Abstract:
A method and apparatus (“utility”) for securing an electrical connection formed by a mating structure including prongs of a male assembly and receptacles of a female assembly are provided. The utility includes a clamping mechanism whereby the very forces that would otherwise tend to pull the connection apart serve to actuate the clamping mechanism, thereby securing the mated pair. The apparatus may be integrated into a standard receptacle, or retrofitted to work with existing devices. In one embodiment, the clamping mechanism acts solely on the ground prong of a standard plug assembly, so that it is unnecessary to consider electrical potentials applied to the clamped prong in relation to the design of the clamping mechanism. Further, the withdrawing movement of the prongs of a plug may cause elongate clamping surfaces of the clamping mechanism to frictionally engage opposing surfaces of the clamped prong.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation-in-part of U.S. patent Ser. No. 12/568,444, entitled, “LOCKING ELECTRICAL RECEPTACLE,” filed on Sep. 28, 2009, which in turn is a continuation-in-part of U.S. patent Ser. No. 12/531,235, entitled, “LOCKING ELECTRICAL RECEPTACLE,” filed on Sep. 14, 2009, which is the U.S. National Stage of PCT Application US2008/57149, entitled, “LOCKING ELECTRICAL RECEPTACLE,” filed Mar. 14, 2008, which claims priority from U.S. Provisional Application No. 60/894,849, entitled, “LOCKING ELECTRICAL RECEPTACLE,” filed on Mar. 14, 2007. U.S. patent Ser. No. 12/568,444 also claims priority from U.S. Provisional Application Ser. No. 61/221,793, filed on Jul. 10, 2009. The contents of all of the above-noted applications are incorporated herein as if set forth in full. 
     
    
     BACKGROUND 
       [0002]    A wide variety of electrical connectors are known to provide electrical contact between power supplies and electrical devices. Connectors typically include prong type terminals, generally referred to as plugs, and female connectors designed for receiving the prong type terminals, generally referred to as receptacles, often described as electrical outlets, or simply outlets. The most common types of outlets include a pair of terminal contacts that receive the prongs of a plug that are coupled to “hot” and “neutral” conductors. Further, outlets may include a terminal contact that receives a ground prong of a plug. A variety of standards have been developed for outlets in various regions of the world. 
         [0003]    Regardless of the standard at issue, the design of the aforementioned most common plug and receptacle system generally incorporates a friction only means of securing the two in the mated position. The frictional coefficient varies depending on a variety of conditions, including, but not limited to, manufacturing processes, foreign materials acting as lubricants, and wear and distortion of the assemblies. This characteristic results in a non-secure means of interconnecting AC power between two devices. It is arguably the weakest link in the power delivery system to electrical or electronic devices utilizing the system. However, it has been adopted worldwide as a standard, and is used primarily due to low cost of manufacture, ease of quality control during manufacture, and efficient use of space for the power delivery it is intended to perform. 
         [0004]    The primary limitation of this connection technique is simply the friction fit component. In some applications where the continuity of power may be critical, such as data or medical applications, a technique to secure the mated connection may be desirable to improve the reliability. This may especially be true in mechanically active locations, such as where vibration is present, or where external activity may cause the cords attached to the plugs and receptacles to be mechanically deflected or strained in any manner. 
         [0005]    It is against this background that the locking electrical receptacle of the present invention has been developed. 
       SUMMARY 
       [0006]    The present invention is directed to securing an electrical connection. In some cases, mating plug and socket electrical connections may be the least secure link in the power delivery system. Conventionally, these connections are secured only by means of a friction fit. A number of factors may affect the security of this connection. The present invention provides a variety of locking mechanisms whereby the very forces that would otherwise tend to pull the connection apart serve to actuate the clamping mechanism thereby securing the mated pair. The invention is of simple construction and highly reliable in operation. Moreover, the invention can be implemented simply in connection with new or retrofitted receptacle devices. Thus, the system is compatible with existing plugs and other infrastructure. 
         [0007]    In accordance with one aspect of the present invention, an apparatus is provided for use in securing an electrical connection. The electrical connection is formed by a mating structure including prongs of a male assembly and receptacles of a female assembly (e.g., a cord cap or outlet receptacle) where the connection is broken by withdrawal of the prongs from the receptacles. It is noted that a wall outlet receptacle is generally female, while cord caps may be either male or female. The apparatus includes a clamping element movable between a clamping configuration, where the clamping element holds the mating structure in a connected state, and a release configuration. An activating element urges the clamping element into the clamping configuration responsive to a force tending to withdraw the prongs from the receptacles. In this manner, a force that would otherwise tend to pull the connection apart will now cause the apparatus of the present invention to clamp the connection in a secure state. 
         [0008]    A variety of structures are possible to implement the noted clamping functionality. Such structure may be associated with the male assembly and/or the female assembly. In one implementation, the apparatus is implemented solely in the female assembly. For example, the clamping element may act on one or more of the prongs of the male assembly. In a particular implementation the clamping element acts on a ground prong, maintained at ground potential, such that it is unnecessary to consider potentials applied to the clamped prong in relation to the design of the clamping element. This also enables or facilitates compatibility with life safety/code regulations. However, it will be appreciated that other prongs may be additionally or alternatively engaged. 
         [0009]    As noted above, the clamping element may include one or more contact surfaces for contacting one or more of the prongs in the clamping configuration. In this regard, the activating element may translate movement of the prongs in relation to the receptacle into movement of the contact surface or surfaces into the clamping configuration. For example, movement of the prongs may be translated into rotational movement of the contact surface into an abutting relationship with the clamped prong. Alternatively, a withdrawal force exerted on the plug/prongs may cause elongate contact surfaces to engage opposing side of the prong. The apparatus may further include a release element for moving the clamping element into the release configuration. For example, the release element may be operated by a user by squeezing, sliding, pulling or pushing an element of the plug housing. In one implementation, a cord cap housing may be formed in two sections that are interconnected for sliding relative to each other in telescoping fashion. The clamping element can then be engaged manually by the user or automatically in response to a tension on the cord or section of the cord cap hence engaging the lock, and later released by selecting and sliding the corresponding section of the sliding housing section to the release position. It will be appreciated that the housing section can thus be readily accessed to release the clamping element even in crowded environments (e.g., in a data center rack). Moreover, the housing section to be gripped for releasing the clamping element may be color coded or otherwise conspicuously identified to assist users. Also, a variety of methods can be used to indicate if the clamping mechanism has been released at one time. 
         [0010]    In accordance with another aspect of the present invention, a method for using a securing device is provided. The securing device includes a clamping element and an activating element as described above. The user can activate the securing device by inserting the prongs of the male assembly into the receptacles of the female assembly or by separately manipulating a locking actuator. In this mated arrangement, the electrical connection is secured as described above. The user can further deactivate the securing device by forcing the clamping element into the release configuration, for example, by squeezing the housing of the male assembly or sliding the housing section or actuating a tab or button or knob that is part of the cord cap or other means. In this manner, the electrical connection can be simply secured and released as desired by the user. 
         [0011]    In accordance with a further aspect of the present invention, the release tension of a locking electrical receptacle can be selected in relation to a defined standard so as to avoid damage to a cord cap, cordage or plug or to meet a standard in relation thereto. In this regard, the release tension of the locking receptacle can be adjusted by varying, among other things, the geometry, thickness, material qualities and detail shaping of a clamping mechanism. It has been recognized that setting the release tension too high could result in damage to the receptacle housing, cordage or a mating plug which could, in turn, result in exposed wires and a safety hazard. Moreover, standards may be defined for release tension in relation to such concerns or others. An associated methodology in accordance with the present invention involves providing a locking electrical receptacle with a clamping element; determining a release tension limit for the receptacle in relation to a standard for safe operation of the electrical connection; determining a specification or setting of the clamping element to conform to the release tension limit; and constructing, or setting an adjustment mechanism of, the locking electrical receptacle in accordance with the specification or setting. For example, the release tension can be coordinated with a structural specification of an end cap or plug or cord so as to substantially ensure that the end cap or plug or cord will not break or fail due to strain associated with excessive release tension. In this manner, the characteristics of the locking electrical receptacle can be varied to address safety concerns or related standards or to match a desired setting of a user (which may change from time-to-time or depending on the application at issue). 
