U.S. patent application number 10/263028 was filed with the patent office on 2003-08-14 for protection device with lockout test.
Invention is credited to Packard, Thomas, Radosavljevic, Dejan.
Application Number | 20030151478 10/263028 |
Document ID | / |
Family ID | 27668487 |
Filed Date | 2003-08-14 |
United States Patent
Application |
20030151478 |
Kind Code |
A1 |
Radosavljevic, Dejan ; et
al. |
August 14, 2003 |
Protection device with lockout test
Abstract
A protective device includes a test button for enabling a test
signal for testing an operating condition of at least one of the
device components, such as the sensor, detector, switch, solenoid
and trip mechanism. The test button also enables a current through
a resistor body which is affixed to a stationary part of the
device. The resistor body keeps a lockout spring under tension.
Failure of the test signal to operate the trip mechanism within a
predetermined time interval causes the resistor body conducting
said current to reach a predetermined temperature, wherein the
resistor body ceases to hold a lockout spring, thereby permitting
the lockout spring to move to a position which causes the set of
interrupting contacts to remain permanently in a disconnected
position.
Inventors: |
Radosavljevic, Dejan; (La
Fayette, NY) ; Packard, Thomas; (Syracuse,
NY) |
Correspondence
Address: |
WALL MARJAMA & BILINSKI
101 SOUTH SALINA STREET
SUITE 400
SYRACUSE
NY
13202
US
|
Family ID: |
27668487 |
Appl. No.: |
10/263028 |
Filed: |
October 2, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60326531 |
Oct 2, 2001 |
|
|
|
Current U.S.
Class: |
335/18 |
Current CPC
Class: |
H02H 3/338 20130101;
H01H 83/04 20130101; H02H 3/05 20130101; H02H 3/335 20130101; H01H
71/20 20130101; H01H 2071/044 20130101; H01H 2083/201 20130101 |
Class at
Publication: |
335/18 |
International
Class: |
H01H 073/00 |
Claims
What is claimed is:
1. A protective device for interrupting power upon detection of an
electrical fault in an electrical distribution system, comprising:
a plurality of line terminals connectable to a source of voltage; a
plurality of load terminals connectable to a load; interrupting
means that connects or disconnects said plurality of line terminals
from said plurality of load terminals; a sensor for sensing said
electrical fault; a detector coupled to said sensor for detecting
said electrical fault; a switch coupled to said detector responsive
to said detected electrical fault; a solenoid coupled to said
switch; a trip mechanism coupled to said solenoid which moves said
interrupting means to a disconnected position upon occurrence and
detection of said electrical fault; a lockout spring; a resistor
body which holds said lockout spring in a first position under
tension; a test button for enabling a test signal for testing an
operating condition of at least one of said sensor, detector,
switch, solenoid and trip mechanism, wherein said test button also
enables a first current through said resistor body; and wherein
failure of said test signal to operate said trip mechanism within a
predetermined time interval causes said resistor body conducting
said first current to reach a predetermined temperature, wherein
said resistor body ceases to hold said lockout spring in said first
position, thereby permitting said lockout spring to move to a
second position, wherein said lockout spring being in said second
position causes said interrupting means to remain permanently in
said disconnected position.
2. The device according to claim 1 wherein said electrical fault
comprises an arc fault or a ground fault.
3. The device according to claim 1 wherein said trip mechanism
further comprises a plunger passing through said solenoid and
responsive to a magnetic field produced thereby by said solenoid;
and a latch spring biasing said plunger in an opposing direction to
a bias from said lockout spring; wherein said bias of said lockout
spring in said second position exceeds said bias of the latch
spring, whereby said interrupting means remains permanently in said
disconnected position.
4. The device according to claim 1 wherein said trip mechanism
further comprises: a plunger passing through said solenoid and
responsive to a magnetic field produced therein; and a latch for
holding said interrupting means in said connected position, said
latch including a tab; wherein said latch is movable under an
applied force from said plunger to release said interrupting means
to said disconnected position; and wherein said lockout spring in
said second position bears against said tab to cause said
interrupting means to remain permanently in said disconnected
position.
5. The device according to claim 1, further comprising a ground
fault circuit interrupter, wherein said resistor body consists of a
test resistor which simulates a ground fault current when said test
button is depressed.
6. The device according to claim 5, wherein a resistance of said
test resistor is about 15 K-Ohms.
7. The device according to claim 1, further comprising: a ground
fault circuit interrupter which includes a test resistor to
simulate a ground fault current; wherein depressing said test
button enables electrical currents through both said test resistor
and said resistor body.
8. The device according to claim 1, further comprising: a ground
fault circuit interrupter which includes a test resistor to conduct
a simulated ground fault current; an interface circuit coupled to
said resistor body; wherein depressing said test button enables
said simulated ground fault current through said test resistor and
a second current to said interface circuit, and wherein said
interface circuit enables said first current through said resistor
body when said test button is depressed; wherein said first current
exceeds said simulated ground fault current, and said simulated
ground fault current exceeds said second current.
