Note: Descriptions are shown in the official language in which they were submitted.
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GROUND FAULT CIRCUIT INTERRUPTER WITH REVERSE WIRING
PROTECTION
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a ground fault circuit interrupter (GFCI) for
load
ground-fault protection. More specifically, the invention relates to a GFCI
receptacle
utilizing an electromagnetic tripper and providing reverse wiring protection.
Discussion of Related Art
Ground fault circuit interrupter (GFCI) devices are designed to trip in
response to
the detection of a ground fault condition at an AC load. For example, the
ground fault
condition may result when a person comes into contact with the line side of
the AC load
and an earth ground at the same time, a situation that 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 line and neutral conductors of the AC
supply, as will
occur when some of the current on the line side is being diverted to ground.
When such
an imbalance is detected, a circuit breaker within the GFCI device is
immediately tripped
to an open condition, thereby opening both sides of the AC line and removing
all power
from the load.
A GFCI generally includes a housing, a tripper, a reset button, a test button,
a
mounting strap with grounding strap and banding screw, a pair of movable
contact
holders with contacts, a pair of fixed contact holders with contacts and a
control circuit.
Currently, GFCIs are widely used to prevent electric shock and fire caused by
a ground
fault.
The ground fault circuit interrupter (GFCI) according to the present invention
comprises a pair of first contact holders, each having a contact at one end; a
pair of
movable contact holders, each having a fixed end and a movable end, each of
the
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movable ends having a contact; a movable assembly that moves between a first
position
and a second position, wherein the first position is a position in which each
of the
contacts of the first contact holders makes contact with one of the contacts
of the
movable end of one of the movable contact holders, and wherein the second
position is a
position in which the contacts of the first contact holders are separated from
the contacts
of the movable contact holders; an electromagnetic resetting component, which,
when
energized, causes the movable assembly to be in the first position; an
electromagnetic
tripping component, different from the electromagnetic resetting component,
which,
when energized, causes the movable assembly to be in the second position; and
a control
circuit, which, upon detection of a fault condition, energizes the
electromagnetic tripping
component, and which, after a reset switch is activated, energizes the
electromagnetic
resetting component.
One particular object of an embodiment of the present invention is to provide
a
GFCI receptacle with reverse wiring protection that incorporates an
electromagnetic
tripper and a corresponding control circuit.
The GFCI receptacle according to a first embodiment of the present invention
comprises an electromagnetic tripper, a rear portion, a central body, a face
portion, a test
button, a reset button, an indicator, a mounting strap with a grounding strap
and a binding
screw, a pair of movable contact holders having one end fixed and the other
end able to
freely bias, a pair of fixed contact holders mounted on the central body, and
a control
circuit.
Because the tripper is electromagnetic, the GFCI receptacle carries out the
breaking and making operation through the interaction of the relevant
electromagnetic
forces produced by the trip coil (J1), the closing coil (J2) produces, and the
permanent
magnet. Furthermore, by using the magnetic force of the permanent magnet to
provide a
retentive force on the tripper, the operating sensitivity is improved, and the
GFCI is more
energy efficient.
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According to another feature of the invention, the GFCI is provided with
reverse
wiring protection in that the control circuit is de-energized when the GFCI is
miswired by
connecting the line to the load so that the GFCI receptacle can not be reset.
When the
GFCI is miswired, the face portion, particularly at the entry ports and the
ground-prong-
receiving openings that accommodate the three-wire plugs, is without a flow of
electricity, which provides additional safety feature for human use.
A further object of the present invention is to provide an electromagnetic
tripper
that is electronically controlled. In such an embodiment (for example, the
implementation
shown in FIG. 10), the tripper comprises a permanent magnet, a coil framework,
a trip
coil, a closing coil, a plunger, a trip spring, a movable bracket, a balance
frame, and a
small spring providing a contact force for the movable contact holders. When
the reset
button is depressed, the closing coil will be energized and will produce an
electromagnetic force that works with the magnetic force of the permanent
magnet to act
on the plunger to overcome the returning force of the trip spring and certain
frictional
forces, thereby closing the tripper, and the magnetic force of the permanent
magnet
maintains the tripper in the closed condition. Because the plunger and the
movable
bracket are coupled, the movement of the plunger directly drives the movable
bracket to
move in the same direction, and the movement of the movable bracket causes the
balance
frame to move. The movement of the balance frame lifts the removable contacts
against
the fixed contacts through the special shape of the movable contact holder
(the movable
contact holder has a V-shaped groove, and when it is in the tripping state,
the bracket of
the balance frame moves into the V-shaped groove). When the tripper is in the
closed
state, the movable contact connects with the fixed contacts, and the small
spring
associated with the balance frame provides a contact force to maintain good
contact,
thereby maintaining the GFCI receptacle in the normal operating condition.
When the GFCI receptacle of the above embodiment is energized, if a ground
fault occurs at the load or there is a factitious fault current, the control
circuit will gate a
silicon controlled rectifier (SCR) into conduction to energize the trip coil.
The trip coil
will then produce an electromagnetic force in the direction which repels the
magnetic
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force of the permanent magnet. The electromagnetic force and the returning
force of the
trip spring act on the plunger, thereby making the tripper open quickly.
