Patent Application
20130278361
1. Field of the Invention
The present invention relates generally to electrical wiring devices, and particularly to electrical wiring devices that include electric circuit protective features.
2. Technical Background
The average consumer is so used to having electric power at his beckon call, that he often forgets, or does not know, how that electric power is delivered to him. The terms “electrical wiring device” or “electrical circuit” are thus very often abstractions to the typical consumer. As such, it may be useful to provide a brief review of the terminology that is used to describe the technologies related to the delivery of electric power within a structure or a residence.
AC electric power service provided by the power utility is usually terminated by a breaker panel located within the residence. Very often the breaker panel is disposed in the basement of the structure if it has one. The breaker panel distributes the electric power to various branch circuits throughout the structure such that each branch circuit is monitored and controlled by a circuit breaker. If the circuit breaker detects a fault condition it will trip the breaker to interrupt the delivery of power to that circuit. Moreover, the consumer may manually actuate the breaker switch to interrupt the delivery of power to that circuit. The breaker switches may be rated at 20A or 15A depending on the nature of the branch circuit.
The backbone of a single phase branch circuit typically includes a cable that has a black (hot) wire, a white (neutral) wire and a green (ground) wire. In some cases, only two wires (hot and neutral) are employed. An additional hot wire is required for each additional phase such that a two phase circuit may include four wires and a three phase circuit may include five wires. The conventional method for installing electrical circuits includes a “rough-in” installation phase and a finish installation phase. In the rough-in phase, conduit or cable is disposed throughout the structure in accordance with the building plans. Junction boxes are installed at appropriate locations to house electrical connection points where two or more conductors can be spliced together. Device boxes are installed throughout the structure where electrical service is desired. After the boxes are placed, the electrical wires are pulled through the conduits (if provided) and all of the circuits are bonded such that the neutral conductors are connected to ground at or near the circuit breaker.
The electrical wiring in a branch electric circuit typically interconnects one or more electrical wiring devices. One or more electrical wiring devices may be mounted to a device box depending on the size of the device box. A single-gang device box typically accommodates one electrical wiring device; a two-gang device box will typically accommodate two electrical wiring devices, and so on and so forth. An electrical wiring device provides the consumer with a point of access to electrical service. For example, a receptacle outlet provides power to a portable device when the device's corded power plug is inserted into an energized receptacle. Once an electrical wiring device is installed inside the device box, a cover plate is disposed over the electrical wiring device to “complete the electrical enclosure” such that individuals are not exposed to “hot” electrical wiring after the electrical power is turned ON.
From a structural standpoint, an electrical wiring device is disposed within an electrically non-conductive housing, and nowadays that non-conductive material is usually made from a hard plastic material. A set of line terminals, a set of load terminals and often a ground connection are provided at the exterior of the electrical wiring device and are connected to electrical components or conductors disposed in the interior of the device. The “line terminals” of an electrical wiring device refers to the terminals that connect the wiring device to conductive wires from the breaker panel. The “load terminals” or the “feed-through load terminals” are connected to downstream wiring that is configured to propagate AC power to one or more downstream electrical loads. The term “receptacle load terminals” refers to a receptacle outlet that provides power to a portable load when a corded power plug is inserted therein. A load, of course, refers to an appliance, a lighting device, or some other kind of device that consumes electrical power during operation.
Certain types of electrical faults are known to occur in branch electric circuits and electrical wiring systems. These faults represent serious safety issues that may result in fire, shock or electrocution if not addressed properly. Electric circuit protection devices are deployed in the branch electric circuits to prevent the consumer from being shocked or electrocuted when such faults occur. These protective devices usually include a circuit interrupter disposed between the line terminals and the load terminals. The circuit interrupter provides power to the load terminals under normal conditions; however, when the protective device detects a fault condition in the load circuit, it will trip the circuit breaker to interrupt electrical connectivity between the line terminals and the load terminals. There are many types of electric circuit protection devices including ground fault circuit interrupters (GFCIs), arc fault circuit interrupters (AFCIs), transient voltage surge suppressors (TVSSs), or surge protective devices (SPDs). This list includes representative examples and is not meant to be exhaustive and a single device may be configured to perform one or more of these functions (e.g., a combination AFCI/GFCI).
There are several drawbacks associated with conventional installation methods and conventional protective electrical wiring devices. Conventional protective electrical wiring devices often do not make efficient use of space. In addition, mounting the wiring device's ground strap to the device box is tedious, time consuming, and therefore costly. The same can be said of mounting the cover plate to the electrical wiring device. Moreover, in multi-gang installations, the finished look is often ragged because the plurality of electrical devices and their respective cover plates are typically not in alignment. This misalignment can be, and very often is, in all three dimensions. Retrofitting an electrical installation can also be problematic from the standpoint of the finished look because the device box, or an old work box, may not be precisely aligned to the plane of the wall surface. This is especially true if the wall surface itself is uneven. After remodeling a space, homeowners often seek to replace an existing wall plate with one that better matches the new décor. Thus, a homeowner may inadvisably remove the faceplate cover from an energized wiring device and inadvertently become exposed to a shock hazard from the “hot” electrical wiring.
