Abstract:
A system protects people and property against electrical shock, using immersion detecting circuits, broken wire test circuits, electromechanical circuit breaking devices including coil/plunger arrangements, and relay circuit breaking mechanisms cooperative with associated circuitry, all of which are able to be incorporated as a system wholly within the load or appliance, and its associated cord set, including a plug.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of application Ser. No. 09/473,785, filed Dec. 29, 1999; which is a continuation of application Ser. No. 09/135,220, filed Aug. 17, 1998, now U.S. Pat. No. 6,016,244, issued Jan. 18, 2000; which is a continuation of application Ser. No. 08/726,252, filed Oct. 4, 1996, now U.S. Pat. No. 5,801,912, issued Sep. 1, 1998; which is a continuation of application Ser. No. 08/524,140, filed Sep. 6, 1995, now U.S. Pat. No. 5,583,730, issued Dec. 10, 1996; which is a continuation of application Ser. No. 08/410,952, filed Mar. 27, 1995, now abandoned; which is a continuation of application Ser. No. 08/138,889, filed Oct. 19, 1993, now U.S. Pat. No. 5,402,298, issued Mar. 28, 1995; which is a continuation of application Ser. No. 07/979/759, filed Nov. 23, 1992, now abandoned; which is a continuation of application Ser. No. 07/758,173, filed Sep. 11, 1991, now U.S. Pat. No. 5,166,853, issued Nov. 24, 1992; which is a continuation of application Ser. No. 07/618,271, filed Sep. 6, 1990, now abandoned; which is a continuation of application Ser. No. 07/471,258, filed Jan. 26, 1990, now abandoned; which is a continuation of application Ser. No. 07/352,077, filed May 15, 1989, now abandoned; which is a continuation of application Ser. No. 07/185,571, filed Apr. 25, 1988, now abandoned; which is a continuation of application Ser. No. 07/082,259, filed Aug. 6, 1987, now abandoned; which is a continuation of application Ser. No. 07/001,715, filed Jan. 9, 1987, now U.S. Pat. No. 4,709,293, issued Nov. 24, 1987; which is a continuation of application No. 06/880,396, filed Jun. 30, 1986, now abandoned; which is a continuation of application Ser. No. 06/558,260, filed Dec. 5, 1983, now abandoned. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    This invention relates generally to electrical hazard prevention, and more specifically to a shock hazard prevention system for disconnecting an electrical load from an electrical source when a shock hazard condition exists within the load.  
           [0005]    2. Description of the Related Art  
           [0006]    Devices for protecting human life and property against electrical shock and damage resulting from a shock hazard condition within an electrical load are known. For example, the model No. 6199 ground fault circuit interrupter (GFCI) marketed by the assignee of the present invention is capable of sensing and responding to the inadvertent grounding of the neutral conductor of an A-C electrical distribution system. It is noted, however, that in certain applications the utilization of such a GFCI is not practical.  
           [0007]    In particular, the GFCI is a relatively expensive and complex device which requires the utilization of several transformers. In addition, the GFCI is often hardwired in a wall outlet or receptacle and is neither portable nor readily disconnected. Thus, unless each outlet in which an electrical device such as, for example, an appliance is to be utilized is protected by a GFCI, the user of the appliance is subject to possible injury if a shock hazard condition should exist in conjunction with a non-protected outlet.  
           [0008]    In addition, in certain environments the utilization of a conventional GFCI would not afford any shock hazard protection to the user of an appliance. More specifically, a conventional GFCI device of the type known to applicants will not be effective or work if the user of an electrical appliance drops the appliance in a plastic insulated bathtub.  
           [0009]    Another potential drawback, exists regarding the use of a GFCI for certain types of portable electrical appliances such as, for example, a hair dryer. Although the owner of a hair dryer may have his or her residence outlets adequately protected by GFCI devices, it is possible that other places, such as hotels, the residence of relatives, friends, etc., where it is desired to use the hair dryer may not be protected by such devices.  
           [0010]    Accordingly, it is clear that what is needed is a shock hazard protector which is associated with the appliance to be protected itself rather than with the electrical outlet in which the appliance is plugged and energized. It is believed that prior to the present invention, this need has gone unfulfilled.  
