Abstract:
A line-side circuit interrupter protection system monitors the current flowing in a circuit in order to determine whether any current is flowing outside of the circuit upstream of the point at which a power supply is connected to a plurality of circuits. The system is located between the power supply and the main circuit panel, which is advantageous in certain applications in which an auxiliary power supply is used when a utility power supply is unavailable. In the event that the system detects current flowing outside of the circuit, the circuit will be broken to eliminate any potentially unsafe conditions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional application Ser. No. 61/711,948, filed Oct. 10, 2012, the entire contents of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to the field of circuit interrupters. More particularly, the present invention relates to a ground fault circuit interrupter on the line side of a main electrical panel, which is before the point at which the neutral of the power supply is connected to the system grounding conductor (commonly known as the bonding point). The bonding point for utility power is typically accomplished at the main electrical panel, also known as the service entrance panel. This panel ma be used in conjunction with a transfer switch or power inlet for use with an auxiliary power supply such as a portable generator. In particular, such a device would be useful when powering a structure from an unbonded power supply such as utility power supply or a floating-neutral portable generator. 
     2. Discussion of the Related Art 
     Ground fault circuit interrupters (GFCI) are commonly used in a number of applications where there is potential for current to flow outside of a load. All known current ground fault protection is located on the load side, meaning that it is located downstream from the bonding point, between the main electrical panel and the user. For example, it is very common for outlets or switches to contain GFCI devices within the receptacle. This means that the current flows from an external source first to the main electrical panel, and flows next to the GFCI receptacle. The GFCI receptacle provides a single, hot supply of current. When properly functioning, there is a single return supply of current that flows through the receptacle. However, in certain dangerous scenarios, at least a portion of the current is routed outside the device that is plugged into the outlet, which creates two current returns: one through the outlet and one outside the outlet. When this occurs, the GFCI is immediately actuated to cut off the hot supply of current such that the electrical circuit is broken. These types of GFCI outlets disconnect the power supply in the event that excessive current flows to the ground. One common application for these types of outlets is in settings where there is frequent water use. 
     A typical GFCI device measures the amount of current flowing from the outlet in comparison with current returning to the outlet. In the event that there is less flow returning (meaning some of that current is flowing through another source to the ground), the hot source is stopped, which prevents further flow of current outside of the circuit. This is an effective means to prevent potentially dangerous situations because the hot source is the only supply of current, and ending such flow will break the electrical circuit. 
     However, this configuration is ineffective where a diversion of power occurs upstream of the main electrical panel. When properly functioning, there is a single return of current from the main electrical panel to the power supply; however, in the event of a diversion in current upstream of the main electrical panel, there are two current paths: one through the wiring to the main electrical panel and one through the diversion to the ground. The traditional load-side GFCI configuration that cuts off the power supply is ineffective on an upstream, line side of the circuit because shutting off the hot supply after the point of diversion does not break the circuit. Rather it would supply the entire flow of current through the diversion. A configuration in which this situation may occur is when an external power supply, such as a portable generator, is present and an individual accidentally interferes with the current flow between the power supply and the main electrical panel. 
     What is needed, therefore, is a current interrupter device that may be installed between the power supply and the main electrical panel such that current flow may be stopped when a diversion upstream of the main electrical panel occurs, such as when an individual accidentally interferes with the supply of power prior to the point at which power is supplied to the main electrical panel. 
     BRIEF DESCRIPTION OF THE INVENTION 
     By way of summary, the present invention is a ground fault circuit interrupter device that is located on the upstream, line side of the circuit prior to the point at which the power supply is connected to the main electrical panel. 