What is needed therefore is a protective electrical wiring device system that addresses the drawbacks articulated above. In particular, what is needed is a protective electrical wiring device that may be employed in a number of different form factors without having to modify the internal electro-mechanical configuration of the device. Stated differently, a protective device is needed that can be configured in a conventional form factor or in another form factor suitable for use in a modular framing system such that it does not require fasteners to be securely installed within the device box.
The present invention addresses the needs described above by providing a protective electrical wiring device system that addresses the drawbacks articulated above. The protective electrical wiring device of the present invention may be employed in a number of different form factors without having to modify the internal electro-mechanical configuration of the device. In other words, the protective device of the present invention can be configured in a conventional form factor or in a form factor suitable for use in a modular framing system such that it does not require fasteners to be securely installed within the device box. In one embodiment of the present invention, the protective device is provided in one or more modular embodiments that are employed within a rigid frame that “completes the enclosure.” Because the frame of the present invention completes the enclosure, it may be employed with new construction, old construction or retrofits. The frame can support a variety of modular electrical wiring devices of differing sizes. As explained below, the modular protective wiring device of the present invention may be configured to be mounted to the frame instead of the device box such that fasteners are not required for installation within the device box. In the modular embodiment, no cover plate is needed because the frame completes the enclosure, and therefore, the cover plate is replaced by an aesthetic overlay that can be removed at any time without exposing the homeowner to shock or electrocution.
As its name suggests, the aesthetic overlay of the present invention may be comprised of a variety of decorator materials without regard to the structural considerations that are concomitant with completing the enclosure. Thus, the modular protective device may be provided in a number of modular form factors to optimize the decorative impact of the system. Accordingly, the protective electrical wiring device of the present invention may present either a two-module or a three-module front cover depending on the aesthetics of the design. In a multi-gang configuration, for example, the form factor of the protective electrical wiring device may be selected to match module size of the other electrical devices within the multi-gang device box such that they conveniently fit within a single aesthetic overlay in perfect alignment in all three dimensions. The present invention may also be adapted to a convention wiring device form factor.
One aspect of the present invention is directed to a protective device that includes a plurality of line terminals, a plurality of feed-through load terminals and a ground connection element accessible via a back body. A cover assembly includes a plurality of receptacle openings, a reset button and a test button. The reset button and the test button are disposed along a first diagonal and in opposite corners of a substantially square area defined by the reset button and test button. At least one receptacle contact structure includes a portion extending across the first diagonal and at least one receptacle contact substantially aligned with one of the receptacle openings. An electromechanical apparatus is disposed in the back body within a region substantially aligned with the substantially square area. The electromechanical apparatus includes a toroidal sensor assembly coupled to an actuator coil arranged along a center axis in substantial alignment with the first diagonal, the center axis forming an acute angle relative to a side wall of the back body. The actuator coil provides an actuation stimulus in response to a detected fault condition. A circuit interrupter is configured to render the plurality of line terminals, the plurality of feed-through load terminals and the at least one receptacle contact structure electrically discontinuous in response to the actuation stimulus and electrically continuous in response to an actuation of the reset button.
In another aspect, the present invention is directed to an electrical wiring system that includes a frame assembly configured to be mounted to a device wall box installed in a structure. The frame includes a first edge formed around a peripheral portion of the frame, the first edge being configured to abut a structural surface disposed around the device wall box. The frame assembly includes a ground portion configured to provide a ground path from the frame assembly to ground. The frame assembly further includes a frame opening corresponding to at least one gang opening. The frame opening substantially defines a second edge configured to extend inwardly toward the device wall box interior such that the frame opening provides sole access to the device wall box interior. A protective device is configured to snap-mount within the frame opening. The protective device includes a plurality of line terminals, a plurality of feed-through load terminals and a ground connection element accessible via a back body. A cover assembly includes a plurality of receptacle openings, a reset button and a test button. The reset button and the test button are disposed along a first diagonal and in opposite corners of a substantially square area defined by the reset button and test button. At least one receptacle contact structure includes a portion extending across the first diagonal and at least one receptacle contact substantially aligned with one of the receptacle openings. An electromechanical apparatus is disposed in the back body within a region substantially aligned with the substantially square area. The electromechanical apparatus includes a toroidal sensor assembly coupled to an actuator coil arranged along a center axis in substantial alignment with the first diagonal, the center axis forming an acute angle relative to a side wall of the back body. The actuator coil provides an actuation stimulus in response to a detected fault condition. A circuit interrupter is configured to render the plurality of line terminals, the plurality of feed-through load terminals and the at least one receptacle contact structure electrically discontinuous in response to the actuation stimulus and electrically continuous in response to an actuation of the reset button. An aesthetic overlay is configured to be removably coupled to the frame assembly, the aesthetic overlay including an overlay opening configured to provide access to at least a portion of the cover assembly.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and operation of the invention.
