Abstract:
A fitting that provides snap-in engagement of EMT to a panel. The fitting includes a hollow, tubular, electrically conductive electrical connector including a fastening arrangement on the leading end to allow snap-in engagement to a panel and a resilient, electrically conductive, cylindrical-shaped split ring within the trailing end to allow snap-in engagement of EMT. A plurality of locking tangs on the split ring are lanced longitudinally and bent inwardly to a smaller diameter than the outer diameter of EMT that the fitting will be used in conjunction with. Arcuate edges included on the leading ends of the locking tangs dig into the outer surface of the EMT thereby holding it fast to the trailing end of connector. The large contact area between the locking tangs and the EMT provide a large amount of surface contact between the locking tangs and the EMT, thereby improving continuity and lowering the millivolt drop. The fastening arrangement on the leading end of the fitting is typically a split ring affixed to the nose of the connector.

Description:
This application is a Continuation-In-Part of U.S. patent application Ser. No. 10/256,641, filed Sep. 27, 2002 and still pending which is a Continuation-In-Part of U.S. patent application Ser. No. 10/053,076, filed Jan. 17, 2002 and still pending and is a Continuation-In-Part of U.S. patent application Ser. No. 09/792,184, filed Feb. 23, 2001 now U.S. Pat. No. 6,604,400 which is a Continuation-In-Part of U.S. patent application Ser. No. 09/603,756, filed Jun. 26, 2000 now U.S. Pat. No. 6,335,488 which is a Continuation of U.S. patent application Ser. No. 09/165,530, filed Oct. 2, 1998, now U.S. Pat. No. 6,080,933 which is a Continuation-In-Part of U.S. patent application Ser. No. 09/007,532, filed Jan. 15, 1998, now U.S. Pat. No. 6,043,432. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to fittings for connecting electrical metallic tubing (EMT) to a panel and specifically to an improved fitting that allows EMT to be snap fitted into the fitting to provide a quick and easy connection to a panel. 
     BACKGROUND OF THE INVENTION 
     Historically, electrical metal tubing (EMT) was connected to electrical boxes by a tubular fitting including a leading end with a threaded nose for insertion into a circular aperture in the box and a trailing end including a screw mounted laterally through the fitting wall for securing the EMT to the fitting. This arrangement, although providing an adequate means for securing EMT to boxes, junctions, and various electrical housings, is time consuming. For every connection, an installer must first stab the leading end of the fitting into the box and thread a lock nut onto the threaded nose to secure the fitting to the box and, secondly, secure the EMT to the trailing end of the fitting by tightening the laterally mounted screw through the fitting wall. For any given installation of EMT in a building or factory, electrical contractors may be required to make hundreds or even thousands of such connections to completely wire the building. Additionally, tools must typically be used to achieve a secure connection, including a wrench on the lock nut and a screw on the laterally mounted screw. Therefore, it should be appreciated that completing all of these connections can be very time consuming, with the contractors typically using both a wrench and a screwdriver on each connection. 
     Recently, snap engagement fittings have become popular as a means of connecting cables or EMT to electrical junction boxes. One such type of snap fitting is disclosed in U.S. Pat. No. 5,373,106 (hereinafter the &#39;106 patent) issued Dec. 13, 1994, and entitled “Snap In Cable Connector”. This patent disclosed a quick connect fitting for an electrical junction box including a split ring member that improved the ease of use and reduced the time involved in securing electrical fittings to electrical junction boxes. However, the fitting of the &#39;106 patent included the traditional method of securing the EMT or cable to the trailing end of the fitting, thereby requiring the use of a screwdriver to complete the connection on the trailing end. 
     Although inclusion of a split ring on the leading end of the fitting in the &#39;106 patent reduced installation time for the fitting to the box, it did not reduce installation time at the trailing end of the fitting, in which the EMT is secured to the fitting in the traditional manner. Therefore, what is needed is a fitting for securing EMT to panels and the like that does not require the use of any tools, at either the leading or trailing end, and that allows the leading end to be snap fitted into the panel and the EMT to be snap fitted into the trailing end. A fitting that allows snap engagement at both ends of the fitting, without the use of tools, would vastly reduce the time involved for installing EMT in a structure. Additionally, the fitting should be designed to work with standard electrical panels, boxes, housings, etc., including snap fit engagement with standard size knockout apertures. 