           [0011]    A need exists for a shock hazard protector which possesses attributes including having a minimum number of components, reliability, cost and portability.  
         BRIEF SUMMARY OF THE INVENTION  
         [0012]    It is accordingly a general object of this invention to overcome the aforementioned limitations and drawbacks associated with the known devices and to fulfill the needs mentioned by providing a hazard protection system having all of the desirable attributes noted above.  
           [0013]    It is a particular object of the present invention to provide a shock hazard protector capable of disconnecting an electrical source from an electrical load in response to the detection of a shock hazard condition within the electrical load.  
           [0014]    Another object of the present invention is to provide a shock hazard protector capable of detecting and responding to a water-related shock hazard condition within an electrical appliance.  
           [0015]    A further object of the present invention is to provide a shock hazard protection system, as above, incorporating immersion detection circuitry.  
           [0016]    A still further object of this invention is to provide a shock hazard protection system, as above, wherein a feature is provided for detecting a possible break or discontinuity in a sensing or guard wire.  
           [0017]    Yet another object of this invention is to provide a system, as above, wherein a solenoid-type electromechanical mechanism acts as a circuit breaking or interrupting means.  
           [0018]    A further object is to provide such a system wherein a relay and associated circuitry and mechanical means enable the desired result.  
           [0019]    Yet a further object of this invention is to provide a detection system which detects or senses the presence of a conductive medium, and which causes an event in response thereto.  
           [0020]    Another object of this invention is to provide a detection system which detects or senses the absence of the presence of a conductive medium, and which causes an event in response thereto.  
           [0021]    Other objects will be apparent from the following detailed description and practice of the invention.  
           [0022]    The foregoing and other objects and advantages which will be apparent in the following detailed description of the preferred embodiment, or in the practice of the invention, are achieved by the invention disclosed herein, which generally may be characterized as a hazard protector. The hazard protector includes detecting means associated with a load for detecting a hazard condition within the load, an interrupting means associated with a source to which the load is operatively connected, and conducting means connected between the detecting means and the interrupting means. In response to the detection of a hazard condition within the load by the detecting means, the interrupting means operatively disconnects the source from the load. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0023]    Serving to illustrate exemplary embodiments of the invention are the drawings, in which similar elements are given similar reference characters, and of which:  
         [0024]    [0024]FIG. 1 is a perspective-type view of a hair dryer and its associated cord set incorporating the system according to the present invention;  
         [0025]    [0025]FIG. 2 is a block diagram of the shock hazard protector, in accordance with the present invention;  
         [0026]    [0026]FIG. 3 is a schematic diagram of one embodiment of the shock hazard protector, in accordance with the present invention;  
         [0027]    [0027]FIG. 4 is a schematic diagram of a second embodiment of the shock hazard protector, in accordance with the present invention;  
         [0028]    [0028]FIG. 5 is an enlarged partial sectional elevational view taken through a cord set plug of a relay embodiment of the present invention;  
         [0029]    [0029]FIG. 6 is a partial fragmentary sectional plan view taken along the line  6 - 6  of FIG. 5;  
         [0030]    [0030]FIG. 7 is a schematic circuit diagram of the embodiment of the present invention associated with FIGS. 5 and 6;  
         [0031]    [0031]FIG. 8 is an elevational view of the cord set plug illustrated in FIG. 1 and taken along line  8 - 8  of that same FIG. 1 depicting the assembled plug with its cover removed;  
         [0032]    [0032]FIG. 9 is a partial sectional elevational view taken along line  9 - 9  of FIG. 8;  
         [0033]    [0033]FIG. 10 is a sectional view taken along line  10 - 10  of FIG. 8;  
         [0034]    [0034]FIG. 11 is a fragmentary sectional view taken along line  11 - 11  of FIG. 8; and  
         [0035]    [0035]FIG. 12 is an exploded-type perspective view of components of the present invention illustrated in FIG. 8. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0036]    Referring now in more detail to the drawings, FIG. 1 is presented in its form to illustrate a hair dryer  12  and its associated cord set  14  as wholly containing and constituting or comprising the shock hazard protection system  10  of the present invention. It is applicants&#39; intention and desire to emphasize here the fact that this invention contemplates an electrical appliance, such as of the personal health care type (hair dryers, etc.) which possesses all of the features and advantages of the invention. It is also an intention of applicants to provide the system of the present invention in the form of an OEM product available for sale to manufacturers of such appliances.  
