Patent Grant
7154718
1. Field of the Invention
The present invention relates generally to protection devices, and particularly to protection devices having power to the receptacle cut-off features.
2. Technical Background
Most residential, commercial, or industrial buildings include one or more breaker panels that are configured to receive AC power from a utility source. The breaker panel distributes AC power to one or more branch electric circuits installed in the building. The electric circuits transmit AC power to one or more electrically powered devices, commonly referred to in the art as load circuits. Each electric circuit typically employs one or more electric circuit protection devices. Examples of such devices include ground fault circuit interrupters (GFCIs), arc fault circuit interrupters (AFCIs), or both GFCIs and AFCIs. Further, AFCI and GFCI protection may be included in one protective device.
The circuit protection devices are configured to interrupt the flow of electrical power to a load circuit under certain fault conditions. When a fault condition is detected, the protection device eliminates the fault condition by interrupting the flow of electrical power to the load circuit by causing interrupting contacts to break the connection between the line terminals and load terminals. As indicated by the name of each respective device, an AFCI protects the electric circuit in the event of an arc fault, whereas a GFCI guards against ground faults. An arc fault is a discharge of electricity between two or more conductors. An arc fault may be caused by damaged insulation on the hot line conductor or neutral line conductor, or on both the hot line conductor and the neutral line conductor. The damaged insulation may cause a low power arc between the two conductors and a fire may result. An arc fault typically manifests itself as a high frequency current signal. Accordingly, an AFCI may be configured to detect various high frequency signals and de-energize the electrical circuit in response thereto.
With regard to GFCIs, a ground fault occurs when a current carrying (hot) conductor creates an unintended current path to ground. A differential current is created between the hot/neutral conductors because some of the current flowing in the circuit is diverted into the unintended current path. The unintended current path represents an electrical shock hazard. Ground faults, as well as arc faults, may also result in fire. GFCIs intended to prevent fire have been called ground-fault equipment protectors (GFEPs.)
Ground faults occur for several reasons. First, the hot conductor may contact ground if the electrical wiring insulation within a load circuit becomes damaged. This scenario represents a shock hazard. For example, if a user comes into contact with a hot conductor within an appliance while simultaneously contacting ground, the user will experience a shock. A ground fault may also result from equipment coming into contact with water. A ground fault may also result from damaged insulation within the electrical power distribution system.
As noted above, a ground fault creates a differential current between the hot conductor and the neutral conductor. Under normal operating conditions, the current flowing in the hot conductor should equal the current in the neutral conductor. Accordingly, GFCIs are typically configured to compare the current in the hot conductor to the return current in the neutral conductor by sensing the differential current between the two conductors. When the differential current exceeds a predetermined threshold, usually about 6 mA, the GFCI typically responds by interrupting the circuit. Circuit interruption is typically effected by opening a set of contacts disposed between the source of power and the load. The GFCI may also respond by actuating an alarm of some kind.
Another type of ground fault may occur when the load neutral terminal, or a conductor connected to the load neutral terminal, becomes grounded. This condition does not represent an immediate shock hazard. As noted above, a GFCI will trip under normal conditions when the differential current is greater than or equal to approximately 6 mA. However, when the load neutral conductor is grounded the GFCI becomes de-sensitized because some of the return path current is diverted to ground. When this happens, it may take up to 30 mA of differential current before the GFCI trips. This scenario represents a double-fault condition. In other words, when the user comes into contact with a hot conductor (the first fault) at the same time as contacting a neutral conductor that has been grounded on the load side (the second fault), the user may to experience serious injury or death.
The aforementioned protective devices may be conveniently packaged in receptacles that are configured to be installed in wall boxes. The protective device may be configured for various electrical power distribution systems, including multi-phase distribution systems. A receptacle typically includes input terminals that are configured to be connected to an electric branch circuit. Accordingly, the receptacle includes at least one hot line terminal and may include a neutral line terminal for connection to the hot power line and a neutral power line, respectively. The hot power line(s) and the neutral power line, of course, are coupled to the breaker panel. The receptacle also includes output terminals configured to be connected to a load circuit. In particular, the receptacle has feed-through terminals that include a hot load terminal and a neutral load terminal. The receptacle also includes user accessible plug receptacles connected to the feed through terminals. Accordingly, load devices equipped with a cord and plug may access AC power by way of the user accessible plug receptacles.
However, there are drawbacks associated with hard-wiring the user accessible plug receptacles to the feed-through terminals. As noted above, when a fault condition is detected in the electrical distribution system, a circuit interrupter breaks the electrical coupling between the line and load terminals to remove AC power from the load terminals. If the protective device is wired correctly, AC power to the user accessible plug receptacles is also removed. However, power to the user accessible plug receptacles may not be removed if the protective device is miswired.
In particular, a miswire condition exists when the power lines and the are connected to the hot output terminal and the neutral output terminal, respectively. For 120 VAC distribution systems, the hot power line and the neutral power line are configured to be connected to the hot line terminal and the neutral line terminal, respectively. If the electrical distribution system includes load wires, the miswire is completed by connecting the load wires to the line terminals. A miswire condition may represent a hazard to a user when a cord connected load is plugged into the user accessible receptacle included in the device. Even if the circuit is interrupted in response to a true or simulated fault condition, AC power is present at the terminals of the receptacle because the feed-thru terminals and the receptacle terminals are hard-wired. Thus, the user is not protected if there is a fault condition in the cord-connected load.