9. The device according to claim 8 wherein said second current and
said simulated ground fault current are derived from a load
terminal and said first current is derived from a line
terminal.
10. The device according to claim 1, further comprising one of a
receptacle, switch, circuit breaker, module, and portable housing
containing said device.
11. The device according to claim 1, further comprising: an
interface circuit coupled to said resistor body; wherein depressing
said test button enables a second electrical current to said
interface circuit, and wherein said interface circuit enables said
first current through said resistor body, said first current
exceeding said second current.
12. The device according to claim 1, further comprising a power
supply, wherein said detector receives power from said power supply
and said power supply is coupled to either the line terminals or
the load terminals.
13. A protective device for interrupting power upon detection of an
electrical fault in an electrical distribution system, comprising:
a plurality of line terminals connectable to a source of voltage; a
plurality of load terminals connectable to a load; a sensor for
sensing said electrical fault; a detector coupled to said sensor
for detecting said electrical fault; a switch coupled to said
detector responsive to said detected fault; a relay, coupled to
said switch, including a solenoid and a plurality of interrupting
contacts wherein said relay disconnects said line terminals from
said load terminals upon occurrence of said electrical fault,
thereby moving said interrupting contacts to a disconnected
position; a fusing element; a test button for enabling a test
signal for testing an operating condition of at least one of said
sensor, detector, switch, solenoid and trip mechanism and for
providing a first current through said fusing element; wherein
failure of said test signal to disconnect said interrupting
contacts within a predetermined time interval causes said fusing
element conducting said first current to reach a predetermined
temperature, wherein said fusing element causes an open circuit,
and wherein said interrupting contacts remain permanently in said
disconnected position.
14. The device according to claim 13 wherein said electrical fault
comprises an arc fault or a ground fault.
15. The device according to claim 13, further comprising: a ground
fault circuit interrupter which includes a test resistor to
simulate a ground fault current; wherein depressing said test
button enables electrical currents through both said test resistor
and said fusing element.
16. The device according to claim 13, further comprising: an
interface circuit connected to said fusing element; wherein
depressing said test button enables a second electrical current to
said interface circuit; and wherein said interface circuit enables
said first current through said fusible element, said first current
exceeding said second current.
17. The device according to claim 16 wherein said second current is
derived from one of said plurality of load terminals.
18. The device according to claim 17 wherein said second current is
less than 0.5 milliamperes.
19. The device according to claim 13, further comprising: a ground
fault circuit interrupter which includes a test resistor to conduct
a simulated ground fault current; an interface circuit coupled to
said fusing element, wherein depressing said test button enables a
simulated ground fault current through said test resistor and a
second current to said interface circuit, and wherein said
interface circuit provides said first current through said fusing
element; and wherein said first current exceeds said second current
and said simulated ground fault current exceeds said second
current.
20. The device according to claim 13, further comprising one of a
receptacle, switch, circuit breaker, module, and portable housing
containing said device.
21. The device according to claim 13 wherein said fusing element is
a resistor.
22. A protective device for interrupting power upon detection of an
electrical fault in an electrical distribution system, comprising:
a plurality of line terminals connectable to a source of voltage; a
plurality of load terminals connectable to a load; a set of bus
bars that connect or disconnect said plurality of line terminals
from said plurality of load terminals, said set of bus bars
including a first bus bar and a second bus bar; a resistor body
one-way moveable between a first and second position, wherein when
said resistor body is in said second position, said set of bus bars
is permanently disconnected from said plurality of line terminals
and said plurality of load terminals; a test button for enabling a
test signal for testing an operating condition of said device to
determine if said device is in good operating condition or bad
operating condition, and for providing a current through said
resistor body; said resistor body being connected on one end to
said test button and on another end to one of said first and second
bus bars; and wherein when said source of voltage is miswired to
said load terminals and said test button is pressed, said resistor
body does not move to said second position when said protective
device is in said good operating condition.
23. A method for locking out a reset mechanism of an electrical
protective device, comprising the steps of: providing a spring
driven lockout for said reset mechanism; providing a resistor body
which holds said lockout in a first position, wherein said first
position permits resetting said electrical protective device;
pressing a test button to check an operating condition of said
electrical protective device; sending a current through said
resistor body in response to pressing said test button; and moving
said lockout to a second position in response to said resistor body
reaching a predetermined temperature as a result of said current
being sent through said resistor body for a longer period of time
than a normal trip time of said electrical protective device,
wherein said second position permanently prevents resetting of said
electrical protective device.
