Patent Application
20070206337
The present invention relates generally to electrical safety devices and more particularly to ground fault circuit interrupters (GFCIs).
Alternating current (AC) power is typically delivered from a power source (e.g., a power plant) to a load (e.g., an electrical appliance plugged into a conventional electrical outlet) through a network of interconnected power cables, each power cable comprising a pair of conducting lines. Specifically, each power cable typically comprises a hot line (which is also commonly referred to in the art as a hot wire or a power line) and a neutral line (which is also commonly referred to in the art as a neutral wire).
The hot line is provided with a first end and a second end. The first end of the hot line (which is commonly referred to in the art as its line end) leads to a high energy source located at the power source. The second end of the hot line (which is commonly referred to in the art as its load end) leads to a load connected thereto.
Similarly, the neutral line is provided with a first end and a second end. The first end of the neutral line (which is commonly referred to in the art as its line end) leads to an electrically neutral source that is located at the power source. The second end of the neutral line (which is commonly referred to in the art as its load end) leads to the load connected thereto.
With the line end of each conductive line connected to a power source and with the load end of each conductive line connected to a load, a closed circuit is effectively created. Because the hot line connects to a high energy source and the neutral line connects to an electrically neutral source, a voltage is created across the circuit which, in turn, serves to power the load. When the closed circuit is operating properly, the current which flows through the hot line is equal to the current which flows through the neutral line.
However, it has been found that, on occasion, the hot line can connect directly to ground (e.g., if someone who is grounded accidentally touches the hot line). The connection of the hot line directly to ground causes the current flowing therethrough to drop, thereby establishing unequal current levels through the hot line and the neutral line. In response to the imbalance of currents flowing through the hot and neutral lines, the closed circuit will naturally adjust the current flow through the hot line to equal the current flow through the neutral line. This adjustment is accomplished through a rapid surge in the current level through the hot line (to a level which is equal to the current level through the neutral line). The resulting surge of electricity through the hot line (commonly referred to in the art as a ground fault condition) can potentially harm an individual who is operating the load at the time of the current surge.
Accordingly, ground fault circuit interrupters are well known in the art and are widely used in commerce to protect against ground fault conditions (i.e., by opening the closed circuit). Examples of ground fault circuit interrupters are found in U.S. Pat. No. 6,052,266 to V. Aromin and U.S. Pat. No. 5,757,598 to V. Aromin, both of which are incorporated herein by reference.
One type of ground fault circuit interrupter (GFCI) which is well known in the art is provided with a pair of electrical outlets which can be used to power most types of conventional electrical appliances. This type of GFCI is typically installed directly into an electrical box which is, in turn, mounted within a bathroom or kitchen wall, the GFCI being commonly referred to as a wall mountable GFCI in the art. As such, wall mountable GFCIs serve two principal functions: (1) to provide a pair of electrical outlets for powering conventional electrical appliances (e.g., hair dryers, toasters, microwaves, etc.) and (2) to trip open the closed circuit upon detecting a ground fault condition in the pair of conducting lines which, in turn, quickly terminates the flow of electricity (and, most importantly, the flow of any surge in current) into the load and both of the electrical outlets.
A ground fault circuit interrupter (GFCI) commonly includes a differential transformer with opposed primary windings, one primary winding being associated with the power line and the other primary winding being associated with the neutral line. If a ground fault condition should occur on the load side of the GFCI, the two primary windings will no longer cancel, thereby producing a flux flow in the core of the differential transformer. This resultant flux flow is detected by a secondary winding wrapped around the differential transformer core. In response thereto, the secondary winding produces a trip signal which, in turn, is used to open a switch located in at least one of the conducting lines between the power supply and the load (as well as between the power supply and the pair of electrical outlets), thereby eliminating the dangerous condition.
