Protective device with miswire protection

The present invention is directed electrical wiring protection device that includes a housing assembly having line terminals, load terminals, and receptacle terminals. A fault detection circuit is configured to generate a fault detection signal in response to detecting fault conditions. First interrupting contacts are configured to electrically couple the line terminals and the load terminals in a reset condition and decouple the line terminals from the load terminals in response to the fault detection signal in a tripped state. A wiring state detection circuit is coupled to at least one of the line terminals. The wiring state detection circuit is configured to generate a first wiring signal when the line terminals are connected to a source of AC power. Second interrupting contacts are configured to electrically couple the at least one receptacle load terminal to the at least one load terminal in response to the first wiring signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to wiring devices, and particularly to protective wiring devices.

2. Technical Background

Electrical distribution systems that provide power to a house, building or some other facility include one or more breaker panels coupled to a source of AC power. The breaker panel provides AC power to one or more branch electric circuits installed in the structure. The electric circuits may typically include one or more receptacle outlets and may further transmit AC power to one or more electrically powered devices, commonly referred to in the art as load circuits. The receptacle outlets provide power to user-accessible loads that include a power cord and plug. Because certain types of faults have been known to occur in electrical wiring systems, each electric circuit typically employs one or more electric circuit protection devices. The most common protective device is a ground fault circuit interrupter (GFCI).

Both receptacle wiring devices and electric circuit protective wiring devices are disposed in an electrically non-conductive housing. The housing includes electrical terminals that are electrically insulated from each other. Line terminals couple the wiring device to wiring that provides AC electrical power from the breaker panel. Load terminals are coupled to wiring that directs AC power to one or more electrical loads. Load terminals may also be referred to as “feed through” terminals because the wires connected to these terminals may be coupled to a daisy-chained configuration of receptacles or switches. The load may ultimately be connected at the far end of this arrangement. As alluded to above, power may be accessed by “user accessible” load terminals, commonly referred to as “receptacle terminals.” The receptacle terminals are in communication with receptacle openings disposed on the face of the housing. This arrangement allows a user to insert an appliance plug into the receptacle openings to thereby energize the device.

As noted above, there are several types of electric circuit protection devices. For example, such devices include ground fault circuit interrupters (GFCIs), ground-fault equipment protectors (GFEPs), and arc fault circuit interrupters (AFCIs). This list includes representative examples and is not meant to be exhaustive. Some devices include both GFCIs and AFCIs. As their names suggest, arc fault circuit interrupters (AFCIs), ground-fault equipment protectors (GFEPs) and ground fault circuit interrupters (GFCIs) perform different protective functions.

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.

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.

A “grounded neutral” is another type of ground fault. This type of fault may occur when the load neutral terminal, or a conductor connected to the load neutral terminal, becomes grounded. While this condition does not represent an immediate shock hazard, it may lead to serious 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. Therefore, if a double-fault condition occurs, i.e., if the user comes into contact with a hot conductor (the first fault) when simultaneously contacting a neutral conductor that has been grounded on the load side (the second fault), the user may experience serious injury or death.

One problem that is associated with protective devices relates to the protective device being miswired, or reverse wired, in the field by an installer. Miswiring refers to a situation wherein an installer connects the line terminals to the load side of the electric circuit and connects the load terminals to the AC power source. Miswiring may result in the protective device not protecting the user from the fault conditions described above. Labels and installation instruction sheets have been used to prevent miswiring. However, instructive material may be ignored by an installer.

Another problem is that protective devices, like all electrical devices, have a limited life expectancy. When the device has reached end of life, certain components may fail, such that the user may not be protected from the fault condition. End of life failure modes include failure of device circuitry, failure of the relay solenoid, and/or failure of the solenoid driving device, typically a silicon controlled rectifier (SCR). Test buttons have been incorporated into protective devices to provide the user with a means for testing the effectiveness of the device. One drawback to this approach lies in the fact that if the user fails to use the test button, the user will not know if the device is functional. Even if the test is performed, the test results may be ignored by the user for various reasons.

What is needed is a protective device configured to reliably protect the user from a fault condition in the electrical power distribution system. A protective device is needed that is configured to detect, and indicate, that a miswire condition is extant. A protective device is further needed that denies power to the portion of the electrical power distribution system experiencing the fault condition. Further, a protective device is needed that is equipped to decouple the load terminals from the line terminals in the event of an end of life condition.

