Abstract:
Apparatus for detecting an overheating condition at an electrical power device and automatically breaking the circuit when the temperature exceeds a setpoint value. In various configurations the device is a receptacle adapted to be used in a wall mounted box or a receptacle unit that is plugged into an existing receptacle and supported in place by the existing receptacle. A temperature switch is wired parallel to a normally open test switch on a ground fault circuit interrupter or other circuit interrupting device. The temperature switch is responsive to the temperature local to the receptacle, such as is caused by poor connections to or in the receptacle. The temperature setpoint is less than the melting temperature of the insulation of the electrical wiring. Upon actuation of the temperature switch, the circuit interrupting device is latched in a tripped position until the device is reset for reuse.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of Invention 
         [0004]    This invention pertains to an electrical device that provides power to an electrical appliance. More particularly, this invention pertains to an electrical receptacle that interrupts the power circuit to the electrical appliance based on the ambient temperature proximate the electrical receptacle. 
         [0005]    2. Description of the Related Art 
         [0006]    Every year there are thousands of electrical fires in homes. Hundreds die every year in these fires, with many more injured. Some of these fires are caused by electrical system failures and defective appliances. But, many more of these fires are caused by the misuse and poor maintenance of electrical appliances, incorrectly installed wiring, and overloaded circuits and extension cords. 
         [0007]    Electrical circuits are protected from overcurrent conditions by circuit breakers. These circuit breakers are centrally located. Fixed wiring runs from the circuit breakers to power receptacles located throughout the home. The typical receptacle is configured to receive two plugs from electrical devices. It is not uncommon for people to use adapters in order to plug more than two electrical devices into such a receptacle. Such misuse, although not commonly resulting in an overcurrent condition that will trip a circuit breaker, often exceeds the capabilities of the adapter, which may result in overheating of the adapter and/or the receptacle. Also, the adapter or one of the multitude of electrical plugs may have a high resistance connection, which results in resistance heating of the connection. Another type of misuse is the continued use of frayed or damage electrical cords. Without the protection of the circuit breaker tripping the circuit, such misuse can result in an electrical fire. 
         [0008]    Ground fault circuit interrupters (GFCIs) are becoming more common. Ground fault circuit interrupters monitor the circuit for ground faults, and trip the circuit when one is detected. A ground fault is a condition where the current flowing through the hot lead to the device is not equal to the current flowing through the neutral lead to the device. When the two current values are not equal, then some amount of current must be flowing through a ground connection, which indicates a potential electrical safety hazard. Although GFCIs provide electrical safety to people, GFCIs do not protect against hazards that typically result in electrical fires. 
         [0009]    Arc fault circuit interrupters (AFCIs) are also becoming common. Arc fault circuit interrupters monitor the circuit for electrical arcs, such as caused by loose connections or frayed wiring that causes a short circuit. The AFCI typically reacts to an arcing condition before a traditional circuit breaker, which operates based on current flow or thermal heating of a trip element. Arc fault circuit interrupters are an important line of defense against electrical fires, but AFCIs do not detect all conditions that result in electrical fires. 
         [0010]    Attempts have been made to provide a device useful for reducing the number of electrical fires. For example, U.S. Pat. No. 7,400,225 discloses a receptacle that includes a fusible link that interrupts the circuit upon detecting an overheating condition, such as a glowing contact or series arcing. The fusible link opens the circuit permanently, thereby requiring replacement of the receptacle in order to return the connected devices back to service. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    A temperature switch is incorporated in a ground fault interrupter (GFI) or other circuit interrupter in such a way that the test feature of the interrupter is actuated upon detection of an elevated ambient temperature, thereby causing the interrupter to break the circuit for the load. The broken circuit is latched until a reset switch is actuated. The temperature switch has a tripping setpoint between the maximum operating rating of the cable and/or wiring and the insulation melting point. In this way, potentially hazardous conditions that do not involve current flow sufficient to trip upstream circuit breakers are prevented from developing into a hazardous condition. The temperature switch is responsive to the ambient temperature proximate the receptacle. 