         [0012]    In accordance with a still further aspect of the present invention, a strain relief mechanism is provided in connection with a locking mechanism of an electrical connection. As noted above, a potential concern in relation to a locking electrical connection is damage to an end cap, plug, cord or other structure, particularly where a high relief tension is desired. To alleviate such concerns, a strain relief structure is provided for transmitting a strain, associated with operation of a clamping mechanism for holding mating connection structure in a connected state, from the clamping mechanism to a power cord or other structure. For example, a clamping mechanism may be provided in a receptacle end cap for engaging one or more prongs of a plug. In such a case, strain relief structure may be provided that extends across the length of the end cap from the clamping mechanism for attachment to the power cord, e.g., by crimping, welding or otherwise joining. Alternatively, the strain may be transmitted to other structure separate from a receptacle/plug, such as a wall receptacle support structure. The strain relief mechanism thereby avoids hazards associated with undue stress on the end cap or other structure and reduces or substantially eliminates the need for other structural enhancement of the end cap or other structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIGS. 1A-1C  illustrate the operation of an embodiment of a clamping mechanism in accordance with the present invention. 
           [0014]      FIGS. 1D-1F  and  1 H- 1 J illustrate the operation of another embodiment of a clamping mechanism in accordance with the present invention. 
           [0015]      FIG. 1G  illustrate the operation of another embodiment of a clamping mechanism in accordance with the present invention. 
           [0016]      FIGS. 2A-2B  illustrate an embodiment of a locking electrical receptacle in accordance with the present invention, using the clamping mechanism described in  FIGS. 1A-1C   
           [0017]      FIG. 2C  illustrates an embodiment of a locking electrical receptacle in accordance with the present invention, using the clamping mechanism described in  FIGS. 1D-1F ,  1 H- 1 J or  1 G. 
           [0018]      FIGS. 3A-3B  illustrate an application for the locking electrical receptacle shown in  FIGS. 2A-2B . 
           [0019]      FIGS. 4A-4C  illustrate an apparatus for providing a locking feature for a standard receptacle in accordance with the present invention. 
           [0020]      FIG. 5  illustrates an embodiment of a standard duplex locking receptacle in accordance with the present invention. 
           [0021]      FIGS. 6A-6B  illustrate an embodiment of a locking receptacle that includes a cam lock in accordance with the present invention. 
           [0022]      FIGS. 7A-7D  illustrate an embodiment of a device for locking a mating assembly of a plug and receptacle in accordance with the present invention. 
           [0023]      FIGS. 8A-8C  illustrate an embodiment of plug that includes a toggle locking mechanism in accordance with the present invention. 
           [0024]      FIGS. 9A-9B  illustrate another embodiment of a plug that includes a divergent spring tip locking mechanism in accordance with the present invention. 
           [0025]      FIGS. 10A-10B  illustrate a further embodiment of an end cap incorporating a locking mechanism in accordance with the present invention. 
           [0026]      FIGS. 11A-11B  illustrates an alternative shaping of a spring prong retainer in accordance with the present invention that enables improved cord retention and increased overall strength. 
           [0027]      FIG. 12  is a perspective view of an alternative embodiment of a spring prong retainer in accordance with the present invention. 
           [0028]      FIGS. 13A-15B  show an alternative embodiment of a locking spring prong retainer electrical receptacles and spring prong retainers in accordance with the present invention 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that it is not intended to limit the invention to the particular form disclosed, but rather, the invention is to cover all modifications, equivalents, and alternatives falling within the scope and spirit of the invention as defined by the claims. 
         [0030]      FIGS. 1A-1C  illustrate the operation of an embodiment of a clamping mechanism for securing a mated electrical connection that may be included in a locking receptacle of the present invention. In each of the  FIGS. 1A-1C , the bottom portion represents a side view of a prong  16  and a clamping mechanism  12 , while the top portion represents a perspective view. Referring first to  FIG. 1A , the prong  16  of a plug is shown prior to insertion into a receptacle  10 . The prong  16  may be a ground prong of a standard plug (e.g., an IEC 320 plug, a NEMA 5-15, or the like) and may be various sizes and shapes. Further, the receptacle  10  may be the ground receptacle or other receptacle(s), of a standard outlet (e.g., a NEMA standard cord cap, an IEC 320 cord cap, or the like) that is operative to receive a standard plug. The receptacle  10  also includes the clamping mechanism  12  that is coupled to a pivot  14 . The clamping mechanism  12  includes an aperture that is sized to be slightly larger than the prong  16 , such that the prong  16  may only pass through the aperture when the length of the clamping mechanism is substantially perpendicular to the length of the prong  16 . That is, the design of the clamping mechanism  12  is such that a simple slide on and capture technique is utilized. 
         [0031]      FIG. 1B  illustrates the prong  16  when inserted into the receptacle  10 . As shown, the prong  16  passes through the aperture in the clamping mechanism  12  and into the receptacle  10 , such that the corresponding plug and outlet are in a mated position. The clamping mechanism  12  further may include a stop (not shown) to prevent the clamping mechanism  12  from pivoting during the insertion of the prong  16 . In this regard, during insertion of the prong  16 , the length of the clamping mechanism  12  will remain substantially perpendicular to the length of the prong  16 , which permits the passage of the prong through the aperture of the clamping mechanism  12 . 
         [0032]      FIG. 1C  illustrates the gripping function of the clamping mechanism  12  in reaction to a force on the prong  16  that tends to withdrawal the prong  16  from the receptacle  10 . In reaction to a withdrawal of the prong  16 , the clamping mechanism  12  angularly deflects (i.e., rotates) about the spring pivot  14 , causing the aperture in the clamping mechanism  12  to grip the prongs  16 . Thus, the very force that tends to withdraw the prong  16  from the receptacle acts to actuate the clamping mechanism  12  to engage the prong  16 , thereby preventing the withdrawal of the prong  16 , and maintaining the electrical connection of the mated assembly. The clamping mechanism  12  may be constructed of any suitable material, including a high strength dielectric with an imbedded metallic gripping tooth. An all-metallic clamping mechanism may also be used if the prong  16  is a ground prong. In this regard, an all-metallic clamping mechanism may be used, e.g., for other prongs, though modifications may be required to obtain approval by underwriting bodies. 
         [0033]      FIGS. 1D-1F  &amp;  1 H- 1 J illustrate the operation of another embodiment of a clamping mechanism for securing a mated electrical connection that may be included in a locking receptacle of the present invention. In each of the illustrations  500 - 505  of  FIG. 1D , the top row of figures represents the end-on views of the clamping mechanism and the bottom row represents side views of the clamping mechanism with an electrical contact prong in the states of: 1) disengagement  500 , 2) being inserted  501 , 3) fully inserted  502 , 4) fully inserted under tension  503 , 5) being released  504  and 6) during contact removal  505 . The example clamping mechanism as shown in  FIG. 1E  has two channels  606  that grip the sides of the contact and cross-link springs  603  connecting the channels. It should be noted that the clamping mechanism can act as both the electrical contact and clamping mechanism together or can be only a clamping mechanism that is integrated with a separate electrical contact.  FIGS. 1H-1J  shows the clamping mechanism acting as both the electrical contact and clamping mechanism and  FIG. 1F  shows a clamping mechanism that is suitable for use with a separate electrical contact. Details of  FIG. 1H  include the gripping channels  902 , the cross-link springs  901 , the integrated electrical conductor crimp  903 , the release shaft  904  and the release shaft contact nub  905 . Possible instantiations can be made of one suitable material or several materials (for example steel and copper) to optimize the functionality of the clamping mechanism, electrical and mechanical properties, ease of manufacture and cost. The materials can joined together or secured to function together by any suitable means such as mechanical interlock, fasteners, gluing, etc. as is needed to optimize their function and minimize their cost. 
