Testguard circuit

1. FIELD OF USE

The present invention relates generally to electrical safety devices and more particularly to a Testguard circuit with auto monitoring and end-of-life circuitry.

2. DESCRIPTION OF PRIOR ART (BACKGROUND)

Conventional electrical appliances typically receive alternating current (AC) power from a power supply, such as an electrical outlet, through a pair of conducting lines. The pair of conducting lines, often referred to as the line and neutral conductors, enable the electrical appliance, or load, to receive the current necessary to operate.

The connection of an electrical appliance to a power supply by a pair of conducting lines creates a number of potentially dangerous conditions. In particular, there exists the risk of ground fault, leakage currents and grounded neutral conditions in the conducting lines. When a ground fault or leakage current condition occurs it creates an imbalance between the currents flowing in the line and neutral conductors. A grounded neutral condition occurs when the neutral conductor is grounded at the load. A ground fault condition is extremely dangerous and can result in serious injury.

Ground fault and leakage current interrupters include circuit breakers, receptacles, portable and cord mounted protection devices. They may be troubled by false tripping, even though they pass all present industry standards. One cause of false tripping is disconnection of the power to inductive appliances, particularly by unplugging the appliances.

Examples of these appliances include electric shavers, high intensity lamps, and small cooling fans, such as are used for cooling electronic equipment. Unplugging these appliances generates an arc between the plug and the receptacle, resulting in the superimposition of several volts of wide band noise onto the power line. Due to the wide band nature of the noise, even a very small stray coupling capacitance will couple the noise from the power line conductor into the ground fault circuit, causing a false trip.

Grounded neutral detection is provided by a dormant oscillator circuit configuration. The detector circuit includes first and second sensor coils through which the line and neutral conductors of the protected circuit pass. If a load side grounded neutral condition occurs, both cores sensor coils are coupled together to create an oscillating signal that is applied through a coupling capacitor to the above-described operational amplifier followed by a window comparator, this action generates a trip signal.

It has been found that wide band noise induced by load related switching phenomena such as is caused by unplugging inductive appliances causes false tripping of the ground fault interrupter.

Ground fault circuit and leakage current interrupters are well known in the art and are commonly used to protect against ground fault, leakage currents and grounded neutral conditions. In general, GFCI devices sense the presence of ground fault and grounded neutral conditions in the conducting lines and in response thereto, open at least one of the conducting lines between the power supply and the load to eliminate the dangerous condition.

In U.S. Pat. No. 5,177,657, to M. Baer et al, there is disclosed a ground fault interrupter circuit which interrupts the flow of current to a pair of lines extending between a source of power and a load. The ground fault interrupter circuit includes a circuit breaker comprising a normally open switch located in one or both of the lines, a relay circuit for selectively closing the normally open switch, an electronic latch circuit operable in first and second bi-stable states and a fault sensing circuit for sensing the presence of a fault condition in at least one of the lines. The electronic latch circuit causes the relay circuit to close the normally open switch and maintain the normally open switch in its closed position when the electronic latch circuit is in the first bi-stable state. The electronic latch circuit also causes the relay circuit to permit the normally open switch to return to its normally open condition when the latch circuit is in its second bi-stable state. A fault sensing circuit senses the presence of a fault condition in at least one of the lines and causes the electronic latch to latch in its second state upon detection of the fault condition.

In U.S. Pat. No. 5,418,678 to T. M. McDonald, there is disclosed an improved ground fault circuit interrupter (GFCI) device which requires manual setting following initial connection to an AC power source or termination of a power source interruption. The improved GFCI device utilizes a controlled switching device which is responsive to a load power signal for allowing the relay contact sets of the GFCI device to be closed only when power is being made available at the output or load terminals. The controlled switching device preferably comprises an opto-isolator or other type of switching device which provides isolation between the GFCI input and output terminals when the relay contact sets are open. The improved GFCI device may be incorporated into portable units, such as plug-in or line cord units, for use with unprotected AC receptacles.