     In accordance with a first aspect of the invention, a GFCI device may be located in a power inlet box connected in a circuit adapted to be powered by an auxiliary power supply, such as a portable electrical generator. The circuit will have hot, neutral, and ground conductors. The power inlet box may be connected to a transfer switch or transfer panel that functions to supply power from the auxiliary power supply to specific circuits. Such a transfer switch is commonly used when the primary utility power supply is lost and an emergency energy supply is needed. The transfer switch is connected to at least one circuit of the main circuit panel. In order to complete the circuit, the return current flows back into the main circuit panel, which is subsequently connected to the transfer switch, with a connection back through the power inlet box, and lastly back to the power supply. In operation, the GFCI will measure the amount of current entering the power inlet box and compare this current to the current returning from the power inlet box. In the event that these values are not the same, such as when there is a power diversion upstream of the power inlet box, the GFCI cuts the neutral so that current returning on the neutral will be interrupted. This effectively breaks the circuit to cease the flow of current elsewhere and, in particular, to the current diversion. The supply of a conduction path via the hot conductor may also be disconnected by the GFCI device, since a circuit with a voltage potential present on the hot supply without a connected neutral may be detrimental to the circuit. 
     Although this system will normally be most applicable to systems utilizing a temporary, emergency power supply such as a portable generator, it may also be applicable with other types of incoming power if the power is directed through an inlet box or the like. The GFCI device may also be located at other points on the upstream, line side of the circuit such as at a transfer switch or at the main electrical panel upstream of the point at which power is supplied to the circuits in the main electrical panel. 
     According to one embodiment of the invention, a circuit interrupter system to disconnect a power supply from a load is disclosed. The power supply has a hot conductor and a neutral conductor, and the neutral connector is electrically connected to an earth ground at a bonding point between the power supply and the load. The circuit interrupter system includes a current sensor generating a signal corresponding to the amplitude of current conducted between the power supply and the load, a switch operatively connected between the power supply and the bonding point, and a control circuit configured to generate the control signal as a function of the signal from the current sensor. The current sensor is operatively connected between the power supply and the bonding point, and the switch is configured to connect the neutral conductor of the power supply to the bonding point in a first position, to disconnect the neutral conductor of the power supply from the bonding point in a second position, and to receive a control signal to selectively operate in one of the first position and the second position. 
     According to another aspect of the invention, the current sensor may include a toroid through which the hot conductor and the neutral conductor are passed and a coil wound around the toroid. The signal is a current inductively coupled into the coil as a function of a differential in the amplitude of current present in the hot conductor and the amplitude of current present in the neutral conductor. The control circuit may include a driver circuit configured to receive the current from the coil, to generate the control signal to operate the switch in the first position when the current from the coil is less than a predefined threshold, and to generate the control signal to operate the switch in the second position when the current from the coil is greater than the predefined threshold. 
     According to yet another aspect of the invention, the current sensor may include a first current sensor generating a first signal corresponding to the amplitude of current present on the neutral conductor and a second current sensor generating a second signal corresponding to the amplitude of current present on the hot conductor. The control circuit may include a comparator circuit configured to generate the control signal as a function of the first signal and the second signal. The comparator circuit generates the control signal to operate the switch in the first position when the first signal is equal to the second signal and to operate in the second position when the first signal is not equal to the second signal. 
     According to still another aspect of the invention, the circuit interrupter system includes a transfer switch having a housing with a first set of inputs configured to receive the hot conductor and the neutral conductor from a power supply and a second set of inputs configured to receive a hot conductor and a neutral conductor from a second power supply. The current sensor, the switch, and the control circuit may each be contained in the housing of the transfer switch. Optionally, the circuit interrupter system may include an inlet box configured to receive the hot conductor and the neutral conductor from the power supply, and the current sensor, the switch, and the control circuit may be contained in the inlet box. 
     According to yet another aspect of the invention, the switch is further configured to connect the hot conductor of the power supply to the load in the first position and to disconnect the hot conductor of the power supply from the load in the second position. The power supply may include a second hot conductor and the switch may be further configured to connect the second hot conductor of the power supply to the load in the first position and to disconnect the second hot conductor of the power supply from the load in the second position. 
     According to another embodiment of the invention, a circuit interrupter protection system for a power supply includes a connection point at which the power supply is connected to a plurality of electrical circuits, a hot conductor connected between the power supply and the connection point, a neutral conductor connected between the power supply and the connection point, and a circuit interrupter located between the power supply and the connection point. The hot conductor and the neutral conductor are connected to the circuit interrupter. The circuit interrupter functions to disconnect the neutral conductor from the connection point in the event of a current differential between the hot conductor and the neutral conductor to thereby break the circuit and stop the flow of current on the hot conductor. 