         [0034]    A possible example of this would be a clamping mechanism that is also an electrical contact made of annealed brass or phosphor bronze or other suitable material. Due to the expansion characteristics of the chosen materials, the expansion associated with heating of the retainer contact (receptacle) and more specifically the expansion of the cross-link springs, from any resistance in the connection of it to the inserted electrical prong (Note that the prong could be different shapes, it could be a pin for example), will result in progressive tightening of the grip function. Even if the receptacle is not “locked” to the prong upon initial insertion, e.g. no extraction force is applied to tighten the gripping mechanism, and the only bearing force applied to the contact surfaces is the force of the cross-link spring action, when current is applied, the resistance at the junction of the socket and prong will result in some degree of heating. If the resistance is high enough, say the prong is under-sized, or damaged and not uniformly in contact with the channels, the temperature of the assembly will start to rise. In addition, the electrical connection between the channels, that is the channel that is connected directly to the incoming wire and the opposing channel connected via the cross-link springs, can be manipulated in cross section to have additional heating at higher current levels such that more heating is occurring in the cross-link springs than elsewhere. In any case, heating of the cross-link springs will result in expansion. Since the heat sinking is largely via the inserted prong, and subsequently the wire of the associated connection, the temperature of the cross-link spring will be higher than the prong temperature average. Hence slightly less expansion of the prong will be present. At some point the differential will allow the natural tendency of the spring loaded and racked socket receptacle to overcome the molecular lock (static friction) between the channels and the edges of the prong. The channels will move slightly with regards to the prong and a new engagement will be established. At this point, the electrical resistance will drop due to the newly established, and slightly tighter connection between the channels and the prong, and the whole thing will start cooling. Now, the cross-link springs will shorten, and the force exerted on the bearing points between the channels and the prong will increase dramatically because the tangential force, similar to the force applied when pull-out force is applied, and the electrical connection will be re-established much more effectively. This in turn will reduce the resistance further and effectively “lock” the receptacle to the prong, and guarantee superior electrical connection, even with imperfect mating surfaces. It is a re-generative condition that is responsive to poor connections, and tends to self-heal a poor electrical connection. 
         [0035]      FIG. 1E  shows the mechanical properties of the clamping mechanism. An electrical contact  600  (or other plug structure) is inserted into the clamping mechanism  601 . The dimensions of the clamping mechanism are set so that the contact will spread the clamping mechanism open. In this regard, the forward end of the clamping mechanism (the end that is first contacted by the electrical contact) may be flanged outwardly to capture the contact and facilitate spreading of the clamping mechanism. This spreading action is shown in  FIG. 1D   511 . The transverse cross-link springs  603  act to resist the spreading open of the clamping mechanism. This insures that the edges of the electrical contact  600  are biased to touch the channels at defined contact points  609 . Differently shaped electrical contacts and/or clamping mechanisms would have different contact points and/or surfaces. In the illustrated embodiment, the contact points/surfaces where clamping occurs are primarily or exclusively on the top and bottom surfaces of the prong, rather than on the side surfaces where electrical connections are typically made. This may be desirable to avoid concerns about any potential degradation of the electrical contact surfaces thought it is noted that such degradation is unlikely given that the clamping forces are spread over a substantial length (and potentially width of the contact. Once the electrical contact prong  600  has been inserted into the clamping mechanism  601 , any pulling force F(pull)  604  that acts to remove the prong  600  from the clamping mechanism  601  will result in a clamping force F (grip)  605  being exerted on the sides of the prong  600 . The clamping force is generated by the action of the transverse cross-link link springs pulling on the channels  606  on each side of the clamping mechanism such that the channels are urged towards one another. The relationship of the forces will be generally F(grip)=F(pull)/tangent (angle theta). Thus, the clamping force F(grip) will increase faster than the force F(pull) that is acting to remove the prong  600  from the clamping mechanism  601 . Therefore the grip of the clamping mechanism  601  on the prong  600  will become more secure as the force trying to extract the prong  600  increases. Once the gripping mechanism has been actuated by a pull force  604 , friction will tend to keep the gripping mechanism tightly engaged. To release the gripping mechanism, the release rod  607  is pushed, generating a force F(release)  608 . This force will decrease the angle theta and urge the channels away from one another, rapidly decreasing the gripping force F(grip)  605  and allowing the prong  600  to be easily removed from the gripping mechanism  601 . The release force  608  needed to effect release can be very small. 
         [0036]    In one possible embodiment, associated with a standard NEMA C-13 outlet, the transverse cross-link spring may be formed from copper or a copper alloy and have a thickness of about 50/1000- 75/1000 of an inch. In such a case, the curve  602  may be generally circular in shape with a radius of curvature of about 75/1000 of an inch. The curve  602  may extend into the cross-link spring  603  so that a narrowed neck, from radius-to-radius, is formed in the cross-link spring  603 . Such a curve  602 , in addition to affecting the operational properties of the gripping mechanism as may be desired, avoids sharp corners that could become starting points for cracks or accelerate metal fatigue. The neck also helps to better define the pivot point of the cross-link spring  603  in relation to the channels as may be desired. It will be appreciated that specific operational characteristics, such as (without limitation) the amount of any slight movement allowed before locking, the total amount and location of clamping forces exerted on the prong, the force level (if any) where the clamping mechanism will release, and the durability of the clamping mechanism for frequent cycling, may be application specific and can be varied as desired. Many other configuration changes and construction techniques are possible to change these operational characteristics. For example, the cross-link spring (or a portion thereof) may be twisted (e.g., at a 90° angle to the plane of stamping of the material) to affect the pivot point and flexing properties of the spring as may be desired. 
         [0037]    The choice of material, thickness and geometry and shaping of the apparatus affect the operational properties of the gripping mechanism  601 . The transverse cross-link springs can have their spring constant affected by all of these variables. For example the radius, location and shape of the curve  602  and the thickness of the neck of the transverse cross-link spring  603  can be varied to achieve differing values of spring constants. This can be desirable to optimize the pre-tension gripping force exerted by the spring on a contact inserted into the retention mechanism or the range of contact sizes the gripping mechanism will function with. Note: The pre-tension gripping force is defined as the gripping force exerted on the contact  600  by the action of the transverse cross-link springs  603  before any pull force  604  is placed on the contact. 
         [0038]    Referring to  FIG. 1G  another possible instantiation is shown. In this instantiation, the operation of the mechanism is similar to the operation described in ( 1 -D through  1 F). As tension is applied to the assembly between Force Pull  710  on the prong  706  and the Counter-Force Pull  711 , bearing forces at the contact points ( 703 , 707 ) of the channels ( 704 ,  705 ) and the inserted contact prong  706  (note that the prong could have different shapes, it might be a pin for example) increase exponentially, resulting in immediate capture of the prong by the channels. As F Pull  710  increases, the tension in the cross-link springs  701  continue to increase as well. The cross-link springs are crescent shaped in this instantiation as opposed to the straight springs described in  FIGS. 1D-1F  &amp;  1 H- 1 J. The crescent shape allows the cross-link springs to now have two actions. First, they have a spring action at the connection point to the channels ( 704 ,  705 ) and secondly they have a spring action along the long axis of the cross-link spring ( 701 ). The addition of the spring action along the long axis allows the cross-link spring to have a predictable ability to lengthen, or stretch. As F Pull  710  continues to increase, the tension in the cross-link springs  701  continue to increase to a point where the cross-link spring begins to stretch along its long axis. At this point, the relationship between the F Pull  710  applied and the resulting grip forces at the contact points ( 703 , 707 ) of the channels ( 704 ,  705 ) and the inserted contact prong  706  ceases to increase. Now, increasing Force Pull  710  results in overcoming the friction at the contact points  703 , 704 , and the contact pin  706  will move in relationship to the channels ( 704 ,  705 ) and hence the gripping mechanism  700 . If Force Pull  710  is maintained, the contact prong  706  will become extracted from the channels ( 704 ,  705 ) completely. This condition allows the assembly  700  to have a predictable point in tensile relationships where a plug and receptacle can be separated without damage to either principal component, the prong or the gripping mechanism (which can be a gripping mechanism that is also an electrical contact or a separate gripping mechanism with integrated electrical contact as noted earlier). 
