Application |
20060285262 |
Kind Code |
A1 |
Neiger; Benjamin |
December 21, 2006 |
GROUND FAULT CIRCUIT INTERRUPTER INCORPORATING MISWIRING PREVENTION
CIRCUITRY
Abstract
A ground fault circuit interrupter (GFCI) with built in
intelligence is described that includes circuitry to automatically
indicate a device miswiring condition. When a GFCI is wired with
its AC and LOAD terminals reversed, downstream devices are still
protected in the event of a ground fault but the duplex receptacle
on the GFCI itself is not. The invention incorporates miswiring
sense circuitry that automatically triggers the generation of
visual and audible alarms in the event a miswiring condition is
sensed. The invention employs an alarm inhibiting technique that
incorporates sense circuitry connected to the AC terminals on one
side of the internal GFCI switches or relays and alarm generation
circuitry connected to the LOAD terminals on the opposite side.
Inventors: |
Neiger; Benjamin; (Floral
Park, NY) |
Correspondence
Address: |
PAUL J. SUTTON, ESQ., BARRY G. MAGIDOFF, ESQ.;GREENBERG TRAURIG, LLP
200 PARK AVENUE
NEW YORK
NY
10166
US
|
Family ID: |
22215963 |
Appl. No.: |
11/467814 |
Filed: |
August 28, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10647044 |
Aug 22, 2003 |
7099129 |
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11467814 |
Aug 28, 2006 |
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10024166 |
Dec 18, 2001 |
6611406 |
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10647044 |
Aug 22, 2003 |
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09828742 |
Apr 9, 2001 |
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10024166 |
Dec 18, 2001 |
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09370352 |
Aug 9, 1999 |
6226161 |
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09828742 |
Apr 9, 2001 |
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09001479 |
Dec 31, 1997 |
5963408 |
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09370352 |
Aug 9, 1999 |
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08746692 |
Nov 14, 1996 |
5706155 |
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09001479 |
Dec 31, 1997 |
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08572811 |
Dec 15, 1995 |
5729417 |
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08746692 |
Nov 14, 1996 |
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08089149 |
Jul 8, 1993 |
5477412 |
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08572811 |
Dec 15, 1995 |
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Current U.S.
Class: |
361/42 |
Current CPC
Class: |
H02H 3/338 20130101;
H02H 3/04 20130101 |
Class at
Publication: |
361/042 |
International
Class: |
H02H 3/00 20060101
H02H003/00 |
Claims
1. A ground fault circuit interrupter comprising: ground fault
current interrupter means electrically connected between a source
of electrical power and a load for interrupting the flow of
electrical current from said source of electrical power to said
load when a ground fault condition exists; and indicating means
responsive to said ground fault current interrupter means for
automatically indicating when said ground fault current interrupter
means is not properly electrically connected to said source of
electrical power.
2. A ground fault circuit interrupter comprising: ground fault
current interrupter means electrically connected between a source
of electrical power and a load for interrupting the flow of
electrical current from said source of electrical power to said
load when a ground fault condition exists; said ground fault
current interrupter means including receptacle means for coupling
said source of electrical power to an external electrical device;
and indicating means responsive to said ground fault current
interrupter means for automatically indicating when said ground
fault current interrupter means is not properly electrically
connected to said source of electrical power thereby alerting a
user that the flow of electrical current from said source of
electrical power to said external electrical device will not be
interrupted when a ground fault condition exists.
3. A ground fault circuit interrupter comprising: ground fault
current interrupter means electrically connected between a source
of electrical power and a load for interrupting the flow of
electrical current from said source of electrical power to said
load when a ground fault condition exists; said ground fault
current interrupter means including receptacle means for coupling
said source of electrical power to an external electrical device;
sensing means electrically connected to said ground fault current
interrupter means for automatically sensing when said ground fault
current interrupter means is properly electrically connected to
said source of electrical power; and alarm generating means
responsive to said sensing means for automatically generating an
alarm when said sensing means fails to sense that said ground fault
current interrupter means is properly electrically connected to
said source of electrical power thereby alerting a user that the
flow of electrical current from said source of electrical power to
said external electrical device via said receptacle means will not
be interrupted when a ground fault condition exists.
4. A ground fault circuit interrupter electrically connected
between a source of electrical power and a load and which
interrupts the flow of electrical current from said source of
electrical power to said load when a ground fault condition exists,
wherein the improvement comprises: indicating means electrically
connected to said ground fault circuit interrupter for
automatically indicating when said ground fault circuit interrupter
is not properly electrically connected to said source of electrical
power.