24. A method for locking out a reset mechanism of an electrical
protective device, comprising the steps of: providing a tripping
mechanism which includes a normally open relay; providing a fusing
element which permits power to said relay so that said relay
remains closed; pressing a test button to check an operating
condition of said electrical protective device; sending a current
through said fusing element in response to pressing said test
button; and blowing said fusing element in response to said fusing
element reaching a predetermined temperature as a result of said
current being sent through said fusing element for a longer period
of time than a normal trip time of said electrical protective
device, wherein said blowing of said fusing element creates an open
circuit to said relay, thereby permanently preventing resetting of
said electrical protective device.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Application Ser. No. 60/326,531 filed Oct. 02, 2001 and entitled
SECONDARY TRIPPING MECHANISM, and from co-pending U.S. application
Ser. No. 09/827,007 filed Apr. 05, 2001 and entitled LOCKOUT
MECHANISM FOR USE WITH GROUND AND ARC FAULT CIRCUIT INTERRUPTERS,
both of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates generally to the field of devices for
protecting electrical circuits in the event of faults, and more
particularly to a device that protects from arc faults and ground
faults, which is provided with a manual test feature that
permanently denies power to the protected circuit should the test
fail.
BACKGROUND OF THE INVENTION
[0003] The electrical distribution system is defined to include the
circuit breaker, branch circuit conductors, wiring devices, cord
sets or extension cords, and electrical conductors within an
appliance. A protective device is incorporated in an electrical
distribution system for protecting a portion of the system from
electrical faults. Ground fault circuit interrupters, also called
GFCIs, are one type of protective device that has become quite
widely used. They provide a very useful function of disconnecting
an electrical power source from the protected portion of the system
when a ground fault is detected. Among the more common types of
ground faults sensed by known GFCIs are those caused when a person
accidentally makes contact with a hot electrical lead and ground.
In the absence of a GFCI, life threatening amounts of current could
flow through the body of the person.
[0004] Arc fault circuit interrupters, also called AFCIs, are
another type of protective device but that has been in use more
recently. AFCIs disconnect an electrical power source from a load
when an arc fault is detected. Among the more common type of arc
faults sensed by known AFCIs are those caused by damaged insulation
such as from an overdriven staple. This type of arc fault occurs
across two conductors in the electrical distribution system such as
between the line and neutral conductors or line and ground
conductors. The current through this type of fault is not limited
by the impedance of the appliance, otherwise known as a load
coupled to the electrical distribution system, but rather by the
available current from the source voltage established by the
impedance of the conductors and terminals between the source of
line voltage and the position of the fault, thus effectively across
the line, and has been known as a "parallel arc fault." Another
type of arc fault sensed by known AFCIs are those caused by a break
in the line or neutral conductors of the electrical distribution
system, or at a loose terminal at a wiring device within the
system. The current through this type of fault is limited by the
impedance of the load. Since the fault is in series with the load,
this type of fault has also been known as a "series arc fault." In
the absence of an AFCI, the sputtering currents associated with an
arc fault, whether of the parallel, series or some other type,
could heat nearby combustibles and result in fire.
[0005] Protective devices are typically provided with line
terminals for coupling to the supply voltage of the electrical
distribution system, and load terminals coupled to the protected
portion of the system and a circuit interrupter for disconnection
of the load terminals from the line terminals. The protective
device is provided with a sensor for sensing the fault, a detector
for establishing if the sensed signal represents a true hazardous
fault, as opposed to electrical noise, and a switch responsive to
the detector sensor, wherein the circuit interrupter comprising the
contacts of a relay or trip mechanism are operated by a solenoid
responsive to the switch to disconnect the load terminals from the
line terminals. The disconnection is also known as tripping. A
power supply may be required to furnish power to the sensor,
detector, switch or solenoid.
[0006] Protective devices are commonly equipped with a test button
which the owner of the protective device is instructed to operate
periodically to determine the operating condition of the sensor,
the detector, the switch, trip mechanism or relay, or power supply,
any of which can fail and which may cause the circuit interrupter
to not operate to remove power from the load side of the protective
device to interrupt the fault. Since the protective device
comprises electronic and mechanical components, failure modes
comprise normal aging of electronic components, corrosion of
mechanical parts, poor connections, mechanical wear, mechanical or
overload abuse of the protective device in the field, electrical
disturbances such as from lightning, or the like. Once the test has
been manually initiated by operating the test button, the outcome
of the test has often been indicated mechanically such as by a
popping out of a button, visually through a lamp display or
pivoting flag that comes into view, or audibly through an
annunciator. As an alternative to a manual test, a self-test
feature can be added to the protective device for automatic testing
such as is described in U.S. Pat. No. 6,421,214 and U.S.
application Ser. No. 09/827,007 filed Apr. 05, 2001 and entitled
LOCKOUT MECHANISM FOR USE WITH GROUND AND ARC FAULT CIRCUIT
INTERRUPTERS, both of which are incorporated herein by reference.
Once the test has been automatically initiated through the
self-test feature, the outcome of the test can be indicated by any
of the previously described methods or by the permanent
disconnection of the load terminals from the line terminals of the
protective device, also known as "lock-out."
[0007] Protective devices have been located in an electrical
distribution system in a variety of conventional device housings
such as but not limited to circuit breakers typically installed
inside a panel at the service entrance having an interrupting
contact that disconnects the load in response to sustained
overcurrent, receptacle outlets or snap switches typically
installed inside a wall box, portable housings typically installed
in plugs or connectors or as protective modules within appliances.