     According to another aspect of the invention, the circuit interrupter is located within an enclosure located between the power supply and the connection point. Optionally, the connection point is a service entrance panel for a building and the circuit interrupter is mounted to the service entrance panel. 
     These and other features and aspects of the present invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating a representative embodiments of the present invention, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A clear conception of the advantages and features constituting the present invention, and of the construction and operation of typical mechanisms provided with the present invention, will become more readily apparent by referring to the exemplary, and therefore non-limiting, embodiments illustrated in the drawings accompanying and tanning a part of this specification, wherein like reference numerals designate the same elements in the several views, and in which: 
         FIG. 1  is a block diagram of an exemplary line side circuit protection system according to one embodiment of the invention; 
         FIG. 2  is a block diagram representation of one embodiment of a circuit interrupter as shown in  FIG. 1 ; and 
         FIG. 3  is a schematic representation of another embodiment of a circuit interrupter as shown in  FIG. 1 . 
     
    
    
     In describing the embodiment of the invention which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word connected, attached, or terms similar thereto are often used. They are not limited to direct connection but include connection, through other elements where such connection is recognized as being equivalent by those skilled in the art. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The various features and advantageous details of the subject matter disclosed herein are explained more fully with reference to the non-limiting embodiment described in detail in the following description. 
     As shown in  FIG. 1 , one embodiment of the circuit interrupter protection system  10  in accordance with the present invention includes a power supply  15 , a power inlet box  20 , a transfer switch  25 , a main electrical panel or service entrance  30 , and a circuit interrupter  60 . The circuit connections between each component include hot (L), neutral (N), and ground (G) conductors. The hot conductor  17  from the power supply  15  will carry the supply current (I L )  50 , while the neutral conductor N will carry the return current (I N )  40 . The power supply  15  may be a portable generator, backup generator, or any other type of power supply having an electrical connection that passes through a power inlet box  20  or other connection device located upstream of the main electrical panel  30 . 
     The supply current (I L )  50  flows from the power supply  15  to the power inlet box  20 , through the circuit interrupter  60  and to the transfer switch  25 . According to the illustrated embodiment, the transfer switch  25  includes a first set of inputs  26  configured to receive the hot conductor  17  and the neutral conductor  18  from the power source  15  and a second set of inputs  27  configured to receive the hot conductor  11  and the neutral conductor  12  from another power source, such as utility power. The transfer switch  25  alternately connects the hot and neutral conductors from one of the power sources to the loads connected to the transfer switch  25 . It is contemplated that the transfer switch may be controlled manually or automatically. As illustrated, the transfer switch  25  may be included in a separate enclosure. Optionally, the transfer switch  25  may be integrated in the main panel  30 . The transfer switch  25  may be configured such that it supplies current to all of the circuits in the main panel  30 , or, more typically, to selective circuits based on the needs as identified by the user. According to yet another embodiment of the invention, each of the power sources may include two hot leads L, each supplying a voltage to the loads. In a split-phase distribution system a first hot lead L 1  and a second hot lead L 2  each provide a voltage having the same amplitude but are one hundred eighty degrees out of phase. 
     In a power distribution system, the neutral conductor from the power source is bonded to an earth ground  13  at a single point, referred to herein as a bonding point  33  within the distribution system. The bonding point  33  may be, for example, a ground bar in the main panel  30 . The ground conductor  19  from the power supply  15  and each of the neutral conductors  18 ,  12  from the power source  15  and the utility grid, respectively, are connected to the bonding point  33 . As illustrated, the ground conductor  19  is solidly connected to the bonding point  33 . Each of the neutral conductors are connected, for example, via intermediate terminals and/or switched connections (not shown) in the main panel  30  and/or the transfer switch  25  according to the application requirements. The bonding point  33  is, in turn, connected to the earth ground  13 . 
