Abstract:
A lay-in lug has two spaced apart and substantially parallel lug walls. A nut plate is supported between the first lug wall and the second lug wall. A plate retainer exerts force on a lug wall and restricts the plate from moving in a direction substantially parallel to the first and second lug walls. The plate retainer has a flexible retaining base and a pair of retaining legs extending from the retaining base. Snap protrusions extend from each of the retaining legs and are formed to interlock with a portion of the wall of the lay-in lug and restrict movement the nut plate. The plate retainer either snaps around the edge of the lug wall or along the wall&#39;s length. It may also clip around the nut plate and prevents its movement in a direction along the inner surfaces of the lug walls.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/955,982 filed Aug. 15, 2007, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to lay-in lugs and more particularly to techniques for securing a nut plate of a lay-in lug. 
     Lay-in lugs are similar to “C” or “J” type lugs, as are known, and are used to secure wires (e.g., electrical cables, wiring, tubing, etc.). Lay-in lugs are often used in electrical and similar applications to electrically connect service and/or feed phase-neutral conductors to electrical metering equipment and/or circuit protection. Lay-in lugs may be used in piping systems, such as electrical conduits and the like, to secure wires transposed vertically in a shaft, such as an electrical conduit riser. That is, lay-in lugs are used to hold (e.g., hang) wires vertically. 
       FIG. 1  is a front perspective view of an exemplary lay-in lug  100  as is known. Lay-in lug  100  has a lug body  102  comprising a base  104  and two opposed and substantially parallel vertical lug walls  106 ,  108 . Supported between and/or atop lug walls  106  and  108  is a removable nut plate  110 , which secures a wire binding screw  112 . 
     In use (e.g., in an installation operation), lay-in lug  100  is secured to a surface (not shown) at its base  104 . In vertical installation operations, lay-in lug  100  is secured such that the “open” ends  114  and  116  (e.g., sides of lug body  102  not dominated by a lug wall  106 ,  108 ) face substantially up and down, respectively (e.g., toward negative X and positive X, respectively). That is, lug walls  106  and  108  will be generally parallel to the direction of a gravity vector G and a secured wire  118 . Nut plate  110 , with wire binding screw  112  secured thereto, is removed from between lug walls  106 ,  108 . This provides top down (e.g., positive Z to negative Z) access to the center channel  120  of lug body  102 . Wire  118  (e.g., electrical cable, wiring, etc.) is laid in, pulled through, or otherwise transposed in the center channel  120  of lug body  102  between lugs walls  106  and  108 , generally along the X axis. Nut plate  110  is returned to placement between and/or on top of lug walls  106 ,  108  and wire binding screw  112  is torqued (e.g., screwed, driven, etc.) to secure wire  118  between base  104  and wire binding screw  112  in the Z direction. Wire  118  is, of course, further secured laterally (e.g., in the Y direction) by lug walls  106 ,  108 . 
       FIG. 2  depicts a top-front perspective exploded view of another known lay-in lug  200 . Lay-in lug  200  is similar to lay-in lug  100  and has a lug body  202  having a lug base  204  and a pair of generally parallel, opposed lug walls  206  and  208 . Lay-in lug  200  also has a nut plate  210  (e.g., a lug cap, top, etc.) attachable to the lug body  202  for capture of a wire  118  (e.g., electrical cable, etc.) with wire binding screw  212 . As with lay-in lug  100 , lay-in lug  200  has “open” ends  214  and  216  and nut plate  210  may be moved along an axis aligned between open ends  214 ,  216  (e.g., the X axis). The nut plate  210  of lay-in lug  200  has a pair of generally parallel nut plate ears  218  and  220  and respective nut plate flanges  222  and  224 . As shown in  FIG. 2 , each of the nut plate flanges  222 ,  224  engages a respective lug body flange  226 ,  228  of the lug body  202 . Such flange arrangements, as well as similar ridged arrangements, are used to secure nut plates (e.g., nut plates  110 ,  210 , etc.) to lug bodies (e.g., lug bodies  102 ,  202 , etc.) in a vertical (e.g., Z) direction. 
