Note: Descriptions are shown in the official language in which they were submitted.
CA 02458758 2004-02-16
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.
In the past, a GFCI receptacle generally utilized a mechanical actuator which
limited the
performance of such products. especially insofar as these GFCIs did not
provide reverse
wiring protection. In addition, these mechanical GFCIs required high standards
in the quality
CA 02458758 2004-02-16
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of the parts and assembling work. Examples of mechanical GFCIs include those
disclosed in
U.S. Patent No. 5,933,063 and U.S. Patent No. 4,802,052.
The GFCI shown in U.S. Patent No. 6,252,407 B1 has reverse wiring protection,
but it is a
visual alarm indicator signaling a miswiring condition to the installer, and
if miswired
(despite the visual alarm indicator) by connecting the line to the load, the
GFCI can still be
reset. Under such circumstances, an unknowing user, faced with a GFCI that has
been
miswired, may press the reset button, which, in turn, will cause the GFCI to
be reset without
reverse wiring protection available. And, such a GFCI that has been reset can
very easily be
tripped again in events like lightning strikes.
The design of these GFCIs allows two means of connection: the load can pass
through the
entry ports of the face portion or can alternatively connect through the load
binding screws.
Consequently, an installer or user can still mistakenly connect the line and
the load in a
reverse direction. When this occurs, without reverse wiring protection, the
GFCI will
function just as a common (non-GFCI) receptacle.
There is a need for a GFCI that, in order to improve the safety features of
the receptacles, is
capable of providing reserve wiring protection; highly responsive; is
convenient to assemble;
and has improved functionality.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a GFCI circuit that has the above
characteristics.
In general, a preferred embodiment of a ground fault circuit interrupter
(GFCI) according to
the invention -w-uliso a pair of first ho!dcrc, .,^.h having 2 conttact at one
end; a
pair of movable contact holders, each having a fixed end and a movable end,
each of the
movable ends having a contact; a movable assembly that moves between first and
second
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positions, 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 an 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 forces of ii,e pclõianicnt,,,dgnet LU plvviuc a iciiAii vc
fore j., the t ippe:,
the operating sensitivity is improved, and the GFCI is more energy efficient.
According to
another feature of the invention, the GFCI is provided with reverse wiring
protection in that
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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.
A further object of an embodiment of the present invention is to provide an
electromagnetic
tripper that is electronically controlled. In such an embodiment (for example,
the
implementation shown in Figure 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 removable contact has a V-
shaped groove,
and when it is in the tripping state, the bracket of the balance frame moves
into in 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 contrui circuit will gait
a siiicou controfleu
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 force of the
permanent
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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 an embodiment 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 iiow;,ig a",iuugi, t,õc. i:,siõg :,.,;; ;a wu ;a, 6-- u,~u ui%.
cnerg;zcd. time is oo 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
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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 operation is more
convenient and the action
is more sensitive compared to GFCIs using mechanical means.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in further detail in conjunction with the
accompanying
drawings, in which:
Figure 1 is a perspective view of a GFCI according to an embodiment of the
present
invention;
Figure 2 is a side view, in longitudinal section, of the GFCI in Figure 1
showing the relative
positions of the assembly in the tripped condition;
Figure 3 is a perspective view of the GFCI in Figure 1 with the face portion
removed,
showing the internal configuration of the GFCI of Figure 1;
Figure 4 is an exploded, perspective view of the GFCI in Figure 1;
Figure 5 is an exploded view of the electromagnetic tripper of the GFCI in
Figure 1;
Figure 6 is a perspective view of the trip actuator and a portion of the GFCI
in Figure 1,
showing the assembled relationship of the trip actuator;
Figure 7 is a detailed, sectional side view of the GFCI in Figure 1 in the
tripped condition;
Figuic o 1b a _.i . deta=,A4 _d t . a _ .., .. .. thc G ulFCI in Fib-;.c 1 in
the tripped
uv u,~; Jl'lLlVllul u,uL. v..f u
condition from a different perspective from Figure 7;
Figure 9 is a detailed, sectional side view of the GFCI in Figure 1 in the
closed condition; and
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Figure 10 is a schematic diagram of a circuit of the GFCI according to an
embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 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 Figure 1, but appearing, for example, in Figure 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
indicate: illuminated.
The GFCI illustrated in Figure 1 may be rated, for example, at 20A. The
present invention
also provides other types of GFCIs, at various amperage ratings, and these
GFCI receptacles
CA 02458758 2004-02-16
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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 20A GFCI with an indicator, the description also
applies to the other
types of GFCIs.