Besides miswiring, failure of the device to interrupt a true fault condition or simulated fault condition may be due to the device having an internal fault condition, also known as an end of life condition. The device includes electro-mechanical components that are subject to reaching end of life, including electronic components can open circuit or short circuit, and mechanical components such as the contacts of the circuit interrupter that can become immobile due to welding, and the like.
In one approach that has been considered, the protective device is configured to trip in response to a miswire condition. Thus, if the power source of the electrical distribution system is connected to the load terminals (i.e., a line-load miswire condition), the circuit interrupting contacts will break electrical connection. The installer is made aware of the miswired condition when he discovers that power is not available to the downstream receptacles coupled to the miswired receptacle. After the miswiring condition is remedied, the interrupting contacts in the device can be reset. One drawback to this approach becomes evident when the protective device is not coupled to any downstream receptacles. In this scenario, the installer may not become aware of the miswire condition.
Accordingly, there is a need to deny power to the user accessible receptacles when the device is tripped. This safety feature is especially needed when the GFCI is miswired.
The present invention is configured to deny power to the user accessible plug receptacles when the device is tripped. Accordingly, the present invention provides a safety feature that eliminates a hazardous condition that may arise when the device is miswired.
One aspect of the present invention is directed to an electrical wiring protection device that includes a housing assembly having at least one receptacle. The at least one receptacle is configured to receive plug contact blades inserted therein. The housing assembly includes a hot line terminal, a neutral line terminal, a hot load terminal, and a neutral load terminal. At least one set of receptacle contacts is disposed in the housing assembly and in communication with the at least one receptacle. The at least one set of receptacle contacts includes a hot user-accessible load contact and a neutral user accessible load contact. A fault detection circuit is coupled to the test assembly. The fault detection circuit is configured to detect at least one fault condition and provide a fault detect signal in response thereto. a four-pole interrupting contact assembly is coupled to the fault detection circuit. The four-pole interrupting contact assembly includes at least one solenoid coupled to the fault detection circuit. An armature is coupled to the at least one solenoid. The armature is configured to move in only a first direction in response to any force generated by the at least one solenoid. A set of four-pole interrupting contacts include a first pair of hot contacts coupling the hot line terminal and the hot load terminal, a second pair of hot contacts coupling the hot line terminal to the hot user-accessible load contact, a first pair of neutral contacts coupling the neutral line terminal and the neutral load terminal, and a second pair of neutral contacts coupling the neutral line terminal to the neutral user-accessible load contact. The set of four-pole interrupting contacts is configured to provide electrical continuity between the first pair of hot contacts, the second pair of hot contacts, the first pair of neutral contacts, and the second pair of neutral contacts in a coupled state. The set of four-pole interrupting contacts is driven by the armature movement in the first direction to thereby interrupt electrical continuity between the first pair of hot contacts, the second pair of hot contacts, the first pair of neutral contacts, and the second pair of neutral contacts in a tripped state. A reset mechanism is coupled to the four-pole interrupting contact assembly. The reset mechanism includes a reset button and a reset actuator that selectively provides a reset stimulus in response to an actuation of the reset button. The first pair of hot contacts, the second pair of hot contacts, the first pair of neutral contacts, and the second pair of neutral contacts are necessarily driven into the coupled state by the reset stimulus.
In another aspect, the present invention includes an electrical wiring protection device that includes a housing assembly having at least one receptacle. The at least one receptacle is configured to receive plug contact blades inserted therein. The housing assembly includes a hot line terminal, a neutral line terminal, a hot load terminal, and a neutral load terminal. At least one set of receptacle contacts is disposed in the housing assembly and in communication with the at least one receptacle. The at least one set of receptacle contacts includes a hot user-accessible load contact and a neutral user accessible load contact. A test assembly is coupled to the hot line terminal and the neutral line terminal, the test assembly being configured to generate a simulated fault condition. A fault detection circuit is coupled to the test assembly. The fault detection circuit is configured to detect at least one fault condition and provide a fault detect signal in response thereto. The at least one fault condition includes the simulated fault condition. A four-pole interrupting contact assembly is coupled to the fault detection circuit and includes a set of four-pole interrupting contacts having a first pair of hot contacts coupling the hot line terminal and the hot load terminal, a second pair of hot contacts coupling the hot line terminal to the hot user-accessible load contact, a first pair of neutral contacts coupling the neutral line terminal and the neutral load terminal, and a second pair of neutral contacts coupling the neutral line terminal to the neutral user-accessible load contact. The set of four-pole interrupting contacts is configured to provide electrical continuity between the first pair of hot contacts, the second pair of hot contacts, the first pair of neutral contacts, and the second pair of neutral contacts in a coupled state and cause electrical discontinuity between the first pair of hot contacts, the second pair of hot contacts, the first pair of neutral contacts, and the second pair of neutral contacts in a tripped state. A reset mechanism is coupled to the four-pole interrupting contact assembly. The reset mechanism includes a reset button and a reset actuator configured to reestablish electrical continuity between the first pair of hot contacts, the second pair of hot contacts, the first pair of neutral contacts, and the second pair of neutral contacts in response to a reset stimulus. An end-of-life mechanism is coupled to the test assembly. The end-of-life mechanism includes an end-of-life circuit, a third pair of hot contacts coupling the hot line terminal and the hot load terminal, and a third pair of neutral contacts coupling the neutral line terminal and the neutral load terminal. The end-of-life circuit is configured to decouple the third pair of hot contacts and the third pair of neutral contacts if the fault detection circuit fails to transmit the fault detection signal within a predetermined period of time after the simulated fault condition is generated. The end-of-life mechanism is independent of the set of four-pole interrupting contacts.