     For simplification of discussion, the XYZ axes of  FIGS. 1 and 2 , as well as  FIGS. 3-6  below, may be assumed to be fixed to the lugs  100 ,  200 ,  300 . Though lugs  100 ,  200 ,  300  may be oriented in other manners in real world applications, the lugs  100 ,  200 ,  300  are described as non-rotating within the coordinate system. For example, in the context of the present application, the Z axis always refers to the “up-and-down” direction extending through nut plates  110 ,  210 ,  310  and bases  104 ,  204 ,  304 , irrespective of whether lugs  100 ,  200 ,  300  are placed on a “ground” surface, mounted to a wall, or are otherwise differently oriented. 
     The top-down (e.g., Z axis) access simplifies installation of wire  118  over prior “C” or “J” type lugs, but introduces a moveable and easily lost component—nut plate  110 / 210  with wire binding screw  112 / 212  attached. That is, since nut plate  110 / 210  is slideable and removable with respect to the rest of lug  100 / 200 , nut plate  110 / 210  may inadvertently slide away from lug walls  106 / 206 ,  108 / 208  in transit and/or in installation. This is especially probable and problematic during the aforementioned electrical conduit riser type installation. Since the open end  116 / 216  of lug body  102 / 202  faces downward along the X axis (e.g., towards the ground or bottom and generally in the same direction as gravity vector G), nut plate  110 / 210  is not secured in lug body  102 / 202  in the vertical (e.g., up and down, along the X axis, etc.) direction and may slide or otherwise fall out due to the force of gravity exerted on nut plate  110 / 210  and wire binding screw  112 / 212 . 
     Efforts have been made to prevent loss of nut plate  110 / 210  and wire binding screw  112 / 212 . Generally, wire binding screw  112 / 212  is driven (e.g., screwed) through nut plate  110 / 210  far enough that wire binding screw  112 / 212  passes through center channel  120  (similarly in  FIG. 2 ) and is bound in lug base  104 / 204 . Lug Body  102 / 202  may have to be additionally machined to have a counterbore to allow wire binding screw  112 / 212  to be driven into base  104 / 204 . With the wire binding screw  112 / 212  driven to contact or otherwise engage (e.g., be limited by) base  104 / 204 , nut plate  110 / 210  is bi-directionally secured along the X axis and will not slide out as it is constrained in the Y and Z axes by the lug walls  106 / 206 ,  108 / 208  and in the X axis by the interaction of wire binding screw  112 / 212  with base  104 / 204 . Wire binding screw  112 / 212  may also engage inner vertical lug walls  106 / 206 ,  108 / 208  (e.g., as with a counterbore, etc.). 
     These efforts fall short in that wire binding screw  112 / 212  must be used to secure nut plate  110 / 210  in the X axis. This is not useful during the installation operations described above because the wire binding screw  112 / 212  must be disengaged from the base  104 / 204  when nut plate  110 / 210  is removed to lay wire  118 . During replacement of the nut plate  110 / 210 , gravitational forces act on the nut plate  110 / 210  in the X direction and the nut plate  110 / 210  and the wire binding screw  112 / 212  may fall before the wire binding screw  112 / 212  is biased against the wire  118  and nut plate  110 / 210  interacts with the lug walls  106 / 206 ,  108 / 208  (e.g., at flanges  218 ,  220 ,  222 , and  224  and similarly in lug  100 ). 
     Therefore, alternative methods and apparatus are required to secure nut plates in lay-in lugs. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides apparatus for securing nut plates in lay-in lugs. 