         [0039]    Referring again to  FIG. 1D , the prong  530  of a plug is shown prior to insertion into a receptacle with an electrical contact represented by  510 . The prong  530  may be a ground prong or other prong of a standard plug (e.g., an IEC 320 plug, a NEMA 5-15, or the like) and may be various sizes and shapes. Further, the receptacle containing the electrical contact  510  may be the ground receptacle or other receptacle(s), of a standard outlet (e.g., a NEMA standard cord cap, an IEC 320 cord cap, or the like) that is operative to receive a standard plug. The receptacle includes the clamping mechanism  520  and may utilize more than one clamping mechanisms in one receptacle. The design of the clamping mechanism  520  is such that a simple slide on and capture technique is utilized. 
         [0040]    Other clamping mechanisms are possible in accordance with the present invention. For example, a wire mesh, formed and dimensioned so as to receive a contact, prong or other plug structure (collectively, “contact”) therein, may be utilized to provide the clamping mechanism. The wire mesh is dimensioned to frictionally engage at least one surface of the contact when plugged in. When a force is subsequently exerted tending to withdraw the contact from the receptacle, the wire mesh is stretched and concomitantly contracted in cross-section so as to clamp on the contact. A Kellem-style release mechanism may be employed to relax the weave of the mesh so that the contact is released. Such a gripping mechanism may be useful, for example, in gripping a cylindrical contact. 
         [0041]      FIG. 2C  illustrate a cross section of one possible embodiment of a locking electrical receptacle  820 . The receptacle  820  is an IEC type 320 cord cap receptacle that includes one or more gripping mechanisms  828 . The receptacle  820  includes an inner contact carrier module  824  that contains a gripping mechanism and electrical contacts  826  and  828 . Attached to the gripping mechanism and electrical contact sockets are wires  836  and  838  that extend out of the receptacle  820  though a cord  834 . The carrier module  824  may be attached to a cord strain relief  832  that functions to prevent the cord from separating from the cord cap or otherwise resulting in damage to the assembly when a force is applied to the cord  834 .  FIG. 2C  demonstrates one possible release mechanism actuation method. Specifically, the receptacle  820  is formed in telescoping fashion with a shell  822  that slides on the carrier module  824  and strain relief  832 . A protrusion  850  on shell  822  engages a release  851  of mechanism  828  such that sliding the shell  822  engages the mechanism  828  to its release configuration. The clamping mechanisms described in  FIGS. 1D-1J  can be combined many of the other release mechanisms described in the incorporated filings. 
         [0042]      FIGS. 2A-2B  illustrate a cross section of one embodiment of a locking electrical receptacle  20 . The receptacle  20  is an IEC type 320 cord cap receptacle that includes a locking mechanism. The receptacle  20  includes an inner contact carrier module  24  that houses contact sockets  26  and  28 . Attached to the contact sockets are wires  36  and  38  that extend out of the receptacle  20  though a cord  34 . The carrier module  24  may be attached to a cord strain relief  32  that functions to prevent the cord from separating from the cord cap or otherwise resulting in damage to the assembly when a force is applied to the cord  34 . A spring prong retainer  40  is disposed adjacent to a surface of the carrier module  24 , and extends across a prong-receiving portion  44  of the receptacle  20 . One end of the spring prong retainer  40  is bent around the end of the inner contact carrier module  24 , which secures it in the assembly (underneath the over-molded material  32 ). 
         [0043]    Alternatively, the spring prong retainer  40  may be secured to the inner contact carrier module  24  by a screw or other fastener, and/or embedded in the module  24 . A section of the spring prong retainer  40  that is embedded in the module  24  or alternatively secured in the cord cap via over molded material may be configured (e.g., by punching a hole in the embedded section and/or serrating the edges or otherwise shaping it) to enhance the anchoring strength in the embedded section. The other end of the spring prong retainer  40  is in contact with a telescopic lock release grip  22 . Similar to the clamping mechanism  12  shown in  FIGS. 1A-1C , the spring prong retainer  40  includes an aperture sized to permit the passage of the ground prong of a plug into the socket  26 . The aperture in the spring prong retainer  40  may be sized to be slightly larger than one prong (e.g., the ground prong) in a standard plug such that the aperture may function as the clamping mechanism for the locking receptacle  20 . It can be appreciated that prongs with different cross-section shapes, for example round prongs, can use the retention mechanism described herein, with a suitable modification of the aperture shape and geometry of the spring prong retainer. Such modifications may be specific to the various shapes of the cross section of various prong types. Such variations will function in substantially the same manner as the retention mechanism described herein. The spring prong retainer  40  may further be shaped and constructed, as will be discussed in more detail below, to inhibit contact with other prongs and provide a desired release tension. Moreover, the retainer  40  may be retained within a recessed channel formed in the module  24  to further inhibit transiting or side-to-side displacement of the retainer  40 . The operation of the clamping feature of the spring prong retainer  40  is discussed in detail below. 
         [0044]      FIG. 2A  illustrates the locking receptacle  20  when there is little or no strain on the cord  34 . As shown, the portion of the spring prong retainer  40  disposed in the prong-receiving portion  44  of the receptacle  20  is not in a substantially vertical position. Similar to the operation of the clamping mechanism  12  shown in  FIGS. 1A-1C , the apertures of the spring prong retainer  40  in this configuration will allow the prongs of a plug to pass freely into the socket  26  when the prong is inserted. This is due to the unrestricted change of position of the spring prong retainer  40  to the substantially vertical position as the prongs of a plug acts upon it. 
         [0045]      FIG. 2B  illustrates the locking receptacle  20  when a force is applied to the cord  34  of the receptacle  20  in the opposite direction of the grip release handle  30 . This is the “release position” of the receptacle  20  and is shown without the mating prongs for clarity of operation. Actions that initiate this position are illustrated in  FIGS. 3A and 3B . 
         [0046]      FIG. 3A  illustrates the operation of the locking electrical receptacle  20  shown in  FIGS. 2A-2B . When a prong  54  of a plug  50  first enters the receptacle  20  via an aperture in the lock release grip  22 , it encounters the spring prong retainer  40 , which is not in the perpendicular orientation at that time. Upon additional insertion, the spring prong retainer  40  is deflected into the perpendicular position by the force applied to it by the prong  54 . The prong  54  then passes through the aperture in the spring prong retainer  40  and into the contact socket  26 , making the electrical connection as required. Upon release of the insertion force, and when no axial strain is applied to the mated plug  50  and receptacle  20 , the spring prong retainer  40  is only partially displaced from the perpendicular axis. It is noted that there is little separation between the forward-most surface of the plug  50  and the end of the receptacle of carrier module  24  adjacent the plug  50  in this connected configuration, i.e., the prong extends to substantially the conventional extent into the receptacle. 
         [0047]      FIG. 3B  illustrates in an exaggerated manner the condition of applying axial tension to the cord  34  of the receptacle  20 . A slight retraction motion pulls on the spring prong retainer  40 , thereby increasing the angle of grip and subsequent tightening of the offset angle of the spring prong retainer  40  and prong  54 . The receptacle  20  and the plug  50  are then fully locked in this condition. Upon application of axial tension between the release grip handle  30  and the plug  50 , the position of the spring prong retainer  40  is returned to the near-perpendicular position as illustrated in  FIG. 3A , thereby releasing the spring prong retainer  40  from the prong  54 . Upon release, the receptacle  20  is easily separated from the plug  50 . Because the release grip handle  30  is mounted to slide in telescoping fashion with respect to the carrier module  24  and can be gripped for prong release from the top or sides, the locking mechanism can be easily released even in crowded or space limited environments such as in data centers. 