Constructional requirements for the different device housings
differ. Some differences arise from the pertinent UL (Underwriters
Laboratories) safety standards, for example, UL standard 943 for
GFCIs and UL standard 1699 for AFCIs. Unlike circuit breaker and
receptacle devices, portable devices are susceptible to a poor
connection between the receptacle and neutral plug blade.
Therefore, only portable devices must continue to afford provide
protection or interrupt load side power due to neutral supply
conductor failure. This requirement for the portable protective
device has often been accomplished using a relay with normally open
contacts serving as the circuit interrupter, such as disclosed in
U.S. Pat. No. 4,574,324, whereas receptacle devices commonly use a
circuit breaker and mouse-trap mechanism such as is disclosed in
U.S. Pat. No. 4,939,615. Other differences arise from the nature of
the housing itself, wherein protective devices that are housed in a
circuit breaker and that require a power supply most conveniently
derive power for the supply power from the load side of the circuit
interrupter.
[0008] The prior art discloses methods for denying power to the
load when there is protective failure. U. S. Pat. Nos. 6,040,967
and 6,282,070 deny power to the load side of the device when there
is a loss of protective function. The device's test button is
manually operated which causes the interrupting contacts to open
via a mechanical linkage. Next, the reset button is manually
operated which initiates a test signal. Failure to detect the test
signal prevents the interrupting contacts of the device from being
connected.
[0009] U.S. Pat. No. 6,262,871 is another example of a self-testing
device but that opens a redundant set of mechanical contacts
permanently upon detection of failure.
[0010] U.S. Pat. No. 6,324,043 denies power through use of a
fusible link that opens when there is a loss of protection.
[0011] International Patent No. 01/97243 discloses the use of a
redundant solenoid that operates in the event of device
failure.
[0012] Prior art protective devices that afford self-test comprise
complicated circuitry that is both expensive and subject to
failure. Prior art protective devices that have required manual
manipulation of test and reset buttons comprise complicated
mechanical linkages. This type of manual lock-out device also
requires the power supply for powering the protective circuitry to
derive power from the line terminals of the protective device which
is not convenient for the protective device housed in a circuit
breaker enclosure that derive power typically from the load side
terminals of the protective device. Manual lock-out devices have
not been suitable for protective devices housed in a portable
enclosure. Portable protective devices typically use a relay with
normally open contacts comprising the interrupting contacts, a
relay not being compatible with prior art manual lock-out
devices.
SUMMARY OF THE INVENTION
[0013] Briefly stated, a protective device includes a test button
for enabling a test signal for testing an operating condition of at
least one of the device components, such as the sensor, detector,
switch, solenoid and trip mechanism. The test button also enables a
current through a resistor body which is affixed to a stationary
part of the device. The resistor body keeps a lockout spring under
tension. Failure of the test signal to operate the trip mechanism
within a predetermined time interval causes the resistor body
conducting the current to reach a predetermined temperature,
wherein the resistor body ceases to hold a lockout spring, thereby
permitting the lockout spring to move to a position which causes
the set of interrupting contacts to remain permanently in a
disconnected position.
[0014] The present invention denies power to the protected side of
the device when there is a loss of protective function. Manual
operation of the device's test button enables an electrical test
signal for testing the device. At the same time, a current is
initiated through a resistor body in an embodiment, or fusible
component in an alternate embodiment. If the test signal does not
cause the interrupting contacts to disconnect within the expected
time interval, the ongoing current through the resistor body causes
solder connections to melt and the resistor body to physically
dislodge to a second position under bias from a spring, the motion
of resistor and spring resulting in the interrupting contacts of
the protective device remaining permanently in the disconnected
position. In an alternate embodiment, a fusible resistor burns open
and ceases to conduct electrical current, resulting in the
interrupting contacts of the protective device remaining
permanently in the disconnected position.
[0015] According to an embodiment of the invention, a protective
device for interrupting power upon detection of an electrical fault
in an electrical distribution system includes a plurality of line
terminals connectable to a source of voltage; a plurality of load
terminals connectable to a load; interrupting means that connects
or disconnects the plurality of line terminals from the plurality
of load terminals; a sensor for sensing the electrical fault; a
detector coupled to the sensor for detecting the electrical fault;
a switch coupled to the detector responsive to the detected
electrical fault; a solenoid coupled to the switch; a trip
mechanism coupled to the solenoid which moves the interrupting
means to a disconnected position upon occurrence and detection of
the electrical fault; a lockout spring; a resistor body which holds
the lockout spring in a first position under tension; a test button
for enabling a test signal for testing an operating condition of at
least one of the sensor, detector, switch, solenoid and trip
mechanism, wherein the test button also enables a first current
through the resistor body; and wherein failure of the test signal
to operate the trip mechanism within a predetermined time interval
causes the resistor body conducting the first current to reach a
predetermined temperature, wherein the resistor body ceases to hold
the lockout spring in the first position, thereby permitting the
lockout spring to move to a second position, wherein the lockout
spring being in the second position causes the interrupting means
to remain permanently in the disconnected position.