     A lay-in lug has two spaced apart and substantially parallel lug walls. A nut plate is supported between the first lug wall and the second lug wall. A plate retainer exerts force on a lug wall and restricts the plate from moving in a direction substantially parallel to the first and second lug walls. The plate retainer has a flexible retaining base and a pair of retaining legs extending from the retaining base. Snap protrusions extend from each of the retaining legs and are formed to interlock with a portion of the wall of the lay-in lug and restrict movement the nut plate. The plate retainer either snaps around the edge of the lug wall or along the wall&#39;s length. It may also clip around the nut plate and prevents its movement in a direction along the inner surfaces of the lug walls. 
     These and other advantages of the invention will be apparent to those of ordinary skill in the art by reference to the following detailed description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front perspective view of a prior art lay-in lug; 
         FIG. 2  is a top-front perspective exploded view of a prior art lay-in lug; 
         FIG. 3  is a front perspective view of a lay-in lug according to an embodiment of the invention; 
         FIG. 4  is a top view of the lay-in lug according to an embodiment of the invention; 
         FIG. 5  is top-front perspective view of the lay-in lug according to an embodiment of the invention; 
         FIG. 6  is a side-front perspective view of the lay-in lug according to an embodiment of the invention; 
         FIG. 7  depicts a top view of a plate retainer according to an embodiment of the present invention; and 
         FIG. 8  depicts a top-side perspective view of the plate retainer according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention generally provides apparatus for securing nut plates in lay-in lugs. 
       FIGS. 3-6  depict a lay-in lug  300  according to an embodiment of the present invention. Lay-in lug  300  may be similar to and improve on lay-in lugs  100  and  200  of  FIGS. 1 and 2 . Accordingly, similar features are not described in further detail except as necessary to elucidate embodiments of the present invention. 
       FIG. 3  is a front perspective view of lay-in lug  300 .  FIG. 4  is a top view of lay-in lug  300 .  FIG. 5  is top-front perspective view of lay-in lug  300 .  FIG. 6  is a side-front perspective view of lay-in lug  300 . 
     Lay-in lug  300  has a lug body  302  comprising a base  304  and two opposed and substantially parallel vertical lug walls  306 ,  308 . Supported between and/or atop lug walls  306  and  308  is a removable nut plate  310 , which secures a wire binding screw  312 . A plate retainer  314  restricts nut plate  310  from moving in direction along lug walls  306 ,  308  (e.g., along the X axis). With nut plate  310  secured by lug walls  306 ,  308  and/or restricted by plate retainer  314 , wire binding screw  312  biases a wire  316  in channel  318  against base  304 . 
     Lay-in lug  300  may be formed and/or manufactured (e.g., extruded, cast, punched, etc.) using any appropriate material. In some embodiments, base  304  and/or lug body  302  may be constructed of conductive material. In the same or alternative embodiments, base  304  and/or lug body  302  may be plated with a conductive material. Body  302  and base  304  may be formed as a single component or may be manufactured separately and attached to each other. 
     Lug walls  306 ,  308  may be constructed in any manner that allows nut plate  310  to be secured between them in the Y axis as well as constrained in the Z axis, such as the configurations of  FIGS. 1 and 2 . Lug walls  306  and  308  each have respective inner surfaces  320  and  322 . Thus, nut plate  310  may be described as moveable and/or slideable in a direction substantially along inner surfaces  320 ,  322  toward and/or away from unconstrained open ends  324 ,  326 . 
     In some embodiments, lug walls  306 ,  308  may have recessed wall channels  328 ,  330 . Nut plate  310  may sit in, be supported in, and/or be moveably and/or slideably arranged in and/or on wall channels  328 ,  330 . As depicted in  FIGS. 3 ,  5 , and  6 , wall channels  328 ,  330  may be closed channels that have some portion of lug walls  306 ,  308  overhanging edges of nut plate  310 . In other embodiments, wall channels  328 ,  330  may be open channels with no portion of lug walls  306 ,  308  above nut plate  310  in the Z axis and nut plate  310  may be secured between lug walls  306 ,  308  in a tight fitting relationship (e.g., the spacing between opposed walls  306 ,  308  is slightly smaller than the width of nut plate  310  in the Y axis). In the same or alternative embodiments, wall channels  328 ,  330  may have wall flanges  332 ,  334  that may interlock with and/or otherwise engage a portion of nut plate  310 , such as nut plate flanges  336 ,  338 . 
     Additionally, respective outer surfaces  340 ,  342  of lug walls  306 ,  308  may have retainer channels  344 ,  346  formed thereon. In some embodiments, retainer channels  344 ,  346  may be recessed into outer surfaces  340 ,  342  of lug walls  306 ,  308 . In the same or alternative embodiments, retainer channels  344 ,  346  may have one or more raised surfaces (e.g., bumps, flanges, etc.) extending from outer surfaces  340 ,  342 . Retainer channels  344 ,  346  may guide, hold, secure, and/or otherwise restrain plate retainer  314  in a preferred position along outer surfaces  340 ,  342 . That is, retainer channels  344 ,  346  may provide a means to guide a portion of plate retainer  314  at a predetermined height in the Z direction. 
     Nut plate  310  may be a removable component formed and/or manufactured of a similar material to lug body  302 . Nut plate  310  may be tapped to accommodate wire binding screw  312 . In some embodiments, nut plate  310  may have a slightly smaller length (e.g., along the X axis) than the length (e.g., along the X axis) of lug walls  306 ,  308 . In this way, nut plate  310  may allow plate retainer  314  to overhang and/or otherwise impinge on a wall channel  328 ,  330  and restrict movement of nut plate  310  as will be described in further detail below with respect to  FIGS. 7 and 8 . 
     Plate retainer  314  is a mechanism for restricting movement of the nut plate  310  along the X axis. Plate retainer  314  may be a fastener such as a spring clip or circlip and may restrict movement at both ends of nut plate  310  along the X axis (e.g., portions of nut plate  310  oriented toward open ends  324 ,  326 ). Plate retainer  314  may be transposed along and/or in retainer channel  344 ,  346  and at least a portion of plate retainer  314  overhangs into a wall channel  328 ,  330  and/or center channel  318 . As a result, plate retainer  314  prevents nut plate  310  from sliding out of lug body  302  in the unconstrained direction (e.g., positive or negative X axis). Further details of plate retainers similar to plate retainer  314  are discussed below with respect to  FIGS. 7 and 8 . 
       FIG. 7  depicts a top view of a plate retainer  700  according to an embodiment of the present invention.  FIG. 8  depicts a top-side perspective view of plate retainer  700 . Plate retainer  700  may be used as plate retainer  314  and accordingly is discussed herein in relation to lay-in lug  300  and  FIGS. 3-6  where appropriate. Plate retainer  700  has a retaining base  702 , which may have one or more indentations or notches  704 . In some embodiments, notch  704  is located at approximately the center of the length of retaining base  702 , dividing retaining base  702  into two portions  702   a  and  702   b . At each end of retaining base  702  is a retaining leg  706 . Each retaining leg  706  has a snap protrusion  708  extending therefrom. 
     Plate retainer  700  may be formed as a single component or may comprise separate base  702 , retaining legs  706 , and/or snap protrusions  708 . Plate retainer  700  and its constituent components may be formed from a flexible or semi-flexible material, such as thermoplastic. As a result, plate retainer  700  may fit around a lug wall  306 ,  308  in a flexible but tight fitting relationship such that a portion of plate retainer  700  (e.g., retaining legs  706 , etc.) exerts a force against an open end  324 ,  326  edge of a lug wall  306 ,  308  in a direction substantially along the lug wall (e.g., along the X axis). In this way, plate retainer  700  exerts a force in one direction along the lug wall (e.g., in the positive X direction) as well as exerting a force in a substantially opposite direction along the lug wall (e.g., in the negative X direction). This secures plate retainer  700  to lug wall  306 ,  308  as well as restricting movement of nut plate  310 . 
     As will be understood from the description herein and the associated figures, the exact direction of the forces applied by the plate retainer  700  are not depicted. Based on the orientation and arrangement of certain portions of plate retainer  700  (e.g., retaining legs  706 , snap protrusions  708 , etc.) the resultant forces exerted on the lug body  302  and/or the nut plate  310  may differ slightly. One of skill in the art would recognize the plate retainer  700  restricts movement of the nut plate  310  as depicted in  FIGS. 3-6  without confining the present invention to a specific point of contact or force direction. 
     Flexible retaining base  702  may be a flexible (e.g., thermoplastic) bar or member with an inner surface  710  that is, in some embodiments, approximately the same length as the length of an outer surface of a lug wall (e.g., outer surface  340 ,  342 ) along the X axis (e.g., in a direction substantially parallel to the direction of movement of nut plate  310 ). In alternative embodiments, inner surface  710  may be slightly shorter than an outer surface of lug wall  306 ,  308 . In these embodiments, retaining legs  706  and/or retaining base  702  may flex to snap fit plate retainer  700  against and/or pinch an edge (e.g., at open end  324 ,  326 , etc.) of nut plate  310 . 
     Retaining base  702  may be more flexible at notch  704 . In this way, a retaining base portion (e.g., portion  702   a ) and/or an end of retaining base  702  (e.g., one of retaining legs  706 ) may be moved independently of the other retaining base portion (e.g., portion  702   b ) and/or the other end of retaining base  702  (e.g., the other of retaining legs  706 ). Thus, a user may move one part or end of plate retainer  700  away from lug  300  while the other part remains secured to the lug wall  306 ,  308 , restricting nut plate  310  at that end. 
     In some embodiments, retaining legs  706  may be shaped as open members (e.g., squares, rectangles, circles, etc.) as depicted in  FIGS. 7 and 8 . In these embodiments, retaining legs  706  form openings  712 . Openings  712  may be of sufficient size to allow a tool (e.g., screwdriver, pen, rod, etc.) or tool tip to enter the opening  712  to allow a user to manipulate plate retainer  700 . In alternative embodiments, retaining legs  706  may be formed in other appropriate shapes, such as a flat grip (e.g., for grasping by a user). 
     Retaining legs  706  may be flexible members with inner surfaces  714  that are, in some embodiments, approximately the same length as the width of an edge surface of a lug wall (e.g., lug walls  306 ,  308  at open end  324  or  326 ) along the Y axis (e.g., in a direction substantially perpendicular to lug walls  306 ,  308  and the direction of movement of nut plate  310 ). In alternative embodiments, inner surface  714  may be slightly shorter than an edge surface of lug wall  306 ,  308 . In these embodiments, retaining legs  706  and/or retaining base  702  may flex to snap fit plate retainer  700  against and/or pinch an edge (e.g., at the opening end) of nut plate  310 . 
     Snap protrusions  708  may be extensions of or may extend from retaining legs  706  for a predetermined distance. In some embodiments, snap protrusions  708  are sufficiently large to extend into wall channels  328 ,  330  and thus restrict movement of plate retainer  700  away from lug body  302  (e.g., in the Y axis). That is, if the plate retainer  314  depicted in  FIG. 3  is pulled in the positive Y direction, snap protrusions  708  will, at least until an overwhelming force is exerted, prevent plate retainer  700  from being pulled away from lug wall  306 . Further, snap protrusions  708  provide a stop against which nut plate  310  may contact if it moves sufficiently far in a direction along lug walls  306 ,  308 . In other words, snap protrusions  708  may restrict movement of nut plate  310  along the X axis by serving as a stop, guard, chock, etc. In some embodiments, nut plate  310  does not contact either snap protrusion  708 . In alternative embodiments, snap protrusions  708  extend sufficiently far to exert a force against nut plate  310  in a direction substantially parallel to inner surfaces  320 ,  322  of lug walls  306 ,  308  and to exert an opposite force against an opposite end of nut plate  310  in a direction substantially parallel to inner surfaces  320 ,  322  of lug walls  306 ,  308 . That is, snap protrusions may pinch or clip nut plate  310  to restrict its movement along the X axis. In the same or alternative embodiments, snap protrusions  708  may exert a force in a direction substantially perpendicular to the lug walls  306 ,  308  (e.g., in the positive Y direction) as snap protrusions  708  and retaining base  702  clip and/or pinch lug wall  306 ,  308 . 