In U.S. Pat. No. 4,816,957 to L. F. Irwin there is disclosed an adapter unit comprising a moisture resistant housing within which is carried an improved, self-testing ground line fault interrupter device. The improved device is electrically interconnected with a connector carried externally of the adapter housing so that the unit can be plugged directly into a standard duplex outlet of an existing circuit. The apparatus includes circuitry that automatically tests the operability of the device when it is plugged into a duplex outlet without the need for manual manipulation of test buttons or other overt action by the user.

In U.S. Pat. No. 4,578,732 to C. W. Draper et al there is disclosed a wall socket type ground fault circuit interrupter having a pair of sockets, a reset button and a test button that are accessible from the front of the interrupter. The interrupter has latched snap-acting contacts and a novel latching relay structure for maintaining the snap-acting contacts in a circuit making position. The snap-acting contacts permit all of the components including the monitoring toroids (sensing transformers) and the power supply to be respectively located and connected at the load side of the snap-acting contacts so that all of the circuits of the interrupter are de-energized when the contacts snap to a circuit opening position. The snap-acting contact mechanism and relay are provided with structures which provide the interrupter with a trip-free mode of contact actuation and accordingly a tease-proof snap-acting contact operation.

One drawback of GFCI devices of the type described above is that the GFCI device generally includes a large solenoid to selectively open and close the switching device. Specifically, the solenoid generally requires a constant supply of line voltage (approximately 120 volts) in order to switch and sustain the solenoid in its energized state. As a consequence, the solenoid acts as a large power drain source.

UL943 now requires all GFCIs to indicate “end of life” if the device fails to trip when the test button is manually operated. However, even if end-users regularly tested their devices, a GFCI device that did not test properly could nevertheless be reset, and continue to provide power, without providing ground-fault protection. Without a built-in power denial feature, a consumer could erroneously and tragically assume that if power is available, so is protection. Many end users were (and continue to remain) unaware of the need for regular testing, despite manufacturers' warnings; and others, who were aware, were not always conscientious in performing the testing. The latest edition of UL943 has introduced requirements for all GFCI's to include “auto monitoring” (AM) and “end of life” (EOL), whereby the GFCI will test itself at regular intervals (AM), in the case of a GFCI circuit failure provide a user indication and remove itself from service (EOL).

Auto monitoring (AM), end-of-life (EOL) typical events are the ground fault sensing components (toroids and integrated circuit) are open or short circuited; the trip solenoid and/or its control circuit is faulty, or the switching semiconductor (SCR) controlling the trip solenoid control circuit is open or short circuited.

Thus, there is a need for a solenoid of sufficient rating for use in a line voltage GFCI device but with reduced tendency to fail due to high voltages and currents associated with typical line voltages. There is also a need for a ground fault interrupter which does not generate a false trip in response to wide band noise in the protected circuit. There is also a need for such a ground fault circuit with improved immunity to wide band noise which also responds to sputtering arc faults.

There is also a need for a Testguard circuit with manual and automatic testing of the often-failed components of a GFCI and denial of power if testing fails.

It is an object of the present invention to provide a new and improved Testguard Circuit comprising a ground fault circuit interrupter (GFCI) and an auto-monitoring and end-of-life (EOL) circuit.

It is another object of the present invention to provide a Testguard Circuit which senses the presence of ground fault and grounded neutral conditions in the conducting lines, and in response thereto, includes a solenoid which opens at least one of the conducting lines between the power supply and the load.

It is yet another object of the present invention to provide a Testguard Circuit of the type described above wherein the solenoid can be energized and sustained in the energized state with minimal power drain.

It is still another object of the present invention to provide a Testguard Circuit of the type described above wherein the solenoid can be energized and sustained in the energized state with minimal heat build-up.

It is another object of the present invention to provide manual and automatic testing of the Testguard Circuit and provide an end-of-life indication if either the manual or automatic testing fails.

A Testguard Circuit constructed according to this invention for interrupting the flow of current through a pair of lines extending between a source of power and a load comprises a circuit breaker having a switch located in each of the lines, the switch having 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 for selectively moving and maintaining the switch in either the first position or the second position. The GFCI circuit includes an auto monitoring and end of life (AMEOL) module for detecting an end of life condition. The monitoring module includes a simulated ground fault generator for simulating a ground fault; a monitoring logic module; a relay synchronized switch; and an end-of-life switch for disabling the GFCI circuit if certain GFCI component failures are detected. Tested components include a GFCI integrated circuit, a relay shut off switch, and GFCI transformer detecting coils.