[0016] According to an embodiment of the invention, a protective
device for interrupting power upon detection of an electrical fault
in an electrical distribution system includes a plurality of line
terminals connectable to a source of voltage; a plurality of load
terminals connectable to a load; a sensor for sensing the
electrical fault; a detector coupled to the sensor for detecting
the electrical fault; a switch coupled to the detector responsive
to the detected fault; a relay, coupled to the switch, including a
solenoid and a plurality of interrupting contacts wherein the relay
disconnects the line terminals from the load terminals upon
occurrence of the electrical fault, thereby moving the interrupting
contacts to a disconnected position; a fusing element; a test
button for enabling a test signal for testing an operating
condition of at least one of the sensor, detector, switch, solenoid
and trip mechanism and for providing a first current through the
fusing element; wherein failure of the test signal to disconnect
the interrupting contacts within a predetermined time interval
causes the fusing element conducting the first current to reach a
predetermined temperature, wherein the fusing element causes an
open circuit, and wherein the interrupting contacts remain
permanently in the disconnected position.
[0017] According to an embodiment of the invention, a protective
device for interrupting power upon detection of an electrical fault
in an electrical distribution system includes a plurality of line
terminals connectable to a source of voltage; a plurality of load
terminals connectable to a load; a set of bus bars that connect or
disconnect the plurality of line terminals from the plurality of
load terminals, the set of bus bars including a hot bus bar and a
neutral bus bar, wherein the hot bus bar connects a hot line
terminal to a hot load terminal, and the neutral bus bar connects a
neutral line terminal to a neutral load terminal; a resistor body
one-way moveable between a first and second position, wherein when
the resistor body is in the second position, the set of bus bars is
permanently disconnected from the plurality of line terminals and
the plurality of load terminals; a test button for enabling a test
signal for testing an operating condition of the device to
determine if the device is in good operating condition or bad
operating condition, and for providing a current through the
resistor body; the resistor body being connected on one end to the
test button and on another end to the neutral bus bar; and wherein
when the source of voltage is miswired to the load terminals and
the test button is pressed, the resistor body does not move to the
second position when the protective device is in the good operating
condition.
[0018] According to an embodiment of the invention, a method for
locking out a reset mechanism of an electrical protective device
includes the steps of (a) providing a spring driven lockout for the
reset mechanism; (b) providing a resistor body which holds the
lockout in a first position, wherein the first position permits
resetting the electrical protective device; (c) pressing a test
button to check an operating condition of the electrical protective
device; (d) sending a current through the resistor body in response
to pressing the test button; and (e) moving the lockout to a second
position in response to the resistor body reaching a predetermined
temperature as a result of the current being sent through the
resistor body for a longer period of time than a normal trip time
of the electrical protective device, wherein the second position
permanently prevents resetting of the electrical protective
device.
[0019] According to an embodiment of the invention, a method for
locking out a reset mechanism of an electrical protective device
includes the steps of (a) providing a tripping mechanism which
includes a normally open relay; (b) providing a fusing element
which permits power to said relay so that said relay remains
closed; (c) pressing a test button to check an operating condition
of said electrical protective device; (d) sending a current through
said fusing element in response to pressing said test button; and
(e) blowing said fusing element in response to said fusing element
reaching a predetermined temperature as a result of said current
being sent through said fusing element for a longer period of time
than a normal trip time of said electrical protective device,
wherein said blowing of said fusing element creates an open circuit
to said relay, thereby permanently preventing resetting of said
electrical protective device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 shows a circuit diagram for a ground fault circuit
interrupter (GFCI) according to the prior art;
[0021] FIG. 2 shows a partial sectional view of a prior art
mechanical implementation of the schematic of FIG. 1;
[0022] FIG. 3 shows the mechanical implementation of FIG. 2 in the
tripped state;
[0023] FIG. 4 shows a partial sectional view of a mechanical
implementation of an embodiment of the invention;
[0024] FIG. 5 shows a partial sectional view of the mechanical
implementation of FIG. 4 is shown in the lock-out position;
[0025] FIG. 6 shows a three-dimensional view of some of the
components of the embodiment of FIG. 4;
[0026] FIG. 7 shows a protective device according to an embodiment
of the invention;
[0027] FIG. 8 shows a protective device according to an embodiment
of the invention;
[0028] FIG. 9 shows a protective device according to an embodiment
of the invention;
[0029] FIG. 10 shows a protective device according to an embodiment
of the invention;
[0030] FIG. 11 shows a protective device according to an embodiment
of the invention;
[0031] FIG. 12 shows a protective device according to an embodiment
of the invention; and
[0032] FIG. 13 shows a protective device according to an embodiment
of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0033] Referring to FIG. 1, a prior art GFCI 2 includes line
terminals 3 and 5 for coupling to a power source of the electrical
distribution system and load terminals 37 and 39 appropriate to the
installed location, whether a circuit breaker, receptacle, plug,
module, or the like. A ground fault represented by resistor 41
produces an additional current in conductor 4 that is not present
in conductor 6. Sensor 12 senses the difference current between
conductors 4 and 6 which is then detected by a ground fault
detector 14. Detector 14 issues a trip command to an SCR 22 which
in turn activates a solenoid 24, which activates a trip mechanism
26 releasing contact armatures 34 and 32, thereby disconnecting
power to the load by breaking the circuit from a line hot 4 to a
load hot 36 and from a line neutral 6 to a load neutral 38. A
contact 10 along with a resistor 8 form a test circuit which
introduces a simulated ground fault. When contact 10 is depressed,
the additional current on conductor 4 is sensed by sensor 12 as a
difference current causing the device to trip. Current flows
through resistor 8 for the interval between depression of the
contact 10 and the release of contact armatures 34 and 32, which is
nominally 25 milliseconds. The device is reset by pressing a reset
button 40 which mechanically resets trip mechanism 26. A resistor
20, a Zener 18, and a capacitor 19 form a power supply for GFCI
2.