SUMMARY OF THE INVENTION

The present invention addresses the needs described above by providing a protective device configured to reliably protect the user from a fault condition in the electrical power distribution system. The protective device of the present invention is configured to detect, and indicate, that a miswire condition is extant. The present invention denies power to the portion of the electrical power distribution system experiencing the fault condition. Further, the present invention is equipped to decouple the load terminals from the line terminals in the event of an end of life condition.

One aspect of the present invention is directed to an electrical wiring protection device that includes a housing assembly including a plurality of line terminals, a plurality of load terminals, and a plurality of receptacle load terminals. A fault detection circuit is coupled to at least one of the plurality of line terminals. The fault detection circuit is configured to generate a fault detection signal in response to detecting at least one fault condition. A first interrupting contact assembly is coupled to the fault detection circuit. The first interrupting contact assembly includes first interrupting contacts disposed between the plurality of line terminals and the plurality of load terminals. The first interrupting contacts are configured to electrically couple the plurality of line terminals and the plurality of load terminals in a reset condition. The first interrupting contacts are configured to decouple the plurality of line terminals from the plurality of load terminals in response to the fault detection signal in a tripped state. A wiring state detection circuit is coupled to at least one of the plurality of line terminals. The miswire detection circuit is configured to generate a first wiring signal when the plurality of line terminals are connected to a source of AC power. A second interrupting contact assembly is coupled to the wiring state detection circuit. The second interrupting contact assembly includes second interrupting contacts disposed between at least one of the plurality of receptacle load terminals and at least one of the plurality of feed-through load terminals. The second interrupting contacts are configured to electrically couple the at least one receptacle load terminal to the at least one feed-through load terminal in response to the first wiring signal.

In another aspect, the present invention includes a method for protecting a user from a fault condition in an electrical circuit. The method includes providing an electrical wiring protection device that includes a housing assembly having a plurality of line terminals, a plurality of load terminals, and a plurality of receptacle load terminals. The electrical wiring protection device also includes first interrupting contacts disposed between the plurality of line terminals and the plurality of load terminals. Second interrupting contacts are disposed between at least one of the plurality of receptacle load terminals and at least one of the plurality of feed-through load terminals. The second interrupting contacts are initially disposed in an open state. A wiring status signal is provided that is configured to indicate whether the plurality of line terminals are coupled to the source of AC power. The second interrupting contacts are closed in response to the wiring status signal indicating that the plurality of line terminals are coupled to the source of AC power.

In another aspect, the present invention includes a method for protecting a user from a fault condition in an electrical circuit. The method includes providing an electrical wiring protection device that includes a housing assembly having a plurality of line terminals, a plurality of load terminals, and a plurality of receptacle load terminals. The electrical wiring protection device also includes first interrupting contacts disposed between the plurality of line terminals and the plurality of load terminals. Second interrupting contacts are disposed between at least one of the plurality of receptacle load terminals and at least one of the plurality of feed-through load terminals. The second interrupting contacts are initially disposed in an open state. The second interrupting contacts are closed in response to the plurality of line terminals being coupled to a source of AC power. At least one fault condition is sensed in the electric circuit. A fault condition signal is generated in response to the step of sensing. The first interrupting contacts are tripped in response to the fault condition signal, whereby the plurality of line terminals are decoupled from the plurality of load terminals.

DETAILED DESCRIPTION

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 inFIG. 1, and is designated generally throughout by reference numeral10.

As embodied herein and depicted inFIG. 1, a schematic of a protective device in accordance with one embodiment of the present invention is disclosed. In particular,FIG. 1provides a schematic diagram of GFCI10. Device10includes a neutral line terminal102and a hot line terminal104. When device10is in service, these terminals are connected to an AC power source, e.g., the wiring connected to the distribution panel. Device10also includes a neutral feed through terminal106and hot feed through terminal108. These terminals provide electrical power to downstream, daisy-chained receptacles or switches that are often included in the branch circuit. Device10also includes neutral receptacle terminal110and hot receptacle terminal112. The receptacle terminals, of course, provide appliances equipped with corded plugs access to AC power.