Reference will now be made in detail to the present exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. An exemplary embodiment of the protective device of the present invention is shown in
As embodied herein and depicted in
Referring to
Note that a frame enclosure lip 90-5 is formed around the outer perimeter of the frame. The frame enclosure lip 90-5 is configured to be disposed over, and abut, the wall surface 1 (not shown in this view). The edge of a properly installed wall box would thus seldom, if ever; touch the rear surface of the frame because of the frame enclosure lip 90-5 provides separation between the frame and the wall surface. This is true even when old work boxes are deployed. Old work boxes, of course, have flanges that mount to the outer surface of the sheet rock. One of the functions of the frame enclosure lip 90-5 is therefore to avoid interference with these flanges such that the frame 90 does contact the wall surface 1.
The frame opening 90-13 is sized to accommodate three device modules. Stated differently, the frame opening can accommodate three one-module devices, a one module device and a two module device, or a three module device. The frame 90 may be equipped with modular alignment connectors that allow the electrical enclosure to be completed with a single two-module sized device. In this case, the device is disposed between two alignment connectors that together take up one module's worth of space within opening 90-13. Reference is made to U.S. patent application Ser. No. 13/608,675, which is incorporated herein by reference as though fully set forth in its entirety, for a more detailed explanation of the frame member 90.
The frame opening 90-13 has edge portions that mate with the snap elements 14-4 (see
Referring to
Note that the reset button 17 includes a visual indicator lens 17-1 formed therein. The lens 17-1 is in optical communication with a light source disposed within the housing of device 10. The nature of the indicator is described below in the discussion of the various schematics. The back body is shown herein to include snap elements 14-1 which are configured to snap into and mate with the serrated edges 90-60 of the frame opening 90-13.
Referring to
Referring to
Referring to
Two different contact embodiments are shown at the same time for purposes of comparison. The contacts (60-11, 60-12, 60-13) in the first embodiment are referred to sandwiched contacts and can be said to be “in-line” (thus, 60-10 and 60-14 are not employed in this embodiment). In this embodiment, the hot side of the circuit interrupter 60-1 includes a line hot contact arm 40-10 and a load hot contact arm 40-20. The line hot contact arm 40-10 includes a dual-sided contact 60-11 which mates with the load hot contact 60-12, respectively, (disposed on the load hot arm 40-20) and the fixed hot load contact 60-13 when circuit interrupter 60 is in the reset state. Contacts 60-11, 60-12, and 60-13 share a common axis. The contacts are separated from one another when circuit interrupter 60 is in the tripped state. Again, contacts 60-10 and 60-14 are omitted in the first alternate embodiment.
In the alternate contact embodiment contacts 60-10 and 60-14 are included and contact 60-12 is omitted. Line contact 60-10 is connected to line hot contact arm 40-10 and load hot contact 60-14 is connected to load hot arm 40-20. Contact 60-11 is still connected to the line hot contact arm 40-10 but since hot line contact 60-12 is omitted it need only be a single sided contact having only to mate with contact 60-13. When circuit interrupter 60 is in the reset state contacts (60-10, 60-14) mate and contacts (60-11, 60-13) mate. Since contact pairs (60-10, 60-14) and (60-11, 60-13) lie on two axes this arrangement is referred to as a “staggered contact” arrangement. In the tripped state contacts (60-10, 60-14) and (60-11, 60-13) are separated.
The neutral side of circuit interrupter 60-2 includes a similar arrangement. The circuit interrupter 60 is configured to work in conjunction with the latch block assembly 50, the reset pin assembly 17, and the fault detection apparatus disposed on PCB 40 to drive the circuit interrupter 60 into the tripped state or the reset state. The fault detection apparatus disposed on PCB 40 is described below in the discussion of the schematic diagrams provided herein. (See, e.g.,
The latch block assembly 50 is shown to include an upper latch block portion 52 and a lower latch block portion 54. The latch block 50 is coupled to the reset button by way of reset pin 17-5. A break spring 17-4 is disposed around the reset pin and exerts a break force during the tripping action. A make spring 50-1 is disposed between the separator 30 and the latch block assembly 50. The make spring 50-1 exerts a force against the latch block in the reset state to ensure that the contacts of the circuit interrupter 60 are closed and do not arc.