5. A ground fault circuit interrupter electrically connected
between a source of electrical power and a load including ground
fault current interrupter means for interrupting the flow of
electrical current from said source of electrical power to said
load when a ground fault condition exists and receptacle means for
coupling said source of electrical power to an external electrical
device, wherein the improvement comprises: sensing means
electrically connected to said ground fault current interrupter
means for automatically sensing when said ground fault current
interrupter means is properly electrically connected to said source
of electrical power; and alarm generating means responsive to said
sensing means for automatically generating an alarm when said
sensing means fails to sense that said ground fault current
interrupter means is properly electrically connected to said source
of electrical power thereby alerting a user that the flow of
electrical current from said source of electrical power to said
external electrical device via said receptacle means will not be
interrupted when a ground fault condition exists.
Description
BACKGROUND OF THE INVENTION
[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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
[0006] A primary object of the present invention is to provide a
system capable of automatically indicating when a GFCI 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.
[0007] 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.
[0008] 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.
[0009] 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 alann 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.
[0010] The foregoing and other objects and advantages which will be
apparent in the following detailed description or in the practice
of the invention, are achieved by the invention disclosed herein,
which generally may be characterized as a ground fault circuit
interrupter comprising ground fault current interrupter means
electrically connected between a source of electrical power and a
load for interrupting the flow of electrical current from the
source of electrical power to a load when a ground fault condition
exists and indicating means responsive to the ground fault current
interrupter for automatically indicating that the ground fault
current interrupter is not properly connected to the source of
electrical power.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Serving to illustrate exemplary embodiments of the invention
are the drawings of which:
[0012] FIG. 1 is a functional block diagram of the preferred
embodiment of the GFCI of the present invention;
[0013] FIG. 2 is a functional block diagram showing the proper
wiring configuration of the GFCI of the present invention;
[0014] FIG. 3 is a functional block diagram showing one improper
method of wiring the GFCI of the present invention to an electrical
wiring system;
[0015] FIG. 4 is a functional block diagram showing a second
improper method of wiring the GFCI of the present invention to an
electrical wiring system;
[0016] FIG. 5 is a functional block diagram showing a third
improper method of wiring the GFCI of the present invention to an
electrical wiring system; and
[0017] FIG. 6 is a detailed schematic diagram of the circuit
comprising the preferred embodiment of the GFCI of the present
invention.
[0018] DETAILED DESCRIPTION OF THE INVENTION
[0019] In order to afford a complete understanding of the invention
and an appreciation of its advantages, a description of a preferred
embodiment in a typical operating environment is presented
below.
[0020] Shown in FIG. 1 is a functional block diagram of the GFCI
Incorporating Miswiring Prevention Circuitry (GFCIMP). The GFCI 98
circuitry is depicted as a black box connected across the AC hot
and neutral terminals with control signals going to both switch
relays 88, 90. The GFCI circuit 98 can be any typical industry
standard type GFCI circuit that removes the power delivered to the
load upon detection of a ground fault. Also included in many
standard GFCIs is a duplex receptacle 100 built into the device.
The duplex receptacle 100 is connected to the LOAD hot and neutral
terminals of the GFCI 10 in order that power to it, besides devices
downstream, be disconnected from the AC power upon the occurrence
of a ground fault.
[0021] Traditional GFCIs consist mainly of these three elements,
GFCI 98, switches 88, 90, and the duplex receptacle 100. The GFCIMP
10 employs additional circuitry to indicate the improper wiring of
the device in an electrical system. The additional elements are a
sense circuit 94, alarm generation circuit 96 and power supply
circuit 92. Each will be explained in detail below. The alarm
generation circuit 96 will automatically generate an alarm if the
following two conditions are met: it is provided with power from
the power supply circuit 92 and it does not receive an inhibit
signal 102 from the sense circuitry 94. The power supply circuit 92
is connected across hot and neutral on both sides of the switches
88, 90. This connection scheme allows the power supply 92 to
receive AC power regardless of how the user wires the GFCIMP 10
into the electrical system. This arrangement provides the alarm
generation circuitry 96 with a reliable source of power to be able
to alert the user if there is a miswiring condition.
[0022] Possible wiring configurations of the GFCIMP 10 are shown in
FIGS. 2, 3, 4 and 5. Assuming power is available, the only way the
alarm generation circuitry 96 can be prevented from generating
audible and visual alarms is if the inhibit signal 102 is produced.
The sense circuitry 94 requires AC power to be present on the AC
hot and neutral terminals in order to generate an inhibit signal
102. It does not matter, however, that hot and neutral are reversed
for the inhibit signal 102 to be generated. Thus, the wiring
arrangement shown in FIG. 2 is the only one that does not cause an
alarm to be generated. AC power must be properly connected to the
AC hot and neutral terminals to suppress alarm generation. The
GFCIMP 10, in FIG. 2, properly protects downstream devices along
with its own receptacle. The inhibit signal 102 remains present to
suppress generation of the alarm by the alarm generation circuitry
96.