         [0037]    A plug assembly  16  is illustrated in FIG. 1 as including polarized blades  18  extending from housing  20 . Whereas commercially available hair dryers, as an example of a personal health care appliance, normally include a cord set having two conductors or wires, a third wire  22  is illustrated in the case of cord set  14  electrically communicating with a bare copper wire  24  whose path (in the example given in FIG. 1) includes proximity to and looped circuit near a dryer housing opening through which an on-off switch assembly  26  extends, and thence upward to another loop proximate a dryer housing air inlet opening through which fan  28  driven by motor  30  pulls air to be heated by heating coil  32  before exiting the dryer housing air outlet opening in which grill  34  is positioned. After leaving the second loop described as being adjacent the air inlet opening, wire  22  extends to a third loop adjacent grill  34 .  
         [0038]    Since heater coil  32  carries and operates on current in the “hot” or phase line, and with the provision of conductor or wire  24  wired as part of the neutral side of the line, the presence of a conductive medium such as, but not limited to, moisture or water between them will create a conductive path contemplated by the invention as enabling interruption of current to the load  12 . This embodiment is distinguishable from another embodiment of the present invention wherein a pair of conductors, as opposed to a single guard or sensing conductor  24 , are located at or near moisture/water housing penetration points. Configurations of one or more sensing or guard conductors other than those illustrated herein are contemplated as coming within the scope of this invention.  
         [0039]    Referring to FIG. 2, a block diagram of a shock hazard protector according to the present invention is illustrated. As shown therein, it comprises a source operatively connected to a load by first and second conductors  110  and  120 , respectively, a detector  200  associated with the load, a control circuit  300  connected to the detector by a sensing or third conductor  130 , and an interrupter circuit  400  associated with the source and connected to the control circuit  300 . In the case of an electrical A-C source, conductors  110  and  120  are tied to a phase and the neutral terminal, respectively, of the A-C source.  
         [0040]    In the normal mode of operation, that is, in the absence of a hazard condition within the load, the control circuit  300 , which changes from a first state to a second state in response to the detection of a hazard condition within the load, remains in the first state. Upon the detection by detector  200  of a predefined fault or hazard condition within the load, the control circuit  300  changes from the first to the second state, which causes the interrupter circuit  400  to operatively disconnect the source from the load.  
         [0041]    It is noted that the present invention contemplates certain applications where the system sensitivity need not be accurately controlled, and the control circuit  300  can be eliminated. In this situation the interrupter circuit  400  is connected to the detector  200  by the third conductor  130 , and responds directly to the detection by detector  200  of a hazard condition within the load.  
         [0042]    In either situation, the sensing or third conductor  130  communicates the presence of the hazard condition within the load to the control circuit  300  or the interrupter circuit  400 .  
         [0043]    Referring now to FIG. 3, a schematic diagram of one embodiment of the invention particularly suited for use in conjunction with water-related shock hazard conditions within ran electrical appliance operatively connected to an A-C source (not shown) by electrical conductors  110 ,  120 , respectively, is illustrated. As shown therein, detector  200  comprises a pair of hazard or immersion detection conductors  210  and  220 , which are positioned in a non-contacting relationship and contained within the electrical load. A pair of immersion detection conductors  210  and  220  are preferably located in proximity to each port of the appliance to be protected where water can enter.  
         [0044]    For ease of description, it will be assumed that the appliance to be protected only contains one port or opening through which water may enter. For this situation, one end of one of the pair of immersion detection conductors  210  is operatively connected to the phase terminal of an A-C source (not shown) via electrical conductor  110 , and one end of the second of the pair of immersion detection conductors  220  is connected to the load end of the third electrical conductor  130 . The other ends of immersion detection conductors  210 ,  220  are unconnected and are maintained in a spaced-apart relationship, typically for example, not more than one inch.  
         [0045]    Shock hazard or immersion detection conductors  210 ,  220  may comprise, for example, a pair of bare electrical conductors or a pair of conducting plated lines on a printed circuit board or other physical configurations that will enable a conductive path between the unconnected ends thereof.  