     These and other advantages will become apparent by reading the attached specification and claims in conjunction with reference to the attached drawings. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a fitting that provides a trailing end designed for snap-in engagement of EMT. The fitting comprises a hollow, tubular, electrically conductive electrical connector having a leading for connecting to a panel and a trailing end for connecting to EMT. A fastening arrangement is provided on the leading end to allow snap-in engagement to a panel. A resilient, electrically conductive, cylindrical-shaped split ring is secured within the trailing end of the connector. A plurality of locking tangs are lanced longitudinally and bent inwardly to a smaller diameter than the outer diameter of EMT that the fitting will be used in conjunction with. Arcuate edges are included on the leading ends of the locking tangs. The arcuate edges are capable of digging into the outer surface of the EMT and holding it fast to the trailing end of connector. The fastening arrangement on the leading end of the fitting is typically a split ring affixed to the nose of the connector. The connector, split ring affixed to the nose of the connector, and the split ring secured within the trailing end of the connector comprise the fitting of the present invention that provides snap-in engagement on both ends of the fitting. The fitting allows the leading end of the connector to be snapped into a standard sized aperture in a panel and also allows EMT to be snapped into the trailing end of the fitting. The large contact area between the locking tangs and the EMT provide a large amount of surface contact between the locking tangs and the EMT, thereby improving continuity and lowering the millivolt drop. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a preferred embodiment of the snap engagement electrical fitting according to the present invention in alignment with an electrical box and with the snap ring exploded away from the connector. 
     FIG. 2 is a plan view of a blank that will be formed into the cylindrical snap ring. 
     FIG. 3 is a front end view of the preferred embodiment of the cylindrical snap ring, or view from the leading end of the ring or the end facing the box in FIG.  1 . 
     FIG. 4 is a back end view of the preferred embodiment of the cylindrical snap ring, or view from the end of the ring facing away from the box in FIG.  1 . 
     FIG. 5 is a sectional view of the snap ring taken along line  5 — 5  of FIG.  3 . 
     FIG. 6 is a sectional view of the snap ring taken along line  6 — 6  of FIG.  3 . 
     FIG. 7 is a sectional view of the snap ring taken along line  7 — 7  of FIG.  4 . 
     FIG. 8 is a perspective view of the snap ring of FIG. 3, from the front side of the ring. 
     FIG. 9 is a perspective view of the snap ring of FIG. 4, from the back side of the ring. 
     FIG. 10 is a perspective view of the snap engagement electrical fitting according to the present invention in alignment with an electrical box and with a portion of the trailing end of the connector cut away to reveal portions of the split ring inserted in the trailing end. 
     FIG. 11 is a sectional view of the trailing end of the fitting with electrical metallic tubing secured therein. 
    
    
     INDEX TO REFERENCE NUMERALS IN DRAWINGS 
       20  snap engagement electrical fitting 
       22  hollow electrical connector 
       24  split ring 
       26  fastening arrangement 
       28  aperture 
       30  junction box 
       32  leading end of connector 
       34  trailing end of connector 
       36  electrically conductive snap ring 
       38  central flange 
       40  leading flange 
       42  blank 
       44  leading edge of split ring 
       46  trailing edge of split ring 
       48  M-shaped slot 
       50  locking tang 
       52  trailing end of locking tang 
       54  leading end of locking tang 
       56  arcuate edge 
       58  U-shaped slot 
       60  securing tab 
       62  stabilizer 
       64  leading end of securing tab 
       66  trailing end of securing tab 
       68  panel engagement tangs 
       70  grounding tangs 
       72  window 
       74  leading end of fitting 
       76  trailing end of fitting 
       78  EMT (electrical metallic tubing) 
       80  inner, wall of split ring 
       82  end of stabilizer 
       84  circular engagement surface 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention comprises a fitting for connecting EMT to a panel or junction box and providing snap-fit engagement of the leading end of the fitting with a panel and snap-fit engagement of EMT to the trailing end. This invention relates to and incorporates herein by reference in its entirety U.S. patent application Ser. No. 10/256,641, filed Sep. 27, 2002, pending U.S. patent application Ser. No. 10/053,076 filed Jan. 17, 2002, pending U.S. patent application Ser. No. 09/792,184, filed Feb. 23, 2001, U.S. Pat. No. 6,335,488 issued Jan. 1, 2002, U.S. Pat. No. 6,080,933 issued Jun. 27, 2000, and U.S. Pat. No. 6,043,432 issued Mar. 28, 2000. 