The line terminals102,104, are coupled to a sensor130, which in a GFCI, is typically a differential transformer. Sensor130is coupled to detector circuit132. When differential transformer130senses a differential current, i.e., unequal amounts of current flowing in the hot and neutral conductors, due to a ground fault condition, detector132provides a fault detection signal on an output line. The output is coupled to silicon controlled rectifier (SCR)133. SCR133is configured to be turned ON by the fault detection signal. SCR133is further coupled to solenoid122. When SCR133conducts, solenoid122is energized. Solenoid122includes an armature. When solenoid122is energized the armature actuates circuit interrupter120. Circuit interrupter120electrically decouples the line terminals from the load terminals in response thereto.

In particular, when solenoid122magnetically actuates the armature, circuit interrupter120displaces bus bars124and126to open the contacts. This is commonly referred to as the tripped position. In the tripped position, air gaps125and127are introduced when the receptacle load terminals110,112and feed through load terminals106,108are disconnected from line terminals102,104. Of course, this interrupts the flow of hazardous current through the fault condition.

In the embodiment shown inFIG. 1, a manual reset button128is coupled to circuit interrupter120. When the reset button128is depressed, bus bars124and126are driven into a reset state, reconnecting the load terminals106,108and the receptacle terminals110,112to the line terminals102,104. In the reset state, the air gaps125and127are eliminated.

It will be apparent to those of ordinary skill in the pertinent art that modifications and variations can be made to circuit interrupter120of the present invention depending on cost and size considerations. For example, circuit interrupter120may include bus bars, cantilever beams, or any other suitable structure. Circuit interrupter120may also be a solid state device that is tripped or reset electronically and that interrupts load current by way of semiconductor switches.

In one embodiment, device10is periodically tested by a circuit that automatically establishes a periodical simulated fault condition. Reference is made to U.S. Pat. No. 6,674,289, patent application Ser. No. 10/668,654, patent application Ser. No. 10/758,530, and patent application Ser. No. 10/868,610, which are incorporated herein by reference as though fully set forth in its entirety, for a more detailed explanation of various embodiments of the automatic test circuit.

In another embodiment, as shown inFIG. 1, device10may be tested by operating a manual test button134. When depressed, test button134generates a simulated fault condition. The test result may be displayed by a visual or audible indicator136. A successful test result may also be indicated by movement of reset button128. In particular, the test is conducted to determine whether the fault circuitry and/or the circuit interrupter is responsive to a fault. Accordingly, reset button128is configured to move from a reset position to a tripped position in response to a successful test.

In another embodiment, if the device is already in a tripped state and the test is unsuccessful, device10prevents circuit interrupter120from being reset, and/or being able to maintain a reset condition. If the device is reset by the user, it will immediately trip thereafter.

A miswire circuit is coupled between line terminals102and104. The miswire circuit includes a fault resistance138that is designed to generate a difference current in excess of a predetermined fault threshold. The fault threshold typically exceeds the level of differential current that the GFCI has been designed to interrupt, typically 6 milliamperes. The miswire resistance138is on the line side of circuit interrupter120and electrically coupled to line terminals102and104. When the GFCI10is both tripped and miswired, i.e., when power is supplied to the load terminals, nothing visible happens, but there is no power to the receptacle terminals110,112.

If the GFCI is in the reset condition, it will immediately trip when power is applied to the load side. Further, the device will trip before miswire resistance138opens because the current flowing through the miswire resistance138is interrupted when the device trips. The estimated time it takes for the miswire resistance138to “clear,” or burn out, is greater than 50 ms. The trip time of the GFCI is less than or equal to 25 ms. If one attempts to reset the device when in the miswired condition, the device repeatedly trips out until such time as the device is wired correctly. GFCI10will not operate until the device is properly wired.

On the other hand, when electrical power is connected in a correct manner to the line terminals, a differential current is created by the miswire resistance138. If the device is reset before power is applied, the device trips as a result of this differential current. If the device is already in the tripped condition before power is applied, nothing visible happens. However, because the miswire resistance is on the line side of the circuit interrupter120, current through fault resistance138continues to flow, regardless of whether the circuit interrupter120is in the tripped condition. As noted previously, the current through miswire resistance138causes the resistance to clear itself in a short time, typically 50 ms to 5 seconds. This can be accomplished by selecting a resistor or resistors whose power rating is greatly exceeded by the current.