         [0046]    Control circuit  300  comprises a solid state switching control circuit and includes a first resistor R 1  connected in-line between the gate of a silicon controlled rectifier SCR and the source end of the third electrical conductor  130 . Resistor R 1  limits the current applied to the gate of the SCR. In addition, control circuit  300  includes a parallel network comprising resistor R 2 , capacitor C and diode D connected between the gate and cathode of the SCR. These components provide a measure of noise immunity and protection against damage across the gate to cathode junction of the SCR.  
         [0047]    Interrupter circuit  400  comprises an electromechanical interrupting circuit and includes an energizing coil L and a first and second contact or switch S 1 , S 2  connected in-line with the first and second electrical conductors  110 ,  120 , respectively. Switches S 1  and S 2  are responsive to the flow of current through energizing coil L and are closed when such current is not flowing. In response to the flow of such current they switch from the normally closed position to the shock hazard condition open position. One end of energizing coil L is connected to the first electrical conductor  110  and the other end thereof is connected to the anode of the SCR. The cathode of the SCR is operatively connected to the second electrical conductor  120 .  
         [0048]    The existence of a water-related shock hazard condition within the electrical appliance is detected when both unconnected ends of the pair of immersion detection conductors  210 ,  220  are immersed in the water. More specifically, the immersion of both unconnected ends of the pair of immersion detection conductors  210 ,  220  causes the electrical A-C source to be operatively connected to the gate of the SCR via the path provided by the first electrical conductor  110 , the first immersion detection conductor  210 , the electrically conducting path provided by the water in which the unconnected ends of the first and second immersion detection conductors  210 ,  220  are immersed, the second immersion detection conductor  220 , the third electrical conductor  130 , and resistor R 1 . In response thereto, the SCR switches from the normally non-conducting state to the shock hazard condition conducting state, thereby providing a path for current to flow through the energizing coil L causing switches S 1  and S 2  to switch from the normally closed position to the shock hazard condition open position and thus operatively disconnecting the A-C source from the electrical appliance.  
         [0049]    To insure that the shock hazard protector is operable prior to utilization of the appliance it protects, a test circuit (not shown) comprising, for example, a resistor in series with a normally open switch connected between the pair of immersion detection conductors  210 ,  220  may be utilized. Closing the normally open switch causes the resistor to be connected across the immersion detection conductors and, if the shock hazard protector is operating, as described above, causes the A-C source to be operatively disconnected from the appliance. Preferably, the test circuit is contained within the electrical appliance. In conjunction with said test circuit, diode D could be replaced with a light-emitting-diode (LED). If the LED is illuminated with the test switch in the closed position it indicates that the shock hazard protector is not operating properly.  
         [0050]    Preferably, electrical conductors  110 ,  120  and  130  comprise a three wire conductor having an A-C source compatible plug at the source end, the control circuit  300  and interrupter circuit  400  are contained in the plug, and the detector  200  is contained within the appliance.  
         [0051]    Thus in the case where the electrical appliance is, for example, a hair dryer, the detector  200  would be located internally within the dryer and, as noted above, in proximity to each port thereof where water can enter the dryer. It should be emphasized here that while water is given as the electrically conductive medium, this invention contemplates a response to any electrically conducting medium, such that the appliance is electrically disconnected from the A-C source in response to the presence of such a conductive medium.  
         [0052]    Exemplary values for the circuit illustrated in FIG. 3 are as follows: R 1 -2000 ohms, R 2 -1000 ohms, C-0.1 microfarads, D-1N4004, SCR-2N5064.  
         [0053]    Referring now to FIG. 4, a schematic diagram of a second embodiment of the present invention particularly suited for use in conjunction with water-related shock hazard conditions within an electrical appliance is illustrated. This embodiment provides an additional feature not present in the first embodiment illustrated in FIG. 3. In particular, the embodiment illustrated in FIG. 3, provides shock hazard protection if any of electrical conductors  110 ,  120 , individually or in combination, are broken, but does not provide shock hazard protection if electrical conductor  130  is broken. The embodiment illustrated in FIG. 4 provides an additional measure of shock hazard protection by rendering the electrical appliance inoperative if any of electrical conductors  110 ,  120  and  130 , individually or in combination, are broken.  