Still another object of the present invention is to provide a special control
circuit
which mainly comprises a DC power source, integrated amplification circuit,
sensing
circuit, trip circuit, reset circuit, and test circuit. In one embodiment of
the invention in
which these objects are satisfied, four diodes form a full-wave bridge
rectifier circuit.
After the AC from the line is commutated by the rectifier circuit, there will
be DC on the
output terminal of the rectifier circuit. This embodiment includes an
integrated
amplification circuit, which may be a special IC (for example, of the type
RV4145A or
RV2145). The sensing circuit may include a sensor that comprises a sensing
transformer
and a neutral transformer. The AC line and neutral conductors pass through the
transformers. In operation, the sensing transformer serves as a differential
transformer for
detecting a current leakage between the line side of the load terminal and an
earth ground,
while the neutral transformer detects current leakage between the neutral side
of the load
terminal and an earth ground. When an imbalance between the currents flowing
in the
line and neutral conductors of the AC supply is detected, a circuit breaker
within the
GFCI device is immediately tripped to an open condition, thereby opening both
sides of
the AC line and removing all power from the load. In the reset control
circuit, the reset
switch is connected to a silicon controlled rectifier (SCR). When the reset
switch is
closed, the SCR will be gated into conduction and will cause a closing coil
connected
with the SCR to be energized to thereby reset the GFCI. Simultaneously, a
capacitor is
connected to the reset switch to keep the closing coil energized for an
instant. In this way,
it prevents the closing coil from being burned out in the event that the
current flowing
through the closing coil is too large and the energized time is too long.
The power supply of the control circuit is connected to the AC supply of the
GFCI, so when the GFCI is energized, the control circuit is also energized.
However, if
the GFCI is miswired by connecting the line to the load, the control circuit
is de-
energized, and the GFCI will not be able to be reset, achieving the reverse
wiring
protection function. Because the reset of the GFCI is electronically
controlled, the
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operation is more convenient, and the action is more sensitive compared to
GFCIs using
mechanical means.
In a further embodiment of the invention, the movable contact holders, the
movable assembly, and the fixed contacts are arranged so as to provide two
separate
contact points between movable contacts and fixed contacts on each side (phase
and
neutral) of the GFCI. In one sub-embodiment, the single movable contact holder
on each
side is replaced with two movable contact holder elements, each having a V-
shaped bend,
the two movable contact holder elements being placed against each other with
the V-
shaped bends arranged opposite each other. One end of each movable contact
holder
element has a movable contact, and the other end is joined with the other end
of the other
movable contact holder element and connected to a conductor coupled to one
side of the
line (i.e., either phase or neutral). In this arrangement, the movable contact
holder
elements remain together, and the movable contacts do not make contact with
the fixed
contacts, in the tripped state, while the movable contact holder elements are
separated (by
the movable assembly), and contact is made, when the GFCI is reset.
In a second sub-embodiment, the movable contact holder is mounted on the
movable assembly and is connected to a flexible conductor on one end. The
other end of
the movable contact holder is provided with the two movable contacts, which
make
contact with the two fixed contacts when the movable assembly is in a first
(closed)
position and does not make contact when the movable assembly is in a second
(tripped)
position.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in further detail in conjunction with the
accompanying drawings, in which:
FIG. 1 is a perspective view of a GFCI according to an embodiment of the
present
invention;
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FIG. 2 is a side view, in longitudinal section, of the GFCI in FIG. 1 showing
the
relative positions of the assembly in the tripped condition;
FIG. 3 is a perspective view of the GFCI in FIG. 1 with the face portion
removed,
showing the internal configuration of the GFCI of FIG. 1;
FIG. 4 is an exploded, perspective view of the GFCI in FIG. 1;
FIG. 5 is an exploded view of the electromagnetic tripper of the GFCI in FIG.
1;
FIG. 6 is a perspective view of the trip actuator and a portion of the GFCI in
FIG.
1, showing the assembled relationship of the trip actuator;
FIG. 7 is a detailed, sectional side view of the GFCI in FIG. 1 in the tripped
condition;
FIG. 8 is another detailed, sectional side view of the GFCI in FIG. 1 in the
tripped
condition from a different perspective from FIG. 7;
FIG. 9 is a detailed, sectional side view of the GFCI in FIG. 1 in the closed
condition;
FIG. 10 is a schematic diagram of a circuit of the GFCI according to an
embodiment of the present invention;
FIG. 11 is a detailed, sectional side view of the GFCI in the tripped
condition,
according to a further embodiment of the invention;
FIG. 12 is a detailed, sectional side view of the GFCI in the tripped
condition,
according to a further embodiment of the invention;
FIGS. 13A-13C conceptually depict a split version of a fixed contact holder
for
use in connection with the embodiments shown in FIGS. 11, 12, and 15;
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FIG. 14 is a modified version of the circuit diagram of FIG. 10 showing the
split
version of the fixed contact holder as in FIGS. 13A-13C; and
FIG. 15 is a detailed, sectional side view of the GFCI in the tripped
condition,
according to a modification of the embodiment of the invention shown in FIG.