The lower latch block 54 is also coupled to an auxiliary switch KR1 disposed at the underside of PCB 40. The plunger 54-1 extends from the lower latch block through an opening formed in PCB 40 to open the auxiliary switch KR1. Accordingly, the auxiliary switch KR1 operates in conjunction with the circuit interrupter such that when the circuit interrupter is opened (i.e., device 10 is tripped), the auxiliary switch KR1 is opened, and vice-versa. The switch KR1 includes switch contacts KR1-1 disposed on either end of a conductive bus bar KR1-4 that make and break contact with switch contacts KR1-2 that are mounted on the underside of the PCB 40. The switch contacts KR1-2 are, in turn, electrically connected to circuit traces formed in PCB 40 in accordance with the present invention (See, e.g., the schematic of
Referring to
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As embodied herein and described in
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Another difference between this embodiment and the embodiment of
Referring to
As before, the test button 15 and the reset button 17 are connected to components that are disposed under the separator cap 20. Reference is made to U.S. Patent Application Ser. No. 13/487,547, filed Jun. 4, 2012 which is incorporated herein by reference as though fully set forth in its entirety, for a more detailed explanation of the shutter assemblies 22.
Referring to
The neutral receptacle conductor 30-2, on the other hand, has a rather complex shape and includes a central leg 30-21 that extends latitudinally from side-to-side within the separator 30. One set of neutral receptacle contacts 30-22 extends longitudinally from one end of the central leg 30-21 towards the movistor MOV1. Another set of neutral receptacle contacts 30-22 extends longitudinally from the other end of the central leg 30-21 away from the test button. A second neutral leg 30-23 is shaped like the number seven (“7”). It includes a base portion that extends from the central leg 30-21 and is disposed between the neutral receptacle contact set 30-22 and the hot receptacle contact set 30-12. Thereafter, the second leg 30-23 includes two ninety degree turns such that it positions the neutral fixed contact 60-12 between the reset button and the hot receptacle contact set 30-12.
Like previous embodiments, the separator 30 accommodates the test PCB 15-1 therewithin. The test wire 15-2 is connected to the hot receptacle conductor 30-1 and test wire 15-3 to the PCB 40.
Referring to
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The latch block 50 includes an upper latch block 52 and a lower latch block 54 which are described in greater detail below. The latch block 50 includes an upper latch block portion 52 and a lower latch block portion 54. A central aperture 52-1 in the upper latch block portion accommodates the reset pin 17-5. The upper latch block 52 further includes breaker arms 52-2 which are configured to force the line conductors 40-10, 40-12 downwardly during a tripping action to break the contact between the fixed contacts 60-13, 60-23 (not shown in this view) and the line contacts (60-11, 60-21). In particular, upper breaker arms 52-2 apply force to extension fingers 40-100 on line conductors (40-10, 40-12.) Similarly, lower breaker arms 52-20 (not shown in this view) apply force to extension fingers disposed on load conductors (40-20,40-22) during a tripping action to break the contact between the line contacts (60-11,60-21) and the load contacts (60-12,60-22.) In particular, lower breaker arms 52-20 apply force to extension fingers on load conductors (40-20, 40-22.) The breaker arms 52-2 assure a position of line conductors arms (40-10,40-12) and breaker arms 52-20 assure a position of load conductors (40-10,40-12) in the tripped state. As such, the upper and lower breaker arms assure a predetermined minimum separation distance between line contacts (60-11,60-21) and load contacts (60-12,60-22) when circuit interrupter 60 is in the tripped state. Note that the extension fingers on the load conductors are not visible in this view, but are similar to the extension fingers 40-100 provided on the line conductors.
The lateral portions of the solenoid bobbin assembly 70 are disposed between the line conductor arms (40-10, 40-12) while its end portions are positioned between the toroidal assembly L1/L2 and the latch block assembly 50. The overall length of the toroidal assembly L1/L2, bobbin assembly 70 and latch block assembly 50 can be greater than the distance between the line terminals (14-10,14-12) and the load terminals (14-20,14-22) since they are mounted to PCB 40 along a diagonal axis. The movistor MOV1 (shown in
As embodied herein and depicted in
As described previously, the central body 54-6 also includes a plunger 54-1 that extends into an opening formed in the PCB 40. When the circuit interrupter 60 is in the tripped state, the plunger 54-1 engages the auxiliary switch KR1 such that it is open. When the circuit interrupter 60 is in the reset state, the plunger 54-1 is retracted such that the auxiliary switch KR1 is closed. See, e.g.,
Referring to
As previously described herein, each side of the upper latch block 52′ includes an upper arm 52-2 and a lower arm 52-20. As more clearly shown in this figure, the line conductors (40-10, 40-12) and load conductors (40-20,40-22) are not cantilevered per se; rather they are driven between the reset and tripped positions respectively by arms (52-2,52-20) and arms 54-2. The positions of the line and load contacts (60-10, 60-11, 60-12, 60-22, 60-21, 60-23) thus rely on arms (52-2, 52-20, 54-2) for positioning.