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:

FIG. 1 is a schematic circuit diagram of a ground fault circuit interrupter (GFCI) with monitoring features of the present invention.

The following brief definition of terms shall apply throughout the application:

The term “comprising” means including but not limited to, and should be interpreted in the manner it is typically used in the patent context;

The phrases “in one embodiment,” “according to one embodiment,” and the like generally mean that the particular feature, structure, or characteristic following the phrase may be included in at least one embodiment of the present invention, and may be included in more than one embodiment of the present invention (importantly, such phrases do not necessarily refer to the same embodiment);

If the specification describes something as “exemplary” or an “example,” it should be understood that refers to a non-exclusive example; and

If the specification states a component or feature “may,” “can,” “could,” “should,” “preferably,” “possibly,” “typically,” “optionally,” “for example,” or “might” (or other such language) be included or have a characteristic, that particular component or feature is not required to be included or to have the characteristic.

Referring now to FIG. 1 , there is shown a Testguard circuit including ground fault circuit interrupter (hereinafter GFCI) circuit constructed according to the teachings of the present invention, and end of life (herein after monitoring) module.

As will be discussed in detail below, the GFCI automatically protects a load from ground fault conditions upon the initial connection of Input L to Load L and Input N to Load N. Furthermore, once GFCI protects the load from a ground fault condition, GFCI 11 can be reset to protect against further ground fault conditions.

GFCI circuit shown in FIG. 1 includes components arranged as shown and discussed herein. The GFCI circuit includes ganged switches SW 1 and SW 2 , a relay circuit 15 , a power supply circuit 17 , a booster circuit 19 , a fault detection circuit 21 for detecting an electrical fault, a bi-stable electronic latch circuit 23 , a filter circuit 25 , and a test circuit 27 . Also shown in FIG. 1 is a monitoring circuit 101 . The monitoring circuit includes a relay synchronized switch 31 , a simulated ground fault generator 33 , an end of life logic circuit 35 , and End of Life Switch 35 A.

Switches SW 1 and SW 2 are located in the line and neutral conductive lines, respectively, between a power source and a load. Switches SW 1 and SW 2 can be positioned in either of two connective positions. In the first connective position, which is illustrated in FIG. 1 , switches SW 1 and SW 2 are positioned such that the input power source is connected to the load and also connected to booster circuit 19 . In the second connective position, which is the opposite position illustrated in FIG. 1 , switches SW 1 and SW 2 are positioned such that the input power source is connected to the load but not to booster circuit 19 . In both positions, the input power source is connected to power supply 17 .

Relay circuit 15 acts to selectively position switches SW 1 and SW 2 in either its first connective position or its second connective position. Relay circuit 15 comprises a solenoid RL 1 a , transistor Q 2 , Zener ZD 2 , Resistors R 4 and R 21 .

Solenoid RL 1 A is ganged to the circuit breaker contacts of switches SW 1 and SW 2 and is responsible for selectively controlling the connective position of switches SW 1 and SW 2 . Before power is applied to GFCI 11 , solenoid RL 1 A positions switches SW 1 and SW 2 are in the first connective position as shown. When solenoid RL 1 A is energized, solenoid RL 1 A positions switches SW 1 and SW 2 to the second connective position.

It should be noted that the particular construction of solenoid RL 1 A is unique for conventional GFCI devices. In particular, RL 1 A is significantly small in size and requires less power than most solenoids used in prior art GFCI devices. Specifically, solenoid RL 1 A has a coil resistance of approximately 5,000 ohms. As a result of the unique construction of solenoid RL 1 A, line voltage (approximately 120 volts RMS) must be directly supplied to solenoid RL 1 A in order to initially energize solenoid RL 1 A.