         [0012]    In one embodiment, the temperature switch is a normally open switch with the switch contacts in parallel with the normally open contacts of the test switch of the interrupter. The temperature switch is positioned proximate the receptacle housing in such a manner that the temperature switch is responsive to heat generated from the various electrical connections within and/or plugged into the receptacle housing. In various embodiments the receptacle is configured for permanent mounting with connections to the service wiring or as a portable unit that plugs into another receptacle. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0013]    The above-mentioned features of the invention will become more clearly understood from the following detailed description of the invention read together with the drawings in which: 
           [0014]      FIG. 1  is a schematic diagram of one embodiment of a heat actuated interrupter receptacle; 
           [0015]      FIG. 2  is a perspective view of one embodiment of a heat actuated interrupter receptacle; and 
           [0016]      FIG. 3  is a perspective view of another embodiment of a heat actuated interrupter receptacle. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Apparatus for interrupting an electrical circuit upon detecting a high temperature is disclosed. The high temperature is greater than the wire/cable temperature rating and less than the melting temperature of the insulation. The high temperature is often caused by misuse of the receptacle  102 , such as by using an adapter to plug multiple devices into the receptacle  102  and/or using frayed or damaged cords. 
         [0018]      FIG. 1  illustrates a schematic diagram of one embodiment of a heat actuated interrupter receptacle device  100 . A receptacle  102  houses an interrupting module  104  that includes a set of input connections  112 , such as those that connect to a power source, and a set of output connections  110 , such as those of a receptacle socket. The receptacle  102  also includes a test switch  106  that is connected to the module  104 . Connected in parallel with the test switch  106  is a temperature switch  108 . 
         [0019]    The module  104 , in one embodiment, is a ground fault interrupting (GFI) module that breaks, or interrupts the circuit between the input connections  112  and the output connections  110 . Corresponding ones of the input connections  112  are connected to the output connections  110  to form a circuit between the input  112  and the output  110  during normal, or non-tripped, operation. The module  104  interrupts the circuit upon detection of a ground fault condition. A ground fault condition is a current imbalance between the hot H and neutral N connections of the input connections  112 , such as when the current flow through the hot H connection  110 -H is greater than the current flow through the neutral N connection  110 -N. In a three-conductor system, such a condition can occur when a portion of the current flowing through the hot H lead  110 -H also flows through the ground G lead  110 -G or through another ground connection, such as an electrical earth. The test switch  106  in such an embodiment simulates an imbalance, or a ground fault, and causes the GFI module  104  to trip, thereby interrupting the circuit connected to the output connections  110 . 
         [0020]    The module  104 , in another embodiment, is a circuit interrupting module that breaks, or interrupts the circuit between the input connections  112  and the output connections  110 . The circuit interrupting module  104  includes a relay or circuit breaker that breaks the circuit between the input connections  112  and the output connections  110 . In such an embodiment, the test switch  106  actuates the relay or circuit breaker and causes the circuit interrupting module  104  to trip, thereby interrupting the circuit connected to the output connections  110 . 
         [0021]    A temperature switch  108  is connected in parallel with the test switch  106 . In the illustrated embodiment, the test switch  106  is a normally open switch and the temperature switch  108  is also a normally open switch before it is actuated by a sensed high temperature. In this way, either the temperature switch  108  or the test switch  106  will actuate the module  104  and interrupt the circuit between the input connections  112  and the output connections  110 . In another embodiment, the test switch  106  is a normally closed switch that opens to test. In such an embodiment, the temperature switch  108  is a normally closed switch in series with the test switch  106 . 