As embodied herein and depicted in
As embodied herein and depicted in
The ground fault circuitry 400 includes a differential transformer L1 which is configured to sense load-side ground faults. Transformer L2 is configured as a grounded neutral transmitter and is employed to sense grounded-neutral fault conditions. Both transformers are disposed in toroid assembly L1/L2 described previously. Both differential transformer L1 and grounded-neutral transformer L2 are coupled to the fault detector integrated circuit 406. Detector 406 is powered by a power supply circuit 408 connected to pin V+ on detector 406. The detector 406 output, provided on output pin SCR, is connected to the control input of SCR 410. Low pass filter 412, comprising resistor R10 and capacitor C7, filter the detector output signal. GFCI 400 also includes a snubber circuit 414 that includes resistor R4 and capacitor C8. Snubber circuit 414 prevents voltage transients from triggering SCR 410.
When SCR 410 is turned ON, solenoid 70 is energized, actuating circuit interrupter 60. Solenoid 70 remains energized for a time period that is typically less than about 25 milliseconds. Circuit interrupter 60 trips, resulting in the line terminals 14-1 being disconnected from respective load terminals 14-2. After the fault condition has been eliminated, the circuit interrupter 60 may be reset by way of reset button 17. In one embodiment, the reset mechanism 17 is purely mechanical in nature and does not include any electrical contacts for test initiation.
GFCI 400 addresses certain end of life conditions by denying power to the load when the device is unable to function. As an example of an end-of-life condition, solenoid 70 is susceptible to burn-out if SCR 410 becomes shorted out, or is permanently turned ON. Solenoid 70 may burn out if it is energized for more than about 1 second. Once the solenoid 70 burns out, the circuit interrupter 60 is incapable of being tripped. Solenoid burn-out prevention is provided by auxiliary switch 422 (KR1). Auxiliary switch 422 is configured to open when the circuit interrupter 60 is in the tripped position. If SCR 410 is shorted out or permanently ON, auxiliary switch 422 ensures that solenoid 70 is not permanently connected to a current source. The user may attempt to reset the device 10 by depressing the reset button 17, but the circuit interrupter 60 will immediately trip in response to the current flowing through the solenoid 70. Because the latch block 50 is coupled to the auxiliary switch 422 by plunger 54-1, auxiliary switch 422 is opened before solenoid 70 can be burned out.
In another embodiment, another failure mode is addressed by GFCI 400; this mode relates to the end-of-life failure mode of movistor MOV1. MOV 1 is disposed in series with auxiliary switch 422 and trip solenoid 70. This arrangement significantly reduces the probability of damage due to an over-current situation. When MOV 1 reaches end-of-life and shorts out, trip solenoid 70 is energized and auxiliary switch 422 is opened. As previously described, when auxiliary switch 422 opens, the flow of short circuit current is terminated before any damage to device 10 ensues.
GFCI 400 also includes trip indication circuit 426. Trip indicator 426 is implemented by placing LED1 and series resistors (R11-R14) in parallel with auxiliary switch 422. LED 1 is configured to emit a visual signal when circuit interrupter 60 and auxiliary switch 422 are in an open state (tripped). In an alternate embodiment LED 1 is replaced by an annunciator that provides an audible signal when interrupter 60 is in the tripped state.
GFCI 400 also includes a test circuit 150. The test circuit 150 is coupled between the line neutral terminal 14-12 and the hot receptacle terminal 30-12. The test circuit 150 includes a test button assembly 15 shown here to include a switch disposed in series with test resistor R1.
As embodied herein and depicted in
As before, the ground fault circuitry 400 includes a differential transformer L1 which is configured to sense load-side ground faults, i.e. ground faults located in loads connected to load terminals 14-2 or receptacle contacts (30-12, 30-22) and transformer L2, which is configured as a grounded neutral transmitter that is configured to sense grounded-neutral fault conditions. Both transformers are disposed in toroid assembly L1/L2 as described above. Both differential transformer L1 and grounded-neutral transformer L2 are coupled to the fault detector integrated circuit 406. Detector 406 receives power from a dual power supply circuit 408 that is described in greater detail below. The output of the detector 406 is connected to the control input of SCR 410. When SCR 410 is turned ON, the dual-solenoid 70′ is energized to actuate the circuit interrupter 60 such that the circuit interrupter 60 and the auxiliary switch 422 are tripped (opened). Solenoid 70′ remains energized for a time period that is typically less than about 25 milliseconds. When the circuit interrupter 60 trips, the line terminals 14-1 are disconnected from their respective load terminals 14-2 or receptacle contacts (30-12, 30-22.) After the fault condition has been eliminated, the circuit interrupter 60 may be reset by way of reset button 17 which has been depicted and described previously.