Once energized, a minimum constant voltage of approximately 28 volts DC is required to be supplied to solenoid RL 1 A in order to keep it in its energized state. As will be discussed in detail below, booster circuit 19 provides the line voltage to initially energize solenoid RL 1 A from its de-energized state and power supply circuit 17 supplies the minimum constant voltage of approximately 28 volts to maintain solenoid RL 1 A in its energized state. The reduction in the voltage required to maintain solenoid RL 1 A in its energized state (approximately 83 volts) significantly reduces the power drain of RL 1 A and also reduces heat build-up which would minimize solenoid RL 1 A useful life.

Transistor Q 2 controls current flow through energized solenoid RL 1 A. When transistor is “off”, current through solenoid RL 1 A is disabled and RL 1 A is deenergized. When transistor Q 2 is “on”, current flows through solenoid RL 1 A, energizing RL 1 A.

Power supply circuit 17 provides power for the GFCI circuit. Power supply circuit 17 comprises rectifier diodes D 15 , D 17 , D 19 , voltage dropping resistors R 9 and R 17 , and capacitor C 8 . It will be appreciated that capacitor C 8 reactance limits the current flowing though rectifiers D 15 and D 17 . Also shown in FIG. 1 , is Varistor MOV 1 which has a value of 150 volts and acts to protect against a voltage surge from the AC power source.

Silicon rectifiers D 15 , D 17 and D 19 convert the AC current in the line from the power source into a DC current. Voltage dropping resistors R 9 and R 17 limit the constant input voltage supplied to solenoid RL 1 A for the reasons noted above. Capacitor C 8 limits the current flowing though rectifiers D 15 and D 17 and the constant voltage supplied to solenoid RL 1 A. It will be appreciated that an objective of the capacitive supply circuit arrangement minimizes heat buildup in a confined space, optimizes relay coil SOL 1 energy to substantially increase the switch contact forces, providing for a smaller, more rugged and higher product performance for the GFCI.

Booster circuit 19 to provide a temporary voltage sufficient to initially energize solenoid RL 1 A from its de-energized state. Booster circuit 19 comprises silicon rectifier D 16 and a surge limit resistor R 18 . When switch SW 1 is in its first position and upon the application of power to GFCI, rectifier D 16 provides an instant DC voltage, approximately 126V DC average, to solenoid RL 1 A causing solenoid RL 1 A to energize which, in turn, causes solenoid RL 1 A to move switches SW 1 and SW 2 to their second connective position. When switches SW 1 and SW 2 are moved to their second connective position, booster circuit 19 is disconnected from the power source. Resistor R 18 protect rectifier D 16 from over currents.

Fault detection circuit 21 detects both ground fault and grounded neutral conditions in the conductive lines when switches SW 1 and SW 2 are in their second connective position. Fault detection circuit 21 comprises a sense transformer T 1 , a grounded neutral transformer T 2 , a coupling capacitor C 7 , a noise suppression capacitor C 6 , a feedback resistor R 3 , and a ground fault interrupter integrated circuit GFCI IC.

Sense transformer T 1 senses an electrical fault such as the current differential between the line and neutral conductive lines and upon the presence of a ground fault condition, transformer T 1 induces an associated output from its secondary windings. Grounded neutral transformer T 2 acts in conjunction with transformer T 1 to sense the presence of grounded neutral conditions and, in turn, induce an associated output. Coupling capacitor C 7 acts to couple the AC signal from the secondary winding of transformer T 1 to GFCI IC. Capacitor C 6 acts to prevent fault detection circuit 21 from operating in response to line disturbances such as electrical noise and lower level faults.

Together capacitor C 6 and resistor R 3 act to set the minimum fault current at which fault detection circuit 21 provides an output signal to latch circuit 23 . GFCI IC amplifies a fault signal generated by transformer T 1 and generates an output pulse on pin 5 to activate latch circuit 23 .

Upon detection of a ground fault or grounded neutral condition GFCI IC generates an output pulse on pin 5 to activate latch circuit 23 . Activated Latch Circuit 23 deactivates or de-energizes solenoid RL 1 A. Latch circuit 23 comprises a silicon-controlled rectifier SCR 1 operable in either a conductive or a non-conductive state, and a noise suppression capacitor C 2 .