[0023] The GFCIMP if connected as shown in FIGS. 3 and 4 will cause
the alarm to be generated because the alarm generation circuitry 96
does not receive an inhibit signal 102 needed to suppress alarm
generation. In FIG. 3 the downstream device is connected to the AC
hot and neutral terminals of the GFCIMP 10. Thus no AC power is
available to produce the inhibit signal 102. The AC power is
connected to the LOAD hot and neutral terminals of the GFCIMP 10.
When the switches 88, 90 are closed, the GFCIMP 10 apparently
operates normally, opening the circuit when a ground fault is
detected. Since power is present at the sense circuitry 94
terminals the inhibit signal 102 is generated and suppresses
alarms. However, the first time the GFCIMP 10 trips for any reason
(i.e., ground fault or manual test) AC power will be removed from
the sense circuitry 94. This causes the alarm to be produced
because of the absence of the inhibit signal 102. The wiring
configuration shown in FIG. 3 depicts the most common GFCI
miswiring by users. Thus use of an GFCIMP with miswiring sensing
and alarm generation circuitry is likely to prevent the potentially
dangerous condition of the GFCI receptacle not being protected.
[0024] Another improper configuration of the GFCIMP 10 is shown in
FIG. 4. Here, the AC power is connected across the AC hot terminal
and the LOAD neutral terminal. Whether the switches 88, 90 are
closed or open, the power supply circuitry 92 has AC power
available to generate DC power for the alarm generation circuitry
96. The downstream device is connected to the AC neutral and LOAD
hot terminals. When the switches 88, 90 are closed, the sense
circuitry 94, being powered, generates the inhibit signal 102
suppressing alarm generation. However, when the switches 88, 90
open, AC power is cutoff from the sense circuitry 94 causing the
inhibit signal 102 to be removed and the alarm to be generated. The
scenario is the same if the AC power and LOAD connections are
reversed. This incorrect wiring arrangement is less likely to occur
since most users do not interconnect AC and LOAD terminals when
installing the GFCI.
[0025] The configuration shown in FIG. 4 is also an improper way of
wiring the GFCIMP 10 into the electrical system. However, when the
device is installed and reset and the power is subsequently
applied, the AC electrical breaker or fuse will trip or blow. This
is because AC power has been wired to short out as soon as power is
applied. This also occurs if the AC power and LOAD connections are
reversed.
[0026] As shown in FIG. 6, the power supply circuitry 92 utilizes
four connections to generate DC power from the AC source. Due to
the various ways a user can wire the GFCIMP 10 device into the
electrical system, connections to hot and neutral are provided on
both the AC and LOAD sides of the switches 88, 90. Consequently,
whether the switches 88, 90 are open or closed the power supply 92
generates DC voltage for the alarm generation circuitry 96. The
power supply 92 is a floating supply meaning that the grounded DC
system created is not referenced to the AC source system it is
generated from. AC power is fed through current limiting resistors
40, 42, 44, 46 to blocking capacitors 48, 54, 65, 58 respectively.
Typical values for the resistors are 47K ohms and for the
capacitors 0.1 uF rated at 250V. If AC power is applied to the AC
terminals of the GFCIMP 10 then diode 64 rectifies the positive
cycle of the AC wave form. If the device is wired incorrectly with
AC power at the LOAD terminals, diode 66 rectifies the positive AC
wave form. If the switch 88 is closed than both diodes 64 and 66
rectify the AC wave. In either case resistor 32, nominally 10K ohm,
provides current limiting for the DC load. Zener diode 24,
typically 12 volts, clamps the rectified AC wave form at the zener
voltage. Current flow though blocking diode 22 and causing
capacitor 86, typically 100 uF rated at 16V, to charge up to the
zener voltage minus a diode drop. The blocking diode 22 prevents
the capacitor 86 from discharging during the time the AC cycle is
lower than the zener 24 voltage.
[0027] Current passes through the DC load, which is the alarm
generation circuitry 96, and returns through the floating ground to
the AC source through diode 72, 70 or both, depending on whether AC
power is connected to the AC terminals or the LOAD terminals and
whether the switches 88, 90 are open or closed. The return path is
through dropping capacitors 54 or 56 and current limiting resistors
42, 44. The current limiting resistors and dropping capacitors are
employed to meet UL standards and for safety. Thus if the diode
bridges 104 or 108 fail, there still will be 50K ohm of resistance
if the switches 88, 90 are closed. Each pair of resistors 40, 46
and 42, 44 in parallel form an equivalent 25K ohms resistor. The
two parallel combinations in series are the equivalent of 50K ohms.