         [0054]    This additional measure of protection is provided by the addition of a first diode D 1  connected in series between the second immersion detection conductor  220  and the third electrical conductor  130 , the replacement of the capacitor connected between the gate and cathode of the SCR with an appropriate charging capacitor, the addition of a first charging circuit comprising resistor R N  and diode D N  connected between the first and third electrical conductors  110 ,  130 , the addition of a zener diode Z in series with the diode D 2  connected between the gate and cathode of the SCR, the addition of a second charging circuit comprising resistor Rp and diode Dp connected between the first electrical conductor  110  and the gate of the SCR, and the elimination of resistor R 2  connected between the gate and cathode of the SCR.  
         [0055]    The operation of the circuit illustrated in FIG. 4 is as follows. Assuming that the sensing or third conductor  130 , is intact, the appliance is not immersed in water and that it is energized, during the negative half cycle of the A-C signal on electrical conductor  110  a negative charging path via diode D N , resistor R N , third conductor  130 , resistor R 1  provides charge to capacitor C, thereby charging it negatively. During the positive half cycle diode D N  blocks, however a positive charging path via resistor Rp and diode Dp provides charge to capacitor C, thereby charging it positively. Since the time constant of resistor R N  and capacitor C, is roughly  33  times greater than the time constant of resistor Rp and capacitor C, the capacitor C charges much faster in the negative sense, so that under steady state conditions a negative voltage exists on the gate of the SCR thereby keeping it in a non-conducting state. In order to limit that negative voltage to a value that would not damage the gate to cathode junction of the SCR a three volt zener diode is added in series with diode D 2 , also in parallel with capacitor C.  
         [0056]    The next condition to look at is a broken third conductor  130 . Under this condition a negative charging path no longer exists for the negative voltage to be impressed on capacitor C, and, therefore during positive half cycles capacitor C will discharge positively and eventually the voltage on the gate of the SCR will get high enough to trip the SCR, causing it to switch to the conducting state thereby operatively disconnecting the A-C source from the appliance, putting the appliance in a safe condition. Exemplary values for the circuit illustrated in FIG. 4 are as follows: D 1 , D 2 , D N , Dp-1N 4004, R N -30,000 ohms, Rp-1,000,000 ohms, R 1 -2000 ohms, C-1 microfarad, SCR-2N5064, Z-3 volt zener diode.  
         [0057]    Preferably, the components comprising the first charging circuit R N , D N  and diode D 1  are contained within the electrical appliance and are waterproof, the components comprising the second charging circuit Rp, Dp and the zener diode D are contained in the plug.  
         [0058]    It is noted that with minor modifications the above described invention has many other applications. For example, in the situation where the electrical appliance comprises a power tool, such as, a drill, having an electrically conducting housing the teachings of the present invention may be utilized by eliminating immersion detection conductor  220  and connecting the third electrical conductor  130  to the electrically conducting housing. The immersion in water of the unconnected end of shock hazard detection conductor  210  provides an electrically conductive path between the shock hazard detection conductor and the electrically conducting housing of the drill causing, as described above, the drill to be operatively disconnected from the A-C source.  
         [0059]    Referring now to an embodiment of the present invention which utilizes the approach of a relay mechanism to accomplish. the circuit interrupting goal of the invention, FIG. 5 illustrates a shock hazard protector embodiment of a plug assembly  510  formed with a housing with a base and cover body halves  514  and  512 , respectively, joined at a housing reference line  516 . A strain relief  518  comprises part of cord  520  and, in cooperative combination with the shape and contour of annular surfaces  522 ,  524 ,  526  and  528 , serves as a means for protecting the integrity of electrical connections during use.  
         [0060]    Blades  530  extend outwardly from surface  532  of base half  514  and serve the function of matingly and electrically engaging electrical contacts within a receptacle (not shown) or electrical outlet in the home, for example. A fixed contact  534  is associated and integral with each of the blades  530 , contacts  534  being fixed or stationary as opposed to movable when assembled.  
         [0061]    A pair of movable contacts  536  are provided and are integral with leaf springs  538  which, in turn, are anchored by means of eyelets  540  extending through openings in an end portion of the leaf springs  538  spaced from the movable contacts  536 . These eyelets further extend through openings through a printed circuit board  542  supported by ledges  544  and  546  adjacent upstanding walls  548  and  550 , as shown in FIG. 5.  