12.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a view of the exterior of a GFCI according to an embodiment of
the
present invention. The GFCI receptacle has a housing consisting of a face
portion 30, a
central body 20 (not shown in FIG. 1, but appearing, for example, in FIG. 2)
and a rear
portion 10. The face portion 30 has entry ports 31 for receiving normal or
polarized
prongs of a male plug of the type normally found at the end of a lamp or
appliance cord
set (not shown), as well as ground-prong-receiving openings 32 to accommodate
three-
wire plugs. The GFCI receptacle also includes a mounting strap 40 for
fastening the
receptacle to a junction box, and the mounting strap 40 has a threaded opening
to receive
a screw 113 for connection to an external ground wire. A test button 50
extends through
an opening in the face portion 30 of the housing. The test button 50 can be
activated to
test the operation of the circuit-interrupting portion disposed in the device.
A reset button
60, which forms a part of a reset portion of the device, extends through an
opening in the
face portion 30 of the housing. The reset button is used to activate a reset
operation,
which reestablishes the electrical continuity in the open conductive paths.
Electrical
connections to existing household electrical wiring are made via binding
screws 110 and
111, where the binding screw 110 is a line phase connection, and the binding
screw 111
is a load phase connection. It should be noted that two additional binding
screws (not
shown) are located on the opposite side of the GFCI receptacle. An indicator
114
(generally a light-emitting diode (LED)) extends through the opening of the
face portion
30 of the housing. When the GFCI is normally energized, the indicator is
illuminated.
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The GFCI illustrated in FIG. 1 may be rated, for example, at 20 A. The present
invention also provides other types of GFCIs, at various amperage ratings, and
these
GFCI receptacles all have two configurations, one without an indicator and the
other with
an indicator. Both configurations operate under the same principle. Therefore,
the
description below, while specifically for the rated 20 A GFCI with an
indicator, also
applies to the other types of GFCIs.
Referring to FIG. 2, the assembled relation of the GFCI receptacle is shown in
the
tripped condition. All of the subassemblies and component parts are fixed
mainly to the
housing (consisting of the face portion 30, the central body 20 and the rear
portion 10) of
the GFCI. An electromagnetic tripper is built into the GFCI receptacle of the
present
invention. A permanent magnet 71 is set into one end of a coil framework 70,
and
covered by an outside shield cover 72. One end of the shield cover 72 is
abutted against
one side of the rear portion 10. The coil framework is mounted on a circuit
board 90 by
four binding pins. A circular core of sensor framework 80 is set into a fixed
hole of the
circuit board 90, and the sensor framework 80 is also mounted on the circuit
board 90 by
four binding pins. The U-shaped portion of the sensor framework 80 is set into
a
corresponding groove on the central body 20. There is an isolation layer 82
between the
sensing transformer 81 and the neutral transformer 83. The sensing transformer
81 may
be composed, for example, of high original magneto-conductivity magnetic alloy
flakes
and enamel-insulated wire. The neutral transformer 83 may, for example, be
composed of
ferrite (high value, large temperature modulus) and enamel-insulated wire. A
plunger
75 is molded into the side of a movable bracket 79. The elasticity of a trip
spring 76
makes one side of the movable bracket 79 abut against the sensor framework 80
in the
trip condition. The upper side of the movable bracket 79 has a central hole,
and a small
spring 78 is set into it to prop up balance frame 77 and to provide a contact
force for the
contacts. Through the interaction of the magnetic force of the permanent
magnet 71 and
the electromagnetic force that the trip coil 74 or the closing coil 73
produces in an
energized condition, the plunger 75 activates the movable bracket 79 to drive
the balance
frame 77 to move back and forth in the U-shaped groove, as shown. Contact
strap 61 is
molded into the underside of reset button 60. One end of reset spring 62 props
up the
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reset button 60, and the other end presses onto mounting strap 40. The test
button 50 is
propped up by test strap 51. In one embodiment of the GFCI, this arrangement
ensures
that the top surface of the test button 50 is substantially level with the
surface of the face
portion 30 until pressed.
Referring to FIG. 3, a pair of fixed contact holders 100A and 100E with
contacts
101 are mounted on the central body 20. A mounting strap 40 with grounding
strap 41
and binding screw 113 is set onto the central body 20, and the face portion 30
impacts it.
One end of a test strap 51 is set into a corresponding slot on the central
body 20; its
outside abuts against the inside of the fixed contact holder 100B; and the
other end of the
test strap 51 can flexibly contact with the test resistor 52 (shown, e.g., in
FIG. 4). The
contact strap 61, which is molded into the underside of the reset button 60,
can flexibly
contact the binding pins 63 through the action of the reset spring 62, which
props up the
reset button 60, thus controlling the reset action of the tripper.
FIGS. 2 and 3 also show the physical relationship among the mounting strap 40,
the central body 20, and coil framework 70 (including both the trip coil 74
and the
closing coil 73). In particular, these figures show that mounting strap 40 is
physically
separated from coil framework 70 by central body 20. Central body 20 may be
constructed of, for example, an insulating material. Central body 20 may thus
be
constructed such that mounting strap 40 does not define a path of a magnetic
field
generated by either trip coil 74 or closing coil 73, i.e., such that mounting
strap 40 is
magnetically isolated from trip coil 74 and closing coil 73.