         [0048]      FIGS. 13A-13C  illustrate an alternative spring prong retainer. In the embodiment described above and illustrated by  FIGS. 1A through 3B , the retention gripping points are along the flat, or semi-flat surfaces of the narrow axis of the prong. The apertures are rectangular in shape and the top and bottom of the rectangle comprise the contact locations on the prong. Forces applied to those contact points are limited to the relationship of the precision of the prong dimensions to the hole dimensions. In the embodiment of  FIG. 13A , the aperture has a rectangular top and a bottom half that narrows down or tapers. This design of aperture contacts the prong at three locations  1100 ,  1101 ,  1104  (see FIG.  13 A—Exaggerated View), on the top of the prong and on each of the sides at the bottom. 
         [0049]    A significant increase in the gripping force is possible due to the amplification of the pull torque via not only the angular displacement of the spring prong, but also the wedging effect at the two adjacent contact points  1100 ,  1101  at each corner of the narrow axis of the mating prong  1103 . As pull force is exerted on the hook tab  1106  of the spring retainer  1110 , an initial action occurs as described for the spring prong retainer in  FIGS. 1A  thru  1 C. After the initial contact is made at points  1100 ,  1101 ,  1104  during the attempt to withdraw the mating prong  1103 , the forces applied to the mating prong  1103  are amplified by the inclined planes of the bottom of the slot  1100   1001 . The tension force formed in the early stage of gripping by the axial displacement of the spring prong retainer  1110  about the fulcrum point  1105  is amplified greatly to apply a compressive force at the contact points of the mating prong  1103  and the spring prong retainer bottom contact points  1100  and  1101 . This force is multiplied by about 10 to 1 due to the tension amplification of the spring prong retainer  1110  about the fulcrum  1105 . A total force amplification of about 80 times can be achieved by this method. It should be appreciated that by adjusting the angles of the inclined planes  1100  and  1101 , and the geometry of metal  1104  forming the fulcrum  1105 , that various amplifications of force can be achieved. It should also be appreciated that by varying the amplification force, the spring prong retainer can be tuned to optimally engage with a variety of mating prong materials and finishes. 
         [0050]    Due to this amplification, and the relatively small contact area between the spring prong retainer, inclined planes  1112  ( FIG. 13C )  1110 ,  1101  and the mating prong  1103 , forces at least as high as 30,000 pounds psi (30 Kpsi) are possible, thus ensuring positive gripping of the mating prong  1103 . It should be appreciated that use of this alternate method of mating prong capture is also more tolerant of manufacturing variances in the prongs. 
         [0051]      FIG. 13B  illustrates the release methodology for this alternate spring prong retainer. It is similar to that of the spring prong retainer previously described. As release force is applied to the end of the spring prong retainer  1111  by the face of the outer shell  1116 , the surface of the spring prong retainer  1110  becomes more perpendicular to the mating prong  1103 . In turn, the point of contact at the fulcrum  1105  is disengaged and the mating prong would normally be free to be extracted, as described for spring prong retainer  40  of previous embodiments. However, at this point the lower contact points (illustrated in  FIG. 13A )  1100 ,  1101  have the mating prong  1103  captured between them, and likely a small deflection of the metal of the mating prong  1103  has occurred at those points. The mating prong  1103  is therefore probably not yet released. As the outer shell  1116  compresses the face of the spring prong retainer  1110 , the molded-in ramp in the outer shell  115  begins to push the spring prong retainer down and in turn pushes the lower contact points  1100  and  1101  (illustrated in  FIG. 13A ) down off of the mating prong  1103 . Eventually the entire assembly is disengaged from the mating prong  1103 . 
         [0052]    It should be appreciated that the shape of the spring prong retainer (illustrated in  FIG. 13A ) contributes to the disengagement characteristics as well. The shoulders of the spring prong retainer  1107  are placed such that, upon force being applied to the spring prong retainer to release, the shoulders contact the interior surface of the outer shell  1116 . Continued rotation of the face of the spring prong retainer closer to perpendicular to the mating prong  1103  results in the entire face of the spring prong retainer  1111  to be forced down. This action, in conjunction with the action of the ramp cast into the outer shell  1115  results in positive down force on the spring prong retainer disengaging the lower contact points  1100  and  1101  (illustrated in  FIG. 13  A) from the mating prong  1103 . 
         [0053]      FIGS. 14A-15B  illustrate an alternate capture mechanism.  FIG. 14C  illustrates the principal mechanical components of the capture mechanism. A saddle and strain relief component  1401  is placed into the plastic connector carrier of the injection molded receptacle. A capture toggle  1402  is inserted into the two holes at the end of the saddle  1401 . The opposite end of the saddle and strain relief component  1401  is the crimp ring that clamps around the cord end just beyond the start of the outer jacket or other suitable location depending on the design of the cord. It will be appreciated that if, e.g., for ease of manufacturing, it is designed to make the strain relief and clamping mechanism from different materials, such as metals of different properties, than the carrier or other cord attachment mechanism, this can easily be done, by separating the attachment method to the cord, such as a crimp ring from the strain relief piece and then connecting them mechanically. It should be appreciated that the strain relief mechanism described herein can be used with the two additional retention mechanisms described earlier 
         [0054]      FIG. 14A  illustrates the assembly of the saddle  1401  and the cord assembly  1400 ,  1407 . The cord assembly includes the main cord  1400 , an electrical interface terminal  1406 , and the interior conductor  1407  of the aforementioned cord that connects to the terminal  1406 . The terminal  1406  rests in the closed end of the saddle and the strain relief component  1401  and the two components are aligned along the long axis by relief ways in the outer contact carrier (not shown). If desired or needed, the terminal  1406  can be mechanically attached or bonded to the saddle and strain relief component  1401  for ease of assembly, greater strength, or other purposes. The capture toggle  1402  is placed during manufacture in the saddle between the two holes in the saddle  1401 . The pre-load spring  1403  will press upon the capture toggle  1402  while the release actuation rod  1404  rests against the opposite side of the toggle. 
         [0055]      FIG. 14B  shows a side view of this assembly. The outer contact component carrier  1409  houses and contains each of the components and prevents injection molding plastic from entering the interior of the carrier during the final outer over-mold injection process.  FIG. 14B  also helps understand the basic operation of the capture assembly. When the prong of the inserted plug  1405  is inserted into the receptacle, it enters into the plastic carrier  1409 , then into the terminal  1406 , and eventually passes under the toggle  1402  until it is fully inserted and is in the position shown. If tension is applied to the power cord in attempt to extract it from the mated plug, the force is transmitted from the cord to the prong  1405  and hence to the toggle  1402  (via the strain relief component and saddle  1401 ) which is pressed against the top of the prong  1405  by the pressure of the saddle  1401  on the bottom of the prong  1405 , transmitted through the electrical terminal  1406 . The toggle is pre-loaded against the top of the inserted prong of the plug connector  1405  by the spring  1403 . As can be appreciated the shape of the toggle where it presses down on the prong can be shaped to control the application of the clamping force to the prong, for example, the toggle can have a groove to control the force on the prong so as not to twist it. This can also be done for the base of the saddle and mating terminal if desired or necessary. A suitably shaped insert between the saddle/strain relief  1401  and a terminal shaped to match the insert could accomplish this function. As the force applied to the cord  1407  causes minute movement along the major axis of the assembly, the mating prong also begins to attempt to retract and the toggle begins to rotate in such a manner as to force down the top of the inserted mating prong of the plug connector  1405 , squeezing it tighter into the terminal  1406 , and hence the terminal is squeezed into the saddle  1401 . The friction between the terminal  1406 , the mating prong of the plug connector  1405  and the saddle  1401  increases rapidly to a point where the movement is ceased. The pressing down of the mating prong  1405  onto the electrical terminal  1406  also improves the quality of the electrical connection. The prong of the plug connector  1405  is now functionally locked to the saddle and strain relief component  1401 , and hence the cord  1407 .  FIG. 15A  illustrates from an end-on view the relationship of all of the components involved in the locking of the components together. The prong of the inserted plug  1405  is located in the terminal  1406 , which is sandwiched between the prong  1405  and the saddle  1401 . 