[0034] Referring to FIG. 2, the mechanical layout for the circuit
diagram of FIG. 1 is shown in which like elements are like
numbered. Trip mechanism 26 is shown in the set state, meaning that
contacts 37 and 35 are closed. Contacts 35 and 37 are held closed
by action of a trapped make-force spring 46 acting on an escapement
55 on a rest stem 54 to lift a reset latch spring 52 and by
interference, an armature 32. Reset latch spring 52 includes a hole
53 and armature 32 includes a hole 33, which holes 33 and 53 permit
entry of a tip 58 of reset stem 54. Reset stem 54 is held in place
by a block 60. Armature 32 and a printed circuit board (PCB) 56 are
mechanically referenced to a housing 48 so that the force in spring
46 is concentrated into armature 32.
[0035] Referring to FIG. 3, the mechanism of FIG. 2 is shown in the
tripped state. The tripped state occurs when SCR 22 activates a
magnetic field in solenoid 24, which in turn pulls in plunger 23 to
displace reset latch spring 52. Displacing reset latch spring 52
allows a flat portion 55 to clear the latch spring 53 interference,
which then releases the interference between latch spring 52 and
armature 32. Armature 32 has a memory which returns armature 32 to
a resting position against solenoid 24, opening contacts 35 and 37
and disconnecting power to the load. The principles shown in FIGS.
1-3 are adaptable to any number of mechanical configurations
including U.S. Pat. No. 5,510,760 which is incorporated herein by
reference.
[0036] Referring to FIG. 4, a partial sectional view of a
mechanical implementation of an embodiment of the invention is
shown. A resistor 8', shown schematically in FIG. 1 as resistor 8,
is designed to withstand self-heating that results from each
depression of contact 10, which causes current to flow through
resistor 8' for the expected trip time of the GFCI. For example,
resistor 8' for a 6 mA GFCI coupled to a 120 VAC supply is required
by UL to be 15 KOhms, which dissipates nominally 0.96 Watts during
each trip time interval. In particular, resistor 8' must survive
several thousand trip time intervals accomplished by depressing
contact 10 and reset button 40 alternately. During normal operation
of GFCI 2, resistor 8' is physically positioned to restrain lockout
spring 400. Resistor 8' is preferably mounted and soldered so that
the body of resistor 8' impedes movement of lockout spring 400.
[0037] Referring to FIG. 5, a partial sectional view of the
mechanical implementation of FIG. 4 is shown in the lock-out
position. The GFCI 2 has failed in some manner such that the trip
time in response to depressing contact 10 is greater than the
expected interval including failure of GFCI 2 to trip altogether.
Examples of failure modes include a defective sensor 12, and for a
sensor 12 comprising a transformer, open or shorted turns. The
detector 14, typically composed of electronic components, may have
poor solder connections or components that have reached end of
life. The SCR 22 may short circuit either due to reaching end of
life or due to a voltage surge from a lightning storm, thereby
causing continuous current through solenoid 24 which burns open
through over activation, or, alternatively, SCR 22 may open
circuit. The mechanical components associated with trip mechanism
26 may become immobilized from wear or corrosion. The power supply,
if provided, may fail to deliver power in accordance with the
design such that sensor 12, detector 14, SCR 22, or solenoid 24 are
non-operative.