In an alternate embodiment, a fuse148is provided in series with the miswire resistance138. The fuse is characterized by a properly selected I2t rating such that the fuse blows instead of the miswire resistance138. Once the device has been properly wired with power connected to the line terminals and the fault has been cleared, device10may be reset and provide its normal protective functions.

An interesting issue with respect to miswire protection relates to performing Underwriters Laboratories required tests, such UL-943, during the manufacture of the protective devices. The differential current produced by the miswire resistance138must not affect the test results, or cause the miswire resistance to clear in the manner previously described. One solution is to place a normally closed switch140in series with the miswire resistance138.

With regard to the mechanical implementation of switch140, switch140may be implemented using a flexible conductive spring arm that normally rests against a contact on the top side of a printed circuit board. A hole is disposed in the printed circuit board directly below the spring arm of switch140. An additional hole is disposed below the first hole in the plastic back body of the GFCI device. When GFCI10is inserted into the test equipment to perform the aforementioned manufacturing tests, a mechanical test probe engages the spring arm of switch140through the two aforementioned holes. The probe causes the spring arm of switch140to be pushed away from the contact to open the differential current circuit path. Manufacturing testing may be performed without clearing miswire resistance138. The last test performed on the GFCI device in the test sequence is to disengage the probe from the spring arm of switch140. The differential current circuit path is reconnected to check the integrity of the differential current circuit path and other GFCI components. The reconnected path should cause the GFCI device to trip if it is operating properly.

In traditional protection devices, the circuit interrupter denies power to the line terminals from the feed-through terminals. However, the denial of power to the feed-through terminals does not guarantee that the miswired condition will be corrected by the installer. For example, the electrical distribution system may not include a daisy chained receptacle or switch, in which case the feed-through terminals are not used. While the traditional device may disconnect the line terminals from the load terminals, it is not configured to disconnect the receptacle load terminals from the feed-through load terminals. As such, traditional devices expose users to possible hazardous conditions when miswired. Thus there is a need to protect a user from a fault condition in the user attachable load even when the protective device has been miswired.

In the present invention the need is addressed by interposing miswire contacts152,154between the hot feed-through terminal108and hot receptacle terminal112, respectively. Contacts152,154are configured to electrically disconnect the hot feed-through terminal108and hot receptacle terminal112when device10is miswired. Thus, power to a fault condition in the user attachable load is cut off by contacts152. Once the miswired condition has been corrected, miswiring contacts152are configured to close, to thereby establish electrical connection between the load terminals106,108and receptacle terminals110,112. In another embodiment, only contact152is implemented between the hot load contact and the hot receptacle contact. Miswire contacts152,154may be implemented using any suitable type of contacts, including a mechanical contact arrangement, a solid state contact arrangement, or any of the other miswire contact arrangements disclosed herein.

However, the use of both contacts provides more protection because contact154serves to protect the user from a fault condition in the user attachable load when the voltage source has been miswired to the feed-through terminals and when the hot and neutral conductors from the voltage source have been transposed. When the conductors are transposed, the shock (or fire) hazard shifts from receptacle hot load terminal112to receptacle neutral load terminal110. The contact pair152,154protect the user regardless of how the power source has been wired to the feed-through terminals. In yet another embodiment, contacts154are included but contacts152are not included. This embodiment also denies power to the user attachable load when the device has been miswired. The denial of power motivates the user to correct the miswired condition before a fault condition in the user attachable load is likely to take place.

Referring back toFIG. 1, the circuit includes resistors142,144,146, and indicator light136. Light136is a trip indication light. The light is off if GFCI10is in the reset condition, and illuminates if the GFCI10is tripped. If device10is miswired, light136is off, regardless of whether the device is reset or tripped. If device10is properly wired, allowing a reset condition to be maintained, light136is off. If device10is properly wired and tripped, light136is illuminated. Light136may also serve to notify the user that the solenoid-driving device is defective and that device10is no longer operational. Light136may be replaced by an audible device. As such, the present invention may include a visual and/or audible indicator. The indicator may have multiple indication meanings.