         [0022]    The temperature switch  108  includes a temperature sensor  118  that is responsive to the ambient temperature around the receptacle  102 . In one embodiment, the temperature switch  118  is a mercury switch in which the mercury level in a capillary rises with increasing temperature. When the temperature setpoint is reached, the mercury bridges a gap between two conductors, thereby causing the temperature switch  108  to close and actuate the module  104 . In other embodiments, the temperature switch  108  includes other temperature sensors that cause the temperature switch  108  to actuate upon detection of a high temperature. 
         [0023]    The temperature switch  108  is responsive to a high local temperature. Typically, the temperature rating of cables and wiring used for a receptacle  102  is 75 degrees Centigrade. The insulation of such cables and wiring often has a melting point of 95 degrees Centigrade. In one embodiment, the temperature switch  108  has a high temperature setpoint between the cable/wiring temperature rating value and the insulation&#39;s melting temperature. In an embodiment with a cable rating of 75 degrees and an insulation melting temperature of 95 degrees, the temperature switch  108  has a setpoint at approximately 85 degrees Centigrade. 
         [0024]    The temperature of a receptacle device  100  will increase above the room&#39;s ambient temperature for various reasons, including high current levels that are not sufficiently high to trip an upstream circuit breaker. The elevated temperature is transferred from the metal conductors to the receptacle  102 . The potentially thermally hot conductors include the prongs on the plug that connects to the output connectors  110  and the service wiring that connects to the input connectors  112 . The temperature sensor  118  is responsive to the temperature of the thermally hot conductors. In one embodiment, the temperature sensor  118  is in thermal contact with the receptacle  102 , which has a temperature corresponding to that of the thermally hot conductors. In another embodiment, the temperature sensor  118  is positioned proximate the conductors, for example, within a cavity containing the input connections  112 . 
         [0025]    The illustrated embodiment also shows a jumper  114 . The jumper  114  plugs into or otherwise connects to the receptacle  102  to connect the neutral N of the power connections  112  to the ground G of the test switch  106 . The ground G of the test switch  108  is also connected to the ground G of the input  112  and output  110 . In other embodiments, the function of the jumper is performed by a switch or other device that selectively connects the neutral N of the power connections  112  to the ground G of the module  104 . With the jumper  114  connected, the embodiment with the GFI module  104  will function when a two-conductor plug is connected to the output connections  110 . With the jumper  114  disconnected, the module  104  is suitable for three-conductor plugs. 
         [0026]      FIG. 1  illustrates a simplified schematic of one embodiment of a heat actuated interrupter receptacle  100 . The simplified schematic does not illustrate various connections, for example, the reset switch connections; however, those skilled in the art will recognize the need for such wiring and understand how to wire such a circuit, based on the components ultimately selected for use. 
         [0027]      FIG. 2  illustrates a perspective view of one embodiment of a heat actuated interrupter receptacle device  100 -A. The illustrated heat actuated interrupter receptacle device  100 -A includes an in-wall mountable receptacle  102 -A that has a pair of sockets for the output connections  110 . The illustrated configuration is configured to be received by a wall mounted electrical box that has fixed wiring installed. Such wall mounted electrical boxes are used to receive electrical receptacles. The illustrated heat actuated interrupter receptacle device  100 -A is dimensioned to replace a conventional receptacle in the box. 
         [0028]    Accessible between the two sockets  110  are pushbuttons for the test switch  106  and a reset switch  202 . On the rear of the receptacle  102 -A are the input connections  112 -A. The input connections  112 -A are configured for connecting to fixed, or service, wiring that is terminated at a central circuit breaker panel. The illustrated input connections  112 -A are screw terminals positioned on the rear of the receptacle  102 -A in a recessed area. 
         [0029]    Attached to the side of the receptacle  102 -A is a temperature sensor  108 -A. In various embodiments, the temperature sensor  108 -A is embedded within the receptacle  102 -A or attached to the surface of the receptacle  102 -A. For the embodiment in which the temperature switch  108  includes a mercury switch, the mercury switch is attached to the receptacle  102 -A such that the mercury switch is positioned with the proper orientation when the receptacle  102 -A is installed. 