FIG. 4 is an exploded view of the GFCI receptacle according to an embodiment
of
the present invention. As shown, the GFCI receptacle comprises a rear portion
10, a
central body 20, a face portion 30, a mounting strap with a grounding strap 41
and a
binding screw 113, a pair of movable contact holders 102A and 102B with
contacts 103,
a pair of fixed contact holders 100A and 100E with contacts 101, an actuator,
a reset
mechanism, a test mechanism and a control circuit. The actuator comprises a
coil
framework 70, a permanent magnet 71, a shield cover 72, a closing coil 73, a
trip coil 74,
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a plunger 75, a trip spring 76, a balance frame 77, a small spring78 providing
a contact
force, a movable bracket 79, and four binding pins 701. The reset mechanism
includes a
reset button 60 molded with a contact strap 61 (shown in FIG. 3), a reset
spring 62, and a
reset binding pin 63. The test mechanism includes a test button 50, a test
strap 51, a test
resistor 52, a sensor framework 80, a sensing transformer 81, an isolation
layer 82, and a
neutral transformer 83. In addition, the line terminal 104 is connected to the
line wire by
the line binding screw 110 associated with the pressure plate 105; the load
can also be
connected to the GFCI through the load binding screw 111 and a corresponding
pressure
plate 105. All subassemblies and component parts are assembled as shown in the
drawing. The rear portion and the face portion of the housing are connected
together by
four fastening screws 115. The reset button 60 extends through the reset
opening 33 on
the face portion 30 of the housing. The test button 50 extends through the
test opening 34
on the face portion 30 of the housing. One of the ends of each of the movable
contact
holders 102A and 102B passes through the sensor framework 80 and is soldered
onto the
circuit board 90. The other end of each can move freely.
FIG. 5 is an exploded view of the electromagnetic tripper of FIG. 4. Because
the
plunger 75 is molded onto the movable bracket 79, the movement of the plunger
75 can
drive the sliding boards 79A and 79B to move back and forth in the runners 70A
and
70B, respectively. The movement of the movable bracket 79 drives the balance
77 to
move to perform the operation of breaking contact and making contact (between
the fixed
and movable contacts). The assembled relationship of the electromagnetic
tripper is
further shown in FIG. 6.
Referring now to FIGS. 7, 8, and 9, when the trip coil 74 or the closing coil
73 is
energized, it produces a corresponding electromagnetic force to interact with
the
magnetic force of the permanent magnet 71 and acts on the plunger 75. In this
manner,
the plunger 75 drives the balance frame 77 back and forth. In the trip
condition, when trip
coil 74 is energized, the bracket 77A of the balance frame 77 is set into the
V-shaped
groove A of the movable contact holder 102A, and the bracket 77B of the
balance frame
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77 is set into the V-shaped groove B of the movable contact holder 102B, as
shown in
FIGS. 7 and 8. As a result, the contacts 101 and 103 are separated from each
other.
On the other hand, when the closing coil 73 is energized, the plunger 75,
under
the magnetic force, drives the balance frame 77 to move such that the brackets
77A and
77B on the two sides of the balance frame 77 force the movable contact holders
to bias.
When one end of the plunger 75 is attracted to and pressed against the
permanent magnet
71 (i.e., when closing coil 73 is energized), the brackets on two sides of the
balance frame
77 are located on the plane position of the V-shaped groove and hold the
contacts 103 of
the movable contact holders against the contacts 101 of the fixed contact
holders, as
shown in FIG. 9. The small spring 78 provides a contact force for the contacts
103 and
101 to help maintain the contact. The special shape of the movable contact
holders 102A
and 102B prevents the plunger 75 from being attracted and closed in the event
of
improper operation and also contributes to making the tripper act quickly.
FIG. 10 shows a general GFCI circuit of the present invention. Diodes D,-D4
form a rectifying circuit, converting the AC input to a DC output. The
junction of D, and
D2 and the junction of D3 and D4 form the AC input terminals and are connected
to the
line of the GFCI. The junction of D2 and D4 forms one terminal for the DC
output, and
this junction is referred to as the "ground" hereinafter. The junction of D,
and D3 forms
the other terminal of the DC output and connects with the resistor R4. The
other end of R4
is connected to the capacitor C5. The other end of C5 is then connected to the
"ground". In
the exemplary 20A-rated GFCI device, an electrical voltage of approximately
26V
formed between the two ends of C5 serves as a DC voltage for the circuit.
As discussed above, the exemplary ground fault circuit interrupter has a
sensor, a
trip circuit, a test circuit and a reset circuit. The sensor has a sensing
transformer N, and a
neutral transformer N2, as shown in FIG. 10. The AC line and the neutral
conductors pass
through both transformers. The two ends of a sensing coil of sensing
transformer N,
connect to opposite ends of the capacitor Co. One end of the sensing coil of
N, serially
connects to the capacitor C1, the resistor R5, and then the terminal 1 of the
IC (which, as
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discussed below, may include an amplifier circuit), and the other end of the
sensing coil
of N, connects to the terminal 3 of the IC, forming a transformer-coupled
circuit that
receives differential voltage inputs. The feedback resistor, R1, connects to
the terminal 1
of the IC at one end and to the terminal 7 of the IC at the other end. The
magnitude of
resistance at R, determines the amplification of the IC, that is, the
threshold value for the
tripping action of the GFCI.
The neutral transformer N2, the capacitor C2, and the capacitor C3 form the
neutral
ground-fault protection circuit. The two ends of the sensing coil of neutral
transformer N2
are connected to opposite ends of the capacitor C2. One end of the sensing
coil of N2 is
further connected to the capacitor C3 and the other end of the sensing coil of
N2 is
connected to the "ground". The other end of the capacitor C3 is connected to
the terminal
7 of the IC.