The indicating circuit operates as follows. When the device10is wired properly, and the device is reset, light136is off. The circuit interrupter120is closed (reset) and no voltage is present across light136and resistor144. If the GFCI trips for any reason, light136is energized by line voltage being applied across light136and resistors144and142. When the circuit interrupter120is reset, voltage is removed and light136turns off. If the device is miswired, light136is off when the circuit interrupter120is reset. However, when the device trips in this condition, there is no return path to neutral through resistor142. Accordingly, light136does not turn on as it would if the GFCI were wired properly. This feature is not dependent on the miswire resistance138. Thus, if the miswire detection circuit has been previously used and the miswire resistance cleared, miswire detection is still possible by energizing light136in conjunction with tripping the GFCI10.

Turning now to end-of-life indication, the circuit branch that includes resistor146is used to indicate that SCR133(i.e., the solenoid driving device) is defective. When SCR133short circuits, a current path to supply neutral is established via resistor146to thereby energize light136. Note that trip solenoid122will open within a few seconds if the line voltage is continuously applied to it. This is exactly the outcome when SCR133short circuits. If solenoid coil122burns out, device10may no longer be tripped after being reset. On the other hand, light136remains energized, indicating a defective solenoid driving device. The value of resistor146must be kept low relative to the value of resistor144, since the two resistors form a voltage divider that limits the voltage across light136. If light136is a neon lamp, the values of resistors144and146are chosen to apply about 60 volts. This voltage level allows the lamp to arc and energize. In this embodiment, resistor146is typically 33 K. This resistance value results in approximately 66 volts being applied across the neon lamp at a worst case line voltage of 102 VAC.

To summarize the switch states, when device10is wired properly and reset, indicator136is OFF. When device10is wired properly and tripped, indicator136is ON. When an end-of-life condition occurs, indicator136is ON in the reset state. Finally, when device10is miswired and tripped, indicator136will be OFF.

As embodied herein and depicted inFIG. 2, a schematic diagram in accordance with another embodiment of the present invention is shown. Protective device200is a general diagrammatic depiction of a protective device in that it may be applied to various protective devices such as ground fault circuit interrupters (GFCIs), arc fault circuit interrupters (AFCIs), or combination devices that provide both AFCI and GFCI protection. The present invention should not be construed as being limited to the examples listed above. Thus, protective circuit202may be configured to detect any number of fault conditions, including ground faults, arc faults, or both. The protective circuit202may include self-diagnostics for detecting an end-of-life condition in the circuit202and/or circuit interrupter206.

As shown inFIG. 2, protective circuit202is coupled between the line terminals102,104. The output of the protective circuit is coupled to SCR204. Solenoid208is disposed between SCR204and the hot line conductor. The miswire detection circuit, including miswire resistor138, is disposed in parallel to solenoid208. Solenoid208is, in turn, coupled to interrupting contacts210, in the manner previously described. During operation, protective circuit202provides SCR204with a fault detection signal. SCR204begins to conduct to thereby energize solenoid208, causing the circuit interrupter206to trip contacts210. As a result, load terminals106,108,110, and112are disconnected from line terminals102,104. Of course, the circuit interrupter206may be implemented using bus bars, cantilevers or other similar structures configured to form an air gap, or by turning off one or more solid state switch.

Resistors142,144,146, and light136are similar to, and have the same functionality as, the circuits depicted inFIG. 1. However, the miswire circuit inFIG. 2operates in a different manner by directly signaling SCR204. If device200is in the reset state and power is miswired to the load terminals, current flows through normally closed switch140, fuse148, miswire resistance138to cause SCR204to activate solenoid208. Interrupting contacts210are opened and device200is tripped. Fuse148, if provided, and miswire resistance138are chosen to withstand the current flow for the time that power is applied to the load terminals to the moment when interrupting contacts210open, which is approximately 25 milliseconds. If line power is connected as intended to the line terminals of the protective device, current flows through normally closed switch140, fuse148, miswire resistance138, and SCR204until such time as resistance138clears, or fuse148(if provided) clears. Afterwards, device200may be reset.

Accordingly, the miswire detection functionality of the circuit shown inFIG. 2differs from the miswire protection circuit inFIG. 1in that the miswire detection signal does not necessarily have to be routed through the fault detection circuitry. The fault detection circuit ofFIG. 1evaluates the miswire detection signal as it would a fault condition signal. On the other hand, the miswire detection signal ofFIG. 2by-passes the fault detection circuit and is applied directly to SCR204. In another embodiment, the miswire detection signal is gated with the fault detection signal to create a Boolean output that is interpreted by detection circuitry.