As its name suggests, the grounded neutral transmitter L2 is configured to detect a grounded neutral condition. As an initial point, note that the line neutral conductor (i.e., the conductor that is connected to neutral line terminal 14-12) is typically grounded in the electrical circuit at the panel—this does not constitute a grounded neutral fault condition. When a grounded neutral condition is not present, the grounded neutral transmitter L2 is configured to couple equal signals into the hot and neutral conductors. Because the differential transformer L1 is configured to sense a current differential, the equal signals provided by grounded neutral transmitter L2 effectively cancel each other out. On the other hand, a grounded neutral condition does occur when the load neutral conductor (i.e., the conductor that is connected to load neutral terminal 14-22 or neutral receptacle contact 30-22) is accidentally grounded. This creates a parallel conductive path (relative to the neutral return path) between the neutral line terminal 14-12 and neutral load terminal 14-22. As a result, another signal circulates around this current loop and it is coupled onto the neutral conductor (but not the hot conductor) to create a differential current. The differential transformer L1 senses the differential current between the hot and neutral conductors and the detector 406 generates a fault detection signal in response thereto. The fault detection signal trips the circuit interrupter 60.
In reference to the dual power supply circuit 408, it is provided to accommodate the needs of both the detection function (described above) and the universal auto-test circuit 401 described below. Dual supply 408 includes power supply portion 408-1 which includes diode D1 in series with resistors R6 and R7. The series circuit is disposed between the cathode of diode D4 and the anode of diode D6. The power supply portion 408-1 is thus connected to line hot via diode D4 and solenoid 70′ and is further configured to provide power to the supply terminal of detector 406 via diode D6. Diode D4 is further connected to power supply portion 408-2 which includes diode D2 in series with resistors R8 and R10; the series circuit is connected to the cathode of diode D6. Power supply portion 408-2 is configured to charge capacitor C6 whereas power supply portion 408-1 is configured to charge the parallel capacitor bank 408-3 (C16-C20). The total capacitance in bank 408-3 is greater than that of capacitor C6. The capacitor bank 408-3 has enough stored energy to maintain the power supply voltage during the negative half cycle auto-test. When the AC line cycle is negative, the diode D6 is forward biased, thereby coupling capacitor bank 408-3 to capacitor C6. Because the power supply is active during the negative half cycle, detector 406 is responsive during the auto-test.
When the GFCI 400 detects a fault condition, it is configured to interrupt the circuit interrupter 60 during the positive half-cycle of the AC line cycle. In order to meet the trip time requirements, power supply portion 408-2 is configured to charge to the full supply voltage in less than about 2 milliseconds. This means that during the positive half cycles, a hazardous ground fault condition is detected and interrupted quickly. On the other hand, power supply portion 408-1 takes longer to come up to full charge due to the large value of capacitor bank 408-3. Power supply portion 408-1 charges with a time constant that is approximately 15 milliseconds. However, due to reverse biasing of diode D6, power supply portion 408-2 is not prevented from charging quickly. In summary, detector 406 relies on power supply 408-2 during the positive half cycles for ground fault detection and relies on power supply 408-1 for auto-testing during the negative half cycles.
At this point, it is helpful to bring the universal auto-test circuit 401 into the discussion since one of the purposes of the dual power supply 408 is to support the auto-test circuit 401. The auto-test circuit 401 generates a simulated grounded neutral test signal by way of wire loop 402 when FET (Q2) is turned ON. When FET 404 (Q2) is turned ON, the grounded neutral transmitter L2 produces an oscillating signal that is a function of the full power supply voltage. The ON state resistance of FET 404 is less than about 4 Ohms Thus, the wire loop 402, in combination with the FET 404 (in the ON state), forms a loop that passes through the differential transformer L1 and neutral transmitter L2 to simulate a grounded neutral condition. In an alternate embodiment, instead of having a third wire passing through the transformers (L1, L2) the wire loop 402 may incorporate a portion of the neutral conductor that is disposed between line neutral terminal 14-12 and load neutral terminal 14-22. One advantage for placing the third wire within the wire loop relates to improved noise immunity. When the third wire is employed, the wire loop 402 and the neutral conductor are isolated such that the current propagating in wire loop 402 during the self-test is not affected by voltage drops or electrical noise propagating in the neutral conductor. Noise propagating on the neutral conductor could otherwise impair the test fault signal and its detection by the GFCI.