In another aspect, the present invention includes an electrical wiring protection device that includes a housing assembly having at least one receptacle. The at least one receptacle is configured to receive plug contact blades inserted therein. The housing assembly includes a hot line terminal, a neutral line terminal, a hot load terminal, and a neutral load terminal. At least one set of receptacle contacts is disposed in the housing assembly and in communication with the at least one receptacle. The at least one set of receptacle contacts includes a hot user-accessible load contact and a neutral user accessible load contact. A fault detection circuit is coupled to a test assembly. The fault detection circuit is configured to detect at least one fault condition and provide a fault detect signal in response thereto. A four-pole interrupting contact assembly is coupled to the fault detection circuit. The four-pole interrupting contact assembly includes a first cantilever connected to the hot line terminal at a first end. The first cantilever includes a first cantilever contact disposed thereon at a second end. The first cantilever contact and a hot load terminal contact form a first contact pair of hot contacts configured to couple the hot line terminal and the hot load terminal. A second cantilever is connected to the hot line terminal at the first end and includes a second cantilever contact disposed thereon at the second end. The second cantilever contact and a hot user-accessible load contact form a second contact pair of hot contacts configured to couple the hot line terminal and the hot user-accessible load terminal. A third cantilever is connected to the neutral line terminal at a first end and includes a third cantilever contact disposed thereon at the second end. The third cantilever contact and a neutral load terminal contact form a first contact pair of neutral contacts configured to couple the neutral line terminal and the neutral load terminal. A fourth cantilever is connected to the neutral line terminal at the first end and includes a fourth cantilever contact disposed thereon at the second end. The fourth cantilever contact and a neutral user-accessible load contact form a second contact pair of neutral contacts configured to couple the neutral line terminal and the neutral user-accessible load terminal. A pivoting latch mechanism is configured to drive the first cantilever, the second cantilever, the third cantilever, and the fourth cantilever between a coupled state and a tripped state, whereby the first pair of hot contacts, the second pair of hot contacts, the first pair of neutral contacts, and the second pair of neutral contacts are decoupled in response to the fault detect signal.
In another aspect, the present invention includes an electrical wiring protection device that includes a housing assembly having at least one receptacle. The at least one receptacle is configured to receive plug contact blades inserted therein. The housing assembly includes a hot line terminal, a neutral line terminal, a hot load terminal, and a neutral load terminal. At least one set of receptacle contacts is disposed in the housing assembly and in communication with the at least one receptacle. The at least one set of receptacle contacts includes a hot user-accessible load contact and a neutral user accessible load contact. A fault detection circuit is coupled to a test assembly. The fault detection circuit is configured to detect at least one fault condition and provide a fault detect signal in response thereto. A four-pole interrupting contact assembly is coupled to the fault detection circuit. The four-pole interrupting contacts include a hot tri-contact member configured to provide electrical continuity between the hot line terminal, the hot load terminal, and the hot user-accessible load terminal in a coupled state, and cause electrical discontinuity between the hot line terminal, the hot load terminal, and the hot user-accessible load terminal in a tripped state. The four-pole interrupting contacts also include a neutral tri-contact member configured to provide electrical continuity between the neutral line terminal, the neutral load terminal, and the neutral user-accessible load terminal in a coupled state, and cause electrical discontinuity between the neutral line terminal, the neutral load terminal, and the neutral user-accessible load terminal in a tripped state.
In another aspect, the present invention includes an electrical wiring protection device that includes a housing assembly having at least one receptacle. The at least one receptacle is configured to receive plug contact blades inserted therein. The housing assembly includes a hot line terminal, a neutral line terminal, a hot load terminal, and a neutral load terminal. At least one set of receptacle contacts is disposed in the housing assembly and in communication with the at least one receptacle. The at least one set of receptacle contacts includes a hot user-accessible load contact and a neutral user accessible load contact. A fault detection circuit is coupled to a test assembly. The fault detection circuit is configured to detect at least one fault condition and provide a fault detect signal in response thereto. A four-pole interrupting contact assembly is coupled to the fault detection circuit. The four-pole interrupting contacts includes a hot cantilever assembly having a hot line cantilever connected to the hot line terminal. The hot line cantilever includes a first hot contact disposed thereon. A fixed second hot contact is coupled to the hot user-accessible load terminal. A hot load cantilever is connected to the hot load terminal and includes a third hot contact disposed thereon. The first hot contact, the second hot contact, and the third hot contact are aligned and configured to provide electrical continuity between the hot line terminal, the hot load terminal, and the hot user-accessible load terminal in a coupled state, and cause electrical discontinuity between the hot line terminal, the hot load terminal, and the hot user-accessible load terminal in a tripped state. A neutral cantilever assembly includes a neutral line cantilever that is connected to the neutral line terminal and has a first neutral contact disposed thereon. A fixed second neutral contact is coupled to the neutral user-accessible load terminal. A neutral load cantilever is connected to the neutral load terminal and includes a third neutral contact disposed thereon. The first neutral contact, the second neutral contact, and the third neutral contact are aligned and configured to provide electrical continuity between the neutral line terminal, the neutral load terminal, and the neutral user-accessible load terminal in a coupled state, and cause electrical discontinuity between the neutral line terminal, the neutral load terminal, and the neutral user-accessible load terminal in a tripped state.