[0038] When failure of GFCI 2 occurs, the current through resistor
8' flows for the time that contact 10 is manually depressed, on the
order of at least seconds, which is two orders of magnitude longer
than if the trip mechanism 26 were to operate in response to
depressing contact 10. Resistor 8', which is preferably coupled
electrically to GFCI 2 through solder, heats from the current and
melts the solder. Resistor 8', no longer restrained by the solder,
or in an alternative embodiment by an adhesive, is physically
dislodged by the bias of lockout spring 400. Force is then applied
by an end 404 of lock-out spring 400 against a feature on the reset
latch spring 52, for example, a tab 402. The force in lockout
spring 400 is greater than the force in reset latch spring 52. As
previously described, reset latch spring 52 is displaced allowing a
flat portion 55 to clear the latch spring 53 interference, which
then releases the interference between reset latch spring 52 and
armature 32. Armature 32 has a memory which returns armature 32 to
a resting position against solenoid 24, opening contacts 35 and 37
and disconnecting power to the load. Thus when the GFCI 2 is
operational, the tripping mechanism 26 is able to operate, and the
armatures 32 and 34 disconnect when plunger 23 applies force to
reset latch spring 52. If GFCI 2 is not operative, lockout spring
400 applies force to reset latch spring 52, likewise causing
armatures 32 and 34 to disconnect. When GFCI 2 is tripped under the
influence of lockout spring 400, armatures 32 and 34 are
permanently disconnected irrespective of depressing contact 10 or
reset button 40 or any further movement in plunger 23. Thus
resistor 8' is integral to the lock-out feature of the present
invention.
[0039] Referring to FIG. 6, components of the embodiment of FIG. 4
are shown in a three-dimensional view including lockout spring 400,
end 404, resistor 8', and latch spring 52. Spring 404 is preferably
affixed to the same structure as resistor 8'.
[0040] Referring to FIG. 7, a protective device 710 shows a
resistor 700 which is then used as the resistor body which
constrains spring 400. There are other ground fault circuit
interrupters whose trip thresholds are greater than 6 milliamperes
intended for a variety of supply voltages or phase configurations,
and intended for personnel protection or fire prevention. Alternate
trip levels typically include 30 milliamperes in the U.S. or
Europe, or 300 or 500 milliamperes in Europe, to which the
invention as described applies. For devices where the current
through resistor 8 may produce insufficient heat during the
anticipated duration that contact 10 is manually depressed to melt
the solder, resistor 8 can be supplemented by a resistor 700 in
parallel with resistor 8 which connects to line 6 on the other side
of sensor 12 from where resistor 8 connects to line 6. Currents
through resistors 8 and 700 are enabled by depressing contact 10.
Resistor 8 generates a simulated test signal comprising a
difference current to test GFCI 2 as previously described. Resistor
700 is coupled so as to conduct common mode current but no
difference current. Since the current through resistor 700 does not
influence the amount of simulated test current required by UL,
which is set by the value of resistor 8, the value of resistor 700
can be whatever value is convenient for producing sufficient heat
in resistor 700 when contact 10 is manually depressed to release
lockout spring 400 when GFCI 2 is not operational. FIG. 7 also
shows how the lockout function is unaffected by whether the power
supply for the GFCI comprising resistor 20, Zener 18, and capacitor
19 are coupled to the load side of armatures 32 and 34. Load side
power derivation may be convenient for GFCIs or protective devices
housed in a circuit breaker. FIG. 7 also shows how SCR 22 can be
replaced by a transistor 22', with either device comprising a
switch for controlling solenoid 24.
[0041] Referring to FIG. 8, a protective device 810 which is an
alternate embodiment to FIG. 7 shows a resistor 800 which serves
the same function as resistor 700 in FIG. 7 but is coupled to the
load side of the interrupting contacts, i.e., contact armatures 32,
34. This may be important for 6 milliampere GFCI receptacles and
portables where the hot and neutral supply conductors are
inadvertently transposed by the installer, wherein the hot side of
the supply voltage from the electrical distribution system is
connected to line terminal 5. If the armatures 32 and 34 in FIG. 7
are disconnected in response to a fault current, a hazardous
current may yet flow through resistors 8 and 700 through ground
fault 702 when contact 10 is depressed. However, if armatures 32
and 34 in FIG. 8 are disconnected, current flows through resistor 8
but not through resistor 800, which is not a problem because the
current flow through resistor 8 alone has already been determined
to be non-hazardous.
[0042] Referring to FIG. 9, a protective device 910 which is an
alternative embodiment to FIG. 8 is shown in which the trip
mechanism comprises one or more bus bars as disclosed in U.S. Pat.
No. 5,510,760, incorporated herein by reference, instead of contact
armatures. Resistor 900 serves the same function as resistor 800 in
FIG. 8 except that resistor 900 is coupled to moveable bus bar
902'. For receptacle housings it is possible for the installer to
miswire a GFCI such that the supply voltage is connected to load
terminals 37 and 39, which would cause resistor 800 (FIG. 8) to
melt solder when contact 10 is depressed, even when device 810 is
in good working condition, i.e., operational. The problem is
alleviated in the embodiment of FIG. 9 whereby resistor 900 melts
solder only when bus bar 902' remains connected when contact 10 is
depressed, that is, when device 910 is non-operational. Miswiring
thus does not cause a permanent lock-out of device 910.
[0043] Referring to FIG. 10, a protective device 1010 which is an
alternate embodiment to FIG. 7 is shown, wherein contact 10 enables
a current through resistor 8, as previously described, and a second
current through a resistor 1000 in which the second current is
preferably less than a tenth of the current through resistor 8. The
second current depends on an interface circuit such as a transistor
switch 1002. Transistor switch 1002 causes current to flow through
a resistor 1004 of identical function to resistor 700 described in
FIG. 7, i.e., resistor 1004 is normally in such a position as to
leave spring 400 (FIG. 6) under tension, but when resistor 1004
heats up from the current through it sufficient to dislodge the
solder affixing resistor 1004 to a fixed reference surface, the
dislodgement of resistor 1004 releases spring 400.