The timing of the FET ON state is controlled by the timing resistor R14. In one embodiment of the present invention, the FET 404 is turned ON near the conclusion of the positive half cycle of the AC power source and remains ON through a portion of the negative half cycle to produce the test fault signal. The grounded neutral transformer L2 generates a differential current in response to the test current propagating in wire loop 402. The differential current is, in turn, sensed by transformer L1. If the circuit is working properly, the sensor signal provided by L1 should be deemed by detector 406 as a fault. As described above, during normal operations and when the GFCI 400 is operating properly, the fault detector 406 provides a fault detection signal that is sufficient to turn SCR 4100N. However, the auto-test is performed during the negative half cycle or late in the positive half cycle such that SCR 410 will not be turned ON during the positive half cycle at a time that could cause nuisance tripping of the circuit interrupter. In one embodiment, SCR 410 is turned ON late in the positive half-cycle of the AC line cycle where the amount of current flowing through the SCR 410 is not sufficient to energize the dual-solenoid 70′. In another embodiment, SCR 410 is turned ON during the negative half cycle, remaining ON until power supply 408 is sufficiently discharged before the next positive half cycle, that occurring before the start of the next positive half cycle. Moreover, SCR 410 is prevented from conducting current through dual-solenoid 70′ during the negative half cycle by diode D4.
One reason for using a relatively lengthy time duration for the simulated fault signal generated by loop 402 is to ensure that detector 406 has sufficient time to detect the self-test. One drawback to this approach relates to the duration of the magnetic flux in the sensor core. Specifically, if the magnetic flux in the core carries over into the subsequent positive half cycle, the resultant sensor output would cause detector 406 to improperly turn SCR 4100N and nuisance trip the device 10. For this reason, the output voltage of the dual power supply 408 is collapsed before the conclusion of the negative half cycle. One reason why the collapsible power supply voltage prevents nuisance tripping relates to the inability of grounded neutral oscillations to persist in the absence of the power supply output voltage. Even when FET 404 is turned ON, there is substantially no magnetic flux in the sensor core once the power supply voltage collapses. Thus, if the power supply voltage is collapsed before the conclusion of the negative half cycle, the grounded neutral oscillations that otherwise would be generated by FET 404, cannot carry over into the positive half cycle. Thus, the dual power supply 408 prevents nuisance tripping.
The nuisance tripping prevention feature is now described in greater detail. During the self-test, FET 404 is turned ON and the grounded neutral transmitter 102 (L2) produces an oscillating signal that is a function of the full power supply voltage. If the detector 406 is operational, SCR 410 is turned ON at about 225°-280° of the AC line cycle (i.e., during a portion of the negative half cycle). As a result, capacitor C6 and capacitor bank 408-3 (by way of resistor R13, opto-coupler U2, and diode D5) are dump-discharged via SCR 410 to thereby collapse the output voltage of the power supply. The discharging process occurs gradually because of the time constant associated with capacitor bank 408-3. As the power supply voltage gradually collapses in accordance with the aforementioned time constant, the magnitude of the oscillating signal produced by the grounded neutral transmitter L2 also diminishes. In turn, the grounded neutral simulation current propagating around loop 402 is also reduced. Finally, the flux in the transformer core is so low that the sensor signal it provides to the fault detector 406 does not represent a fault condition. The above stated process transpires before the conclusion of the negative half cycle. Accordingly, little or no flux is present in the transformer core at the start of the subsequent positive half cycle. In one embodiment of the present invention, the capacitor bank 408-3 time constant is about 0.5 milliseconds and the period of the grounded neutral oscillation is about 0.15 milliseconds.
As noted above, SCR 410 turns on during the negative half cycle, however current through SCR 410 is prevented from conducting through dual-solenoid 70′ during the negative half cycle because diode D4 is reverse biased. Watchdog circuit 421 monitors whether SCR 410 is turned ON or not, and it functions as follows: When SCR 410 turns ON indicative that GFCI 400 is operational, power supply 408 discharges via resistor R13, the diode portion of opto-coupler U2, diode D5, and SCR 410. Because of the current through its diode portion, the transistor portion of opto-coupler U2 turns ON to discharge the watchdog capacitor C12. Stated differently, the negative half—cycle test is performed every AC line cycle such that the charge accumulated on C12 should be discharged every line cycle. However, when there is an end of life condition, SCR 410 or opto-coupler U2 will fail to turn ON. If there is failure to turn on within four or five line cycles, the voltage on C12 becomes greater that the breakover voltage of diac Q3 and Q3 will conduct to turn opto-coupler U3 ON. The transistor portion of U3 is connected to the control input of secondary SCR Q4, and therefore, when U3 conducts, SCR Q4 is turned on such that the secondary side of the dual-solenoid 70′ is energized to trip the circuit interrupter 60 and the auxiliary switch 422. In other words, if the self-test performed by universal auto-test circuit 401 fails for a predetermined period of time, the watchdog circuit 421 will trip the device 10.