Referring to Figure 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 set 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
a shield
cover 72 outside. One end of the shield cover 72 is abutted against one side
of the rear
portion 10. Shield cover 72 may be constructed of metal and may define a path
of a magnetic
field generated by at least one of the coils. 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 .t 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 75 has a central h oic, allU Q slllall spl lllg 7o is set into
ii 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 an electromagnetic force that
the trip coil 74
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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 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 Figure 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 Figure 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.
Figures 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 rnagncticaiiy isoiatcu f,un, uip coil 744
and closing coil 73.
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Figure 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 IOOA 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, a plunger 75, a trip
spring 76, a balance
frame 77, a small spring 78 providing a contact force, a movable bracket 79,
and four binding
pins 701. The reset mechanism mainly comprises a reset button 60 molded with a
contact
strap 61 (shown in Figure 3), a reset spring 62, and a reset binding pin 63.
The test
mechanism mainly comprises 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 11.1 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.
Figure 5 is an expA)dcd v,c;'~%v .;f .;.c it c,ina :ciic tripe- :.f Figure 4.
Bccause 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.
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respectively. The movement of the movable bracket 79 drives the balance 77 to
move to
perform the operation of breaking and making. The assembled , relation of the
electromagnetic tripper is further shown in Figure 6.
Referring now to Figures 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 77 is set into
the V-shaped
groove B of the movable contact holder 102B, as shown in Figures 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
Figure 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
makes the tripper
break quickly.
Figure 10 shows a general GFCI circuit of the present invention. Diodes D1-D4
form a
rectifying circuit, converting the AC input to a DC output. The junction of D,
and D2 and the
CA 02458758 2004-02-16
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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 D1 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 has a sensor, a trip
circuit, a test
circuit and a reset circuit. The sensor has a sensing transformer N1 and a
neutral transformer
N2, as shown in Figure 10. The AC line and the neutral conductors pass through
both
transformers. The two ends of a sensing coil of sensing transformer N1 connect
to opposite
ends of the capacitor Co. One end of the sensing coil of N1 serially connects
to the capacitor
C1, the resistor R5, and then the terminal I of the IC (which, as discussed
below, may include
an amplifier circuit), and the other end of the sensing coil of N1 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 I 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.
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Given the above-described apparatus, neutral ground-fault protection occurs as
follows. The
transformers N1 and N2 form a sigmoid-wave oscillator with a transformer-
coupled
oscillating frequency of 5 kHz. When 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. In
other words, in operation, the sensing transformer (N1) 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 (N1). 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 I). When the flux increases beyond a predetermined value, it
will give rise to a
potential at the output of the sensing transformer (N1), 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 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 (N1)
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
likewise give rise to the trip signal on the output terminal 5.
As discussed above, resistor R1 is utilized as a feedback resistor for setting
the gain of the
circuit and, r1e11Lc, ILS Se11S1ii'Vliy iv g1UUi1u AQLI L . iiiL. ~ulpu.ivio
C1 aild 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
CA 02458758 2004-02-16
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a silicon controlled rectifier (SCR) VD7 is connected to the ground of the
full-wave bridge
rectifier formed by D,-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 J, . 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.
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 uric terminal; the ouici enu of K is coõnccteu to the load
iernminai. 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
CA 02458758 2004-02-16
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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
-40ms to gate the SCR VD5 into conduction. Consequently the closing coil 73 is
energized
for a duration of about 20--40ms. That is, the closing coil 73 produces an
electromagnetic
force for about 20-40ms 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 Figure 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 R0 form the test
circuit. The current
limiting resistor Ro is connected to the power source, and the other end of
resistor R0 is
connected to the test switch. The other end of the test switch TEST is
connected to the other
end of the load. The test circuit constantly provides the GFCI a 8mA fault
current for
periodically checking of the working status of the GFCI. When the test switch
is
momentarily depressed, sufficient current will flow through the resistor R0 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, iCrtm,,,a, 3 that pit,,o 'L,,% SCR VD/ and
energizes the trip coil. The resulting movement of the plunger causes the
contacts to open, as
will occur during an actual ground fault condition.
CA 02458758 2004-02-16
-16-
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.
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
electro-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 electro-controlled means to control reset. This
GFCI
receptacle has reverse wiring protection function and the advantages of
tripping rapidly,
operating conveniently, and reasonable configuration.
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.