     Current returning from the load circuits flows back to the power supply  15  via the neutral conductor  18 . The return current (I N )  40  is conducted from the main panel  30  back through the transfer switch  25 , the power inlet box  20 , and the circuit interrupter  60  before returning to the power supply  15 . As illustrated, the circuit interrupter  60  is located in the power inlet box  20 . Optionally, the circuit interrupter  60  may be included in the transfer switch  25  or in the main panel  30  as long as the neutral conductor  18  from the power supply  15  is connected through the circuit interrupter  60  prior to being connected to the bonding point  33 . 
     The circuit interrupter  60  is configured to selectively connect the neutral conductor  18  of the power supply  15  to the bonding point  33 . The circuit interrupter  60  includes a current sensor  62  monitoring the current flowing on the hot conductor  17  and the neutral conductor  18  between the power supply  15  and the load. If the power source  15  includes multiple hot conductors  17 , the current sensor  62  may be configured to monitor the current flowing on each of the hot conductors  17  and the neutral conductor  18  between the power supply  15  and the load. A control circuit  70  receives a signal from the current sensor  62  corresponding to this monitored current. The control circuit  70  is configured to generate a signal  68  which, in turn, opens and/or closes a switch  66  to connect the neutral conductor  18  to the bonding point  33 . It is contemplated that the switch  66  may be an electromechanical device, such as a relay, a solid state device, such as a transistor, or a combination thereof. As illustrated, the switch  66  may also be used to connect/disconnect the hot lead  17  from the load. 
     In the event there is exterior contact with the conductors connecting the power supply  15  to the power inlet box  20 , some of the supply current (I L )  50  on the hot conductor  17  may be diverted through an alternate conduction path  90 . A portion of the supply current  50  becomes diverted current (I D )  45  conducted through the alternate conduction path  90  and the remainder of the supply current  50  is illustrated as residual current (I R )  55  conducted on the hot conductor  17  beyond the diversion point for supply to power inlet box  20 . When there is no diverted current  45 , the supply current  50  flows in an uninterrupted manner to power inlet box  20 , and the return current  40  on the neutral conductor  18  is equal to the supply current  50  on the hot conductor  17 . However, when there is diverted current  45  via the alternate conduction path  90 , such as by a person standing on the ground coming into contact with the hot conductor  17 , the residual current  55  flowing on the hot conductor  17  will not equal the return current  40  on the neutral conductor  18 . The residual current  55  flows through the power inlet box  20  and the circuit interrupter  60  on the hot conductor  17  at the same time the return current  40  flows through the power inlet box  20  and the circuit interrupter  60  on the neutral conductor  18 . 
     In operation, the current sensor  62  in the circuit interrupter  60  measures the amount of residual current  55  entering the inlet box  20  from the power supply  15  on the hot conductor  17 . Additionally, the current sensor  62  measures the return current  40  entering the power inlet box after flowing through the circuits in the main panel  30  and back through the transfer switch  25 . This return current  40  continues from the inlet box  20  and returns to the power supply  15 . A signal, or multiple signals,  64  corresponding to the amplitude of current is provided from the current sensor  62  to a control circuit  70 . When the residual current is not equal to the return current, this indicates that a portion of the current is being diverted through the alternate conduction path  90 . The control circuit  70  generates a control signal  68  which causes a switch  66  to disconnect the neutral conductor  18  between the power source  15  and the bonding point  33  thereby breaking the electrical circuit and interrupting current flow from the power source  15  via either the hot conductor  17  or the alternate conduction path  90 . 