Given the above-described apparatus, neutral ground-fault protection occurs as
follows: The transformers N, and N2 form a sigmoid-wave oscillator with a
transfomer-
coupled oscillating frequency of 5 kHz. When a neutral ground fault occurs,
this
oscillator starts to oscillate. When the magnitude of the oscillation reaches
the IC
threshold value, then the terminal 5 of the IC delivers a signal, putting the
tripper in
motion and the GFCI breaks contact. In other words, in operation, the sensing
transformer (N,) serves as a differential transformer for detecting a current
leakage
between the line side of the load terminal and an earth ground, while the
neutral
transformer (N2) detects current leakage between the neutral side of the load
terminal and
an earth ground. In the absence of a ground fault condition, the currents
flowing through
the conductors will be equal and opposite, and no net flux will be generated
in the core of
the sensing transformer (N,). In the event that a connection occurs between
the line side
of the load terminal and ground, however, the current flowing through the
conductors
will no longer precisely cancel and a net flux will be generated in the core
of the sensing
transformer (N, ). When the flux increases beyond a predetermined value, it
will give rise
to a potential at the output of the sensing transformer (N,), which is applied
to the inputs
1 and 3 of the IC and trip circuit, sufficient to produce a trip signal on the
output terminal
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5. If the ground fault condition results from the neutral side of the load
terminal being
connected to ground, a magnetic path is established between the sensing
transformer (Ni)
and the neutral transformer (N2). When this occurs, a positive feedback loop
is created
around an operational amplifier within the IC and trip circuit, and the
resulting
oscillations of the amplifier (IC) will cause the trip signal to appear on the
output
terminal 5.
As discussed above, resistor R, is utilized as a feedback resistor for setting
the
gain of the circuit and, hence, its sensitivity to ground faults. The
capacitors C, and C3
provide AC input coupling. In the absence of a ground fault condition, no
output is
produced by the amplifier (IC) and trip circuit on the output terminal 5.
Under these
circumstances, the negative pole of a silicon controlled rectifier (SCR) VD7
is connected
to the ground of the full-wave bridge rectifier formed by Di-D4 (described in
detail
above), and the positive pole of the SCR VD7 is connected to trip coil J, to
maintain it in
a non-conducting state. Similarly, the negative pole of an SCR VD5 is
connected to the
ground of the full-wave bridge rectifier, and the positive pole of the SCR VD5
is
connected to closing coil J2 to maintain it in a non-conducting state. Since
the current
drawn by the resistor R4 and amplifier and trip circuit is not sufficient to
operate the trip
coil, the plunger remains motionless.
The occurrence of a ground fault condition causes the amplifier and trip
circuit to
produce an output on terminal 5 of the IC, which is applied to the gate
terminal of the
SCR VD7, thereby rendering the SCR VD7 conductive. This produces a short
circuit
across the outputs of the full-wave bridge rectifier, thereby providing a low-
impedance
path for current to flow through the trip coil J1. The resulting movement of
the plunger
causes the movable contacts to move to the open position, thereby removing
power from
the entry ports of the face portion and the load terminals. This ensures that
the GFCI
receptacle remains in a condition to detect a ground fault condition
immediately upon
being reset.
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The reset switch RESET, the resistors R2 and R3, the capacitors C6 and C7, the
SCR VD5, the closing coil J2, and the breaking switch K form the reset control
circuit.
One end of the reset switch RESET is connected to the junction of R4 and C5,
the other
end of the reset switch RESET is connected to one junction of R2 and C6, which
are
connected in parallel. The other junction of R2 and C6 is connected to the
gate pole of the
SCR VD5, R3, and C7. Capacitor C7 is connected between the gate and cathode of
the
SCR VD5 to serve as a filter for preventing narrow noise pulses from
triggering the SCR
VD5. One end of the breaking switch K is connected to the line terminal; the
other end of
K is connected to the load terminal. It is noted that the contact point
between the breaking
switch K and the line terminal corresponds to the contact 103 of the movable
contact
holder, and the contact point between the breaking switch K and the load
terminal
corresponds to the contact 101 of the fixed contact holder. The power supply
of the
control circuit is connected to the line of the GFCI, so when the GFCI is
energized, the
control circuit of the GFCI is also energized. When the reset switch RESET is
closed, the
capacitor C6 is charged up, generating a trigger signal of about 20-40 ms to
gate the SCR
VD5 into conduction. Consequently, the closing coil 73 is energized for a
duration of
about 20-40 ms. That is, the closing coil 73 produces an electromagnetic force
for about
20-40 ms to act on the plunger 75, sufficient to reset the GFCI.
The IC may be a special integrated circuit, for example, of type RV4145A or
RV2145.
As discussed above, capacitor C4 is connected between the gate and cathode of
the SCR VD7 to serve as a filter for preventing narrow noise pulses from
triggering the
SCR VD7. For additional protective purposes, the circuit shown in FIG. 10 also
includes
a metal oxide varistor (MOV) connected across the input terminals of the AC
power
source, in order to protect the whole control circuit from transient voltage
surges.