A ground fault circuit interrupter is traditionally constructed to include an exterior casing which is constructed out of a non-conductive material, such as plastic. Disposed within said casing is the ground fault circuit electronics (which are commonly mounted on a single double-sided printed circuit board). As noted above, a pair of electrical outlets are commonly integrated into the exterior casing and in electrical connection with the ground fault circuit electronics.
It should be noted that a plurality of conductive terminals are coupled to the ground fault circuit electronics and are externally accessible through small openings in the exterior casing, these conductive terminals serving as the point of connection for the GFCI to the power source and the load. In particular, the GFCI is provided with a pair of line side terminals, one of the terminals being designated for connection to the cable which leads to the hot line of the power source and the other terminal being designated for connection to the cable which leads to the neutral line of the power source. In addition, the GFCI is provided with a pair of load side terminals, one of the terminals being designated for connection to the cable which leads to the hot line of the load and the other terminal being designated for connection to the cable which leads to the neutral line of the load. Furthermore, the GFCI is often provided with a single grounding terminal (often marked in green to facilitate its identification) which is designated for connection to ground (i.e., for increased safety).
In U.S. Pat. No. 5,757,598, to V. V. Aromin, there is disclosed an example of a ground fault circuit interrupter (GFCI) which protects against ground fault conditions present in a pair of conducting lines that extend between a source of power and a load. The GFCI includes a circuit breaker having a switch located in one of the pair of the lines. The switch has a first position in which the source of power in its associated line is not connected to the load and a second position in which the source of power in its associated line is connected to the load. A relay circuit is coupled to the switch for selectively positioning the switch in either the first or second position. The relay circuit includes a solenoid which operates in either an energized or a de-energized state. When energized, the solenoid positions the switch in its second position and when de-energized, the solenoid positions the switch in its first position. The GFCI also includes a booster circuit for selectively supplying a first voltage through the switch and to the solenoid which is sufficient to cause the solenoid to switch from its de-energized state to its energized state. A power supply circuit supplies a second voltage to the solenoid which is less than the first voltage. The second voltage is sufficient to maintain the solenoid in its energized state after being initially energized by the first voltage but is insufficient to switch the solenoid from its de-energized state to its energized state. A latch circuit operable in first and second bi-stable states allows the solenoid to switch from its de-energized state to its energized state and remain in its energized state when in its first bi-stable state and allowing solenoid to switch from its energized state to its de-energized state and remain in its de-energized state when in its second bi-stable state. A fault detection circuit detects the presence of a fault condition in at least one of the lines extending between the power source and the load and causes the latch circuit to latch in its second bi-stable state upon detection of the fault condition.
While GFCIs of the type described above are well known in the art and widely used in commerce to protect electrical appliances from ground fault conditions, it has been found that these types of GFCIs suffer from a notable shortcoming.
Specifically, GFCIs of the type described above are typically designed to provide ground fault protection in only one direction (i.e., in the direction from terminals designated for connection to the power source to the terminals designated for connection to the load). As a result, GFCIs of the type described above are only capable of providing ground fault protection to its pair of electrical outlets as well as the load coupled thereto if the power source and load are properly connected to their designated terminals on the GFCI.
However, it has been found that, on occasion, consumers incorrectly connect the line and load side cables to the ground fault circuit interrupter. Specifically, consumers often inadvertently connect the cables leading to the power source (i.e., the line side cables) to the load side terminals on the GFCI and the cables leading to the load (i.e., the load side cables) to the line side terminals on the GFCI. This inadvertent mistake in the connection of the line and load side cables to the GFCI still serves to electrically connect the line to the load and, as a consequence, supply voltage to the load. In addition, this inadvertent mistake in connection still affords the load connected to the line side terminals of the GFCI with ground fault protection. However, this inadvertent mistake in connection precludes the electrical outlets which are integrated into the GFCI from providing ground fault protection. As a result of this common wiring mistake, a consumer who utilizes an electrical appliance that is plugged into one of the electrical outlets of the GFCI is rendered highly susceptible to the risk of a shock hazard, which is highly undesirable.