Solenoid208is designed not to burn out during the interval that SCR204is turned ON. The interval is typically on the order of approximately 100 milliseconds. Accordingly, the miswire protective functionality described in the embodiment shown inFIG. 1is provided without necessarily requiring a differential current transformer130to detect the miswired condition. Further, neither the miswire resistance nor the fuse circuit need be attached to both the hot and neutral line conductors. If an electronic switching device other than an SCR is used, e.g., a bipolar transistor, the connection to the gate of the SCR would instead be made to the base of the bipolar transistor.

The miswire resistance138or fuse148(if provided) are susceptible to damage from lightning storms and types of loads that impose voltage impulse transients on the electrical distribution system. The susceptibility may be eliminated by electrically coupling a metal oxide varistor (MOV)212across the line terminals. There are many alternate methods for suppressing voltage transients. Reference is made to U.S. patent application Ser. No. 10/964,217 and the U.S. patent application Ser. No. 11/080,574, which are incorporated herein by reference as though fully set forth in its entirety, for a more detailed explanation of alternate methods for suppressing voltage transients.

As previously described, contacts152and/or154serve to protect the user from a fault condition in the user attachable load. The contacts are configured to open in response to a miswire condition. The contacts are configured to close (or be closeable) if the protective device has been properly wired.

Referring toFIG. 3, a plan view of the miswire resistance circuit300is shown. Circuit300includes at least one heating device such as resistor302in combination with wire304. Wire304has a predetermined melting point. When device10is properly wired, resistor302produces I2R heating. When the temperature rises above the pre-determined threshold, wire304melts and an air gap is formed. The air gap is configured to block surge currents resulting from impulse voltages. It will be apparent to those of ordinary skill in the pertinent art that modifications and variations can be made to wire304of the present invention depending on the desired temperature threshold and the value of the resistance chosen. Accordingly, wire304may be of any number of alloys familiar to those skilled in the art, including tin/lead alloys.

Referring toFIG. 4andFIG. 5, a second mechanical implementation of the miswire circuit is shown.FIG. 4is an elevation view of miswire circuit400in a closed state. Miswire circuit400includes at least one heating resistor402coupled to a spring member404by connective element408. Connective element408may be implemented using solder, or some other similarly conductive alloy. Spring member404, solder408, and miswire resistor402are electrically continuous in a closed state. Of course, connective element408is designed to have a predetermined melting threshold. When device10is properly wired, resistor402produces I2R heating. When the temperature rises above the pre-determined threshold, connective element408melts, spring member404is released, and an air gap410is formed.

FIG. 5is an elevation view of the miswire circuit400depicted inFIG. 4in an open state. As alluded to above, once the solder attachment408fails, spring404opens to a pre-biased position to form an air gap410.

FIG. 6is a sectional view illustrating a receptacle contact structure152in accordance with an embodiment of the present invention. WhileFIG. 1shows two receptacle contacts152,154,FIG. 6only shows one such contact structure (152) for ease of illustration. A duplicate structure may be implemented to form contact154.

FIG. 6shows the receptacle contacts152in an open state. Referring back toFIG. 1, contacts152disconnect the hot feed-through terminal108and hot receptacle terminal112until device10is wired properly. Thus, the implementation shown inFIG. 6eliminates any potentially hazardous condition caused by a miswire condition. Once the miswired condition has been corrected, miswiring contacts152,154are configured to close, to thereby establish electrical connection between the load terminals106,108and receptacle terminals110,112.

Referring back toFIG. 6, miswire circuit600includes at least one heating resistor602coupled to arm606by way of connective element604. Connective element604may be implemented using solder, or a connective element formed from a similarly conductive alloy. Miswire contacts152include a movable contact1520and a fixed contact1522. Movable contact1520is disposed on spring member608. Spring member608is coupled to circuit board610. Arm606extends through a hole612formed in circuit board610. At one end, arm606is fixedly attached to circuit board610by connective element604. At the other end, arm606is connected to spring member608. Accordingly, resistor602, connective element604, arm606, spring member608, and movable contact1520are electrically continuous. However, power is denied to the receptacles because of the air gap disposed between movable contact1520and fixed contact1522, i.e., miswire contacts152are in an open state.