The test switch TEST and the current limiting resistor Ro form the test
circuit. The
current limiting resistor Ro is connected to the power source, and the other
end of resistor
Ro is connected to the test switch. The other end of the test switch TEST is
connected to
CA 02458785 2010-09-17
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the other end of the load. The test circuit constantly provides the GFCI an
8mA fault
current for periodically checking the working status of the GFCI. When the
test switch is
momentarily depressed, sufficient current will flow through the resistor Ro to
cause an
imbalance in the current flowing through the sensing transformers. This will
simulate a
ground fault condition, causing the amplifier and trip circuit to produce an
output signal
on the output terminal 5, which gates the SCR VD7 into conduction and thereby
momentarily energizes the trip coil. The resulting movement of the plunger
causes the
contacts to open, as will occur during an actual ground fault condition.
Simultaneously, the GFCI receptacle also provides an indication circuit, where
a
current limiting resistor R6 is connected in series with a light-emitting
diode (LED) VD6,
and they are connected directly to the terminals of the load. When the reset
button is
depressed and the GFCI receptacle is energized, the LED is illuminated. This
affords a
visual indication to the installer and the user that the GFCI receptacle is in
the normal
conduction state.
If the GFCI receptacle is inadvertently miswired by connecting the line to the
load, before the breaking switch K closes, the control circuit is de-
energized. Because the
GFCI utilizes an electronically-controlled means for reset, when the control
circuit is de-
energized, the closing coil can not be energized. In this manner, the closing
coil can not
produce a corresponding electromagnetic force to act on the plunger, thereby
keeping the
GFCI also de-energized, achieving the reverse wiring protection function.
In summary, the present invention provides a GFCI receptacle that utilizes an
electromagnetic tripper and an electronically-controlled means to control
reset. This
GFCI receptacle has reverse wiring protection function and the advantages of,
for
example, tripping rapidly and operating conveniently.
Recent changes in electrical standards have indicated the desirability of,
instead of
having a single fixed contact holder IOOA or 100E (each having a respective
fixed
contact 101) on each side conducting current to/from the line, having a pair
of fixed
contact holders, one for the GFCI receptacle and one for the output load
connection, for
CA 02458785 2010-09-17
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each side, phase and neutral, of the GFCI receptacle. By so doing, should the
GFCI
receptacle be miswired, with the load side wires connected to the binding
screws for the
line side, and vice versa, no current will be conducted into the GFCI
receptacle (i.e., to a
user load plugged into the receptacle). The invention is adaptable to this
type of
arrangement, and FIGS. 11 and 12 depict embodiments of the invention that have
such
arrangements.
In the embodiment shown in FIG. 11, which shows a side view of the GFCI in the
tripped position, the single movable contact holder on each side (the view
shown
corresponds to the view shown in FIG. 7, so the equivalent movable contact
holder in
FIG. 7 is 102A) is replaced with a movable contact holder assembly 102A'.
Movable
contact holder assembly 102A' comprises two movable contact holder elements,
102A'-1
and 102A'-2. Each of the movable contact holder elements 102A'-I and 102A'-2
has a V-
shaped bend. Movable contact holder elements 102A'-1 and 102A'-2 are arranged
against
each other at one end, as shown, with the V-shaped bends arranged opposite
each other.
At the end where they are arranged against each other, the two movable contact
holder
elements 102A'-1 and 102A'-2 electrically connected to a line-side conductor,
which
comes through the sensor assembly 80; alternatively, the two movable contact
holder
elements 102A'-1 and 102A'-2 may extend through the sensor assembly 80 and
electrically connected (e.g., soldered) directly to printed circuit board 90
to provide
contact with the line-side conductor. At the other end, each movable contact
holder
element, 102A'-l or 102A'-2, has a movable contact, 103A or 103B,
respectively. The
movable contacts 103A and 103B, as well as fixed contacts lOIA and 101B, may,
for
example, be riveted, soldered, or otherwise electrically connected to their
respective
contact holders, or they may, as a further example, comprise conductive
rivets.
As in the previous embodiments, the GFCI includes a movable bracket 79 and a
balance frame 77 mounted on the movable bracket 79. Alternatively, movable
bracket 79
and balance frame 77 may be combined into a unitary structure; while the
remainder of
this description is written under the assumption of separate components, it is
equally
applicable to the unitary design.
CA 02458785 2010-09-17
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Balance frame 77 is equipped with a bracket 77A' extending from each side (see
also, for example, FIG. 5). In this embodiment, however, bracket 77A' has a
somewhat
different shape from bracket 77A as shown in FIG. 7. In particular, bracket
77A' is
shaped so as to be able to separate movable contact holder elements 102A'-1
and 102A'-
2, in the directions of arrows B 11 and C 11, when bracket 77A' is moved from
point a to
point b, in the direction of arrow A11. The amount of separation of movable
contact
holder elements 102A'-1 and 102A'-2, when bracket 77A' is at point b, must be
sufficient
to cause movable contacts 103A and 103B to make contact with fixed contacts
IOTA and
101B. As shown in FIG. 11, the shape of bracket 77A' may be as if a bracket
77A were
fused to a second bracket 77A that was flipped vertically; however, bracket
77A' may
take any other suitable shape such that it fits between the V-shaped grooves
of movable
contact holder elements 102A'-1 and 102A'-2 when in the trip position (a) and
such that it
causes sufficient separation of movable contact holder elements 102A'-1 and
102A'-2
when in position b. Typical shapes of bracket 77A' include a rounded
trapezoidal shape,
as shown in FIG. 11, and a rounded triangular shape.