     Referring to FIG. 1, there is shown a preferred embodiment of the snap engagement electrical fitting  20  for EMT according to the present invention. The snap engagement fitting  20  includes a hollow, tubular, electrically conductive electrical connector  22 , a resilient, electrically conductive, cylindrical-shaped split ring  24 , and a fastening arrangement  26  for snap engagement with an aperture  28  in a panel or junction box  30 . The electrical connector  22  includes a leading end  32  facing the box  30  and a trailing end  34  facing away from the box. A preferred embodiment of the fastening arrangement  26  includes an electrically conductive snap ring  36  disposed on the leading end  32  of the connector  22  between a central  38  and a leading  40  flange. The split ring  24  fits within the hollow interior of the trailing end  34  of the tubular connector  22  as will be described herein. 
     The cylindrical-shaped split ring is formed from a flat piece or blank  42  of spring steel as shown in FIG.  2 . Details of the split ring will be described with reference to its eventual alignment with the junction box. The edge  44  of the blank  42  shown on the top of FIG. 2 will therefore become the leading edge  44  of the split ring after it is formed into its cylindrical shape and the opposite edge is the trailing edge  46 . In the preferred embodiment of the blank  42  shown in FIG. 2, four M-shaped slots  48  are cut in the blank to form eight locking tangs  50  arranged substantially along the length of the blank near the leading edge  44 . The locking tangs  50  include a trailing end  52  that is integral with the blank and a free leading end  54  that include arcuate edges  56 . The arcuate edges  56  have radii that will maximize surface contact of the arcuate edges with the particular standard sized EMT that they will be used in conjunction with. It should be noted that the pairs of locking tangs  50  are staggered different distances from the leading edge  44 , with the first and third pairs of locking tangs  50 , as numbered from the left to right hand side of FIG. 2, closer to the leading edge  44  than the second and fourth pairs of locking tangs  50 . This will insure that, once the split ring  24  is formed into its cylindrical shape, such as shown in FIG. 3, the pairs equidistant from the leading edge will be approximately opposite each other across the split ring  24 . 
     As shown in FIG. 2, the preferred embodiment of the blank  42  includes two U-shaped slots  58  near the trailing edge  46  that define securing tabs  60 . Four stabilizers  62  have also been formed in the blank  42  near the trailing edge  46 . 
     FIG. 3 depicts the blank  42  of FIG. 2 after it has been formed into its cylindrical-shaped split ring  24  as viewed from the leading end  44 . The locking tangs  50  have been bent with the arcuate edges  56  of the free ends  54  facing inwards as shown. The trailing ends  52  of the locking tangs  50  are cantilevered from the split ring  24 . The securing tabs  60  are bent outwards of the ring. 
     Referring now to FIG. 4, the cylindrical-shaped split ring  24  as viewed from the trailing end  46  shows the stabilizers  62 , which are raised areas pressed inwards of the ring near the trailing edge  46 . The stabilizers  62  narrow the effective inner diameter of the split ring  24  near the trailing edge  46 . 
     As shown in the sectional view of the split ring  24  in FIG. 5, the securing tabs  60  are bent outwards of the split ring  24  and include a leading end  64  cantilevered from the ring and a free end  66 . Two securing tabs  60  are depicted in the preferred embodiment of the split ring  24 . 
     The sectional view of the split ring  24  in FIG. 6 depicts the locking tangs  50  bent inwards of the ring. The locking tangs  50  include a trailing end  52  that is cantilevered from the split ring  24  and a free leading end  54  that extends inwards of the ring. The locking tangs  50  include sharp arcuate edges  56  that point toward the leading edge  44  of the split ring  24  as shown. 