FIG. 7is the miswire contact structure depicted inFIG. 6in a closed state. In other words, once the installer properly wires device10such that the line terminals are connected to the AC power source (i.e., the wiring from the distribution panel), current begins to flow through resistor602generate I2R heating in the manner previously described, causing the temperature of connective element604to exceed a predetermined temperature threshold. Once the connective element fails, arm606is released, and becomes slidable. Because spring member608is biased toward the closed state, arm606moves in the direction shown to close contacts152. Once contacts152have closed, miswire resistance602is configured to open. Opening may be accomplished by clearing fuse148(FIGS. 1,2), clearing resistor602, or failure of solder attachment604.

FIG. 8is a sectional view illustrating a receptacle contact structure152in accordance with an alternate embodiment of the present invention. In this embodiment, miswire circuit800includes at least one heating resistor802and a spring member806that is fixedly attached near, or to, one lead of resistor802using solder element804. As noted above, the solder connection may be replaced by any suitable means for releasably attaching spring806to resistor802. For example, solder element804may be replaced by a similarly conductive alloy. As shown byFIG. 8, resistor802, connective element804, spring member806, and movable contact1520are electrically continuous. On the other hand, an air gap exists between fixed contact1522and movable contact1520. Accordingly, power is denied to the receptacles110,112(FIG. 1) because device10has not been properly wired.

FIG. 9shows the mechanical implementation depicted inFIG. 8in a closed state. Once the installer properly wires device10such that the line terminals are connected to the AC power source (i.e., the wiring from the distribution panel), current begins to flow through resistor802generate I2R heating in the manner previously described, causing the temperature of connective element804to exceed a predetermined temperature threshold. Once the connective element804fails, spring806is released. Spring member806is biased toward the closed state and moves to close contacts152once released, forming air gap808.

FIG. 10is an alternate embodiment of a receptacle miswire contact structure. Miswire circuit1000includes at least one heating resistor1002attached using solder1004, or a similarly conductive alloy. Resistor1002is mechanically coupled to plunger1008. Plunger1008extends from resistor1004through a hole in board1020. Plunger1008is coupled to buss bar1006. Spring member1010exerts a biasing force against bus bar member1006. However, plunger1008is fixed in place by solder1004such that contacts152are open. When the protection device is properly wired, the solder attachment1004fails in the manner previously described.

FIG. 11shows the receptacle miswire contact structure depicted inFIG. 10in a closed position. Again, Once device10is wired properly, current flows through resistor1002to thereby generate I2R heating of solder1004. Of course, the solder1004gives way when the temperature exceeds a predetermined temperature threshold. Once the solder fails, resistor1002is pushed out of position by the movement of plunger1008. Plunger1008is urged through the hole by the biasing force exerted by spring1010. The force applied by spring1010moves contacts152into the closed state.

As noted previously, the embodiments provided above have been described with respect to hot conductor contacts152. However, the structures disclosed herein are equally applicable to neutral conductor contacts154.

As embodied herein and depicted inFIG. 12, yet another receptacle miswire contact arrangement in accordance with the present invention is disclosed.FIG. 12is employs a single miswire circuit1200to couple both hot and neutral miswire contacts152,154to their respective conductive paths. Miswire circuit1200includes at least one heating resistor1202attached using solder1204, or some other similarly conductive alloy. Solder1204and miswire resistor1202are electrically continuous and therefore conduct electricity. Hot contact152and neutral contact154are disposed on movable arms1212,1214. Latch block1208is constructed of an electrically non-conductive material. Latch block1208is constrained between resistor1202and arms1212,1214, forcing contacts154and152into an open state. When the protection device is properly wired, the solder attachment1204fails, causing the resistor to give way. The force applied by spring1210moves contacts152and154into the closed state. In an alternate embodiment, arms1212and1214are spring members. In this embodiment, spring1210is not required. Of course, spring members1212and1214are pre-biased to close contacts154and152after solder attachment1204has failed.

In another embodiment, the body of fuse148may be used to capture latch block1208(or arm1008.) After device10has been properly wired, the clearing of fuse148permits motion of the latch block (or arm) to close the miswire contacts.

Referring toFIG. 13, an end-of-life mechanism1300is depicted. Mechanism1300is configured to permanently disconnect the power source form the load terminals when device10is experiencing an end-of-life condition that would prevent device10from interrupting a predetermined fault condition. End-of-life conditions include one or more of the following: a failure in sensor130, detector132, SCR133, or circuit interrupter120.