It is important to note that the consumer would not become aware of the aforementioned mistake in wiring because power would still be delivered to the load as well as to both electrical outlets. In addition, GFCIs which include test and reset buttons would function as if the GFCI were properly wired. As such, the user would believe that the GFCI is providing ground fault protection to the pair of electrical outlets when, in fact, no ground fault protection is actually being provided to the outlets.
It is an object of the present invention to provide a new and improved ground fault circuit interrupter (GFCI) which, when properly wired, protects against ground fault conditions present in the hot and neutral lines that connect a power source to a load.
It is another object of the present invention to provide a GFCI of the type described above which includes a first pair of conductive terminals which are designated for connection to the power source and a second pair of conductive terminals which are designated for connection to the load.
It is yet another object of the present invention to provide a GFCI of the type described above which includes a pair of electrical outlets that are ground fault protected.
It is still another object of the present invention to provide a GFCI of the type described above which provides an indication to the consumer that the line side cables and the load side cables have been connected to the GFCI in reverse.
It is yet still another object of the present invention to provide a GFCI as described above which may be mass produced, has a minimal number of parts, and can be easily assembled.
Accordingly, there is provided a ground fault circuit interrupter (GFCI) for regulating the flow of current through a pair of lines extending between a power source and a load, the pair of lines comprising a hot line and a neutral line, the ground fault circuit interrupter comprising (a) a first pair of terminals located at one end of the pair of lines, the first pair of terminals being designated for connection to the power source, (b) a second pair of terminals located at the other end of the pair of lines, the second pair of terminals being designated for connection to the load, (c) an electrical outlet connected to the pair of lines at a location between the first and second pairs of terminals, (d) a circuit breaker having a first switch, the first switch being located in one of the pair of lines at a location between the first pair of terminals and the electrical outlet, the first switch having an open position and a closed position, (e) a relay circuit for selectively moving and maintaining the first switch in either its open position or its closed position, (f) a ground fault detection circuit for detecting the presence of a ground fault condition in the pair of lines between the first and second pairs of terminals, the ground fault detection circuit providing a trip signal upon detecting a ground fault condition, the relay circuit moving and maintaining the first switch in its open position in response to the trip signal, and (g) a reverse wiring circuit for generating an artificial ground fault condition when the power source is improperly connected to the second pair of terminals.
Additional objects, as well as features and advantages, of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention. In the description, reference is made to the accompanying drawings which form a part thereof and in which is shown by way of illustration specific embodiments for practicing the invention. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.
The accompanying drawings, which are hereby incorporated into and constitute a part of this specification, illustrate various embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings wherein like reference numerals represent like parts:
Referring now to
As seen most clearly in
GFCI 11 includes a pair of metal brackets 27, one bracket 27-1 extending at an approximate right angle relative to top surface 19 and the other bracket 27-2 extending at an approximate right angle relative to bottom surface 21. Together, brackets 27 enable GFCI 11 to be installed into a conventional electrical box which, in turn, is fixedly disposed within a bathroom or kitchen wall. For this reason, GFCI 11 is commonly referred to in the art as a wall mountable GFCI.
Front surface 15 at least partially defines a pair of standard electrical outlets 29, as seen most clearly in
An externally accessible test button 33 and an externally accessible reset button 35 project through corresponding openings formed in front surface 15. Buttons 33 and 35 are coupled to associated switches which are located inside casing 13 (as will be described further below) and can be used to perform selected operations for GFCI 11.
A plurality of externally accessible conductive terminals 37, 39 and 41 are provided which serve as connection points for coupling the power source, load and ground to GFCI 11. Terminals 37, 39 and 41 are coupled, at one end, to the GFCI electronics (shown in schematic form in
It should be noted that each of conductive terminals 37, 39 and 41 is represented herein as being in the form of a threaded metal screw which can be driven inward (e.g., using a screwdriver) to draw a conductive lead, or wire, into electrical contact against a metallic plate (not shown). However, it is to be understood that various alternative types of connection means (e.g., push-in wire receptacles) are commonly utilized to connect a GFCI to a load, line and/or ground.