[0044] FIG. 10 shows an alternative to FIG. 8 wherein a hazardous
current does not occur when the hot and neutral supply conductors
are inadvertently transposed as described in FIG. 8. In addition,
FIG. 10 shows another remedy for the issue described in the FIG. 9
embodiment wherein resistor 1004 melts solder only if protective
device 1010 is non-operational and not when protective device 1010
is miswired.
[0045] Referring to FIG. 11, a protective device such as GFCI 1110
according to an alternate embodiment is shown, wherein the so
called mouse trap mechanism, i.e., the tripping mechanism of the
GFCI of FIGS. 1-5, is replaced by a relay 1100 having normally open
contacts 1102 that connect or disconnect line terminals 3 and 5
from load terminals 37 and 39 respectively, and a solenoid 1104,
which is designed to carry current when contacts 1102 of GFCI 1110
are connected, a construction that is common to, but not limited
to, portable GFCI devices. Solenoid 1104 is designed to conduct
current for the unlimited duration that GFCI 1110 is in use,
wherein solenoid 1104 is not susceptible to burn out caused by
over-activation as previously described with respect to solenoid
24. A fusible element 1106 is in series with the solenoid and is
designed to carry the continuous current through solenoid 1104 when
transistor 22' is closed. Contact 10 enables current through
resistor 8 which produces a difference current as previously
described, and a common mode current, which, if the device is
non-operational, enables a lock-out feature. The common mode
current, which is greater than the solenoid current, is conducted
through fusible element 1106.
[0046] If GFCI 1110 is operational, the load side is disconnected
from the line side, causing the device to trip and resistor 8 and
common mode currents to stop flowing even if contact 10 continues
to be manually depressed. Fusible resistor 1106 must survive
several thousand cycles of common mode current exposures from
alternately depressing contact 10 to trip GFCI 1110 and switch 1108
to electronically reset GFCI 1110. The duration of each common mode
current exposure is the expected time that GFCI 1110 requires for
tripping after contact 10 has been depressed. If GFCI 1110 fails in
some manner such that the trip time in response to depressing
contact 10 is greater than the expected interval including the
failure of GFCI 1110 to trip altogether, fusible element 1106 burns
to an open circuit, permanently eliminating current through
solenoid 1104 and rendering interrupting contacts 1102 in a
permanently disconnected position. Fusible element 1106 can include
a resistor.
[0047] Referring to FIG. 12, elements of the circuit diagram of
FIG. 11 are combined with elements of the circuit diagram of FIG. 8
in a protective device 1210, wherein components having like
functions bear like numbers. The concept shown in FIG. 11 is thus
combined with the embodiment of FIG. 8 to protect against the
inadvertent transposing of the hot and neutral supply conductors to
terminals 3 and 5 from the electrical distribution system. For
protective devices not equipped with a resistor 8, the value of
resistor 1000 can be chosen so that current passing therethrough is
less than 0.5 mA, which limit has been identified to be the
perception level for humans.
[0048] Referring to FIG. 13, an alternate embodiment is shown in
which the preceding concepts are applied to a general protective
device 1310 representative of the class of general protective
devices including AFCIs that require a contact 10 but that are not
necessarily equipped with a GFCI or a sensor capable of sensing
difference current. Such devices are disclosed in U.S. Pat. No.
6,421,214 which is incorporated herein by reference. Components
having like functions bear like numbers. Sensor 1300 is similar to
sensor 12 but may be a current sensor or shunt for sensing load
current through either conductor 6 or through conductor 4. A
detector 1302 is similar to detector 14 (FIG. 1) but senses
particular signatures in the load current as has been demonstrated
in other patent applications as a method of identifying arc faults.
A contact 1304 is similar to contact 10 (FIG. 1), which initiates a
test of protective device 1310 when depressed. The test signal can
be controlled by detector 1302 to test sensor 1300, detector 1302,
switch 22, and trip mechanism 26. A resistor 1306 is similar to
resistor 700 (FIG. 7) which is affixed to a fixed reference
surface. If armatures 32 and 34 fail to operate due to a
malfunction of protective device 1310, the longer duration of
current through resistor 1306 causes sufficient self-heating of
resistor 1306 to melt the solder affixing resistor 1306 to the
fixed reference surface, wherein resistor 1306 is dislodged due to
force exerted by lockout spring 400 (FIG. 4), wherein lockout
spring 400 causes armatures 32 and 34 to be permanently
disconnected.
[0049] While the present invention has been described with
reference to a particular preferred embodiment and the accompanying
drawings, it will be understood by those skilled in the art that
the invention is not limited to the preferred embodiment and that
various modifications and the like could be made thereto without
departing from the scope of the invention as defined in the
following claims.
* * * * *