         [0030]    Operating the test switch  106  interrupts the electrical circuit between the input connections  112 -A and the output connections  110 . When the temperature switch  108  actuates upon sensing a rising temperature greater than or equal to the setpoint, the electrical circuit between the input connections  112 -A and the output connections  110  is broken or interrupted. Operating the reset switch  202  resets the heat actuated interrupter receptacle device  100 -A and completes the interrupted circuit between the input connections  112 -A and the output connections  110 . 
         [0031]      FIG. 3  illustrates a perspective view of another embodiment of a heat actuated interrupter receptacle device  100 -B. The illustrated embodiment includes an adapter receptacle  102 -B that is portable, that is, the adapter receptacle  102 -B is configured to be plugged into a mating receptacle and the adapter receptacle  102 -B is not permanently installed to the wiring connected to the central circuit breaker panel. 
         [0032]    The adapter receptacle  102 -B has an enclosure with input connections  112 -B configured as a conventional plug that mates with a receptacle socket. In various embodiments, the adapter receptacle  102 -B has one or a pair of input connections  112 -B. In the illustrated embodiment, the temperature switch  108 -B is positioned proximate the surface of the housing of the adapter receptacle  102 -B. The position of the temperature switch  108 -B is such that the temperature switch  108 -B is responsive to heat generated by the input connections  112 -B, the output connections  110 , and/or internal to the interrupter receptacle device  100 -B. 
         [0033]    The heat actuated interrupter receptacle device  100  includes various functions. The function of sensing misuse that results in an elevated operating temperature of the receptacle  102  is implemented, in one embodiment, by the temperature switch  108  that is positioned at a location that has a thermally conductive path between the temperature switch  108  and the heat generating component. 
         [0034]    The function of repeatedly detecting an over-temperature condition is implemented, in one embodiment, by a temperature switch  108  that is capable of being repeatedly actuated. In one such embodiment, the temperature switch  108  is one that does not self-destruct upon actuation, such as one that relies upon a material to melt in order to operate. An example of a temperature switch  108  that is capable of being operated repeatedly is a switch in which a sensor or material  118  moves as the temperature increases until the material causes a circuit to be completed between two conductors, thereby operating the switch. In various embodiments, the material is a liquid, such as mercury, or a metal, such as a bimetallic member. In other embodiments, the temperature switch  108  is an electronic device that senses the temperature and causes a switch to operate. In one such embodiment, the temperature switch includes a temperature sensor such as a resistance temperature device (RTD) connected to a switching circuit. 
         [0035]    The function of interrupting a circuit is implemented, in one embodiment, by the module  104  that contains a circuit interrupting component. In one such embodiment, the module  104  is a ground fault circuit interrupter that breaks the circuit upon detection of a ground fault and also when the test switch  106  is actuated. In another such embodiment, the module  104  is a circuit interrupter, such as a relay or circuit breaker similar to that in a GFCI, that includes a test switch  106 . 
         [0036]    The function of resetting the interrupted circuit is implemented, in one embodiment, by the reset switch  202  that causes the module  104  to restore the interrupted circuit, providing that the over-temperature condition that caused the module  104  to interrupt the circuit has been cleared. In other words, the module  104  latches the interrupted condition when the module  104  is actuated. The module  104  is reset only when the condition causing the circuit interruption is cleared. 
         [0037]    From the foregoing description, it will be recognized by those skilled in the art that a reusable heat actuated interrupter receptacle device  100  has been provided. The interrupter receptacle device  100  includes an interrupting module  104  that is actuated by a temperature switch  108  that is responsive to the temperature of the receptacle  102 . The temperature switch  108  is a non-destructive switch that is operable repeatedly. The interrupting module  104  is resettable after the circuit interrupting condition is corrected and the device  100  is ready for use without requiring replacement of any components. 
         [0038]    While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant&#39;s general inventive concept.