     Referring to FIG. 7, the stabilizers  62  are raised areas in the wall of the split ring  24 . The stabilizers  62  are located near the trailing edge  46  of the split ring  24  and will serve to reduce the effective diameter of the trailing end of the split ring  24 . 
     FIG. 8 depicts a perspective view of the split ring  24  as viewed from the leading end  44 . The locking tangs  50  are spaced around the periphery of the split ring  24  near the leading end  44  and include arcuate edges  56  that extend inward of the ring and are directed toward the leading end  44 . Securing tabs  60  include leading ends  64  that are cantilevered from the split ring  24  and free trailing ends  66 . 
     FIG. 9 depicts a perspective view of the split ring  24  as viewed from the trailing end  46 . The stabilizers  62  project into the inner bore through the split ring  24  and reduce the effective diameter at the trailing end  46 . 
     The operation of the snap engagement electrical fitting may best be understood by reference to FIG.  1 . The fitting  20  typically includes a hollow, tubular, electrically conductive connector  22  that having a central  38  and leading  40  flange. A securing arrangement on the leading end  32  of the connector typically consists of an electrically conductive snap ring  36 . The snap ring  36  is typically constructed of spring steel and is formed to a smaller diameter than the leading end  32  of the connector  22  between the two flanges  38  and  40 . The snap ring  36 , being constructed of the resilient spring steel, therefore is typically slid over the leading flange  40  and snaps to its relaxed diameter over the leading end of the connector. The snap ring  36 , thus seated on the leading end  32  of the connector  22 , forms a fastening arrangement  26  for securing the leading end of the connector  22  to a panel. In the preferred embodiment of the fastening arrangement  26  as depicted in FIG. 1, the snap ring  36  includes outward bent panel engagement tangs  68  and grounding tangs  70 . 
     On its trailing end  34 , the tubular bore of the electrically conductive connector  22  includes windows  72  into which securing tabs  60  extend from the electrically conductive split ring  24 . The electrically conductive split ring  24  is formed to a larger diameter than the interior diameter of the trailing end  34  of the connector  22 . Therefore, the split snap ring  24  may be secured to the trailing end  34  of the connector  22  by compressing the ring  24  from its relaxed diameter to a smaller diameter and inserting the ring  24  in such a manner that the securing tabs  60  align with the windows  72  in the connector  22 . After being inserted into the hollow trailing end  34  of the connector  22 , the split ring  24  may be released, and, being constructed of spring steel, will spring back to the diameter of the hollow trailing end  34 , whereupon the securing tabs  60  lock into the windows  72  and secure the split ring  24  to the connector  22 . 
     As shown in FIG. 10, the snap engagement electrical fitting  20  according to the present invention consists of the connector  22 , the split ring  24  disposed within the trailing end  34  of the connector  22 , and the fastening arrangement  26  on the leading end  32  of the connector  22 . 
     With reference to FIG. 10, the fitting  20  of the present invention is operated by simply snapping the leading end  74  of the fitting  20  into an appropriately sized knockout aperture  28  in a panel or junction box  30 . After the leading end  74  of the fitting  20  is secured to the box  30 , Electrical metallic tubing  78  is then simply inserted into the trailing end  76  of the fitting  20  until the EMT  78  is inserted past the locking tangs  50  of the split ring  24 . The arcuate edges  56  of the locking tangs  50  dig into the outer surface of the EMT  78  and secure it within the trailing end  76  of the fitting  20 . As should be appreciated by those skilled in the art, the snap engagement electrical fitting  20  according to the present invention simplifies the task of connecting EMT to panels, junction boxes, and the like. The fitting of the present invention saves time over prior art fittings by eliminating the time required to fasten locking nuts on the leading end of the connector to fasten it to a panel or to tighten lateral screws on the trailing end of the connector to secure the EMT. 