     According to one embodiment of the invention, the current sensor  62  generates one signal  64  corresponding to a differential in the amplitude of current in the hot conductor  17  and the neutral conductor  18 . With reference to  FIG. 2 , the current sensor  62  may be in the form of a coil  82  wound about a toroid  80 . Each of the hot conductor  17  and the neutral conductor  18  are passed through the toroid  80 . Current conducted in either conductor  17 ,  18  establishes a magnetic field about the conductor. The toroid  80  is selected from a suitable core material to conduct the magnetic field which, in turn, induces a current in the coil  82  wound around the toroid. The direction of current flow in the hot conductor  17  and the neutral conductor  18  is opposite of each other. As a result, magnetic fields of opposite polarity are established in the toroid  80 . The amplitude of the magnetic field and the resulting current induced in the coil  82  is proportional to the amplitude of current flowing in the conductor passing through the toroid  80 . Thus, if the amplitude of current in each of the hot conductor  17  and the neutral conductor  18  is the same, each establishes a magnetic field of equal amplitude and opposite polarity, resulting in a magnetic field having a net amplitude of zero and no current induced in the coil  82 . If there is a difference in the amplitudes of the current in the hot conductor  17  and the neutral conductor  18 , a magnetic field having a non-zero amplitude is established in the toroid  80 , resulting in a current being induced in the coil  82 . The control circuit  70  may monitor the amplitude of current being generated on the coil  82  and define a set point, above which the control signal  68  is set to open the switch  66 . 
     According to another embodiment of the invention, the current sensor  62  may include multiple sensors, each configured to generate a signal  64  corresponding to the amplitude of current flowing in one of the conductors. With reference to  FIG. 3 , the current sensor may include a current sense resistor  84  and an amplifier  86  operatively connected to each conductor  17 ,  18  to generate a signal  64  corresponding to the amplitude of current in the corresponding conductor  17 ,  18 . Each current signal  64  is provided to the control circuit  70  which is configured to generate the control signal  68  to open the switch  66  when the difference in amplitude between the control signals  68  exceeds a predefined set point. It is contemplated that still other current sensing circuits, devices or sensing arrangements may be utilized to sense a current differential and generate a control signal without deviating from the scope of the invention. 
     Upon receiving the signal  64  from the current sensor  62 , the control circuit  70  determines whether to interrupt the current flowing on the neutral conductor  18 . The control circuit  70  may include, for example, one or more operational amplifiers comparing a single input signal  64 , such as the current signal from the toroidal coil  82 , against a voltage reference to determine whether the current differential in the hot conductor  17  and the neutral conductor  18  exceeds a maximum predetermined level. Optionally, one or more operational amplifiers may compare multiple input signals  64 , first against each other, for example, with independent current sense resistors  84  and subsequently compare the difference against a voltage reference to determine whether the current differential in the hot conductor  17  and the neutral conductor  18  exceeds a maximum predetermined level. According to yet another embodiment of the invention, the control circuit  70  may include a processing device, such as a microprocessor, configured to receive the current signal, or signals.  64  as an input and generate a control signal  68  responsive to the current signal, or signals,  64 . It is contemplated that still other combinations of analog and/or digital electronic devices may be utilized to monitor the current signal  64  and generate a control signal  68  without deviating from the scope of the invention. 
     The control signal  68  is used to control a switch  66  to selectively disconnect the neutral lead  18  between the power source  15  and the bonding point  33 . According to one embodiment of the invention, a relay may be used. The contacts of the relay are connected in series with the neutral lead  18  and the control signal  68  is connected to the solenoid controlling the relay. Optionally, a power electronic device, such as a power transistor may be used. The neutral conductor  18  may be connected in series with the transistor and the control signal  68  may be connected, for example, to the gate pin of the transistor to enable/disable the transistor and open/close the conduction path of the neutral conductor  18 . According to yet another embodiment of the invention, a relay having multiple contacts or multiple power electronic devices may be used to disconnect both the hot lead  17  and the neutral lead  18  between the power source  15  and the bonding point  33  responsive to the control signal  68  in order to prevent potential damage to the loads that may result from leaving a hot conductor connected while disconnecting the neutral conductor. 
     Although the above embodiment provides that the circuit interrupter  60  is contained within the inlet box  20 , in alternative embodiments the circuit interrupter  60  may be located within other portions of the circuit. For example, the circuit interrupter  60  may be contained in the main panel  30 , the transfer switch  25  or other panel, subpanel, enclosure or housing, or included in a utility meter. Regardless of where the circuit interrupter  60  is located, it will measure the residual current  55  and return current  40  at a location upstream of the bonding point  33  and prevent ground fault injury to a person that comes in contact with the conductors for the power source  15  coming into a building. 
     It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention.