CROSS-REFERENCE TO RELATED APPLICATIONS 
     This invention claims benefit of U.S. Provisional Patent Application 60/782,041 filed Mar. 13, 2006, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the field of electric-power outlets, and more particularly to a method and apparatus for an electrical power outlet and mating plug having low- or zero-insertion force required, and having a contact-tightening mechanism to provide a highly reliable, low-resistance, high-current-capable, and/or lockable connection. 
     BACKGROUND OF THE INVENTION 
     Vehicles often need to obtain power (e.g., 110-volt or 220-volt AC, or sometimes 12 or 24-volt DC) from a land-based supply (e.g., by connection to the electrical utility power grid). Some conventional vehicles include a conventional 110-volt power cord running from the vehicle and having a conventional three-prong NEMA-standard plug on the end (National Electrical Manufacturers Association), which plug is inserted into a residential-type 110-volt outlet. Such a configuration has proved unsuitable or lacking for high-current needs, in that the plug can come unplugged or can have too little contact force, resulting in arc faults (where intermittent high-resistance contact is made, and where an arc across a small gap will form), which have a possible fire hazard for the vehicle and or docking facility. 
     Residential electrical circuitry originally used a “two-pole, two-wire, two-prong” configuration with each receptacle having a hot slot (also called the phase, line, or hot slot), and a neutral/ground slot. These receptacles did not have a separate equipment-grounding mechanism or connection. One pole is called the hot, phase, line, or hot wire, and the other pole is called the neutral. In the two-pole configuration, the neutral also served as a ground. A receptacle is a device with recessed male or female contacts that is part of an outlet typically installed in a wall or on equipment, and which is intended to establish electrical connection with, and provide power to, an inserted plug. A wall-mounted duplex outlet will have two receptacles. A plug is a device with male blades which, when inserted into a receptacle, establishes connection between the conductors of the attached flexible cord and the conductors connected to the receptacle. With the original “two-pole, two-wire” scheme, the only grounding point was at the service entrance, where the neutral (white) conductor was grounded. At some point, the NEMA (National Electrical Manufacturers Association) configuration 1-15R required that the receptacle slot for the neutral wire (typically having white-colored insulation) be longer than the slot for the hot wire (typically having black- or red-colored insulation), and that the blade of the neutral wire on the plug be wider than the hot blade, in order that it could not be inserted into the shorter hot slot. This enables certain types of equipment, like power-supply transformers and home appliances, to have their external metal parts or casing grounded through the white neutral wire connection. Such equipment uses a polarized plug where the neutral plug blade is wider than the hot plug blade, ensuring that it can only be inserted into a NEMA 1-15R configuration receptacle with the correct orientation. 
     Many modern residential and industrial power outlets and power plugs now have what is termed a two-pole, three-wire, three-prong design, which in the U.S. is typically used for conventional 120 V.A.C. (volts alternating current) convenience power outlets. Such power outlets typically include two receptacles and are known as duplex outlets. These configurations provide a separate ground wire from the receptacle that is typically connected to neutral and ground/earth at the residential circuit-breaker box. A modern three-prong power plug has three male blades or prongs that are typically nickel plated, tin, or brass, and that are inserted into three respective female slots or sockets of a wall receptacle. The prongs of the power plug and the female slots or sockets of the wall-mounted power receptacle vary in terms of size and shape based upon the purpose that they serve. One of the prongs (the “ground prong”) is typically longer than the other two prongs, and in some embodiments is circular, semi-circular, or rounded in shape. Another of the prongs (the “neutral prong”) has a blade that is slightly wider than the third prong&#39;s blade (the “hot prong”). Many power plugs are still made with only the hot and neutral prongs (“two-prong power plugs”), and omit the ground prong. Such two-prong plugs are often polarized, with the neutral blade wider than the hot blade. A three-socket power receptacle will accept either two-prong or three-prong power plugs. 
     Corresponding to the three male prongs of the plug are three female slots or sockets (i.e., the hot socket, neutral socket, and ground socket) of the power receptacle into which the plug&#39;s prongs are inserted. The power receptacle&#39;s sockets are designed to accommodate the size and length variations and allow either two-prong or three-prong power plugs to be inserted, while preventing or making it difficult to insert a two-prong plug the wrong way (e.g., with the neutral prong of the plug inserted into the hot socket of the power receptacle). The neutral socket of the power receptacle and the neutral prong of the plug are wider than the hot socket that accepts the hot prong, such that the neutral plug is too wide to be inserted into the hot socket. As an additional safety feature, the ground prong of the plug is typically made longer than either the hot prong or the neutral prong, in order that it makes contact with the power receptacle first. Correspondingly, the ground socket that accepts the ground prong is deeper than the other two sockets so as to accommodate the increased length of the ground prong. 
     One reason for the three-prong design, and in particular the use of a ground prong, is to provide an electrical ground that can be connected to the outside of a device, or its metal frame or chassis, such that a person who is standing on or otherwise connected to ground will not get a shock from the device if the hot power voltage or a portion thereof is connected to the device frame by accident damage, aged components, insulation degradation, impact, or wiring mistake. If the person and the outside of the device are both at a ground voltage, there will be no current flow when the person is touching the outside of the device. 
     Another reason for the three-prong design relates to the need to dissipate and/or direct ambient and non-ambient electrical charges. A system of interconnected electrical circuits, such as those found in the typical residential house, acts like a capacitive antenna that can either build up and/or conduct ambient and non-ambient electrical power found in the atmosphere. For example, when a house is struck by lightening, absent the use of various ground prongs, the electrical energy of the lightening could be routed through all the ungrounded electrical circuits including appliances connected to these circuits. This electrical energy would destroy many of these ungrounded appliances. One solution to this problem is to provide a ground path to allow this electricity to be dissipated into the earth or ground. 
     Yet another reason behind the three-prong design, when mounted with the ground socket uppermost, may be to lessen the likelihood that a circuit could be formed directly across the hot and neutral prongs. Namely, the ground prong can act as a barrier or guard that prevents a piece of conductive material (for example, a cookie sheet) from slipping into the space between the power plug and power receptacle and forming a short circuit between the hot and neutral prongs. Were such a short circuit to occur, the high current can vaporize the metal prongs, which could cause a fire or other damage. 
     Power receptacles are typically set in a dual- or duplex-outlet configuration whereby two power receptacles are stacked one on top of one another. In most of these duplex-outlet power-receptacle configurations, the power-receptacle sockets are arranged such that the hot, neutral, and ground sockets have the same orientation, and wherein each feature of the upper receptacle is approximately 39 millimeters above the corresponding feature of the lower receptacle. Further, typically, the screw connectors for the neutral and ground wires are all on one side of the outlet device, and the screw connectors for the hot wire(s) are on the opposite side of the device. Further still, many companies and electrical inspectors recommend that conventional duplex outlets be installed having the hot and neutral slots, which are set parallel to each other, oriented vertically, with the hot slot on the left and the neutral slot on the right, and the ground socket of each receptacle set above these parallel slots, in what is called a ground-up orientation or configuration. Some electricians and homeowners prefer to have the ground socket below the hot and neutral sockets (with the hot slots on the right and the neutral slots on the left), in what is called a ground-down orientation or configuration. 
     One problem that occurs with such conventional residential plugs and sockets is that sliding and compressive forces must be overcome when inserting and withdrawing such plugs from their sockets. As current requirements increase (particularly for 50 amperes and above), it is quite difficult for a person of ordinary strength to insert or withdraw the plug, or, on the other hand, the spring force becomes weakened after repeated uses and the contacts are electrically unreliable and the resulting high-resistance connections can heat up and become a fire hazard. 
     Some conventional plug-outlet designs have twist-lock or screw-on covers that substantially prevent pulling force from withdrawing the plug. These are undesirable for vehicle connections, since if the vehicle moves, the plug and/or outlet are destroyed rather than simply unplugging as the boat or RV backs away from the docking station. 
     What is needed is an improved plug-outlet design that overcomes shortcomings of conventional outlet designs, while providing improved usability and/or safety characteristics. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus to address the problems of simultaneously providing low or zero insertion force, while providing high compressive force and good wiping action as the electrical contact is being made and used. Further, some embodiments provide the high contact force without actually locking the plug to the outlet, in order that if the plug or power cord is pulled on, it will eventually come unplugged before the plug, cord, or outlet is damaged. One advantage of some embodiments of the present invention is that it allows for the utilization of the conventional three-prong power plug. 
     In some embodiments, the present invention provides an independently tightening collet surrounding each socket for each of a plurality of corresponding prongs, wherein the collet is loosened for normal (low-insertion-force) insertion and withdrawal of the plug from the outlet. Once the plug is inserted, the collet is tightened, providing a high-contact force to lower the contact resistance and to help keep the plug from coming unplugged. In some embodiments, the plug is not “locked”, in that a tension force (e.g., from the vehicle pulling away, or from a person pulling on the cord hard enough) pulling on the plug will overcome the contact force at a point before the plug or outlet is damaged, and the plug is allowed to come unplugged. In some embodiments, engaging the collet will also provide a wiping or sliding motion between the prong and socket for each connection, thus wiping at least some dirt or corrosion away and providing a lower-resistance better electrical contact. 
     In various embodiments, the “outlet” portion is on a surface of the vehicle (e.g., on the hull of a boat, or back wall of a recreational vehicle (RV) or mobile home, or otherwise on a surface of the vehicle) and the power cord from the docking station is run out to the vehicle and plugged into the vehicle. In other embodiments, the “outlet” portion is on a surface of the docking station, and the power cord is run from the vehicle and plugged into the docking station. In some embodiments, an outlet of the present invention is provided on both the vehicle and the docking station, and the power wiring cord has a plug according to the present invention on both ends of the cord. 
     In some embodiments, the outlet of the present invention includes a plurality (e.g., three, in some embodiments) of recessed fixed prongs (male connectors), and the plug includes a corresponding number of sockets each having a tightenable, independent collet that can be activated to tighten onto its respective prong upon manual activation by the user (e.g., by pushing or pulling on one or more activation handles). In some embodiments, each collet has its own spring that imparts a predetermined amount of contact force, resulting in a reliable, repeatable force being applied on each electrical contact. In some embodiments, each socket has a plurality of fingers (e.g., three fingers arranged 120 degrees from each other in a circle around the prong) that, when they are squeezed by the collet, impart a slight wiping action against the sides of the prong. In other embodiments, no wiping action is applied, and the fingers simply tighten on the prong. By placing the prongs in a recessed fixed configuration on the outlet portion of the connection, there are no moving parts on the outlet (which is harder and more costly to repair or replace), and the moving parts in the power cord can be replaced more inexpensively. 
     In other embodiments, the fixed prongs are on the cord&#39;s plug (as with conventional household cords and plugs), and the outlet has the socket portions of the connection and the collets that tighten the sockets on their respective prongs. 
     In still other embodiments, the outlet has fixed socket portions of the connection (with no collets), and the cord&#39;s plug includes expanding prongs that tighten by expanding on the insides of their respective fixed sockets. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-section plan view of an electrical plug  100 . 
         FIG. 2A  is a cross-section side view (at right angles to the view of  FIG. 1 ) of electrical socketed plug  100 . 
         FIG. 2B  is a cross-section bottom view (at right angles to the view of  FIG. 1 ) of electrical plug push plate  116 . 
         FIG. 2C  is a cross-section side view of electrical plug compressible socket  110 . 
         FIG. 2D  is a cross-section end view of electrical plug compressible socket  110 . 
         FIG. 2E  is a cross-section close-up view of electrical plug socket finger  109  showing the wiping action achieved when the collet  112  slides onto finger  109  tightening it on the prong. 
         FIG. 3A  is a cross-section plan view of electrical connection system  300  having a socketed plug  302  with collet releaser  330 , where the plug  302  is inserted and clamped in pronged receptacle  301 . 
         FIG. 3B  is a cross-section plan view of electrical connection system  303  having a socketed plug  304  with collet releaser  330 , where the plug  304  is inserted and clamped in receptacle  301 . 
         FIG. 3C  is a cross-section plan view of electrical connection system  305  having a socketed plug  309  with collet releaser  330 , where the plug  309  is inserted and clamped in receptacle  301 . 
         FIG. 4  is a cross-section plan view of electrical connection system  400  having a pronged plug  402  with collet releaser  430 , where the plug  402  is inserted and clamped in socketed receptacle  401 . 
         FIG. 5A  is a cross-section plan view of pronged receptacle  501 . 
         FIG. 5B  is a cross-section plan view of socketed electrical plug  502  with collet releaser  530 . 
         FIG. 5C  is a cross-section plan view of electrical connection system  500  having a socketed electrical plug  502  with collet releaser  530 , where the plug  502  is inserted and clamped in pronged receptacle  501   
         FIG. 5D  is a plan view of a small version of socketed electrical plug  502 ′. 
         FIG. 5E  is an exploded cross-section plan view of socketed electrical plug  502  with collet releaser  530 . 
         FIG. 5F  is a front view of one embodiment pronged electrical receptacle  501 A. 
         FIG. 5G  is a front view of one embodiment pronged electrical receptacle  501 B. 
         FIG. 5H  is a front view of one embodiment pronged electrical receptacle  501 C. 
         FIG. 5I  is a front view of one embodiment pronged electrical receptacle  501 D. 
         FIG. 6A  is a cross-section plan view of compressible-socket socketed receptacle  601  with collet releaser  630 . 
         FIG. 6B  is a cross-section plan view of fixed-prong pronged electrical plug  602 . 
         FIG. 6C  is a cross-section plan view of electrical connection system  600  having a fixed-prong pronged plug  602  inserted into compressible-socket socketed receptacle  601  with collet releaser  630 , where the plug  602  is inserted and clamped in socketed receptacle  601 . 
         FIG. 6D  is a plan view of a small version of pronged plug  602 ′. 
         FIG. 6E  is an exploded cross-section plan view of compressible-socket socketed electrical receptacle  601  with collet releaser  630 . 
         FIG. 6F  is a front view of one embodiment of a compressible-socket electrical receptacle  601 A. 
         FIG. 6G  is a front view of one embodiment of a compressible-socket electrical receptacle  601 B. 
         FIG. 6H  is a front view of one embodiment of a compressible-socket electrical receptacle  601 C. 
         FIG. 6I  is a front view of one embodiment of a compressible-socket electrical receptacle  601 D. 
         FIG. 7A  is a cross-section plan view of socketed receptacle  701 . 
         FIG. 7B  is a cross-section plan view of pronged electrical plug  702  (having expanding prongs) with collet releaser  730 . 
         FIG. 7C  is a cross-section plan view of electrical connection system  700  having a pronged plug  702  with collet releaser  730 , where the plug  702  is inserted and clamped in socketed receptacle  701   
         FIG. 7D  is an exploded cross-section plan view of pronged electrical plug  702  (having expanding prongs) with collet releaser  730 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although the following detailed description contains many specifics for the purpose of illustration, a person of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the following preferred embodiments of the invention are set forth without any loss of generality to, and without imposing limitations upon the claimed invention. 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
     The leading digit(s) of reference numbers appearing in the Figures generally corresponds to the Figure number in which that component is first introduced, such that the same reference number is used throughout to refer to an identical component that appears in multiple Figures. Signals and connections may be referred to by the same reference number or label, and the actual meaning will be clear from its use in the context of the description. 
     For the purpose of this description, the phrase “power receptacle” is synonymous with the phrases electrical-power receptacle, main power receptacle, plug-in, outlet, power receptacle, female power prong, or any other phrase denoting an apparatus designed to provide access to electrical power using a plurality of (e.g., three) slots or sockets. 
     Below are alternative embodiments for certain features of the connector. In some embodiments, the split contact extends through the stationary block with a threaded end. At the top of the threaded end the contact has a shoulder area that is received by a complimentary shoulder area within the stationary block. The bottom of the threaded end receives a nut, which locks the contact into the stationary block. This threaded end is also hollow to receive wire that has had its insulation stripped. 
     A description of contact and wire installation is as follows: Prior to installing the contact, the wire is stripped, the nut is placed on the wire and then the wire is inserted through the stationary block and the split contact compressors. The wire is then inserted into the hollow lower shaft of the contact and it is either crimped or soldered in. The wire and the contact are then pulled down through the above-mentioned parts until the contact shoulder is resting on the mating shoulder of the stationary block. The nut is then threaded onto the threaded end of the contact and tightened, pulling the contact into firm communication with the stationary block and securing the contact in place. 
     Another preferred element are cams which are rotated with the lock/unlock handles. As the handles are rotated forward linked to one-another by gears between the handle assemblies, a captured ball bearing (or roller) attached to the end of the push rods rides on the cams. As the cams rotate just beyond their high points, the ball bearing (roller)/push rod assemblies drop into the detents, which positively lock the handles into locked position. When in locked position, the push rods are fully pushed up and the split contact compressors have fully compressed and clamped the split contact onto the mating male pin that is being supplied with power. 
     Some embodiments combine the flatted cams with the other type of push-rod ends as presented earlier. Some embodiments use a split-contact compressor-retraction device shown. 
     An electrical connector for use particularly in high-power applications where the connector is large and frequently must be installed and removed. An electrical connector that also is installed and removed from its mating connector with little or no friction (little or no force applied to each prong by its respective socket). The connector includes an outer housing and at least one electrical socket contact, typically several. The socket contact has a split configuration that is compressed onto the mating pin from the device that is being powered. Mechanical means are provided for handling the connector, actuating an electrical socket compression device and as a result providing positive individual electrical-pin contact. 
     The present invention relates to a power connector that may be preferably used for, but is not restricted to, supplying power to mobile devices such as boats, ships and airplanes when they are in port being serviced or temporarily docked. 
     There are several well-known problems with existing power connectors that should be fixed, as they represent nuisance, functionality, damage and safety issues. A list of problems with existing power connectors is as follows:
         Most have multiple large socket contacts that provide a friction fit to mate with the male pin to which power is being provided. This makes it very difficult to install and remove them from the mating connector.   Given that a friction fit is provided, each time the connector is installed and removed, a small amount of material is eroded from the pin and socket. As wear progresses the pin-to-socket contact may become quite loose, representing increased electrical resistance. Depending on the pin arrangement within the connector, the sockets may be differentially worn such the pin/socket electrical resistance from one contact to the next will be different. As the electrical resistance increases, heat builds up and oxidizes the contact surface. This in turn causes an increased rate of contact erosion and increased heat, which can cause internal damage to both the power connector and wires as well as the connector receiving power and its wires. This ultimately may result in the requirement for expensive repairs; power-failure and potential short-circuit conditions representing a human safety problem.   Large power connectors typically do not have a defined location for the user to handle them and provide an appropriate point of leverage to apply force for the installation and removal of the connector. Given this, the user many times will inappropriately use the insulated cable that contains the electrically conductive wires to remove the connector. This may eventually stress the wires, loosen the cable within the connector and stress and loosen the wires at the electrical contact internal to the connector. The user will also wiggle the connector from side to side to break friction with jerks, which will result in damaging the electrical sockets, expanding and deforming their internal surface.       

     Given the above-described problems, there remains a need for a power connector that provides means to deal with and correct these problems. 
     DETAILED DESCRIPTION 
     Description of Operation 
       FIG. 1 : Starting from the bottom of the cross-sectional plan view of  FIG. 1  (which illustrates one embodiment of the present invention), one can see the insulated electrical cable providing multiple insulated wire conductors which (shown with arrows) connect with the split electrical socket contacts above. At the sides are shown actuation handles that are connected to a rotational cam, which, when the handles are rotated forward, causes the cam to rotate. As the cam rotates, a cam follower (a captured ball or roller bearing) which is attached to the base of a cylindrical push rod rolls on the cam surface and lifts the push rod as the cam height increases. At the peak of cam height and full travel of the handles, the cam follower drops into a detent, which tends to lock the handles and push rods into place. 
     As the push rods are pushed up they are guided by bushings and then by a stationary block above the bushings. The stationary block also locks the electrical contacts into place, is conformed to, and mates with a push plate above. The push plate has bushed reception sites into which the push rods fit. As the push rods are lifted the push plate is also lifted. Riding on top of the push plate are compression-force-equalizing springs. Above and riding on the springs are tapered bushings which, as they ride up on the mating tapered surface of the split electrical contact socket, compress the socket, closing the gap between the socket&#39;s split segments. As socket compression takes place the socket is brought into positive contact with the pin it is mating to. The springs below the tapered bushing tend to equalize the compression force from socket to socket and ensure that when one socket/pin contact is made the force is directed to the others that are then individually made. 
     Once the sockets are all compressed this tends to lock the power connector onto its mating connector. However the outer shell configuration of the connector must still be designed to mate correctly with its mating connector so that the load of the cable and connector weights is carried by the connector&#39;s outer shell. 
     When it is desired to remove the power connector from the device it is servicing, the user pulls the handles back to their initial position, which drops the push rod assembly and unlocks the compressed sockets from the mating pins. The user then uses the leverage of the handles to apply force to remove the connector. 
     Problems Solved:
         This connector does not employ a push-on-type friction fit, so it will be “very” much easier for the user to install and remove, as the user will only be dealing with the weight of the connector and cable, not having to overcome friction forces.   Since these contacts do not rely on a friction fit, they are not eroded, sprung open, and/or damaged as the connector is installed and removed. In addition, since each electrical socket contact conforms individually to the mating pin (prong), a positive electrical connection between the pin and socket is ensured. This prevents excessive heating due to electrical resistance build-up because of mechanical-fit issues, and resulting increase in material oxidation and erosion. As a result, many of the historical power-connector problems typically resulting in power conduction failure, connector internal damage and danger of short circuit due to burnt wires are avoided.   Since this connector has handles which define the location at which the user will apply installation and removal force, it is much less likely that the user will inappropriately pull on the conductive cable or wiggle the connector back and forth to break friction. This will result in much less tendency for wire fatigue and breakage as well as increased wear on other connector parts.       

       FIG. 1  is a cross-section plan view of an electrical plug  100 . In some embodiments, plug  100  includes a plurality of sockets  110  (e.g., 3, 4, 6, or other suitable numbers of sockets), each socket configured to be compressed around a corresponding pin in the receptacle (e.g., outlet  301  of  FIG. 3A ), each socket having a plurality of fingers  109  having tapered outer portions configured to be pushed inward by collet  112  when collet  112  is (independently of the other collets) pushed upward by spring  114  driven by push plate  116 , which is driven by push rods  120 , which are guided by bushings  122 . Stationary insulator block  118  holds the shaft ends  111  of sockets  110 . In some embodiments, push rods  120  have entrapped ball bearing  121 , which drop into detent  125  of cam  124  when rotated by handles  127  on the ends of arms  126 . A plurality of wires  130  extend from cable holder  132  to respective ones of the shaft ends  113  of sockets  110 . Cable  134  extends to a source of power that is to be supplied to the vehicle (e.g., a boat, RV, or other vehicle) when plug  100  is inserted into a corresponding receptacle on the vehicle. In some embodiments, the handles  127  are extended outward (such that detent  125  allows push rods  120  to extend downward) for inserting or withdrawing the plug  100  from the receptacle, and handles are push inward to the position shown, with the cams  124  pushing the push rods  120  upward to push collets  112  with individual springs  114  to tighten the sockets at even and independent pressures around their respective prongs in the receptacle. Plug body  136  is made of a suitable insulator, such as plastic material. In some embodiments, the size of plug  100  is as small as an ordinary household electrical cord plug, while in other embodiments, the size is as large as needed for high-current (e.g., 100s of amps or more) applications needed by a larger vehicle such as an ocean-going ship. The even clamping forces provided by individual springs and collets means that even predetermined clamping forces are applied to each individual pin of the receptacle, resulting in a high-quality electrical connection. In the embodiment shown, there are three columns of sockets  110 . In other embodiments, these sockets  110  can be arranged in patterns other than straight rows and columns. 
     Referring further to  FIG. 1 , in some embodiments, the handles  127  are spring loaded (pulled downwards by springs  177 ), such that the operator must force the handles  127  up into the “release” position in order to plug the plug  100  into its receptacle (e.g., receptacle  501  of  FIG. 5A ), and when the handles  127  are released, the spring loading of springs  177  automatically pulls down and closes the handles  127  to the in and down, locked, and clamping configuration. This helps prevent an operator from accidentally not forcing the handles into the engaged position, since when the operator releases the handles, they automatically move to the clamping position by springs  177 . Also, by pushing on the handles  127  to insert the plug  100  into its receptacle, the operator automatically pushes the handles into the non-compression configuration for the sockets; then holding the handles to keep the plug inserted and in place, the handles are pushed or released inward, clamping the plug in place on its prongs. In some embodiments, such a spring-loaded handle-engaging embodiment is used with other systems described herein. 
     Referring again to  FIG. 1 , reference number  110  refers to split electrical contact sockets (to accept power pin). Reference number  112  refers to tapered bushings (to compress split electrical socket). Reference number  114  refers to springs (for equalized socket compression). Reference number  116  refers to an insulating push plate (moves ⅛ inch with actuation). Reference number  111  refers to an electrical contact retention tab (holds contact in block). Reference number  113  refers to wire. Reference number  118  refers to an insulating block. Reference number  122  refers to bushing (guides push rod). Reference number  120  refers to a push rod. Reference number  121  refers to a cam follower (ball bearing). Reference number reference  125  refers to a cam detent. Reference number  126  refers to an actuation handle. Reference number  130  refers to wire (broken out). Reference number  134  refers to a power cable. Reference number  146  refers to webbing. Reference number  177  refers to a closing spring. 
       FIG. 2A  shows a partial cross-section view from the side (90 degrees to  FIG. 1 ) of electrical socketed plug  100 . The cam  124  and handle attachment sites  142 , and axle  143  and bushings  144  that support and allow cam rotation are seen in the lower left. In the embodiment shown, there are two rows of sockets  110 . The cam follower  121 , push rod  120 , stationary block  118 , push plate  116  and the bottom portion of the electrical contact  111  and wire attachment  113  are presented. In the connector presented there are a total of six (6) electrical contacts, three (3) in each of two (2) rows. 
     Referring again to  FIG. 2A , which is a partial side view of the frictionless locking power connector, reference number  118  refers to a stationary block. With further regard to  FIG. 2A , refer to front view for other details of this connector because the clamping portion of split electrical contact, handle, and feeder wires are not shown. Reference number  111  refers to the electrical contact (only bottom shown). Reference number  142  refers to the handle attach point. Reference number  143  refers to the axle. Reference number  144  refers to the axle bushing. Reference number  145  refers to the push-rod reception site. 
       FIG. 2B  is a bottom cross-section bottom view (at right angles to the view of  FIG. 1 ) of electrical plug push plate  116 .  FIG. 2B  a bottom view of the push block  116  is shown indicating the location of the push-rod reception site  145  (having internal bushing  149 ) and webbing  146  cast into the push block for increased strength. 
     Referring again to  FIG. 2B , which is a bottom view of push plate  116 , reference number  146  refers to webbing reinforcement. 
     In  FIG. 2C  is a representation of the split electrical socket contact showing the split segments  109  in the socket  110 , the tapered outer surface and in  FIG. 2D  is an end view of the circumference of the socket showing the split segments  109 . 
     In some embodiments, an electrically conductive radial compressible sleeve  107  is added to provide a secondary electrical-current path to ensure and improve current conduction as shown in  FIG. 2C . Initially this sleeve is bowed inward toward the center of the electrical socket. As the mating pin is inserted and makes contact, the sleeve is flattened out and maintains a spring force on the surface of the mating pin. This arrangement is typical of some power connectors, except that in this case the length of the sleeve is not the same as the length of the socket. The length of the sleeve is much reduced so as to provide much less frictional force upon pin insertion. In this case both the compression of the split socket  110  and the compression of the conductive sleeve  107  provide electrical-current conduction. 
       FIG. 2C  is a cross-section side view of electrical plug compressible socket  110 . In some embodiments, socket  110  includes a plurality of fingers  109  (e.g., in some embodiments, three fingers), separated by slots  108 . Some embodiments include a radial compressive sleeve  107 . In some embodiments, the shape of each finger  109  is slightly S-shaped, such that when the collet is pushed upward on the finger  109 , both an inward compression and an upward (or downward) sliding force is applied, thus cleaning the contact area. 
       FIG. 2D  is a cross-section end view of electrical plug compressible socket  110  showing fingers  109  and slots  108 . 
       FIG. 2E  is a cross-section close-up view of electrical plug socket finger  109  showing the wiping action achieved when the collet  112  slides onto finger  109  tightening it on the prong. The middle portion  167  of finger  109  (i.e., the lowest portion of ramp  168 ) is initially bent outward (to the left). As collet  112  raises, it presses against ramp  168  which straightens the lower portion  167  of the finger and causes contact surface  169  to slide both inward (rightward in  FIG. 2E ) and vertically upward against the inserted prong (since the straightened finger  109  reaches further upward than the initially bent finger  109 ), wiping and cleaning the contact area of the prong and contact surface  169 . 
       FIG. 3A  is a cross-section plan view of electrical connection system  300  having a socketed plug  302  with collet releaser  330  (alternatively, collet withdrawer  330 ), where the plug  302  is inserted and clamped in pronged receptacle  301 . This embodiment is similar to  FIG. 1 , except with the addition of collet releaser  330 , which acts to pull collets  312  down when the handles are released, relieving the compressive force on pins or prongs  306 . Receptacle  301  includes an insulator body  308  holding three pins  306 , each connected to a respective wire  307  leading to interior connections in the vehicle. Plug  302  includes a plurality of sockets  310  (e.g., 3, 4, 6, or other suitable numbers of sockets), each socket  310  configured to be compressed around a corresponding pin  306  in the receptacle  301 , each socket  310  having a plurality of fingers  309  having tapered outer portions configured to be pushed inward by collet  312  when collet  312  is (independently of the other collets) allowed to be pushed upward by smaller spring  314  when released by collet withdrawer  330 , which is driven by push/pull rods  320 , which are biased downward by larger springs  344 . Stationary insulator block (not shown) holds the threaded shaft ends  311  of sockets  310 , screwed into nuts  317 . In some embodiments, push rods  320  have entrapped ball bearing  321 , which drop into detent  325  of cam  324  when the cam is rotated by handles  327  on the ends of arms  326 . A plurality of wires  331  extend from cable holder  332  to respective ones of the shaft ends  313  of sockets  310 . Cable (electrical power cord)  334  extends to a source of power that is to be supplied to the vehicle (e.g., a boat, RV, or other vehicle) when plug  302  is inserted into a corresponding receptacle  301  on the vehicle. In some embodiments, the handles  327  are extended outward and backward (down in the  FIG. 3A , such that detent  325  allows push rods  320  to extend downward) for inserting or withdrawing the plug  302  from the receptacle  301 , and handles are pushed forward, upward and inward to the position shown, with the cams  324  pushing the push rods  320  upward to release collets  312  with individual springs  314  to tighten on the sockets  310  at even and independent pressures around their respective prongs  306  in the receptacle  301 . Pushing the handles in the direction of the plug insertion allows the force used to tighten the handles  327  to also force the plug into a tighter embrace to receptacle  301 , while pulling on the handles  327  both loosens the clamping on the pins and withdraws the plug  302  from receptacle  301 . Plug body  336  is made of a suitable insulator, such as plastic material. In some embodiments, the size of plug  302  is as small as an ordinary household electrical cord plug, while in other embodiments, the size is as large as needed for high-current (e.g., hundreds of amps or more) applications needed by a larger vehicle such as an ocean-going ship. The even clamping forces provided by individual springs and collets means that even predetermined clamping forces are applied to each individual pin of the receptacle, resulting in a high-quality electrical connection. In the embodiment shown, there are three columns of sockets  310 . In other embodiments, these sockets  310  can be arranged in patterns other than straight rows and columns. 
     Referring again to  FIG. 3A , reference number  321  refers to a captured ball bearing or roller. Reference number  344  refers to big springs to withdraw collets. 
       FIG. 3B  is a cross-section plan view of electrical connection system  303  having a socketed plug  304  with collet releaser  330 , where the plug  304  is inserted and clamped in receptacle  301 . This is similar to system  300  of  FIG. 3A , except that the detents  325  are flat portions of cams  324 . When the bearing surfaces  321  are on flats  325 , the springs  344  overpower springs  314  and collet holder  330  moves downward to force collets  312  down, releasing the pressure of sockets  310  on pins  306 . 
       FIG. 3C  is a cross-section plan view of electrical connection system  305  having a socketed plug  309  with collet releaser  330 , where the plug  309  is inserted and clamped in receptacle  301 . System  305  is similar to system  303  of  FIG. 3B , except that a direct link  360  moves collet holder  330  upward to allow springs  314  to force collets  312  to tighten sockets  310  to connect, or downward to force collets  312  down, releasing the pressure of sockets  310  on pins  306  to unplug. 
       FIG. 4  is a cross-section plan view of electrical connection system  400  having a pronged plug  402  with prong-base releaser  430 , where the plug  402  is inserted and clamped in socketed receptacle  401 . This system  400  is conceptually the opposite of system  303  of  FIG. 3B , in that the plug  402  has expanding pins  410  (instead of contracting sockets  310 ), and receptacle  401  has fixed sockets  406  (instead of fixed pins  306 ). Receptacle  401  includes an insulator body  408  holding a plurality of fixed sockets  406  (e.g., three, four, six, or other suitable numbers of sockets  406 ), each connected to a respective wire  407  leading to interior connections in the vehicle. Plug  402  includes a plurality of expanding pins  410  (e.g., three, four, six, or other suitable numbers of sockets), each expanding pin  410  configured to be expanded outward a corresponding socket  406  in the receptacle  401 , each expanding pin  410  having a plurality of fingers  409  having tapered outer portions configured to be pushed outward by tapered shaft  412  when shaft base  413  is (independently of the other shaft bases) allowed to be pushed upward by smaller spring  414  when released by shaft withdrawer  430 , which is driven by push/pull rods  420 , which are biased downward by larger springs  444 . Stationary insulator block (not shown) holds the threaded shaft ends  411  of expanding pins  410 , screwed into nuts  417 . In some embodiments, push rods  420  have entrapped ball bearing  421 , which drop into detent  425  of cam  424  when the cam is rotated by handles  427  on the ends of arms  426 . A plurality of wires  431  extend from cable holder  432  to respective ones of the wire receiver on shaft ends  413  of expanding pins  410 . Cable (electrical power cord)  434  extends to a source (or destination, in the case where the vehicle is supplying power to an electrical load off the vehicle, such as a trailer or the like) of power (not shown) that is to be supplied to the vehicle (e.g., a boat, RV, or other vehicle) when plug  402  is inserted into a corresponding receptacle  401  on the vehicle. 
       FIG. 5A  is a cross-section plan view of pronged receptacle  501 . This embodiment receptacle  501  is similar to receptacle  301  in  FIG. 3A : collet releaser  530  acts to pull collets  512  down when the handles are released, relieving the compressive force on pins or prongs  506 . Receptacle  501  includes an insulator body  508  holding three pins  506 , each connected to a respective wire  507  leading to interior connections in the vehicle. 
       FIG. 5B  is a cross-section plan view of socketed electrical plug  502  with collet releaser  530 . In some embodiments, plug  502  includes a plurality of sockets  510  (e.g., 3, 4, 6, or other suitable numbers of sockets), each socket  510  configured to be compressed around a corresponding pin  506  in the receptacle  501 , each socket  510  having a plurality of fingers  509  having tapered outer portions configured to be pushed inward by collet  512  when collet  512  is (independently of the other collets) allowed to be pushed upward by spring  514  when released by collet withdrawer  530 , which is driven by push/pull rods  520 . Stationary insulator block  518  holds the threaded shaft ends  511  of sockets  510 , screwed into nuts  517 . In some embodiments, push/pull rods  520  are moved up and down by rotating handles  527  on the ends of handle arms or shafts  526 . A plurality of wires  531  extend from cable holder  532  to respective ones of the shaft ends  511  of sockets  510 . Cable  534  extends to a source of power that is to be supplied to the vehicle (e.g., a boat, RV, or other vehicle) when plug  502  is inserted into a corresponding receptacle  501  on the vehicle. In some embodiments, the handles  527  are extended outward and backward (down in the  FIG. 5A , such that push rods  520  pull downward) for inserting or withdrawing the plug  502  from the receptacle  501 , and handles are pushed forward, upward and inward to the position shown, pushing the push rods  520  upward to release collets  512  with individual springs  514  to tighten on the sockets  510  at even and independent pressures around their respective prongs  506  in the receptacle  501 . Pushing the handles in the direction of the plug insertion allows the force used to tighten the handles  527  to also force the plug into a tighter embrace to receptacle  501 , while pulling on the handles  527  both loosens the clamping on the pins and withdraws the plug  502  from receptacle  501 . Plug body  536  is made of a suitable insulator, such as plastic material. In some embodiments, the size of plug  502  is as small as an ordinary household electrical cord plug, while in other embodiments, the size is as large as needed for high-current (e.g., hundreds of amps or more) applications needed by a larger vehicle such as an ocean-going ship. The even clamping forces provided by individual springs and collets means that even predetermined clamping forces are applied to each individual pin of the receptacle, resulting in a high-quality electrical connection. In the embodiment shown, there are three columns of sockets  510 . In other embodiments, these sockets  510  can be arranged in patterns other than straight rows and columns. 
       FIG. 5C  is a cross-section plan view of electrical connection system  500  having a socketed electrical plug  502  with collet releaser  530 , where the plug  502  is inserted and clamped in pronged receptacle  501 . When handles  527  are pushed forward, they urge plug  502  toward socket  501  while also releasing the spring-loaded collets to clamp upon prongs  506  with a pre-determined force that is determined by the strength of the springs  514  and which is substantially independent of the force applied to the handles  527 , thus ensuring the correct amount of force on the collets  510 . 
       FIG. 5D  is a plan view of a small version of a socketed electrical plug  502 ′. The body  536 ′ of plug  502 ′ forms the tightening taper into which collet-socket  512 ′ is pushed by springs  514  when released by collet holder  530  connected to handles  526 . Operation of plug  502 ′ is substantially the same as for plug  501  of  FIG. 5C , except that plug  502 ′ is smaller and uses little thumb-operated handle shafts  526  rather than hand-operated handles  527  at the ends of the handle shafts  526  of  FIG. 5C . 
       FIG. 5E  is an exploded cross-section plan view of socketed electrical plug  502  of  FIG. 5B  with collet releaser  530 . The various parts are described above in the description of  FIG. 5B . 
       FIG. 5F  is a front view of one embodiment pronged electrical receptacle  501 A. In some embodiments, this pin configuration is used with any of the above plugs or receptacles. 
       FIG. 5G  is a front view of one embodiment pronged electrical receptacle  501 B. In some embodiments, this pin configuration is used with any of the above plugs or receptacles. 
       FIG. 5H  is a front view of one embodiment pronged electrical receptacle  501 C. In some embodiments, this pin configuration is used with any of the above plugs or receptacles. 
       FIG. 5I  is a front view of one embodiment pronged electrical receptacle  501 D. In some embodiments, this pin configuration is used with any of the above plugs or receptacles. 
       FIG. 6A  is a cross-section plan view of compressible-socket socketed receptacle  601 . In some embodiments, receptacle  601  includes an insulator body  608  holding a plurality of sockets  610  (e.g., 3, 4, 6, or other suitable numbers of sockets), each socket  610  configured to be compressed around a corresponding pin  606  in the plug  602 , each socket  610  having a plurality of fingers  609  having tapered outer portions configured to be pushed inward by collet  612  when collet  612  is (independently of the other collets) allowed to be pushed outward (downward in  FIG. 6A ) by spring  614  when released by collet withdrawer  630 , which is driven by push/pull rods  620 . Stationary insulator block  618  holds the threaded shaft ends  611  of sockets  610 , screwed into nuts  617 . In some embodiments, push/pull rods  620  are moved up and down by rotating handles  627  on the ends of arms  626 . A plurality of wires  607  extend from inside vehicle  99  to respective ones of the shaft ends  611  of sockets  610 . 
       FIG. 6B  is a cross-section plan view of fixed-prong pronged electrical plug  602 . Cable  634  extends to a source of power that is to be supplied to the vehicle (e.g., a boat, RV, or other vehicle) when plug  602  is inserted into a corresponding receptacle  601  on the vehicle  99 . 
     Referring back to  FIG. 6A , in some embodiments, the handles  627  are extended outward and upward (down in the  FIG. 6A , such that push rods  620  push upward) for inserting or withdrawing the plug  602  from the receptacle  601 , and handles are pushed downward and inward to the position shown in  FIG. 6C , pulling the push rods  620  downward to release collets  612  with individual springs  614  to tighten on the sockets  610  at even and independent pressures around their respective prongs  606  in plug  602 . Pulling the handles in the downward direction shown allows the handles to capture and hold the plug  602 , allowing handles  627  to also force the plug  602  into a tighter embrace to receptacle  601 , while pulling open the handles  627  both loosens the clamping on the pins and allows withdrawal of the plug  602  from receptacle  601 . Plug body  636  is made of a suitable insulator, such as plastic material. In some embodiments, the size of plug  602  is as small as an ordinary household electrical cord plug, while in other embodiments, the size is as large as needed for high-current (e.g., hundreds of amps or more) applications needed by a larger vehicle such as an ocean-going ship. The even clamping forces provided by individual springs and collets means that even predetermined clamping forces are applied to each individual pin of the receptacle, resulting in a high-quality electrical connection. In the embodiment shown, there are three columns of sockets  610 . In other embodiments, these sockets  610  can be arranged in patterns other than straight rows and columns. 
       FIG. 6C  is a cross-section plan view of electrical connection system  600  having a fixed-prong pronged plug  602 , where plug  602  is inserted and clamped in compressible-socket socketed receptacle  601 . 
       FIG. 6D  is a plan view of a small version of pronged electrical plug  602 ′. 
       FIG. 6E  is an exploded cross-section plan view of socketed electrical receptacle  601  with collet releaser  630 . 
       FIG. 6F  is a front view of one embodiment of a compressible-socket receptacle  601 A. 
       FIG. 6G  is a front view of one embodiment of a compressible-socket receptacle  601 B. 
       FIG. 6H  is a front view of one embodiment of a compressible-socket receptacle  601 C. 
       FIG. 6I  is a front view of one embodiment of a compressible-socket receptacle  601 D. 
       FIG. 7A  is a cross-section plan view of a fixed-socket socketed receptacle  701 , which includes a plurality of fixed sockets  706  held in an insulating body  708  and connected to wires  707  that lead electrical power into vehicle  99 . 
       FIG. 7B  is a cross-section plan view of pronged electrical plug  702  (having expanding prongs) with collet releaser  730 . In some embodiments, pronged plug  702  with prong-base releaser  730 , where the plug  702  is inserted and clamped in socketed receptacle  701 . As shown in  FIG. 7C , this system  700  is conceptually the opposite of system  600  of  FIG. 6C , in that the plug  702  has expanding pins  705  (instead of contracting sockets  610 ), and receptacle  701  has fixed sockets  706  (instead of fixed pins  606 ). Receptacle  701  includes an insulator body  708  holding a plurality of fixed sockets  706  (e.g., three, four, six, or other suitable numbers of sockets  706 ), each connected to a respective wire  707  leading to interior connections in the vehicle. Plug  702  includes a plurality of expanding pins  705  (e.g., three, four, six, or other suitable numbers of sockets), each expanding pin  705  configured to be expanded outward in a corresponding socket  706  in the receptacle  701 , each expanding pin  705  having up-down moving outer portion  712  having a plurality of fingers  709  having tapered outer portions configured to be pushed outward by tapered shaft  710  when shaft base  713  is (independently of the other shaft bases) allowed to be pushed upward by spring  714  when released by shaft withdrawer  730 , which is driven by push/pull rods  720 . In some embodiments, plug body  736  is made of a suitable insulator, such as plastic material. Stationary insulator block  718  holds the threaded shaft ends  711  of tapered pins  710 , screwed into nuts  717 . In some embodiments, push rods  720  are hingedly connected to arms  726 , which are rotated by handles  727  on the ends of arms  726 . A plurality of wires  731  extend from cable holder  732  to respective ones of the wire receiver on shaft ends  713  of expanding pins  710 . Cable  734  extends to a source of power that is to be supplied to the vehicle (e.g., a boat, RV, or other vehicle) when plug  702  is inserted into a corresponding receptacle  701  on the vehicle. 
       FIG. 7C  is a cross-section plan view of electrical connection system  700  having a pronged plug  702  with collet releaser  730 , where the plug  702  is inserted and clamped in socketed receptacle  701 . 
       FIG. 7D  is an exploded cross-section plan view of pronged electrical plug  702  (having expanding prongs) with collet releaser  730 . 
     In summary: The life of the connector can be expected to be longer; the ease of use is dramatically improved; there is means for correctly handling the connector; there is much less tendency for heating damage internal and external to the connector, so expensive installation and assemblies do not have to be repaired, saving money and time for the user; safety is dramatically improved as the failure modes that typically exist are either dramatically reduced or prevented; power conduction is assured so the primary function of supplying power is dramatically improved. 
     Referring again to  FIG. 5B , in some embodiments, the handles  527  are spring loaded (pulled upwards by springs  577 ), such that the operator must force the handles  527  down into the “release” position in order to plug the plug  502  into the receptacle  501 , and when the handles  527  are released, the spring loading of springs  577  automatically lifts and closes the handles  527  to the up, locked, and clamping configuration. This helps prevent an operator from accidentally not forcing the handles into the engaged position, since when the operator releases the handles, they automatically move to the clamping position by springs  577 . In some embodiments, such a spring-loaded handle-engaging embodiment is used with other systems described herein. 
     In some embodiments, the amount of connection force (e.g., the force applied between the fingers  309  of a socket  310  and the prong  306  inserted into that socket when the handles  327  are pushed or pulled to release the spring force (from springs  314 ) to the collet  312  that tightens the fingers  309  onto the prong  306 ) is substantially higher than the amount of insertion force (e.g., the force imparted between fingers  309  and prong  306  during insertion of prong  306  into socket  310 ). For example, in some embodiments, the connection force applied on each prong is at least about 2 times the insertion force. In some embodiments, the connection force applied on each prong is at least about 5 times the insertion force. In some embodiments, the connection force applied on each prong is at least about 10 times the insertion force. In some embodiments, the connection force applied on each prong is at least about 25 times the insertion force. In some embodiments, the connection force applied on each prong is at least about 50 times the insertion force. In some embodiments, the connection force applied on each prong is at least about 100 times the insertion force. 
     In various embodiments, each of the sockets described above are or can be implemented either in the plug side of the connection or in the receptacle side of the connection, and conversely, each of the prongs described above are or can be implemented either on the receptacle side of the connection or in the plug side of the connection. 
     In some embodiments, the present invention provides an apparatus that includes a power outlet. In some embodiments, the power outlet (e.g., receptacle  601  of  FIG. 6A  and  FIG. 6B ) includes a plurality of power sockets including a first and a second power socket, each socket having a tightening mechanism that includes a plurality of socket fingers, each socket configured to allow a respective prong of a plug to be inserted with low insertion force and then to have the plurality of socket fingers of that socket tightened against the respective prong to an amount of connection force higher than the insertion force, in order to provide the amount of connection force to be set substantially independent of the force applied to the tightening mechanism. 
     In some embodiments of the power outlet, a low-resistance high-reliability non-locking connection is formed on each prong that permits the plug to be withdrawn without damage upon application of a sufficient tension force on the plug. 
     In some embodiments of the power outlet, the tightening mechanism includes a spring-loaded collet that surrounds the plurality of fingers. 
     In some embodiments of the power outlet, the tightening mechanism further includes at least one handle that, when activated, releases the spring-loaded collet to tighten around the plurality of fingers. 
     In some embodiments of the power outlet, the at least one handle, when deactivated, withdraws the spring-loaded collet from its tightened position around the plurality of fingers. 
     In some embodiments of the power outlet, the plurality of fingers for each socket includes at least three fingers spaced around a perimeter of the socket, and wherein the tightening mechanism includes a spring-loaded collet that surrounds the plurality of fingers. 
     In other embodiments, the present invention provides an apparatus that includes a power-cord plug (e.g., plug  100  of  FIG. 1A , plug  302  of  FIG. 3A , plug  304  of  FIG. 3B , plug  306  of  FIG. 3C , plug  502  of  FIG. 5B  and  FIG. 5C ) having a plurality of power sockets including a first and a second power socket, each having a tightening mechanism, each socket configured to allow a respective prong of an outlet to be inserted with low insertion force and then a plurality of socket fingers to be tightened to a higher connection force, in order to provide an amount of connection force that is set substantially independent of the force applied to the other connections. 
     In some embodiments of the socketed plug, a low-resistance high-reliability non-locking connection is formed on each prong that permits the plug to be withdrawn from the outlet without substantial damage upon application of a sufficient tension force. 
     In some embodiments of the socketed plug, the tightening mechanism includes a spring-loaded collet that surrounds the plurality of fingers. 
     In some embodiments of the socketed plug, the tightening mechanism further includes one or more handles that, when activated, release the spring-loaded collet to tighten around the plurality of fingers. 
     In some embodiments of the socketed plug, the one or more handles, when deactivated, withdraw the spring-loaded collet from its tightened position around the plurality of fingers. 
     In some embodiments of the socketed plug, the one or more handles are spring loaded, such that they must be pushed into a deactivated position, in order to withdraw the spring-loaded collet from its tightened position around the plurality of fingers, and when the handles are released, the spring loading moves the handles to a clamping position. 
     In some embodiments of the socketed plug, the plurality of fingers for each socket includes at least three fingers spaced around a perimeter of the socket, and wherein the tightening mechanism includes a spring-loaded collet that surrounds the plurality of fingers. 
     In other embodiments, the present invention provides an apparatus that includes a power-cord plug (e.g., plug  402  of  FIG. 4 , plug  702  of  FIG. 7B  and  FIG. 7C ) having a plurality of power prongs including a first and a second power prong, each having a expanding mechanism, each prong configured to insert into a respective fixed socket of an outlet, such that it can be inserted with low insertion force and then tightened to a higher connection force, in order to provide an amount of connection force that is set substantially independent of the force applied to the other connections. 
     In some embodiments of the pronged plug, a low-resistance high-reliability non-locking connection is formed in each socket by the respective expanding prong also permits the plug to be withdrawn from the outlet without substantial damage upon application of a sufficient tension force. 
     In some embodiments of the pronged plug, the tightening mechanism includes a spring-loaded expanding shaft having a plurality of fingers surrounding a tapered center shaft. 
     In some embodiments of the pronged plug, the tightening mechanism further includes one or more handles that, when activated, release the spring-loaded shaft to tighten the plurality of fingers around a tapered shaft in a fixed socket. 
     In some embodiments of the pronged plug, the one or more handles, when deactivated, withdraw the spring-loaded shaft base from its tightened position around the tapered shaft. 
     In some embodiments of the pronged plug, the one or more handles are spring loaded, such that they must be pushed into a deactivated position, in order to move each prong to its non-expanded configuration from its expanded-tightened position, and when the handles are released, the spring loading moves the handles to a clamping position where each prong is expanded in circumference. 
     In some embodiments of the pronged plug, the tightening mechanism includes an expanding shaft having a plurality of fingers surrounding a tapered spring-loaded center shaft, wherein the plurality of fingers for each prong includes at least three fingers spaced around a perimeter of the center shaft. 
     In some embodiments, the present invention provides a method for connecting to a power outlet. In some embodiments, the power outlet (e.g., receptacle  601  of  FIG. 6A  and  FIG. 6B ) includes a plurality of power sockets including a first and a second power socket, each socket having a tightening mechanism that includes a plurality of socket fingers. The method includes inserting respective prongs of a plug with low insertion force into the outlet, and tightening the plurality of socket fingers of each socket against the respective prong to an amount of connection force higher than the insertion force, in order to provide the amount of connection force to be set substantially independent of the force applied to the tightening mechanism. 
     Some embodiments of the power-outlet method further include forming a low-resistance high-reliability non-locking connection on each prong, and permitting the plug to be withdrawn without damage upon application of a sufficient tension force on the plug. 
     Some embodiments of the power-outlet method further include releasing a spring-loaded collet that surrounds the plurality of fingers so the collet squeezes the fingers against the respective prong. Some embodiments of the power-outlet method further include coupling at least one handle to the spring-loaded collet such that, when activated, the at least one handle releases the spring-loaded collet to tighten around the plurality of fingers. 
     Some embodiments of the power-outlet method further include connecting the at least one handle to the collet such that, when deactivated, the at least one handle withdraws the spring-loaded collet from its tightened position around the plurality of fingers. 
     In some embodiments of the power outlet method, the plurality of fingers for each socket includes at least three fingers spaced around a perimeter of the socket, and wherein the tightening includes releasing a spring-loaded collet that surrounds the plurality of fingers. 
     In other embodiments, the present invention provides a method for electrically connecting a power-cord plug (e.g., plug  100  of  FIG. 1A , plug  302  of  FIG. 3A , plug  304  of  FIG. 3B , plug  306  of  FIG. 3C , plug  502  of  FIG. 5B  and  FIG. 5C ) to a receptacle, the plug having a plurality of power sockets including a first and a second power socket, each having a tightening mechanism. This method includes inserting a respective prong of an outlet to a corresponding socket of the receptacle with low insertion force, and then tightening a plurality of socket fingers to a higher connection force, in order to provide an amount of connection force that is set substantially independent of the force applied to the other connections. 
     Some embodiments of the socketed-plug method further include forming a low-resistance high-reliability non-locking connection on each prong that permits the plug to be withdrawn from the outlet without substantial damage upon application of a sufficient tension force. 
     In some embodiments of the socketed-plug method, the tightening mechanism includes a spring-loaded collet that surrounds the plurality of fingers, and the method further includes releasing the spring-loaded collet to tighten the fingers. 
     In some embodiments of the socketed-plug method, the tightening mechanism further includes one or more handles that, when activated, the method further includes releasing the spring-loaded collet to tighten around the plurality of fingers. 
     In some embodiments of the socketed-plug method, the one or more handles, when deactivated, the method further includes withdrawing the spring-loaded collet from its tightened position around the plurality of fingers. 
     In some embodiments of the socketed-plug method, the one or more handles are spring loaded, and the method includes manually pushing the handles into a deactivated position, in order to withdraw the spring-loaded collet from its tightened position around the plurality of fingers, and when the handles are released, the method further includes automatically moving the spring-loaded handles to a clamping position. 
     In some embodiments of the socketed-plug method, the plurality of fingers for each socket includes at least three fingers spaced around a perimeter of the socket, and the method further includes spring loading the collet-tightening mechanism that surrounds the plurality of fingers. 
     In other embodiments, the present invention provides a method for electrically connecting a power-cord plug (e.g., plug  402  of  FIG. 4 , plug  702  of  FIG. 7B  and  FIG. 7C ) the plug having a plurality of power prongs including a first and a second power prong, each having a expanding mechanism. This method includes inserting each prong into a respective fixed socket of an outlet, such that it can be inserted with low insertion force and then tightened to a higher connection force, in order to provide an amount of connection force that is set substantially independent of the force applied to the other connections. 
     In some embodiments of the pronged plug method, the method further includes forming a low-resistance high-reliability non-locking connection in each socket by the respective expanding prong, and permitting the plug to be withdrawn from the outlet without substantial damage upon application of a sufficient tension force. 
     In some embodiments of the pronged plug method, the method further includes spring loading the tightening mechanism that includes an expanding shaft having a plurality of fingers surrounding a tapered center shaft. 
     In some embodiments of the pronged plug method, the tightening mechanism further includes one or more handles that, when activated, the method further includes releasing the spring-loaded shaft to tighten the plurality of fingers around a tapered shaft in a fixed socket. 
     In some embodiments of the pronged plug method, the one or more handles, when deactivated, the method further includes withdrawing the spring-loaded shaft base from its tightened position around the tapered shaft. 
     In some embodiments of the pronged plug method, the one or more handles are spring loaded, such that method includes manually pushing the handles into a deactivated position, in order to move each prong to its non-expanded configuration from its expanded-tightened position, and when the handles are released, the method further includes moving the spring-loaded handles to a clamping position where each prong is expanded in circumference. 
     In some embodiments of the pronged plug method, the tightening mechanism includes an expanding shaft having a plurality of fingers surrounding a tapered spring-loaded center shaft, the method further includes spacing the at least three fingers for each around a perimeter of the center shaft. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. Although numerous characteristics and advantages of various embodiments as described herein have been set forth in the foregoing description, together with details of the structure and function of various embodiments, many other embodiments and changes to details will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should be, therefore, determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively. Moreover, the terms “first,” “second,” and “third,” etc., are used merely as labels, and are not intended to impose numerical requirements on their objects.
In some embodiments, the present invention provides an independently tightening collet surrounding each socket for each of a plurality of corresponding high-electrical-power prongs, wherein the collet is loosened for normal (low-insertion-force) insertion and withdrawal of the plug from the outlet. Once the plug is inserted, the collet is tightened, providing a high-contact force to lower the contact resistance and to help keep the plug from coming unplugged. In some embodiments, the plug is not "locked", in that a tension force pulling on the plug will overcome the contact force at a point before the plug or outlet is damaged, and the plug is allowed to come unplugged. In some embodiments, engaging the collet will also provide a wiping or sliding motion between the prong and socket for each connection, thus wiping at least some dirt or corrosion away and providing a lower-resistance better electrical contact.