         [0062]    A tab  552  associated with each leaf spring  538  further anchors the leaf springs to the printed circuit board in spaced relationship with respect to the aforesaid eyelets, thereby serving an additional function of preventing undesirable rotation of the leaf springs  538 , assuring alignment and reliably repeated engagement between the fixed and movable contacts  534  and  536 , respectively. Leaf springs  538  are configured to normally bias the movable contacts  536  away from the fixed contacts  534  when in an unstressed condition, thereby normally interrupting an electrical path between these contacts. The ends of leaf springs  538  are formed with upstanding flanges  554  to which conductors  556  are connected.  
         [0063]    A plunger or core  558  is disposed vertically within a bobbin coil  560 , as illustrated in FIG. 5. A reset button  564  contacts the uppermost portions of plunger  558 , while a butterfly cross bar  562  extends laterally across the plug housing and in contact with upper surfaces of leaf springs  538 . The upward biasing forces of leaf springs  538  maintain the cross bar  562 , plunger  558  and reset button  564  in the positions shown in FIG. 5, while a metal strap  566  extends about portions of coil  560  as shown. The cross sectional shape of reset button  564  is polygonal, such as square, to prevent rotation thereof, while the cross sectional shape of core or plunger  558  is round to provide maximum electromagnetic efficiency in its interaction with bobbin coil  560 . FIG. 6 illustrates in a cross sectional view of the “butterfly” cross bar  566  with arms  568  being splayed outwardly from a center rivet member  570  aligned with plunger  558 .  
         [0064]    In operation, power for the printed circuit board electronic components is supplied by a copper path on the board via pins  572  extending downwardly from the bobbin coil  560 . Prior to a shock hazard predetermined condition, the system of FIG. 5 is “set” by means of depressing set or reset button  564  inwardly, which results in movement of the plunger  558  and the cross bar  562  against the opposing biasing forces of leaf springs  538 . This depression of the set or reset button  564  will result in movement of the leaf springs  538  until the movable contacts  536  engage the fixed contacts  534 , thereby completing an electrical circuit.  
         [0065]    The completion of the electrical circuit just described results in current flow to the bobbin coil  560  which, in turn, electromagnetically “keeps” and holds the plunger in its depressed position until an interruption of such current flow. The interengagement of the movable and fixed contacts  536  and  534 , respectively, further serves to enable the supply of power to the load or appliance with which the inventive assembly of FIG. 5 is associated, again, until an interruption in current flow to the bobbin coil  560 .  
         [0066]    In the event of the presence of a shock hazard condition, as a result of the operation of circuitry of FIG. 7 described in detail below, current to the bobbin coil  560  is interrupted, with the result that the upward biasing forces of leaf springs  538  rapidly cause a separation of the movable contacts  536  away from the fixed contacts  534 , thereby in turn causing an interruption of power from the source through the blades  530  to the load or appliance.  
         [0067]    Referring now to FIG. 7 of the drawings, the aforesaid circuitry associated with the device of FIG. 5 is illustrated with like components in FIGS. 5 and 7 carrying like reference characters. With the relay of FIG. 5 being fed with half wave rectified alternating current, or pulsating direct current, there is some current flow during the negative half cycle or the half cycle other than that when line current is flowing. A free wheeling diode FWD continues current flow.  
         [0068]    The main contacts  534 ,  536  are normally open. When it is desired to turn on the appliance after plugging it into a receptacle power source, pushing a momentary double pole, single throw switch DPST, (set or reset button  564 ) closes the circuit from the power source to the bobbin core  560 . This applies half wave rectified direct current to the bobbin coil  560 . This results in applying a voltage from the phase line through the double pole single throw switch DPST, through a diode D 1 , thence through the bobbin coil  560 , with the other end of the coil going through another contact of the double pole switch DPDT to neutral line. Thus, by pushing the switch or reset button  564 , the coil  560  is energized, and the main contacts  534 ,  536  are closed.  
         [0069]    Once the main contacts  534 ,  536  are closed, a parallel path for the current is provided through another diode D 2 , such that there is current flow from phase line through diode D 2  through the coil  560  with its free wheeling diode FWD in parallel with it, thence through the collector of a transistor Q 1 , the emitter of the transistor Q 1  being connected to neutral line. The transistor Q 1  is kept on by a resistor R 1  going from phase line to the base.  