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 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 wiring device of the present invention is shown in
As embodied herein, and depicted in
With regard to contact assembly 15, neutral line terminal 20 is connected to cantilever member 22 and cantilever member 26. Cantilevers 22 and 26 are coupled to latch mechanism 80. Cantilever member 22 includes a moveable contact 24. In the reset position, moveable contact 24 is configured to mate with stationary contact 32. Stationary contact 32 is coupled to neutral load feed-through terminal 30. Cantilever member 26 includes moveable contact 28. In the reset position, moveable contact 28 is configured to mate with stationary contact 46. Stationary contact 46 is coupled to the neutral contact 42 in receptacle 40. Hot line terminal 200 is connected to cantilever member 220 and cantilever member 260. Cantilevers 220 and 260 are also coupled to latch mechanism 80. Cantilever member 220 includes a moveable contact 240. In the reset position, moveable contact 240 is configured to mate with stationary contact 320, which is coupled to hot load feed-through terminal 300. Cantilever member 260 includes a moveable contact 280. In the reset position, moveable contact 280 is configured to mate with stationary contact 460, which is coupled to the hot contact 48 in receptacle 40.
Accordingly, when SCR 106 signals trip solenoid 52, latch mechanism 80 pulls the cantilevers 22, 26, 220, and 260 such that moveable contacts 24, 28, 240, and 280 are separated from stationary contacts 32, 46, 320, and 460, respectively. When reset button 60 is depressed, reset solenoid 64 is actuated. Solenoid 64 causes latch mechanism 80 to close the aforementioned pairs of contacts to thereby restore AC power.
The reset mechanism includes reset button 60, contacts 62, and reset solenoid 64. When reset button 60 is depressed, contacts 62 are closed to thereby initiate a test procedure. If the test procedure is successful, reset solenoid 64 is actuated, and latch mechanism 80 is toggled to reset device 10. When device 10 has an internal fault condition, the test procedure is unsuccessful, and the circuitry does not transmit a reset signal. The reset solenoid 64 is not actuated, and the device is not reset. As described above, latch mechanism 80 is toggled between the tripped state and the reset state by trip solenoid 52 and reset solenoid 64, respectively.
Latch mechanism 80 may be toggled to the tripped position by the fault detection circuitry, as described above, or by a user accessible test button 50. Alternatively, latch mechanism 80 may be tripped by the fault detection circuitry, as described above, and by an electrical test button 50′. The electrical test button 50′ produces a simulated condition configured to test a portion of, or all of, the detection circuitry. A test acceptance signal toggles latch mechanism 80 to the tripped position. The simulated condition may be a test signal or an induced fault signal. Hereinafter, both of these signals will be referred to as simulated fault conditions.
Referring to
Line neutral cantilevers 22, 26 are connected at one end to line neutral terminal 20. At the other end, line cantilever 22 includes a terminal contact 24. In similar fashion, line cantilever 26 includes a terminal contact 28 adjacent to contact 24. Cantilevers 22 and 26 are flexibly connected to latch mechanism 80 by way of wiper arm 82. Load neutral terminal 30 is coupled to load neutral contact 32. Load neutral contact 32 and line neutral contact 24 form a pair of separable contacts. Receptacle neutral contact 42 is connected to member 44. Member 44 includes neutral contact 46. Neutral contact 46 and line neutral contact 28 also form a pair of separable contacts.
Latch mechanism 80 is actuated by test button 50 and reset button 60. Test button 50 is a mechanical actuator that is coupled to latch mechanism 80. When test button 50 is depressed, each separable contact pair is separated to remove power to the feed through terminals and the receptacle terminals. Reset button 60 is an electric switch mechanism that is actuated when button 60 closes contacts 62. Contacts 62 actuates solenoid 64. If the test is successful, each separable contact pair is closed. The operation of dual-solenoids 52, 64 will be discussed below in more detail.
Referring to
Referring to
Referring to
In this embodiment, the device is typically tripped before being installed by the user. If the device is miswired by the installer, source power is not available to the reset solenoid due to the tripped condition. The device cannot be reset. As a result, AC power is denied to the receptacles until device 10 is wired correctly.