A wiring state detection circuit 420 is configured to prevent miswiring upon initial installation. Detection circuit 420 includes resistors R9, R15, and fusible element 51. When power is initially applied to the load terminals 14-20, 14-22 and the protective device is reset, the interrupting contacts 60 are tripped within about 25 milliseconds because detection circuit 420 creates an imbalance in the differential current flowing through sensor L1. The imbalance is detected by detector 406, SCR Q1 is turned ON and the device is tripped in the manner described above. Once AC power is properly connected the line terminals 14-10, 14-12, the fusible element S1 is cleared after the device is again tripped. Subsequently, the interrupting contacts 60 may be closed by reset assembly 17. The dual-solenoid 70′ may be energized for about 100 milliseconds before it is damaged and burns out; thus, it is not designed to burn out during the interval that SCR Q1 is conductive (i.e., about 25 milliseconds).
Miswiring is also prevented on re-installation. Referring back to the watchdog circuit 421, the charging path includes resistors R21, R27 and diode D9 disposed between load hot and watchdog capacitor C12 coupled to load neutral. When the device is miswired, i.e., when the AC source voltage is connected to the load terminals, the capacitor C12 is charged up. As with an end of life condition, the voltage on C12 becomes greater than the breakover voltage of diac Q3. When the reset button 17 is manually operated attempting to reset the device, the watchdog circuit 421 will energize the dual-solenoid 70′ to thereby trip the circuit interrupter 60. Each time reset is attempted; this process keeps repeating itself, until device 10 is properly wired. When power is properly applied to the line terminals and circuit interrupter 60 is in the tripped state, capacitor C12 will not charge due to the circuit interrupting contacts being open, and so device 10 can be reset.
Miswire protection on re-installation is afforded by coupling the watch-dog capacitor C12 to the load side of circuit interrupter 60. The other circuitry including the GFCI detector is coupled to the line side of circuit interrupter 60. The two opto-isolators, (U2, U3) electrically isolate these line side and load side circuits when circuit interrupter 60 is in the tripped state. Summarizing, opto-isolator U2 couples a drive signal from the line side circuit to the load side circuit. Opto-isolator U3 couples a drive signal from the load side circuit back to the line side circuit.
In reference to the indicator circuit 418, once the device 10 trips, the current from line hot 14-10 is diverted from the auxiliary switch 422 and through LED D10, depicted as LED 17-2 in
Referring to
A circuit interrupter 902 is disposed between the line conductor 901 and the load 99. This embodiment incorporates a first stage arc sensor 920, shown as a current transformer, which is configured to respond to the rate of change of neutral and/or hot conductor current with respect to time. Sensor 920 may be designed with a physically small core of a type and number of secondary turns which gives optimum sensitivity during arcing. Either a single conductor (hot line) or both conductors can pass thru the sensor. The arc fault detector detects arcs that are either hot to ground or hot to neutral. The sensor 920 provides two detector/amplifiers 921, 922 with sensor data. The detectors 921, 922 may be implemented using any suitable device, such as an integrated circuit used to detect ground faults (e.g., RV4141A). The detector 921 is referred to as the di/dt stage, because it detects the change in current with respect to time. Detector 921 also has a high pass filter capacitor 911 on its input side. The detector 922 is referred to as the 60 Hz or “threshold” stage, and uses a low pass filter capacitor 912 in a feedback stage. The 60 Hz threshold detector 922 controls the level at which an arcing condition is to be detected, e.g., at a 75 Ampere or greater load current.
The outputs of both stages are combined by a logic AND gate 913, and this output is further combined by a second logic AND gate 914 with a timer output. Stated differently, the input current signal must exhibit a rate of change that exceeds a predetermined rate, and a magnitude in excess of a predetermined threshold, within the time frame selected by the dimmer delay timer 952. If these conditions are met, a positive pulse is applied to the base of Q3 such that SCR 954 is turned ON. This energizes the solenoid 960 to trip the circuit interrupter 902.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The term “connected” is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening.
The recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein.
All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments of the invention and does not impose a limitation on the scope of the invention unless otherwise claimed.
No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. There is no intention to limit the invention to the specific form or forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention, as defined in the appended claims. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
This is application is a continuation-in-part of U.S. patent application Ser. No. 13/608,675 filed on Nov. 19, 2012, the content of which is relied upon and incorporated herein by reference in its entirety, and the benefit of priority under 35 U.S.C. §120 is hereby claimed, U.S. patent application Ser. No. 13/608,675 claims priority under to U.S. Provisional Patent Application No. 61/635,432 filed on Apr. 19, 2012, the content of which is relied upon and incorporated herein by reference in its entirety, and the benefit of priority under 35 U.S.C. §119(e) is hereby claimed.
| Number | Date | Country | |
|---|---|---|---|
| 61635432 | Apr 2012 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13608675 | Sep 2012 | US |
| Child | 13761846 | US |