In order to provide separate conductive paths on each side (neutral and phase)
of
the GFCI for conduction of electricity to/from the receptacle and to/from the
output load
conductor, fixed contact holders IOOA and 100B (as shown, e.g., in FIG. 4) are
each split
into two parts. This is depicted conceptually in FIGS. 13A-13C, which show a
split
version of fixed contact holder 1OOA. This is also depicted in the circuit
diagram shown
in FIG. 14, as part of switching apparatus K; the circuit of FIG. 14 operates
in a manner
similar to that shown in FIG. 10, and will, therefore, not be further
described (like parts
have been labelled with identical reference numerals). In particular, fixed
contact holder
100A is split into first contact holder component IOOA-1, shown in FIGS. 13A
and 13B,
and second contact holder component 100A-2, shown in FIG. 13C. In the
depiction of
FIGS. 13A-13C, the first contact holder component IOOA-1 is connected to an
output
load via binding screw 111. First contact holder component IOOA-1 includes a
contact
holder part IOOA-1', on which is situated fixed contact IOTA. Second contact
holder
component 100A-2 is shown connected to (one side of) an electrical outlet.
Second
contact holder component 100A-2 includes a contact holder part 100A-2', on
which is
CA 02458785 2010-09-17
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situated fixed contact 101B. First and second contact holder components 100A-1
and
I00A-2, including contact holder parts IOOA-I' and 100A-2', are shaped and
oriented in a
manner appropriate to the particular embodiment and implementation of the
invention
(e.g., as shown in FIG. 11 or FIG. 12).
The sub-embodiment of FIG. 11 operates as follows. In the tripped position,
bracket 77A' is located at point a, where it fits within the V-shaped grooves
of movable
contact holder elements 102A'-1 and 102A'-2. In this position, no contact is
made
between movable contacts 103A and 103B and fixed contacts 101A and 101B,
respectively. When the reset button 60 (see, e.g., FIG. 6) is pressed
(assuming the
absence of a reverse wiring or other fault condition), the reset mechanism
described
above causes movable bracket 79 (and, hence, balance frame 77) to move along
the
direction of arrow All, which, in turn, causes bracket 77A' to move from point
a to point
b. This causes the ends of movable contact holder elements 102A'-1 and 102A'-2
having
movable contacts 103A and 103B, respectively, to separate (i.e., along the
directions of
arrows B11 and C11, respectively). This, in turn, causes movable contacts 103A
and
103B to make contact with fixed contacts 101 A and 101 B, thus permitting the
conduction
of current to/from, for example, an electrical appliance plugged into the GFCI
receptacle
and to/from an output load terminal (e.g., binding screw 111, as shown, for
example, in
FIG. 3).
On the other hand, when bracket 77A' is initially at point b and a fault (or
test)
occurs, movable bracket 79 (and balance frame 77, along with it) moves in the
direction
along arrow A 11 so as to move bracket 77A' to point a. As a result, the ends
of movable
contact holder components 102A'-1 and 102A'-2 bearing movable contacts 103A
and
103B are no longer kept apart by bracket 77A', which is now situated in the
area formed
by the V-shaped bends in movable contact holder components 102A'-1 and 102A'-
2. As a
result, contact between movable contacts 103A and 103B and fixed contacts IOTA
and
101 B, respectively, is broken.
CA 02458785 2010-09-17
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In the sub-embodiment shown in FIG. 12, the movable contact holder 102A" is
mounted on a movable assembly 77', which is the equivalent of movable bracket
79 and
balance frame 77 of FIG. 4, but without any brackets 77A (and which may be of
unitary
construction), and is connected to a flexible conductor 122 at one end. The
other end of
the movable contact holder 102A" is provided with the two movable contacts,
103A and
10313, which make contact with the two fixed contacts, 1 O l A and 10113, when
the
movable assembly 77' is in a first position (reached, e.g., by pressing reset
button 60).
The movable and fixed contacts do not make contact when the movable assembly
77' is
in a second (tripped) position, which is what is depicted in FIG. 12. That is,
the entire
movable contact holder 102A" is arranged to shift in the direction along arrow
A12 when
a condition causes movable assembly 77' to shift in the direction along arrow
A12. Note
that while FIG. 12 depicts, and this discussion describes, only one side of
the apparatus,
and thus only a single movable contact holder 102A", there are actually two
movable
contact holders, one connected to each of two conductors (phase and neutral),
both of
which are mounted on movable assembly 77'.
Movable assembly 77' is further equipped with a contact spring 121. The force
provided by contact spring 121 serves to ensure good contact between movable
contacts
103A and 103B and fixed contacts lOlA and 101B.
As discussed above, movable assembly 77' in FIG. 12 is the equivalent of
movable bracket 79 and balance frame 77 of FIG. 4. As a result, movable
assembly 77' is
coupled to and driven by plunger 75 in the same fashion as is movable bracket
79 in the
embodiment of FIG. 4.