     FIG. 11 depicts a sectional view of the trailing end  76  of the fitting  20  after EMT  78  has been secured therein. EMT with a nominal conduit size of ½-inch has an outer diameter of 0.706 inch. The locking tangs  50  typically are at an angle of 60° from the walls of the split ring  24  and extend into the inner bore of the split ring to an extent such that the distance between the opposing arcuate edges  56  of the locking tangs  50  is typically 0.645 inch. The distance between the opposing arcuate edges  56  of the locking tangs  50  is therefore approximately 0.060 inch less than the outer diameter of the conduit  78 . Insertion of the ½-inch conduit  78  into the trailing end  76  of the fitting  20  therefore deflects the locking tangs  50  and displaces them 0.030 inch toward the inner wall  80  of the split ring  24 , or a total deflection of approximately 0.060 inch for the opposing locking tangs. After insertion of the EMT  78 , the locking tangs  50  are typically at an angle of 45° with respect to the inner wall  80 . The arcuate edges  56 , which extend substantially around the outer perimeter of the EMT  78 , bite into the outer wall of the EMT and hold it fast within the fitting  20 . As the EMT  78  is inserted into the fitting  20 , the split ring  24  is restrained from expanding in diameter by the inner wall  80  of the trailing end  76  of the fitting  20 . The stabilizers  62  extend into the inner bore of the split ring  24  such that the opposing ends of the stabilizers  82  are typically 0.730 inch apart. Insertion of the 0.706 inch diameter EMT  78  therefore allows a clearance of 0.024 inch on each side of the conduit. The stabilizers thus act to restrain the inserted conduit from sideways movement caused by a force applied to some portion of the conduit  78 . 
     As shown in FIG. 3, the arcuate edges  56  on the locking tangs  50  form a circular engagement surface  84  for engaging the outer periphery of the conduit (not shown). The radii of the arcuate edges  56  preferably approximate the radius of the conduit (EMT) that it will be used in conjunction with. For a ½-inch nominal size conduit then, with an outer diameter of 0.706 inch, the radius of curvature of the conduit is therefore 0.353 inch. The radius of curvature of each arcuate edge  56  in the preferred embodiment is preferably 0.323 inch. When the locking tangs  50  engage a conduit  78 , such as shown in FIG. 11, the engaged locking tangs  50  are at an angle of approximately 45° to the wall  80 , and the radius of the arcuate edges  56  are selected to maximize surface contact with the outer periphery of the conduit  78  at the selected angle of engagement. 
     The material of construction of the split ring is typically hardened spring steel. A preferred material of construction is AISI (American Iron and Steel Institute) 1050 CRS (cold rolled steel), annealed #3 edge, hardened to Rc 42-44, zinc plated to 0.0005″ thick minimum. With a Rockwell C hardness of 42-44, the arcuate edges  56  of the locking tangs  50  easily penetrate the outer surface of the conduit  78  that is typically manufactured to the standards of the National Electrical Code (Article 348 of the NEC). A typical thickness for the split ring  24  is 0.020 inch, which insures that the arcuate edges are sharp enough to penetrate the softer EMT  78 . 
     Displacement of the locking tangs as described herein and the intimate contact of the arcuate edges on the inserted conduit create a connection between the box and the conduit that exhibits improved continuity and lowers the millivolt drop across the fitting. The locking tangs and arcuate edges also serve to lock the conduit within the fitting, thereby providing proper strain relief to the conduit and preventing accidental withdrawal of the conduit from the fitting and box. Use of the fitting saves a lot of time over traditional prior art fittings, as snap in engagement on both ends of the fitting eliminates the need for manual manipulation of tools to connect the prior art device. 
     Electrical metallic tubing of course is supplied in a myriad of nominal conduit sizes. The snap engagement electrical fitting of the present invention can therefore be produced in a myriad of sizes to accommodate the various conduit sizes. Although the relative sizes of the connector and split ring will vary with the conduit size, the principle of controlling the angle of the locking tangs with respect to the wall of the split ring and the sideways displacement of the locking tangs to create a hold on the inserted conduit remains the same. Additionally, the fastening arrangement including the electrically conductive snap ring can be varied in size to fit different standard aperture sizes that are typically provided for EMT connection to panels, boxes, and the like. 
     Although the description above contains many specific descriptions, materials, and dimensions, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.