         [0070]    Once the coil energizes itself as described, the transistor Q 1  is turned on and then the momentary contact of the double pole, single throw switch is released and the coil is self-holding. Should the load or appliance be dropped into water, creating a shock hazard condition, the current in the sense line  220  is rectified by diode D 3  and a resistor R 2  puts a negative voltage onto the base of the transistor Q 1 . A capacitor C 1  is provided between the transistor base and the emitter which will essentially store whatever voltage was present to smooth it out. By setting the value of resistor R 2  relatively small with respect to the value of resistor R 1 , the time constant of the negative current is shorter than that of the positive current and in this way there is a negative charge turning off the transistor with the result that the movable contacts  536  separate from the fixed contacts  534  (FIG. 5).  
         [0071]    The reader is cautioned not to construe the examples presented in this specification, such as in describing hair dryers or other appliances, as limiting the invention to these examples. Any electrical appliance or apparatus with which a shock hazard may be associated is contemplated as being favorably affected by the advantages and features of the present invention.  
         [0072]    Referring now to another embodiment of the present invention illustrated in FIGS.  8 - 12 , wherein a novel electromechanical and electromagnetic combination provides a circuit interrupting or breaking function, as well as other functions. In FIG. 8 a plug assembly  600  of the type designated reference character  16  in FIG. 1 is shown with cover housing half  602  removed to illustrate base housing half  604  with its assembled subassemblies in place. A pair of movable contact arms  606  and  608  are each anchored at their respective angled depending legs  610  and  612  within slots or recesses  614  and  616  of base housing half  604 . Near ends  618  and  620  of movable arms  606  and  608 , respectively, remote from their depending legs  610  and  612 , silver contacts  622  and  624  are riveted to its arm.  
         [0073]    Flexible conductors  626  are welded at  628  to depending legs  610  and  612  at one of their ends, and at their other ends  630  the flexible conductors are welded to plug insertion blades  632 . Blades  632  are configured with mounting shoulders  634  so as to be held relatively integral with base  604  when assembled.  
         [0074]    Movable contact arms  606  and  608  are normally biased in the direction shown in phantom lines within FIG. 11 such that they bias the silver contacts  622  and  624  away from fixed silver contacts  636  and  638  which are riveted to fixed contact terminals  640  and  642 , respectively. The fixed contact terminals  640  and  642  themselves are physically and electrically connected to a printed circuit board  644  which carries one of the electrical circuit embodiments described above and contemplated by the invention.  
         [0075]    A latch member  646  formed with a tang  648  is associated with each movable contact arm and each is mounted and pivoted at its upper end on pivot points  650  formed on legs  652  of a set/reset button  654 . At their lower ends  656 , latches  646  are formed with downward bend or leg, as viewed in FIG. 11, these latter legs giving the latches structural stability for added reliability. The full lines of FIG. 11 illustrate latches  646  in their latched or set position, with tangs  648  holding the ends of movable contact arms  606  and  608  such that movable silver contacts  622  and  624  are in physical and electrical engagement with fixed silver contacts  636  and  638 , thereby enabling current flow through blades  632  from a source such as an electrical receptacle to a load, such as hair dryer  12 .  
         [0076]    Reset button  654  is normally biased in a direction away from blades  632  by means of helical compression springs  658  shown in FIGS. 9 and 12, for example. Springs  658  are held captive between and exert forces against opposing surfaces  660  and  662  of the underside of the reset button  654  and a metallic frame  664  (see FIG. 9). Set/reset button  654  is visible to the user through a window  668  formed within cover housing half  602  and preferably carries indicia of the type illustrated in FIG. 8 to draw attention to its function.  
         [0077]    When the movable contact arms  606  and  608  are in the positions shown in FIG. 11 in phantom outline, resting against a wall  666  formed in base housing half  604 , such that the electrical circuit is in an interrupted state with the movable and fixed contacts  622 ,  624  and  636 ,  638 , respectively, spaced in opposition with respect to one another, the user of the present invention is able to close the circuit, assuming no hazard condition is present, by depressing with his or her finger the set/reset button  654 . This depression of the button  654  causes latches  646  to move in the same direction as the movable button  654  and in sliding engagement with the ends of the movable contact arms  606  and  608  until and such that tangs  648  ride over these arm ends. Release of the formerly depressed button  654  results in its only partially returning under the influence of springs  658  towards its original position, with a resulting pulling of the movable contacts  622  and  624  into engagement with their respective opposing contacts  636  and  638  by latch tangs  648  against the undersides of the movable arm ends  618 ,  620 , thereby setting the system and closing the circuit.  