     Though described herein as extensions from retaining legs  706 , snap protrusions  708  may be of any appropriate shape and/or size to facilitate restriction of movement of nut plate  310  as described herein. For example, snap protrusions  708  may have an additional protrusion and/or be shaped in such a way as to hook around, interlock, or otherwise engage a portion of lug wall  306 ,  308  and/or nut plate  310  similar to the interlock of flanges  332 - 338  described above. 
     In operation, lay-in lug  300  is secured to a surface (not shown) at and/or by its base  304  (e.g., using mounting apparatus, etc.). In vertical installation operations, lay-in lug  300  is secured such that “open” ends  324  and  326  (e.g., sides of lug body  302  not dominated by a lug wall  306 ,  308 ) face substantially up and down, respectively (e.g., toward negative X and positive X, respectively). That is, lug walls  304  and  306  will be generally parallel to the direction of a gravity vector G and a secured wire  316 . Nut plate  310 , with wire binding screw  312  secured thereto, is removed from between lug walls  306 ,  308 . This provides top down (e.g., positive Z to negative Z) access to the center channel  318  of lug body  302 . Wire  316  (e.g., electrical cable, wiring, etc.) is laid in, pulled through, or otherwise transposed in the center channel  318  of lug body  302  between lugs walls  306  and  308 , generally along the X axis. Nut plate  310  is returned to placement between and/or on top of lug walls  306 ,  308  by sliding nut plate  310  along wall channels  328 ,  330  and interlocking flanges  332 - 338 . Wire binding screw  312  is torqued (e.g., screwed, driven, etc.) to secure wire  316  between base  304  and wire binding screw  312  in the Z direction. Wire  316  is further secured laterally (e.g., in the Y direction) by lug walls  306 ,  308 . 
     Plate retainer  314 / 700  is clipped to lug body  302 . Retaining base  702  is set into a retainer channel  344 ,  346  and retaining legs are secured around a portion (e.g., a portion at an open end  324 ,  326 ) of a lug wall  306 ,  308 . Snap protrusions  708  exert a force on an inner surface  318 ,  322  (generally inside a wall channel  328 ,  330 ) and/or retaining legs  306  exert a force on the end portion of the lug wall  306 ,  308 . In this way, plate retainer  314 / 700  is secured to, clipped to, pinching, etc. a lug wall  306 ,  308 . Plate retainer  317 / 700  thus serves as a stop which restricts the movement of nut plate  310  along the walls  306 ,  308 . In practice, only one plate retainer  314 / 700  may be used. However, any number and/or arrangement of plate retainers  314 / 700  may be used. For example another plate retainer may be similarly attached on the opposing lug wall  306 ,  308 , a plate retainer  314 / 700  may be placed without guidance from a retainer channel  344 ,  346 , a plate retainer  314 / 700  may contact and exert forces on the nut plate  310  to further restrict movement, etc. 
     The foregoing Detailed Description is to be understood as being in every respect illustrative and exemplary, but not restrictive, and the scope of the invention disclosed herein is not to be determined from the Detailed Description, but rather from the claims as interpreted according to the full breadth permitted by the patent laws. It is to be understood that the embodiments shown and described herein are only illustrative of the principles of the present invention and that various modifications may be implemented by those skilled in the art without departing from the scope and spirit of the invention. Those skilled in the art could implement various other feature combinations without departing from the scope and spirit of the invention.