Referring to
Subsequently, if the protection circuit senses and detects a fault condition, trip solenoid 52 is activated causing latch 80 to toggle in the other direction. Wiper arm 82 overcomes the spring loaded bias of the cantilevered arm and drives the cantilevers downward to thereby open the contacts and trip the device. As a result, power is removed from receptacles 40 and load terminals 30 and 300.
Referring to
Trip solenoid 52 is activated when sensor 100 and detector 104 detect a fault condition. The contacts pairs 24 and 32, 28 and 46, 480 and 460, and 240 and 320 electrically decouple in response thereto, disconnecting the line, load, and receptacle contacts. TEST button switch 50′ is accessible to the user and introduces a simulated ground fault, providing a convenient method for the user to periodically test the GFCI operation.
Device 10 may include a trip indicator. When device 10 is tripped, trip indicator 130 is activated. Trip indicator 130 includes components R9, R13, R14, and D1 (LED) which are connected in parallel with switch S7. When device 10 is tripped, LED D1 is illuminated. However, when the contacts are reset, there is no potential difference to cause illumination of LED and D1. Those of ordinary skill in the art will recognize that indicator 130 may include an audible annunciator as well as an illumination device.
After device 10 is tripped, the user typically depresses reset switch 60 to reset the device. Switch S7 is disposed in a position to supply power to the reset solenoid 64 via switch 60, 62. Once reset button 60 is depressed, a simulated fault is introduced through R1. The GFCI power supply (located at the anode of D1) supplies current to charge capacitor C9. When the detector 104 responds to the simulated fault, SCR Q1 is turned on. When SCR Q1 is turned on, the charge stored in C9 will discharge through the R16 and SCR Q2. As a result of the discharge current, SCR Q2 is turned on, current flows through reset solenoid 64, and the device 10 is reset.
Device 10 includes a timing circuit that is configured to limit the time that the reset solenoid is ON, irrespective of the duration that the reset button is depressed by the user. Momentary activation of the reset solenoid avoids thermal damage to the reset solenoid due to over-activation. This feature also avoids the possibility of the reset solenoid interfering with circuit interruption when the trip solenoid is activated.
Timing circuit 140 includes: diode D2; resistors R15, R12, and R11; capacitor C10; and transistor Q3. When the reset button 60 is depressed, C10 begins charging through D2 and R15 while the simulated fault signal through R1 is being introduced. C10 is charged to a voltage that turns transistor Q3 ON after a predetermined interval, typically one and a half line cycles (25 milliseconds). Transistor Q3 discharges capacitor C9, causing Q2 to turn off. Thus, reset solenoid 64 is activated when reset button 60 is pressed and causes SCRs Q1 and Q2 to turn on, and deactivates when transistor Q3 turns on and causes SCR Q2 to turn off. Reset solenoid 64 can be reactivated for another momentary interval if the reset button 60 is released by the user for a pre-determined duration that allows C4 to discharge to a voltage where Q3 turns off. Alternatively, a timer can establish momentary reset solenoid actuation by controlling the duration of the simulated test signal or the closure interval of contact 62. Alternatively, the timer can employ mechanical and/or electrical timing methods.
Referring to
End-of-life (EOL) circuit 120 includes resistors R19–R25, SCR Q4, and diode D5. Resistor R23 is configured to heat to a temperature greater than a pre-established threshold when device 10 has an internal fault. When the temperature of resistor R23 is greater than the threshold, the line terminals decouple from the load terminals, independent of the four-pole interrupter contacts previously described. Alternatively, a resistor can be dedicated to each terminal. The resistors are heated independently to decouple the load terminals from the line terminals.
EOL circuit 120 operates as follows. With device 10 reset, the user pushes the TEST button 50′, and a simulated fault is introduced through R25. Accordingly, 120V AC power is applied to EOL circuit 120. If the GFCI is operating properly, sensor 100, detector 104, and other GFCI circuitry will respond to the simulated fault and trip switches S3–S7 (contact pairs 24,32; 28,46; 240,320; 280,460) within a predetermined time (typically 25 milliseconds for GFCIs.) The circuit is designed such that the simulated fault current flowing through R25 is terminated while TEST button 50′ is continuously being pushed. As such, power is removed from EOL circuit 120 before resistors R23 and/or R24 reach the temperature threshold.
Resistors R20–R22 and SCR Q1 form a latch circuit. When device 10 is not operating properly. The uninterrupted current through R21 will cause the resistance value of R21 to increase significantly. When resistor R21 changes value, the voltage divider formed by R21 and R22 is likewise changed. The voltage across R20 and R19 becomes sufficient to turn on Q4 and current begins to flow through resistors R23 and R24. In a short period of time, R23 and R24 begin to overheat and the solder securing R23 and R24 to printed circuit board 12 fails. After the solder melts, resistors R23 and R24 are displaced, actuating a mechanical disconnect mechanism 121. Alternatively, the response time of R23, R24 can be designed such that the solder is melted within the time test button 50 is depressed, in which case, the latch circuit can be omitted. R23 and R24 are directly coupled to the test circuit in this embodiment.