As seen most clearly in
Conductive terminals 39 are designated as the load side terminals for GFCI 11. Specifically, conductive terminal 39-1 is designated for connection to the wire which leads to the hot line H of the load. In addition, conductive terminal 39-2 is designated for connection to the wire which leads to the neutral line N of the load. It should be noted that each of load side terminals 39 is identified on rear surface 17 to ensure proper connection thereto.
Conductive terminal 41 is designated as the ground terminal for GFCI 11. Specifically, conductive terminal 41 is designated for connection to the wire which leads to ground. It should be noted that, in order to ensure the proper connection to ground, conductive terminal 41 is often colored green (which is recognized in the industry as representing a ground connection) and rear surface 17 of casing 13 is also provided with a suitable identifying marker.
Referring now to
GFCI 11 includes a circuit breaker 43 for regulating the delivery of power along conductive lines H and N from the power source to both the load and outlets 29, a relay circuit 45 for controlling the operation of the circuit breaker 43, a power supply circuit 47 for supplying power to selected electrical components in GFCI 11, a fault detection circuit 49 for sensing the presence of a ground fault condition in hot and neutral lines H and N, a latch circuit 51 for converting a fault condition signal produced by fault detection circuit 49 into the appropriate signal which can be used to regulate relay circuit 45, and a test circuit 53 for verifying that GFCI 11 is operating properly.
Circuit breaker 43 includes a pair of normally closed, single-pole, single-throw switches K1 and K2 which are located in hot and neutral conductive lines H and N, respectively, between the power source and the load (as well as between the power source and outlets 29). Switches K1 and K2 can be disposed in either of two positions: a first position in which switches K1 and K2 are open (as illustrated in
Relay circuit 45 is responsible for controlling the connective position of switches K1 and K2. Specifically, relay circuit 45 includes a solenoid SOL that is ganged to the circuit breaker contacts of switches K1 and K2. Before power is applied to GFCI 11, solenoid SOL positions switches K1 and K2 in their second connective position (i.e., their closed positions). After power is applied to GFCI 11, solenoid SOL will retain switches K1 and K2 in their second connective positions (i.e., their closed positions). However, once solenoid SOL is energized, solenoid SOL moves switches to their first connective positions (i.e., their open positions).
Power supply circuit 47 supplies power to selected components in GFCI 11. Power supply circuit 47 comprises a metal oxide varistor MOV, four silicon controlled rectifiers D1, D2, D3 and D4, a voltage dropping resistor RDROP, and a storage capacitor CSTORAGE. Varistor MOV helps to protect the load against a voltage surge from the AC power source. Rectifiers D1-D4 (each having a model number of IN4004) together form a conventional diode rectifier bridge and serve to convert the alternating current (AC) power from the power source into direct current (DC) power. Voltage dropping resistor RDROP has a value of 24 Kohms and acts to limit the input voltage to solenoid SOL so as to prevent against inadvertent switching of circuit breaker 43. Storage capacitor CSTORAGE has a value of 0.01 uF and acts to charge to full line potential when reset button 35 is depressed.