         [0056]      FIG. 14B  illustrates the mechanism to release the connection of the toggle  1402  and the prong of the plug connector  1405 . The opposite end of the release rod  1404  can extend through the entirety of the receptacle and protrude out the back of the connector or assembly where it is user accessible. The release rod  1404  can also be actuated by other means such as is shown in  FIG. 14D . A telescopic section of the cord cap  1412  which includes a mechanical linkage  1408  can push the release rod  1404  against the toggle  1402  when the telescoping section  1412  is pulled back by the user to separate the plug assembly from the receptacle assembly (line  1413  indicates the fully inserted depth of the front face of the plug). In this regard, the range of motion of the telescoping section  1412  is controlled by elements  1410  and  1411 . Pressure on the opposite end of the rod  1404  transmits to the back of the toggle  1402  and compresses the spring  1403  slightly. This action rotates the bottom of the toggle  1402  up and away from the prong of the inserted plug connector  1405  and reduces or eliminates the contacting force between the toggle  1402  and the mating prong  1405  allowing the mating prong to move in the retraction direction. The receptacle can then be separated from the plug. The system can be designed so that the spring  1403  functions to return the telescopic section  1412  to the locked configuration when the user releases the section  1412 . 
         [0057]      FIG. 15A  illustrates the end-on view of the principal components of the inserted prong of the plug connector  1405  and the locking components of the receptacle in cross section. As mentioned previously, the toggle  1402  has been rotated into a position such that it is pressing on the prong of the inserted plug connector  1405 . The prong  1405  is in turn pressing on the terminal  1406  and in turn the terminal  1406  is pressing on the bottom of the saddle  1401 . It should be appreciated that as axial tension on the cord is increased the downward force exerted by the toggle  1402  will also increase. With suitable angles selected, and suitable dimensions of the components, the force amplification can be about 10 to 1. In other words, 10 pounds of strain force on the cord will result in about 100 lbs of force exerted on the prong. 
         [0058]    It also should be appreciated that the bottom of the saddle and strain relief component  1401  can be manufactured with a crown shape as shown. This crown shape allows the bottom of the saddle and strain relief component  1401  to act like a leaf spring when pressed down by the prong. The spring in the bottom of the saddle allows a very controllable and predictable force to be applied to the prong  1405  by the combination of the toggle pressing down on the prong and the spring resisting that force as transmitted by the prong and terminal. The maximum clamping force of the toggle on the prong is controlled by the resistance and travel of the spring. This feature can be used as follows. When strain is put on the cord to pull apart the connection, the toggle increases its force on the prong and eventually a point will be reached where the spring in (or under as described in alternative embodiments discussed below) the bottom of the saddle and strain relief component  1401  starts to flatten out. This action allows the distance from the base of the saddle and strain relief component  1401  and the tip of the toggle  1402  to increase, allowing the toggle  1402  to rotate. As the tension on the cord continues to increase, a point will be reached where the distance between saddle and strain relief component  1401  and the toggle  1402  is great enough that the toggle  1402  will rotate and be perpendicular to the prong. At this point the tab on the toggle  1402  can no longer add any additional pressure to the prong  1405 , and the prong  1405  will move under the tension applied to the cord  1407  which separates the plug and receptacle. It should also be appreciated that the tension at which the release occurs can be reliably predicted to occur and can be varied by the strength and travel of the spring. The design is somewhat tolerant of manufacturing variances of both the inserted connector prong and the mechanical components of the locking mechanism. It should also be appreciated that the tension at which the mated connection releases under strain can be reliably pre-set. 
         [0059]    In this design,  FIG. 15A  illustrates the end-on view of the saddle and strain relief component  1401  with the cord crimp end away from the viewer. The crown spring depicted in the front  1521  view has the function of controlling the release point of the connected assembly under strain conditions. In  FIG. 15B  the crown spring is shown with a hole  1541  that is used to modify the strength and travel of the crown spring. However, other means such as the thickness or type or temper, etc., of the material used can be selected to control the spring function. Observing that the location of the hole  1541  is located directly under the saddle section of the saddle and strain relief component  1401 , it should be appreciated that the strength of the crown spring action is modified. The absence of a hole will allow maximum resistance to compression of the spring crown, and a large hole will introduce significant reduction in spring strength. By reducing the spring strength, the release point of the mated connector components is subsequently reduced. Hence, the retention capacity of the locking receptacle can reliably set to specific release tensions. It will be appreciated that this design further promotes ease and lower cost of manufacture. The die that stamps the strain relief can have an insert that can be changed to vary the size of the hole  1541  in the leaf spring for various values of release tension. Other means of setting the strength and travel of the spring can be used, for example the thickness and shape of the material or other means. Also, other means that use a uniform or variable strength spring of a suitable type (hairpin, leaf, elastomer, etc) to press on the bottom of the saddle  1401  directly below the toggle  1402  can be used. The saddle in this case would not need to incorporate a spring, the spring would be separate from the saddle. This would permit the addition of a factory and/or end user spring force adjustment mechanism, such as a screw. This mechanism would control the strength and travel of the spring pressing on the saddle and hence the release tension of the gripping mechanism as was described earlier. The range of adjustment could be controlled to meet any needed requirement. It can be appreciated that being able to reliably set the release tension is extremely useful—it allows a locking cord to be made that does not require a separate release mechanism. The release is done by the locking mechanism at the desired tension level. 
         [0060]      FIG. 14C  depicts an orthogonal view of the saddle and strain relief component  1401 . The grip ring  1408  at the end of the saddle and strain relief component  1401  is shown as an integral part of the saddle and strain relief component  1401 . This ring can also be a separate compression ring that is inserted over the end of the saddle and strain relief component  1401 , where the end of the saddle and strain relief component  1402  can be shaped appropriately to be sandwiched between said compression ring and the end of the attached cord. The alternate method of attaching the saddle and strain relief component  1401  to the cord is mentioned due to the potential difficulties in compound heat treatment along the length of the saddle and strain relief component  1401 . The saddle end of the saddle and strain relief component  1401  will generally be heat treated, while the crimp ring end must remain malleable. Although it is possible to manufacture the saddle and strain relief component  1401  with these characteristics, it may be more economical to manufacture an alternately shaped saddle and strain relief component  1401  and assemble it to the cord with a separate compression ring. It can be appreciated that the retention mechanism described will work well with other shapes of prongs than those illustrated, which are flat blade type prongs. For example, the retention mechanism will work well with round prongs such as used in NEMA 5-15 and other plugs. Only minor changes are needed such as shaping the end of the toggle where it contacts the round prong to have a suitable matching shape and thickness to optimize how the force is applied to the material of the prong. This is desirable, since many round prongs are formed of tubular, not solid material and therefore can be deformed or crushed by too much force applied to too small an area of the material they are made of. Similarly, the bottom of the saddle and/or the electrical contact could be shaped to spread the clamping force more evenly on to the round prong and/or an insert between the saddle and the terminal could be used for this purpose. Although the embodiment of  FIGS. 14A-15B  has been illustrated and described in relation to a conventional cord cap, it will be appreciated that similar structure can be incorporated into other types of receptacle devices including, for example, the structure described in PCT Application PCT/US2008/57140 entitled, “Automatic Transfer Switch Module,” which is incorporated herein by reference. 
         [0061]    By utilizing a clamping mechanism (e.g., the spring prong retainer  40 ) that captures the ground prong of the plug  50  only, the safety of the receptacle  20  may be greatly improved. In this regard, the effect of the application of various electrical potentials to clamping mechanism of the assembly is avoided, which may simplify the manufacturing of the receptacle, as well as improve its overall safety. 
         [0062]      FIGS. 4A-4C  illustrate a locking device  60  for providing a locking feature for a standard cord-cap receptacle. As shown in  FIG. 4A , the locking device  60  includes a top holding member  62  and a bottom holding member  64  for positioning the locking device  60  onto a standard receptacle. The locking device  60  also includes a portion  66  that couples the holding member  62 ,  64  in relation to each other to provide a secure attachment to a receptacle. The locking device  60  also includes a clamping mechanism  68  that is coupled to a pivot  70 . The operation of the clamping mechanism  68  is similar to that of the clamping mechanism  12  illustrated in  FIGS. 1A-1C . It can be appreciated that the other clamping mechanisms described earlier could also be employed. As described earlier some of these eliminate the need to provide a separate release and could optionally provide a factory and/or user adjustable release tension feature. The locking device  60  may also include a release mechanism  72  that is operative to enable a user to disengage the clamping mechanism  68  when it is desired to remove a receptacle from a plug. 