As embodied herein and depicted in
The schematic shown in
If device 10 is miswired, the constant flow of current through resistor 522 is not present for a sufficient amount of time, and resistor 522 fails to open-circuit. However, the current that does flow through resistor 522 is sensed by differential transformer 100 as a differential current and detected by detector 104. Detector 104 signals SCR 106 to turn ON to thereby actuate solenoid 52. In turn, solenoid 52 is energized, tripping the mechanism 528. Accordingly, the current flowing through resistor 522 is interrupted before it fails. The duration of the interrupted current flow through resistor 522 is approximately the response time of device 10, e.g., less than 0.1 seconds. The duration of the current flow is too brief to cause opening of resistor 522. If reset button 526 is depressed to reset trip mechanism 528, current starts to flow again through resistor 522, however, the current is detected and mechanism 528 is immediately tripped again before resistor 522 is opened. In this manner, trip mechanism 528 does not remain in the reset state when the source of power of the power distribution system is miswired to the load terminals. Thus power is removed automatically from the receptacle terminals when the power source has been miswired to the load terminals.
Referring to
Both neutral contact mechanism 506 and hot contact mechanism 516 are configured to be moved upward and downward with respect to the fixed contacts 500, 501, 502, 508, 510 and 512 Neutral contacts 505, are disposed on curvilinear arms 534. As shown, one contact 505 corresponds to line contact 500, another to load contact 502, and yet another to fixed neutral contact 501. Referring to hot contact mechanism 516, contacts 514 are disposed on arms 536. Load hot contact 510 is not shown in
Referring to
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As embodied herein, and depicted in
Referring to
Contact 808 is a fixed contact. Neutral load contact 804 is a two-way contact that is disposed on flexible member 814, which is connected to load terminal 30. Line neutral contact 800 is connected to flexible member 816. Flexible member 816 is connected to neutral line terminal 20. When solenoid 52 is energized, latch mechanism 801 releases contacts 800, 804, and 808 and device 10 is tripped. Latch mechanism 801 includes a cylindrical hole that is configured to accommodate a reset pin (not shown). Reference is made to U.S. Pat. No. 6,621,388, U.S. application Ser. No. 10/729,392, and U.S. application Ser. No. 10/729,396 which are incorporated herein by reference as though fully set forth in its entirety, for a more detailed explanation of the reset mechanism.
As embodied herein and depicted in
GFI circuit 900 includes a differential sensor 100 that is configured to sense a load-side ground fault when there is a difference in current between the hot and neutral conductors. Differential sensor 100 is connected to detector circuit 104, which processes the output of differential sensor 100. Detector 104 is connected to power supply circuit 902. Power supply 902 provides power to detector 104. Detector 104 is configured to detect a ground fault during both the positive half-cycle and the negative half cycle of the AC power. As such, detector circuit 104 provides an output signal on output line 903. The output line 903 is coupled to SCR 106 by way of filter circuit 904. When detector circuit 104 senses a fault, the voltage signal on output line 903 changes and SCR 106 is turned on. SCR 106 is only able to turn on during the positive half cycles of the AC power source. Further, snubber network 907 prevents SCR 106 from turning on due to spurious transient noise in the electrical circuit. When SCR 106 is turned on, solenoid 52 is activated. Solenoid 52, in turn, causes the trip mechanism 80 (528, 801) to release the four pole interrupter contacts, i.e. contacts 950, 952, 954, and contacts 956, 958, 960. When the interrupter contacts are released, the load-side of device 10 and the receptacle 40 are independently decoupled from the line-side power source of the electrical circuit.
GFI circuit 900 also includes a grounded neutral transmitter 102 that is configured to detect grounded neutral conditions. Those skilled in the art understand that the conductor connected to neutral line terminal 20 is deliberately grounded in the electrical circuit. A grounded neutral condition occurs when a conductor connected to load neutral terminal 200 is accidentally grounded. The grounded neutral condition creates a parallel conductive path with the return path disposed between load terminal 200(42) and line terminal 20. When a grounded neutral condition is not present, grounded neutral transmitter 102 is configured to couple equal signals into the hot and neutral conductors. As noted above, differential sensor 100 senses a current differential. Thus, the equal signals provided by grounded neutral transmitter 102 are ignored. However, when a grounded neutral condition is present, the signal coupled onto the neutral conductor circulates as a current around the parallel conductive path and the return path, forming a conductive loop. Since the circulating current conducts through the neutral conductor but not the hot conductor, a differential current is generated. Differential sensor 100 detects the differential current between the hot and neutral conductors. As such, detector 104 produces a signal on output 903 in response to the grounded neutral condition.
As noted initially, Device 10 includes a checking circuit 901. Checking circuit 901 causes GFI 900 to trip due an internal fault also known as an end of life condition. Examples of an end of life condition include, but are not limited to, a non-functional sensor 100, grounded neutral transmitter 102, ground fault detector 104, filtering circuit 906, SCR 106, snubber 907, solenoid 52, or power supply 902. An internal fault condition may include a shorting or opening of an electrical component, or an opening or shorting of electrical traces configured to electrically interconnect the components, or other such fault conditions wherein GFI 900 does not trip when a grounded neutral fault occurs.
Checking circuit 900 includes several functional groups. The components of each group are in parenthesis. These functions include a fault simulation function (928, 930, 934), a power supply function 924, a test signal function (52, 916, 918, 912), a failure detection function (920), and failure response function (922, 910, 914).