The sub-embodiment of FIG. 12 operates as follows. FIG. 12 shows the movable
assembly 77' in the tripped position (i.e., in its right-hand position along
the direction of
arrow A12 in FIG. 12). In this position, no contact is made between movable
contacts
103A and 103B and fixed contacts 101 A and 10113, respectively. When the reset
button
60 (see, e.g., FIG. 6) is pressed (assuming the absence of a reverse wiring or
other fault
condition), the reset mechanism described above causes movable assembly 77' to
move
CA 02458785 2010-09-17
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along the direction of arrow Al 1, in the left-hand direction in FIG. 12
(i.e., toward fixed
contact holders 100A-1 and 100A-2). This causes the movable contact holder
102A" to
move as well. This, in turn, causes movable contacts 103A and 103B to make
contact
with fixed contacts 101A and 10113, thus permitting the conduction of current
to/from,
for example, an electrical appliance plugged into the GFCI receptacle and
to/from an
output load terminal (e.g., binding screw 111, as shown, for example, in FIG.
3).
On the other hand, when movable assembly 77' is initially in its left-hand
position
(as it would be following the operations in the previous paragraph) and a
fault (or test)
occurs, movable assembly 77' moves in the right-hand direction along arrow
A12, as
shown in FIG. 12. As a result, movable contact holder 102A" bearing movable
contacts
103A and 103B is moved in the right-hand direction, away from fixed contact
holders
100A-1 and 100A-2. As a result, movable contacts 103A and 103B and fixed
contacts
101A and 101 B, respectively, are separated, and contact is broken.
While the above discussion focuses on the specific implementation of the sub-
embodiment of FIG. 12, it is apparent that variations are possible. For
example, contact
holder 102A" need not cover or surround (part of) movable assembly 77', as
shown in
FIG. 12. Contact holder 102A" need only be attached to movable assembly 77'
and
provide movable contacts 103A and 103B in a position for making contact with
fixed
contacts 101A and 10113 when movable assembly 77' moves contact holder 102A"
into
an appropriate position. For example, if movable assembly 77' has a squared
shape, as
shown in FIG. 12, contact holder 102A" need only be a conductive plate on
which
movable contacts 103A and 103B are mounted, and contact with flexible
conductor 122
may be provided by electrically connecting flexible conductor 122 to spring
121, which
may be made of a conductive material and have a portion extending through a
side or
back of movable assembly 77' to accommodate such electrical connection.
Alternatively,
spring 121 may be omitted, and the flexible conductor 122 may be inserted
through a
hole in movable assembly 77' to make contact with contact holder 102A", or
some other
type of electrical connection (e.g., a conductive post extending through the
back of
CA 02458785 2010-09-17
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movable assembly 77') may be provided between contact holder 102A" and
flexible
conductor 122.
Furthermore, movable assembly 77' may take on numerous shapes and forms. As
discussed above, it may be of unitary form, and both movable contact holders
(for the
phase and neutral sides) may be mounted on it. Additionally, for example,
movable
assembly 77' may have a base portion coupled to the plunger from which extend
two
supports, on each of which is mounted one of the movable contact holders.
Movable
assembly 77' may, alternatively, comprise a phase side movable assembly and a
neutral
side movable assembly, both of which are coupled to, and move with, the
plunger.
Flexible conductor 122 may comprise a pair of conductors (e.g., two mutually
insulated wires) together (one for phase and one for neutral), or there may be
two flexible
conductors, where flexible conductor 122, as shown in FIG. 12, would be one of
them. In
the conductive contact spring implementation, for example, as discussed above,
each
flexible conductor, or each of the conductors within the flexible conductor,
would be
electrically-connected to one of the two contact springs.
FIG. 15 depicts a variation on the sub-embodiment shown in FIG. 12. In this
variation, the flexible conductor 122 is split into two portions, both of
which are
electrically connected to a line-side conductor. For example, in the specific
implementation shown, a conductive assembly 123, which may, for example,
comprise
copper, extends through sensor assembly 80, and the two portions of flexible
conductor
122 are coupled (e.g., soldered or otherwise coupled) to conductive assembly
123.
Alternatively, the two portions of flexible conductor 122 may be dual
extensions of
conductive assembly 123.
In the variation of FIG. 15, the movable contact holder 102A" of FIG. 12 is
split
into two portions, similar to the sub-embodiment of FIG. 11, denoted 102A'-1
and 102A'-
2. Each of movable contacts 103A and 103B is electrically coupled to a
respective one of
the movable contact holder portions 102A'-1 and 102A'-2. Movable contact
holder
portions 102A'-l and 102A'-2 are shown extending through movable assembly 77',
and
CA 02458785 2010-09-17
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each is electrically connected to the one of the respective portions of
flexible conductor
122. Movable contact holder portions 102A'-t and 102A'-2 may include
projections that
prevent them from becoming dislodged from movable assembly 77'. In conjunction
with
the two movable contact holder portions, contact spring 121 is shown as being
replaced
by two contact springs, 121A-1 and 121 A-2, each of which helps maintain
contact
between a respective one of movable contacts 103A and 103B and a respective
one of the
fixed contacts 101 A and 10113. In an alternative embodiment (not shown), a
single, non-
conducting contact spring may be used to help maintain contact between both
pairs of
movable and fixed contacts. The operation of this variation of the sub-
embodiment of
FIG. 12 is substantially as described for the sub-embodiment of FIG. 12.
While only the fundamental features of the present invention have been shown
and described, it will be understood that various modifications and
substitutions and
changes of the form and details of the device described and illustrated and in
its operation
may be made by those skilled in the art, without departing from the spirit of
the
invention.