Fault detection circuit 49 acts to detect the presence of ground fault conditions in conductive lines H and N when switches K1 and K2 are disposed in their second connective position (i.e., their closed positions). Fault detection circuit 49 comprises a sense transformer T1, a grounded neutral transformer T2, a coupling capacitor CCOUPLING, a noise suppression capacitor CNOISE, a tuning capacitor CTUNE, a sense resistor RSENSE and a ground fault interrupter chip U1. Sense transformer T1 senses the current differential between the hot and neutral conductive lines H and N, and upon the presence of a ground fault condition, transformer T1 induces an associated output from its secondary windings. Grounded neutral transformer T2 acts in conjunction with transformer T1 to sense the presence of grounded neutral conditions and, in turn, induce an associated output. Coupling capacitor CCOUPLING has a value of 10 uF and acts to couple the alternating current signal from the secondary winding of sense transformer T1 to chip U1. Noise suppression capacitor CNOISE has a value of 0.01 uF and acts to prevent fault detection circuit 49 from operating in response to line disturbances such as electrical noise and lower level faults. Tuning capacitor CTUNE has a value of 0.03 uF and sense resistor RSENSE has a value of 1.0 Mohms. Together tuning capacitor CTUNE and sense resistor RSENSE act to set the minimum fault current at which fault detection circuit 49 provides an output signal to latch circuit 51. Interrupter chip U1 is an RV4145 low power ground fault interrupter circuit which is sold by Raytheon Corporation. Chip U1 serves to amplify the fault signal generated by sense transformer T1 and provide an output, or trigger, pulse (at pin 5) to activate latch circuit 51.
Latch circuit 51 acts to take the electrical signal produced by fault detection circuit 49 (i.e., at output pin 5) upon the detection of a ground fault condition and, in turn, energize solenoid SOL. Latch circuit 51 comprises a silicon controlled rectifier SCR which is operable in either a conductive or non-conductive state and a filter capacitor CFILTER. Preferably, reset switch 35 is provided as part of latch circuit 51 and is connected at one end to the anode of rectifier SCR and at the other end to the cathode of rectifier SCR (although reset switch 35 is not shown in the schematic shown in
Test circuit 53 provides a means for determining whether GFCI 11 is operating properly. Test circuit 53 comprises a current limiting resistor RTEST having a value of 15 Kohms and test switch 33 (which is of the conventional push-in type design). When test switch 33 is depressed to energize test circuit 53, resistor RTEST provides a simulated fault current to sense transformer T1 which is similar to a ground fault condition.
Outlets 29-1 and 29-2 are connected to hot and neutral conductive lines H and N at a location between circuit breaker 43 and load-side terminals 39. Specifically, each outlet 29 includes a neutral line conductive terminal 55 which is connected to neutral line N at a location between terminal 39-2 and switch K2, each conductive terminal 55 being externally accessible through a corresponding opening 31-1 in casing 13. Similarly, each outlet 29 includes a hot line conductive terminal 57 which is connected to hot line H at a location between terminal 39-1 and switch K1, each conductive terminal 57 being externally accessible through a corresponding opening 31-2 in casing 13. Furthermore, each outlet 29 includes a ground terminal 59 which is connected to ground G, each ground terminal 59 being externally accessible through a corresponding opening 31-3 in casing 13.
As noted above, GFCI 11 connects a power source (represented as POWER SOURCE in
With the power source connected to line side terminals 37 and the load connected to load side terminals 39, GFCI 11 operates in the following manner. In the absence of a ground fault condition, switches K1 and K2 are normally disposed in their closed positions, thereby enabling AC power to pass from the power source to both the load and outlets 29 through hot and neutral conductive lines H and N. As alternating current (AC) power is being supplied from the power source to the load and outlets 29, fault detection circuit 49 monitors conductive lines H and N for the presence of a ground fault condition (i.e., unequal current values along hot and neutral lines H and N). If a ground fault condition is detected along conductive lines H and N (e.g., if test button 33 is depressed), fault detection circuit 49 sends a signal to latch circuit 51 which, in turn, energizes solenoid SOL. The activation of solenoid SOL causes switches K1 and K2 (which are ganged together to solenoid SOL) to open. With switches K1 and K2 open, the potentially dangerous ground fault condition present along hot and neutral lines H and N (in particular, between line side terminals 37 and circuit breaker 43) is unable to pass onto the load or electrical outlets 29. In this manner, the load as well as outlets 29 are protected against receiving the ground fault condition from the power source, which is highly desirable. Once the fault condition is eliminated, GFCI 11 can be reset through the depression of reset button 35 which, in turn, causes solenoid SOL to return switches K1 and K2 to their closed positions.