Fault simulation is provided by polarity detector 928, switch 930, and test loop 934. Polarity detector 928 is configured to detect the polarity of the AC power source, and provide an output signal that closes switch 930 during the negative half cycle portions of the AC power source, when SCR 106 cannot turn on. Test loop 934 is coupled to grounded neutral transmitter 102 and ground fault detector 100 when switch 930 is closed. Loop 934 has less than 2 Ohms of resistance. Because polarity detector 928 is only closed during the negative half cycle, electrical loop 934 provides a simulated grounded neutral condition only during the negative half cycle. However, the simulated grounded neutral condition causes detector 104 to generate a fault detect output signal on line 903.
The test signal function provides an oscillating ringing signal that is generated when there is no internal fault condition. Capacitor 918 and solenoid 52 form a resonant circuit. Capacitor 918 is charged through a diode 916 connected to the AC power source of the electrical circuit. SCR 106 turns on momentarily to discharge capacitor 918 in series with solenoid 52. Since the discharge event is during the negative half cycle, SCR 106 immediately turns off after capacitor 918 has been discharged. The magnitude of the discharge current and the duration of the discharge event are insufficient for actuating trip mechanism 80 (528, 801), and thus, the interrupting contacts remain closed. When SCR 106 discharges capacitor 918 during the negative AC power cycle, a field is built up around solenoid 52 which, when collapsing, causes a recharge of capacitor 918 in the opposite direction, thereby producing a negative voltage across the capacitor when referenced to circuit common. The transfer of energy between the solenoid 52 and capacitor 918 produces a test acceptance signal as ringing oscillation. Winding 912 is magnetically coupled to solenoid 52 and serves as an isolation transformer. The test acceptance signal is magnetically coupled to winding 912 and is provided to reset delay timer 920.
The failure detection function is provided by delay timer 920 and SCR 922. Delay timer 920 receives power from power supply 924. When no fault condition is present, delay timer 920 is reset by the test acceptance signal during each negative half cycle preventing timer 920 from timing out. If there is an internal fault in GFI 900, as previously described, the output signal on line 903 and associated test acceptance signal from winding 912 which normally recurs on each negative half cycle ceases, allowing delay timer 920 to time out.
SCR 922 is turned on in response to a time out condition. SCR 922 activates solenoid 910 which in turn operates the trip mechanism 80 (528, 801.) Subsequently, the four-pole interrupter contacts are released and the load-side terminals (30, 300) and receptacle(s) 40 are decoupled from the power source of the electrical circuit. If a user attempts to reset the interrupting contacts by manually depressing the reset button 962, the absence of test acceptance signal causes device 10 to trip out again. The internal fault condition can cause device 10 to trip, and can also be indicated visually or audibly using indicator 914. Alternatively, solenoid 910 may be omitted, such that the internal fault condition is indicated visually or audibly using indicator 914, but does not cause device 10 to trip. Thus the response mechanism may be a circuit interruption by mechanism 80 (528, 801), an indication by indicator 914 or both in combination with each other.
Checking circuit 901 is also susceptible to end of life failure conditions. Checking circuit 901 is configured such that those conditions either result in tripping of GFI 900, including each time reset button 928 is depressed, or at least such that the failure does not interfere with the continuing ability of GFI 900 to sense, detect, and interrupt a true ground fault or grounded neutral condition. For example, if SCR 922 develops a short circuit, solenoid 910 is activated each time GFI 900 is reset and GFI 900 immediately trips out. If one or more of capacitor 918, solenoid 910 or winding 912 malfunction, an acceptable test signal will not generated, and checking circuit 901 is configured to cause GFI 900 to trip out. If polarity detector 928 or switch 930 are shorted out, the grounded neutral simulation signal is enabled during both polarities of the AC power source. This will cause GFI 900 to trip out. If polarity detector 928 or switch 930 open circuit, there is absence of grounded neutral simulation signal, and delay timer 920 will not be reset and GFI 900 will trip out. Solenoids 52 and 910 are configured to operate trip mechanism 80 (528, 801) even if one or the other has failed due to an end of life condition. Therefore if solenoid 910 shorts out, trip mechanism 80 is still actuatable by solenoid 52 during a true fault condition. If power supply 924 shorts out, power supply 902 still remains operational, such that GFI 900 remains operative.
Although to the likelihood of occurrence is low, some double fault conditions cause GFI 900 to immediately trip out. By way of illustration, if SCR 922 and SCR 106 simultaneously short out, solenoids 52 and 910 are both turned on, resulting in activation of trip mechanism 80 (528, 801.)
In another embodiment, solenoid 910 may be omitted and SCR 922 re-connected as illustrated by dotted line 936. During a true fault condition, solenoid 52 is turned on (activated) by SCR 106; when an end of life condition in GFI 900 is detected by checking circuit 901, solenoid 52 is turned on by SCR 922. The possibility of a solenoid 52 failure is substantially minimized by connecting solenoid 52 to the load side of the interrupting contacts.