Mechanism1300includes end-of-life contacts1302,1316, that are operated essentially in a different manner than miswire contacts, e.g., contacts1302,1316are in the closed state at the time of installation and throughout the life of the product and are configured to open when an end-of-life condition has occurred. Contacts1302,1316are disposed in series with circuit interrupter120(refer toFIG. 1.) Mechanism1300includes at least one heating resistor1304attached using solder1306, or another similarly conductive alloy. Solder1306and resistor1304share electrical continuity, and therefore are in a conductive state. Contacts1302are connected to bus bar1308. Spring1310is constrained between resistor1304and bus bar1308to close contacts1302.

FIG. 14is an elevation view of the end-of-life mechanism depicted inFIG. 13in an end-of-life state. When the protection device reaches an end-of-life condition, current through the heating resistor1304begins to flow. The solder attachment1306fails once the temperature level exceeds the melting point of the solder. At that point resistor1304is pushed away by the action of spring1312and spring1310, which are no longer constrained by resistor1304. The force applied by spring1312moves contacts1302into the open state. Force applied by spring1312may also break electrical continuity to resistor1304by forming an air gap1314.

As noted above, the end-of-life mechanism described inFIGS. 13 and 14includes contacts1302that are disposed between the hot line and hot load terminals. In an alternate embodiment, another set of end-of-life contacts (not shown) are disposed between the neutral line and neutral load terminals in a manner similar to the arrangement shown inFIG. 12. Both sets of contacts (1302, neutral path contacts) may be operated by a single resistor in a similar manner as has been described inFIG. 12.

Those of ordinary skill in the art will recognize that the end-of-life mechanism and miswire contacts described herein may both be included in device10.

As embodied herein and depicted inFIG. 15, a schematic of a protective device in accordance with yet another embodiment of the present invention is disclosed. The fault detection circuitry includes sensor130coupled to detector132. If a fault is present, detector132provides a fault detection signal to SCR133causing it to conduct. When SCR133conducts, solenoid122is energized causing its armature to actuate interrupting contact assembly120.

Device10also includes miswire contacts902and/or904. Miswire contacts902,904disconnect the feed-through load terminals108,106from the receptacle load terminals112,110respectively. Contacts902,904are coupled to miswire solenoid900. When device10has been miswired, the source voltage from the electrical distribution system is connected to feed-through terminals106,108. There is no voltage applied to solenoid900because contacts902,904are in the open state. Since contacts902,904cannot close until voltage is applied to solenoid900, the contacts remain in the open state. On the other hand, when device10is properly wired, voltage is applied to solenoid900, and solenoid900is energized causing contacts902,904to close. The configuration results in permanent closure of contacts902,904. The device may employ a magnetic latching device such as a permanent magnet or a mechanical latching device. Those skilled in the art will recognize that any suitable latching mechanism may be employed herein.

In an alternate embodiment, contacts902,904re-open each time there is loss of source voltage on the line terminals. In this manner, the miswire detection feature is available each time device10is removed from the installation and re-installed. Another alternate embodiment includes miswire solenoids that are intended to be only momentarily connected to voltage. Such solenoids overheat if connected to a permanent voltage. The overheating problem is resolved by disposing contacts906in series with solenoid900. Contacts906are opened after contacts903,904have successfully closed. Closure of contacts906may be accomplished by coupling them to solenoid902or to contacts902,904.

Those skilled in the art will recognize that circuit interrupter120is constructed to reliably perform many trip/reset operations. In particular, device10is typically designed to perform 3,000 trip/reset cycles. On the other hand, miswire contacts152154(FIGS. 1,2) and miswire contacts902,904(FIG. 15) may be actuated only a handful of times over the course of the operating life of device10. End-of-life contacts1302,1304(FIGS. 13-14) may be actuated only once—when the device reaches an end-of-life state. Accordingly, miswire contacts and end-of-life contacts may be implemented using a simpler construction. For example, circuit interrupter120may be implemented using silver rivets. Such rivets provide reliable operation for a few thousand trip/reset operations. As such, they may be omitted, and a simpler, less expensive construction may be employed to implement the miswire contact assembly and the end-of-life contact assembly.