Although rear surface 17 of casing 13 is provided with markings to facilitate proper connection, it has nonetheless be found that, on occasion, consumers incorrectly connect the power source and load to GFCI 11. Specifically, consumers often inadvertently connect the cables leading to the power source (i.e., the line side cables) to load side terminals 39 and the cables leading to the load (i.e., the load side cables) to line side terminals 37. With the line side cables and the load side cables wired in reverse, the power source is still able to supply voltage to both the load and outlets 29 through conductive lines H and N when switches K1 and K2 are in their closed positions. In addition, reverse wiring of the line and load side cables does not compromise the ability of GFCI 11 to provide the load with ground fault protection. However, with the power source and load coupled to GFCI 11 in reverse, it should be noted that outlets 29 are not provided with ground fault protection, which is highly undesirable.
Specifically, power is supplied from the power source via load side terminals 39 to the load via line side terminals 37. The power supplied by the power source travels through circuit breaker 43 and is ultimately measured by fault detection circuit 49. When a ground fault condition is detected along conductive lines H and N by fault detection circuit 49, solenoid SOL opens switches K1 and K2 of circuit breaker 43, thereby suspending further application of power from the power source to the load.
However, it should be noted that opening switches K1 and K2 does not serve to protect electrical outlets 29 from the ground fault condition in the conductive lines. Rather, with switches K1 and K2 open, any ground fault condition in the conductive lines that is derived from the power source will still pass into outlets 29. As a result, even though switches K1 and K2 have been opened in response to the detection of a ground fault condition, a closed circuit remains between outlets 29 and the power source and, accordingly, any current imbalance (as well as any resulting current surge) present along the conductive lines at the power source will flow into outlets 29. Accordingly, any electrical appliance which is connected to outlets 29 remains susceptible to potentially dangerous electrical shock conditions, which is highly undesirable.
It is important to note that, with the load and power source improperly wired to GFCI 11 as set forth above (i.e., in reverse), the consumer would be unaware of the lack of ground fault protection being provided to outlets 29. Specifically, in the absence of a ground fault condition, the load and outlets 29 would receive power from the power source as if the connections were proper. In addition, test button 33 and reset button 35 would operate as if GFCI 11 were properly wired. As a result, a consumer may power an electrical appliance through outlets 29 with the understanding that the appliance is being provided with ground fault protection when, in fact, GFCI 11 provides the consumer with neither (i) ground fault protection for the appliance nor (ii) notification of reverse wiring.
Accordingly, referring now to
GFCI 111 is identical in all respects with GFCI 11 with one notable distinction. Specifically, GFCI 111 additionally includes a reverse wiring circuit 113 which generates an artificial ground fault condition (which, in turn, trips fault detection circuit 49) when the power source and the load are connected to GFCI 111 in the reverse order, as will be described further below. Reverse wiring circuit 113 includes a reverse wiring resistor RREV (having a value preferably in the range of 68-470 ohms). Reverse wiring resistor RREV extends through sense transformer T1 and is connected at one end to hot line H at a location between metal oxide varistor MOV and first switch K1 and is connected at its other end to neutral line N at a location between metal oxide varistor MOV and conductive terminal 37-2.
In use, with the power source connected to line side terminals 37 and the load connected to load side terminals 39 (i.e., in the proper manner as designated), GFCI 111 operates in a similar manner as prior art GFCI 11. Specifically, in the absence of a ground fault condition, switches K1 and K2 remain closed, thereby enabling AC power to pass from the power source to both the load (at load side terminals 39) and outlets 29. If a ground fault condition is detected along conductive lines H and N, solenoid SOL opens switches K1 and K2. With switches K1 and K2 open, the load as well as outlets 29 are electrically disconnected from the power source and, as a consequence, the ground fault condition. In this manner, GFCI 111 protects both the load and outlets 29 from the ground fault condition, which is highly desirable.