         [0063]      FIG. 4B  illustrates the locking device  60  positioned onto a standard receptacle  80 . 
         [0064]    To facilitate the installation of the locking device  60 , the holding members  62  and  64  may be made of an elastic material such that a user may bend them outward and position the device  60  onto the receptacle  80 . For example, the holding members  62 ,  64  may be made of plastic. Further, as shown, the holding members  62 ,  64  are shaped such that once installed onto the receptacle  80 , the device  60  is not easily removed without a user deforming the holding members  62 ,  64 . That is, the holding members  62 ,  64  may be shaped to closely fit onto standard receptacle, such that normal movements will not disengage the device  60  from the plug  80 . 
         [0065]      FIG. 4C  illustrates the operation of the locking device  60  when the receptacle  80  is mated with a standard plug  84 . The ground prong  86  of the plug  84  passes through an aperture in the clamping mechanism  68  and into the receptacle  80 . If a withdrawing force tending to break the mated connection is applied to either the cord of the standard plug  84  or the cord of the receptacle  80 , the clamping mechanism  68  will rotate, causing it to grip the ground to prong of the standard plug  84 , thereby maintaining the electrical connection. If the user desires to break the connection, the user may engage to release element  72 , which is operative to maintain the clamping mechanism  68  in a substantially perpendicular position relative to the ground prong  86 , thereby permitting the prong  86  of the standard plug  84  to be withdrawn from the receptacle  80 . It should be appreciated that although one particular embodiment of a locking device  60  has been illustrated, there may be a variety of ways to implement a locking device that may be retrofitted to a standard receptacle that uses the techniques of the present invention. 
         [0066]      FIG. 5  illustrates an embodiment of a standard duplex locking receptacle  100 . In this embodiment, clamping mechanisms  112  and  114  are integrated into the receptacle  100 . The top portion of the receptacle  100  includes sockets  102 ,  104  for receiving the prongs  128 ,  130 , respectively, of a standard plug  126 . Similarly the bottom portion of the receptacle  100  includes sockets  106 ,  108  for receiving a second standard plug. The clamping mechanisms  112 ,  114  are each pivotable about the pivots  116 ,  118  respectively. Further the receptacle  100  also includes release elements  120 ,  122  that are operative to permit a user to break the connection when desired. The operation of the clamping mechanism  112 ,  114  is similar to that in previously described embodiments. That is, in response to a force tending to withdraw the plug  126  from the receptacle  100 , the clamping mechanism  112  rotates in the direction of the plug  126 , and engages the ground prong  130 , preventing the mated connection from being broken. If a user desires to intentionally removed the plug  126  from the receptacle  100 , the user may activate the release mechanism  120  and withdraw the plug  126 . It can be appreciated that the other clamping mechanisms described earlier could be employed in a standard duplex locking receptacle. As discussed earlier, some of these eliminate the need to provide a separate release mechanism and could optionally provide a factory and/or user adjustable release tension feature. 
         [0067]      FIGS. 6A-6B  illustrate side views of a receptacle  150  that includes a cam lock  152  for locking the prong  162  of a plug  160  to preserve a mated connection between the receptacle  150  and the plug  160 .  FIG. 6A  illustrates the receptacle prior to the insertion of the plug  160 , and the cam lock  152  may hang freely from a pivot  153 . In this regard, an end of the cam lock  152  is positioned in the opening of the receptacle  150  that is adapted for receiving the prong  162  of the plug  160 . 
         [0068]      FIG. 6B  illustrates the mated connection of the plug  160  and the receptacle  150 . As shown, in the mated position the prong  162  has deflected the cam lock  152  about the pivot  153 , causing the cam lock  152  to be angled away from the plug  160  and abutted with the prong  162 . Thus, when an axial strain is applied to the plug  160  or the receptacle  150 , the friction between the cam lock  152  and the prong  162  will tend to force the cam lock  152  downward toward the prong  162 , which functions to retain the plug  160  in its mated position. If a user desires to intentionally remove the plug  160  from the receptacle  150 , they may press the actuating mechanism  154 , which may be operable to rotate the cam lock  152  out of the way of the prong  162 , thereby enabling the user to freely withdraw the plug  160  from the receptacle  150 . It should be appreciated that the cam lock  152  and the actuating mechanism may be constructed from any suitable materials. In one embodiment, the cam lock  152  is constructed out of metal, and the actuating mechanism  154  is constructed from an insulating material, such as plastic. 
         [0069]      FIGS. 7A-7D  illustrate a device  170  that may be used to secure a mated connection between a plug and a receptacle. As shown, the device  170  includes a top surface  173 , a bottom surface  175 , and a front surface  171 . The three surfaces  171 ,  173 ,  175  are generally sized and oriented to fit around the exterior of a standard receptacle  178  at the end of a cord (i.e., a cord cap). The top and bottom surfaces  173  and  175  each include hooks  174  and  176 , respectively, that are used for securing the device  170  to the receptacle  178  (shown in  FIG. 7D ). The operation of the hooks  174  and  176  is described herein in reference to  FIG. 7D , which shows a side view of the device  170  when it is installed around the exterior of the receptacle  178 . The hooks  174 ,  176  may be bent inward towards each other, and wrapped around an end  179  of the receptacle  178  to secure the device  170  to the receptacle  178 . The other end of the receptacle  178  (i.e., the end with the openings  181  for receiving the prongs of a plug) may be abutted with the face surface  171  of the device  170 . 
         [0070]    The device further includes tabs  172  that are used to securing the prongs of a plug in place. The operation of the tabs  172  is best shown in  FIG. 7B , which illustrates the device  170  when installed over the prongs  182 ,  184  of a plug  180 . The plug  180  may be any plug that includes prongs, including typical plugs that are disposed in the back of electrical data processing equipment. As shown, when the device  170  is installed by sliding it axially toward the plug  180 , the tabs  172  deflect slightly toward the ends of the prongs  182 ,  184 . In this regard, if an axial force that tends to withdraw the device  170  from the plug  180  is applied, the tabs  172  will apply a downward force against the prongs  182 ,  184 . Since the openings in the device  170  are only slightly larger than the prongs  182 ,  184 , this downward force retains the prongs  182 ,  184  in their position relative to the device  170 . Further, because the device  170  may be secured to a standard receptacle as illustrated in  FIG. 7C , the tabs  172  prevent the connection between the receptacle  178  and the plug  180  from being broken. The device  170  may be constructed of any suitable non-conductive material. In one embodiment, the device  170  is constructed from a semi-rigid plastic. In this regard, the device  170  may be a single use device wherein a user must forcefully withdraw the installed device  170  from the prongs  182 ,  184  of the plug  180 , thereby deforming the plastic and/or breaking the tabs  172 . It should be appreciated that if a user desired to unplug the receptacle  178 , they may simply unwrap the hooks  174 ,  176  from the end  179  and separate the mated connection, leaving the device  170  installed on a plug. 
         [0071]      FIG. 8A  illustrates a plug  190  that includes a locking mechanism prior to insertion into a receptacle  210 . As shown in a simplified manner, the receptacle  210  includes recesses  212  and  214 . Most standard receptacles include a recess or shoulder inside the openings that are adapted to receive the prongs of a plug. This recess may be present due to manufacturing requirements, such as the molding process used to manufacture the receptacles. Further, the need to include various components (e.g., electrical connections, screws, etc.) in the receptacles may cause the need for the small recesses. If the recesses are not already present, they could be designed into the receptacle. 