As has been described, wire loop 934 includes a portion of the neutral conductor. A segment of the hot conductor can be included in electrical loop 934 instead of the neutral conductor to produce a similar simulation signal (not shown).
Other modifications may be made as well. The neutral conductor (or hot) conductor portion has a resistance 964, typically 1 to 10 milliohms, through which current through the load flows, producing a voltage drop. The voltage drop causes a current in electrical loop 934 to circulate which is sensed by differential sensor 100 as a ground fault. Consequently, ground fault detector 104 produces a signal on output 903 due to closure of test switch 930 irrespective of whether or not an internal fault condition has occurred in neutral transmitter 102. In order to assure that grounded neutral transmitter 102 is tested for a fault by checking circuit 901, electrical loop 934 can be configured as before but not to include a segment of the neutral (or hot) conductor, as illustrated by the wire segment, shown as dotted line 966.
Device 10 may also be equipped with a miswiring detection circuit 520, such as has been described. If device 10 has been correctly wired, resistor 522 fuses open. Thus, the miswire detection circuit will not be available to afford miswire protection if device 10 happens to be re-installed. However, the checking circuit 901 can be configured to provide miswiring protection to a re-installation. During the course of re-installation, the user depresses test button 50′ to trip GFI 900. If device 10 has been miswired, power supply 924, connected to the load side of interrupting contacts, provides power to delay timer 920. Power supply 902 is configured to the circuit interrupting contacts, such that when GFI 900 is tripped, power supply 902 does not receive power. Since GFI 900 is not powered and thus inoperative, test acceptance signal is not communicated by winding 912. As a result, checking circuit 901 trips device 10. Whenever the reset button is depressed, the trip mechanism is activated such that the interrupter contacts do not remain closed. Thus, the checking circuit 901 interprets a re-installation miswiring in a similar manner to an end-of-life condition. Device 10 can only be reset after having been wired correctly.
Referring to
A simulated grounded neutral condition is enabled by polarity detector 928 and switch 930. Polarity detector 928 closes switch 930 during the negative half cycle. Thus, the current spikes occur during the negative half cycle portions but not during the positive half cycle portions of the AC power source. As described above, the output of detector 104 (line 903) during the negative half cycle portions of the AC power source are unable to turn on SCR 106. However, the output signal is used by checking circuit 901 to determine whether or not an end of life condition has occurred.
Switch 934 may be implemented using a MOSFET device, designated as MPF930 and manufactured by ON Semiconductor. In another embodiment, switch 934 may be monolithically integrated in the ground fault detector 104.
In response to a true ground fault or grounded neutral condition, ground fault detector 900 produces an output signal 903 during the positive half cycle portions of AC power source. The signal turns on SCR 106 and redundant SCR 922 to activate solenoid 52. Solenoid 52 causes trip mechanism 80 (528, 801) to operate.
When a simulated grounded neutral condition is introduced in the manner described above, a test acceptance signal is provided to delay timer 920 during the negative half cycle portions of the AC power source. Delay timer 920 includes a transistor 1006 that discharges capacitor 1008 when the test acceptance signal is received. Capacitor 1008 is recharged by power supply 902 by way of resistor 1010 during the remaining portion of the AC line cycle. Again, if there is an internal failure in device 10, the test acceptance signal is not generated and transistor 1006 is not turned on. As a result, capacitor 1008 continues to charge until it reaches a predetermined voltage. At the predetermined voltage SCR 922 is activated during a positive half cycle portion of the AC power source signal. In response, solenoid 52 causes the trip mechanism 80 (528,801) to operate. Alternatively, SCR 922 can be connected to a second solenoid 910 (see
Both GFI 900 and checking circuit 901 derive power from power supply 902. Redundant components can be added such that if one component has reached end of life, another component maintains the operability of GFI 900, thereby enhancing reliability, or at least assuring the continuing operation of the checking circuit 901. For example, the series pass element 1012 in power supply 902 may include parallel resistors. Resistor 1014 may be included to prevent the supply voltage from collapsing in the event the ground fault detector 104 shorts out. Clearly, if the supply voltage collapses, delay timer 920 may be prevented from signaling an end of life condition. Those of ordinary skill in the art will recognize that there are a number of redundant components that can be included in device 10, the present invention should not be construed as being limited to the foregoing example.
Alternatively, SCR 922 may be connected to end-of-life resistors R23, R24, as have been described, as shown by dotted line 1016, instead of being connected to solenoid 52 or 910. When SCR 922 conducts, the value of resistors R23, R24 is selected to generate an amount of heat in excess of the melting point of solder on its solder pads, or the melting point of a proximate adhesive. The value of resistors R23, R24 are typically 1,000 ohms. Resistors R23, R24 function as part of a thermally releasable mechanical barrier.
Since end of life resistors R23, R24 afford a permanent decoupling of the load side of device 10 from the AC power source, it is important that the end of life resistors R23, R24 only dislodge when there is a true end of life condition and not due to other circumstances, such as transient electrical noise. For example, SCR 922 may experience self turn-on in response to a transient noise event. Coupling diode 1018 may be included to decouple resistors R23, R24 in the event of a false end of life condition. Coupling diode 1018 causes SCR 922 to activate solenoid 52 when it is ON.
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. 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.
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