It should be noted that, if GFCI 111 is wired in the proper manner, the first application of power through hot and neutral conductive lines H and N will ultimately travel through reverse wiring resistor RREV. Due to the relatively small resistance of reverse wiring resistor RREV (i.e., in the range of approximately 68-470 ohms), the reverse wiring resistor RREV will instantly overheat and burn out upon the first application of power through the hot and neutral line terminals. Once the reverse wiring resistor RREV burns out, reverse wiring circuit 113 is rendered permanently inoperable.
However, it should be noted that GFCI 111 operates differently than prior art GFCI 11 when the power source is connected to load side terminals 39 and the load is connected to line side terminals 37 (i.e., in the reverse manner as designated). Specifically, by wiring the power source to load side terminals 39, a current is supplied directly into reverse wiring resistor RREV which, in turn, causes sense transformer T1 to detect the presence of a current imbalance in the conductive lines. In response thereto, solenoid SOL opens switches K1 and K2. With switches K1 and K2 open, the load and outlets 29 are electrically disconnected from the power source and, as a result, any appliance connected thereto will not receive power. In this sense, the current which passes through reverse wiring resistor RREV creates an artificial ground fault condition which, in turn, suspends the application of power from the power source to both the load and outlets 29.
With GFCI 111 tripped open upon the detection of the above-described artificial fault condition, it is to be understood that any future depression of reset button 35 will immediately cause reverse wiring circuit 113 to generate another artificial fault signal which will, in turn, trip open GFCI 111 once again. In fact, GFCI 111 will continue to trip open every time reset button 35 is depressed. In this manner, the consumer is provided with an intuitive means of deducing that GFCI 111 was wired incorrectly (i.e., in reverse) and requires immediate attention. Until GFCI 111 is rewired properly, the load and outlets 29 will never be supplied the unprotected power from the power source, which is highly desirable.
Referring now to
The sole distinction between GFCI 211 and GFCI 111 relates to the fact that GFCI 211 includes a reverse wiring circuit 213 which differs slightly in construction from reverse wiring circuit 113 in GFCI 211. Specifically, reverse wiring circuit 213 is similar to reverse wiring circuit 113 in that reverse wiring circuit 213 includes a reverse wiring resistor RREV which extends through sense transformer T1 and is connected at one end to hot line H at a location between metal oxide varistor MOV and first switch K1 and at its other end to neutral line N at a location between metal oxide varistor MOV and terminal 37-2. However, reverse wiring circuit 213 differs from reverse wiring circuit 113 in that reverse wiring circuit 213 additionally includes a fuse 215 which is connected in series with reverse wiring resistor RREV. It is to be understood that fuse 215 is provided in reverse wiring circuit 213 to facilitate the opening (i.e., burning out) process of reverse wiring circuit 213 when GFCI 211 is wired properly.
The versions of the present invention described above are intended to be merely exemplary and those skilled in the art shall be able to make numerous variations and modifications to it without departing from the spirit of the present invention. For example, although the majority of the fireguard circuits described in detail above are shown for use as a safety device for a power cable which comprises three conducting lines, it is to be understood that these fireguard circuits could also be used as a safety device for a power cable which comprises two conducting lines without departing from the spirit of the present invention. All such variations and modifications are intended to be within the scope of the present invention as defined in the appended claims. For example, it should be noted that the particular components which make up the aforementioned embodiments may be interchanged or combined to form additional embodiments.
The present application is a continuation-in-part of presently-pending U.S. patent application Ser. No. 10/972,080, filed Oct. 22, 2004 which in turn claims the benefit under 35 U.S.C. 119(e) of U.S. provisional Patent Application Ser. No. 60/513,469, filed Oct. 22, 2003, both of the above-identified disclosures being incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60513469 | Oct 2003 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10972080 | Oct 2004 | US |
| Child | 11705563 | Feb 2007 | US |