         [0078]    Latches  646  and their tangs  648  hold the movable contacts  622 ,  624  in the position just described until a hazard condition is sensed or detected. In such an event, a plunger  670  shown in FIGS. 8 and 9 as being normally biased away from its associated winding or coil  672  by means of a helical compression spring  674  is caused to rapidly approach the core of coil  672  as a result of its being energized. Plunger  670  is formed with a neck  676  adjacent its end remote from coil  672 , with which a clevis  678  of what will here by referred to as a banger  680  matingly engages. Banger  680  is further formed with pairs of trip and reset dogs  682  and  684  movable paths that coincide with latch  646 . Upon energization of coil  672 , trip dogs  682  rapidly come into contact with and “bang” against the surfaces of latches  646  facing wall  666 , forcibly disengaging the latches  646  and their tangs  648  from the movable contact arms  606 ,  608 , with the result that these arms  606 ,  608  return to their rest positions against wall  666 , and interrupt current flow through the movable and fixed contacts  622 ,  624  and  636 ,  638 , respectively. Once the current is interrupted, the compression forces within spring  674  cause the plunger  670  and its interconnected banger  680  to return to the position illustrated in FIG. 9, with the reset dogs  684  coming into contact with and biasing the latches  646  against the ends  618 ,  620  of the movable contact arms  606  and  608 .  
         [0079]    Frame  664  comprises part of the magnetic circuit associated with an operating winding or coil  672 , and for that purpose encloses a portion of the coil  672 . A strain relief  686  formed in the insulation of a cord set  688  is shown in FIGS. 8 and 9 held between opposing annular walls  690  and  692 , respectively, of housing halves  602  and  604  which, in turn, are releasably secured together by means of fasteners  694 . Cord set  688  corresponds to the cord set  14  illustrated in FIG. 1.  
         [0080]    [0080]FIG. 8 illustrates the printed circuit board  644  in broken-line outline in the position it occupies atop the banger assembly  680  and the fixed contacts  636 ,  638 . FIG. 8 further illustrates the three wires, phase/neutral  696  and the guard or sensing wire  698  which extend through and as part of cord set  688 , through the strain relief  686 , and into the confines of plug assembly  600 . Sensing wire  698  corresponds to the third wire  22  of FIG. 1 which electrically communicates with a sensing wire in the load, such as sensing wire  24  of FIG. 1, and wire  698  is coupled to the PC board  644  while the phase and neutral lines are electrically secured to the fixed contact terminals  640  and  642 . Terminals  640  and  642  are soft soldered to the PC board  644  by means of mounting tabs  700 .  
         [0081]    The present invention thus provides the user with a shock hazard protection system which has a response time that conforms to Underwriters Laboratories requirements; is trip free; possesses a double pole interrupting mechanism with an air gap switch; operates with reverse polarity; requires only a 2 pole receptacle; operates in an ungrounded environment, such as a plastic tub; is of a reasonable size and cost; provides the user with a visible trip indication; meets Underwriters Laboratories overload, short circuit, and endurance requirements; possesses electrical noise immunity so as to minimize false tripping; provides protection in the event the cord is broken, with proper polarity assumed; provides adequate strain relief; is usable with a combination switch/receptacle; and provides protection whether the load or appliance switches are on or off, or are at medium or high settings.  
         [0082]    The embodiments of the present invention herein described and disclosed are presented merely as examples of the invention. Other embodiments, forms and structures coming within the scope of this invention will readily suggest themselves to those skilled in the art, and shall be deemed to come within the scope of the appended claims.  
         [0083]    While there has been shown, described, and pointed out the fundamental novel features of the invention as applied to the preferred embodiment, as is presently contemplated for carrying it out, it is to be understood that various omissions, substitutions, and changes of the form and details of the invention illustrated and described herein and in its use and operation may be made by those skilled in the art, without departing from the spirit of the invention.