SCR 1 selectively turns on and off transistor Q 2 in relay circuit 15 via Relay Synchronized Switch 31 , discussed in more detail herein. Noise suppression capacitor C 2 acts to prevent rectifier SCR 1 , when in its nonconductive state, from firing as a result of electrical noise. Reset switch is a conventional push-in type switch and when depressed, effects the removal of holding current from the anode of rectifier SCR 1 , causing rectifier SCR 1 to turn off when it is in its conductive state.

Test circuit 27 provides a means of testing whether the GFCI circuit is functioning properly. Test circuit 27 comprises a test switch of conventional push-in type design. When the test switch is depressed to energize test circuit 27 , resistor R 12 provides a simulated fault current to transformer T 1 which is similar to a ground fault condition.

In use, GFCI 11 functions in the following manner. Prior to initial connection, switches SW 1 and SW 2 are normally in their first connective position as shown in FIG. 1 .

Upon initial connection of GFCI 11 at one end to the load and at the other end to the power source, line voltage of approximately 120 volts RMS is applied to solenoid RL 1 A through booster circuit 19 and energizes solenoid RL 1 A. Once solenoid RL 1 A is energized, solenoid RL 1 A causes switches SW 1 and SW 2 to move into their second connective position (opposite the position shown in FIG. 1 ), thereby eliminating the supply of power into solenoid RL 1 A from booster circuit 19 . However, since a minimum constant 28 volts is supplied to solenoid RL 1 A from power supply circuit 17 , solenoid RL 1 A is maintained in its energized state.

With solenoid RL 1 A maintained in its energized state rectifier SCR 1 is in a nonconductive state and transistor Q 2 is on, which enables current to pass to solenoid RL 1 A. Upon the detection of a ground fault or grounded neutral condition, fault detection circuit 21 sends a gate signal to rectifier SCR 1 causing rectifier SCR 1 to be in a conductive state which, in turn, turns off transistor Q 2 . With transistor Q 2 off, current does not pass through solenoid RL 1 A and therefore solenoid RL 1 A becomes de-energized. Once de-energized, solenoid RL 1 A causes switches SW 1 and SW 2 to return to its first connective position, thereby cutting off power from the power source to the load.

Once the fault condition is removed, the GFCI circuit can be reset by manually depressing the RESET switch. Depression of RESET switch effects the removal of SCR 1 holding current, which turns off rectifier SCR 1 . This, in turn, turns transistor Q 2 back on when the RESET switch is released which enables solenoid RL 1 A to become re-energized.

With the load plugged into the power source, if there is a loss of power at the power source, solenoid RL 1 A will become de-energized, moving switches SW 1 and SW 2 back to their first connective position. When power is subsequently restored, solenoid RL 1 A will become re-energized again, which in turn moves switches SW 1 and SW 2 to their second position.

Auto Monitoring and End of Life

The monitoring module 101 includes a relay synchronized switch 31 , a simulated ground fault generator 33 , an auto monitoring and end of life circuit 35 , and End of Life Switch 35 A.

Simulated ground fault generator circuit 33 includes the logic and means necessary to simulate a periodic ground fault.

Relay Synchronized Switch 31 includes the logic and means necessary to temporarily turn off the normal GFCI fault detection described above when the simulated ground fault generator circuit 33 simulates a periodic ground fault for the purpose of testing the ground fault detection circuit. The tested GFCI components include the sense transformer T 1 , the grounded transformer T 2 , the GFCI IC and the bi-stable electronic latch circuit SCR 1 .

The auto-monitoring and EOL logic (monitoring) circuit 35 measures a predetermined number of simulated GFCI fault detection failures. Upon determining the GFCI fault detection circuitry is defective the EOL switch 35 A is activated, thus turning off Q 2 and solenoid RL 1 a . In addition, the monitoring circuit includes the logic and means for auto-monitoring the monitoring logic module and the EOL switch.

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. 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. For example, the AMEOL circuitry described may be used in any suitable device that requires auto monitoring and end of life features.