         [0072]    The plug  190  uses the recess  214  to assist in creating a locking mechanism. As shown, a hollow prong  194  (e.g., the ground prong) of the plug  190  includes a toggle  196  that is attached via a pivot to the  193  inner portion of the prong  194 . A spring  198 , piston  199 , and an actuating mechanism  200  function together to enable the toggle  196  to be oriented in a lock configuration (shown in  FIG. 8B ), and a release configuration (shown in  FIG. 8C ). In one embodiment, the spring  198  acts to bias the tab  198  in the release position, which may be a substantially aligned with horizontal position inside the prong  194 . Furthermore, the actuating mechanism  200  may be operable to rotate the toggle  196  into the unlock position (shown in  FIG. 8C ) where the toggle  196  retracts into the prong  194  at an angle substantially parallel to the body of the prong  190 . A user may control the actuating mechanism  200  through a control switch  202 , which may be positioned on the front of the plug  190 . 
         [0073]      FIG. 8B  illustrates the plug  190  when in a mated position with the receptacle  210 . As shown, the tab  196  has been placed in the lock position by the pressure asserted by the spring  198  and piston  199 . In this configuration, the tab  196  will resist any axial force that tends to withdraw the plug  190  from the receptacle  210 . This is the case because the recess  214  acts as a stop for the tab  196 . Therefore, the plug  190  may be securely fastened onto the receptacle  210 .  FIG. 8C  illustrates when a user desires to remove the plug  190  from the receptacle  210 , they may depress the control switch  202  on the front of the plug  190 , which causes the actuating mechanism  200  and the spring  198  to rotate the tab  196  into the release position. 
         [0074]      FIGS. 9A-9B  illustrate another embodiment of a plug  220  that includes a divergent spring tip locking mechanism prior to insertion into a receptacle  240 . Similar to the plug  190  shown in  FIGS. 8A-8B , the plug  220  may be adapted to work with the standard receptacle  240  that includes recesses  242  and  244 . The plug  220  may include a hairpin spring  226  that is disposed inside a hollow prong  224  (e.g., the ground prong). In a release position, the ends  227  of the spring  226  are disposed inside of the prong  224  and adjacent to openings in the prong  224 . The plug  220  may further include an actuating mechanism  228 , couple to a control switch  230  on the front of the plug  220 , for biasing the spring  226  into a lock position, where the ends  227  of the spring  226  protrude outside of openings in the prong  224  (see  FIG. 9B ). 
         [0075]      FIG. 9B  illustrates the plug  220  when installed into the standard plug  240 . As shown, the actuating mechanism  228  has been moved axially toward the spring  226  into the standard receptacle  240 , causing the ends  227  to spread apart and out of the openings in the prong  224 . The openings of the prong  224  are aligned with the recesses  242  and  244  such that the ends of the spring  226  are disposed in the recesses  242  and  244  when in the lock position. Thus, as can be appreciated, when an axial force that tends to withdraw the plug  220  from the receptacle  240  is applied, the ends  227  of the spring  226  are pressed against the recesses  242  and  244 , which prohibits the prong  224  from being removed from the receptacle  240 . When a user desires to remove the plug  220  from the receptacle  240 , they may operate the control switch  230  which causes the actuating mechanism to axially withdraw from the spring  226 . In turn, this causes the ends  227  of the spring  226  to recede back into the prong  224 , such that the user may then easily remove the plug  220  from the receptacle  240 . 
         [0076]      FIGS. 10A and 10B  show a locking electrical receptacle  1000  according to a further embodiment of the present invention. The receptacle  1000  is generally similar in construction to the structure of  FIGS. 2A-2B . In this regard, the illustrated receptacle  1000  includes an end cap formed from an outer lock release grip  1002  that is slideably mounted on an inner contact carrier module  1004 . The inner contact carrier module carries a number of sockets or receptacles generally identified by reference numeral  1006 . The illustrated receptacle  1000  further includes cord strain relief  1010  and spring prong retainer  1008 . 
         [0077]      FIG. 10B  shows a perspective view of the spring prong retainer  1008 . As shown, the retainer  1008  includes a number of gripping tabs  1012  for gripping the contact carrier module  1004 . In this regard, the gripping tabs  1012  may be embedded within the molded contact carrier module  1004  so as to more firmly secure the retainer  1008  to the carrier module  1004 . Alternatively, the tabs  1012  may be pressed into the carrier module  1004  or attached to the module  1004  by an adhesive or the like. In this manner, the tabs  1012  assist in securing the spring prong retainer  1008  to the contact carrier module  1004  and maintaining the relative positioning between the spring prong retainer  1008  and the contact carrier module  1004 . It will be appreciated from this discussion below that this relative positioning is important in assuring proper functioning of the locking mechanism and controlling the release tension. The locking electrical receptacle of  1000  otherwise functions as described above in connection with  FIGS. 2A-3B . 
         [0078]      FIGS. 11A and 11B  show a further embodiment of a locking electrical receptacle  1100 . Again, the receptacle  1100  is generally similar to the structure described above in connection with  FIGS. 2A and 2B  and includes an outer lock release grip  1102 , and inner contact carrier module  1104  including a number of receptacles  1106 , and a cord strain relief structure  1110 . The illustrated embodiment further includes a spring prong retainer  1108  incorporating strain relief structure. It will be appreciated that the locking mechanism of the present invention can result in significant strain forces being applied to the end cap in the case where large tension forces are applied to a plug against the locking mechanism. Such forces could result in damage to the end cap and potential hazards associated with exposed wires if such forces are not accounted for in the end cap design. 
         [0079]    Accordingly, in the illustrated embodiment, the spring prong retainer  1108  includes strain relief structure for transmitting such strain forces directly to the power cord. Specifically, the illustrated spring prong retainer  1108  is lengthened and includes a cord grip structure  1114  at a rear end thereof. The cord attachment grip structure  1114  attaches to the power cord or is otherwise connected with a crimping band  1112  that can be secured to the power cord via crimping and/or welding, etc. or the like. In this manner, strain forces associated with operation of the spring prong retainer  1108  to grip prongs of a plug are transmitted directly to the power cord. 
         [0080]    Various characteristics of the locking electrical receptacle of the present invention can be varied to control the release stress of the locking electrical receptacle. In this regard, the geometry, thickness, material qualities and detail shaping of the gripping component can be used to control the release tension of the locking mechanism. As an example, increasing the thickness and/or stiffness of the material of the gripping component increases the release tension of the locking mechanism. 
         [0081]    The geometry of these spring prong retainers may also be varied to provide improved safety and performance.  FIG. 12  shows on example in this regard. The illustrated spring prong retainer  1200 , which may be incorporated into, for example, the embodiments of  FIGS. 2A-2B ,  10 A- 10 B, or  11 A- 11 B, includes a narrowed neck portion on  1202  between the flex point  1204  of the spring prong retainer and the prong engagement opening. This neck portion may provide a number of desirable functions. For example, the neck portion  1202  maybe positioned to provide greater clearance between the spring prong retainer  1200  and the other prongs of plug. In addition, the narrow portion  1202  may be designed to provide a defined breakpoint in the case of structural failure. That is, in the event breakage occurs due to stress or material fatigue, the neck portion  1202  provides a safe failure point that will not result in electrical hazards or failure of the electrical connection. 
         [0082]    It can be appreciated that all of the retention mechanisms described herein that can have their release tension changed by varying their design parameters, can have a release tension that is coordinated with the receptacle design or a standard or specification so as to ensure that the cord cap or receptacle will not break resulting in a potentially hazardous exposure of wires. Thus, for example, it may be desired to provide a release stress of forty pounds based on an analysis of an end cap or receptacle structure, a regulatory requirement, or a design specification. The locking mechanism may be implemented by a way of a spring prong retainer as shown, for example, in  FIGS. 2A-2B ,  10 A- 10 B and  11 A- 11 B. Then, the material and thickness of the spring prong retainer as well as the specific geometry of the spring prong retainer may be selected so as to provide a release stress of 40 lbs. The locking mechanism with a release stress of 40 lbs can also be implemented in the toggle and saddle mechanism as shown, for example in  FIGS. 14A-14D  and  15 A- 15 B. The values of these various design parameters may be determined theoretically or empirically to provide the desired release point. 
         [0083]    The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other embodiments and with various modifications required by the particular application(s) or use(s) of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.