If the switches 88, 90 are open, two 50K ohms combine to form 100K
ohms in series with the AC power. Either scenario limits the
current to 1 or 2 mA, which is within UL standards.
[0028] The sense circuitry 94 functions to generate an inhibit
signal 102 only when AC power is applied to the AC hot and neutral
terminals. As already mentioned, this can be achieved in a number
of ways while the switches 88, 90 are closed. However, when the
switches 88, 90 are open, the only one way the AC power can be
connected to the GFCIMP 10 and consequently cause the sense
circuitry 94 to generate an inhibit signal 102 is with the AC power
connected to the AC hot and neutral terminals.
[0029] In a typical wiring configuration AC power, during the
positive half cycle, passes through current limiting resistor 40
and dropping capacitor 50. Diode 80 rectifies the AC wave form and
subsequently capacitor 84 charges. Resistor 38 further current
limits the signal and zener diode 34, typically 12 volts, limits
the voltage of the inhibit signal 102. Resistors 38 and 26 act as
voltage dividers. Both typically being 50K ohms, they divide the
voltage roughly in half. Resistors 38, 26 also serve as a path for
current since the gate on JFET 14 has an extremely high input
impedance. Capacitor 84 also serves to maintain a DC level of the
gate of JFET 14 which could be a National Semiconductor 2N5457, for
example. It is noted that almost any device with low current
requirements could perform adequately in place of JFET 14. The
return path for ground is through diode 76 of bridge 106.
[0030] The scenario for the negative half cycle is similar except
that current now flows through diode 78 to charge capacitor 84 and
subsequently produce the inhibit signal 102. The ground return path
is now through diode 82.
[0031] The alarm generation circuitry 96 section of the GFCIMP 10
is responsible for controlling and generating audible and visual
alarms in response to an inhibit signal 102. The visual element
consists of an LED 16 that could be of a variety that includes
blinking circuitry built in or does not. The audible element is a
piezo transducer 20 or other suitable element that likewise could
incorporate circuitry built in that turns the element on and off at
an appropriate rate. Alternatively, blinking circuitry 110 can be
included that provides this feature. Blinking circuitry is
preferred because a low duty cycle for the LED 16 and piezo
transducer 20 means much less current is required for alarm
generation. This causes less of a current drain on the capacitor
86, allowing it to better maintain the zener 24 voltage. Thus the
few milliamps charging capacitor 86 is sufficient to provide power
to generate the alarms.
[0032] The inhibit signal 102 generated by the sense circuitry 94
discussed earlier is fed to the gate of n-channel JFET 14. When the
inhibit signal 102 is being present, the JFET 14 turns on effecting
a very low impedance path from drain to source. Subsequently,
current flows through gate current supply resistor 30 to ground.
Thus capacitor 28 is discharged and is prevented from further
charging. This in turn deprives the SCR 12 of sufficient gate
current to turn on. Current through the LED 16 and piezo transducer
20 is prevented from flowing because there is no return path
through the SCR 12. When the GFCIMP 10 is properly wired into the
electrical system this is the state the device remains in whether
the switches 88, 90 are open or closed.
[0033] When AC power is first applied to the GFCIMP 10, it is
possible that SCR 12 might trigger and cause the alarm to be
generated before the inhibit signal 102 appears at the gate of WET
14. Thus the alarm sounds even though the GFCIMP 10 is properly
wired into the electrical system. Capacitor 28 serves to prevent
this from occurring by delaying the gate signal to SCR 12 in
reference to the inhibit signal 102. In order for the SCR 12 to
trigger and turn on, capacitor 28 must charge to a sufficient
voltage. This delay time gives the sense circuitry 94 a chance to
generate the inhibit signal 102 when the GFCIMP 10 is properly
wired.
[0034] When the GFCIMP 10 is miswired to prevent the inhibit signal
102 from being generated, due to the lack of AC power on the AC hot
and neutral terminals, the JFET 14 does not receive any gate drive
voltage. The JFET 14 now has a very high impedance from drain to
source and current flows through resistor 30, providing gate
current for SCR 12, and charging capacitor 28. Sufficient gate
current is now available to turn on SCR 12 and current can flow
through LED 16 and piezo transducer 20 causing the audible and
visual alarms to be generated. Once SCR 12 is triggered and turns
on it becomes latched and cannot be turned off. This has the effect
of forcing the user to rewire the GFCIMP 10 correctly if he wants
to prevent the alarms being generated.
[0035] It is clear that the above description of the preferred
embodiment in no way limits the scope of the present invention
which is defined by the following claim.
* * * * *