Abstract:
A connector is attachable to an extending transformer stud. The connector includes a single hole or bore within the body of a connector to accept threaded transformer studs of different thread sizes. The connector can accommodate different size studs while still providing a compact design. The connector provides increased physical contact with the stud. The connector can be easily installed and removed from a stud without undue effort on the part of the installer. The stud connector includes an elongated passageway with three bore centers, wherein the thread center is slightly offset from the elongated passageway center and the elongated passageway having a diameter just slightly larger than the stud to be received. The elongated passageway includes more than one thread size milled or tapped into the bore circumference.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority to U.S. Provisional Patent Application No. 60/703,778, filed on Jul. 29, 2005, which is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates generally to a connector for connecting to a transformer having a single stud hole with superimposed multiple threads. More particularly, the present invention relates to a transformer stud connector, having an easy-off stud mounting hole, for installing on studs of different sizes and which permits the connector to disengage the stud and slide off without the need for moving the connector from side to side. 
   BACKGROUND OF THE INVENTION 
   Electrical transformers are typically used to distribute electrical power from main utility lines for secondary distribution. The transformer accepts the main utility line on the primary side of the transformer and distributes the power from a secondary side of the transformer. An electrical step-down is provided by the transformer so as to provide for the proper secondary distribution of electrical power for residential and commercial use. 
   The transformer is normally housed in a steel cabinet. A threaded copper stud extends from the secondary side of the transformer from which secondary distribution is provided. Plural electrical conductors, connected to the threaded stud, provide for distribution of power to the end user. 
   In order to connect the conductor to the stud, a transformer stud connector is employed. These transformer stud connectors are elongate, electrically conductive members which are inserted over the copper stud extending from the secondary side of the transformer. The stud connector may be threadingly attached to the transformer stud. Extending longitudinally therefrom are a plurality of conductor accommodating ports wherein the ends of conductors may be inserted. Each conductor port has an associated set screw to effect mechanical and electrical connection to the transformer stud connector. Examples of transformer stud connectors are shown in U.S. Pat. Nos. 5,931,708; 5,848,913; 5,690,516; DES 377,782; DES 346,150; and DES 309,664. 
   In a typical arrangement, the utility distribution transformer has threaded studs typically ⅝-11 or 1-14, oversized applications can have larger 1¼-12, 1½-12 threaded studs or possibly a custom size dictated by customer needs. A connector, sometimes referred to as a bus bar, is used to connect to the stud and provide ports for multiple wire connections. The connector is threaded with the same pitch tread but the threaded hole is equal or larger to the diameter of the transformer stud. This allows the connector to be slipped on to the stud, known as a slip fit connector, instead of being spun onto the treaded shaft. This allows the connector to be installed and removed without having to remove any of the conductors. An orthogonally mounted set screw is typically used to secure the connector to the studded shaft. However, slip fit connectors, due to the presence of threads around the inside of the stud hole can sometime be difficult to remove from the stud. In many cases, once the setscrews securing the connector are loosened, the connector must still be wiggled up and down or side to side to get the connector to slide off. This can make removal of the connector a difficult and time consuming process as well as damaging the connector and stud threads by repeated contact between the threads while trying to wiggle the connector off of the stud. This problem can be exacerbated when the connector is adapted to receive more than one size stud due to the close tolerances that are required for the stud connector hole when more than one size stud can be accommodated within the connector. 
   In prior art connectors, various means were provided so that a single connector could be used to service studs of various sizes. One way is to provide at least two threaded holes, one for each of the stud sizes serviced by the connector. However, the disadvantage of such design is that it requires at least two holes, and therefore needs to be larger than necessary. Also, because by design the stud hole has to meet a certain depth to accommodate the stud, the portion of the connector receiving the threaded stud in not usable for conductor connections, thus additionally requiring a longer connector to accommodate an equal number of conductors. This problem is exacerbated for connectors having multiple threaded holes. In addition, a multi hole connector does not address the problems of easy installation and removal. 
   A further prior art design utilizes a tear-drop design of two holes which overlap and therefore produce a large diameter threaded hole having an arc-section of a smaller hole at the bottom of the larger hole, which extends beyond the perimeter of the larger hole. The disadvantage of this design is that it requires pre-drilling a smaller hole, followed by drilling of the second larger hole, partially overlapping the smaller hole. Alternately, the larger hole can be bored first, followed by milling or broaching of the bottom arc section to create the “tear-drop”. Both methods therefore require a two-step process, which adds complexity and expense to the manufacturing process. 
   A third alternative prior art design utilizes a slider system mounted to the connector which has grooved sides at various levels on the connector body. By moving the slider, in the grooves, various gap sizes between the slider and the connector body can be formed. However, this design requires a second element, the slider, to be added to the connector, which adds complexity and expense to the manufacturing process. 
   It is therefore desirable to provide a transformer stud connector, which can be mounted on studs of various sizes without the complexity, or cost of prior art designs, has a more compact design, provides greater physical contact between the connector and the stud and provides for easy installation and removal of the connector with out extra effort or steps on the part of the user. 
   SUMMARY OF THE INVENTION 
   The present invention provides a connector, which can be attached to transformer studs of various sizes with a single threaded hole. 
   The present invention uses a single hole or bore within the body of a connector to accept two or more threaded studs of different thread sizes. Furthermore, the present invention can accommodate one or more different size studs while still providing a connector that has a compact design, provides increased physical contact between the stud and connector, is easily manufactured and can be easily installed and removed from a stud without undue effort on the part of the installer. This is accomplished in the present invention by producing a stud connector having an elongated passageway with three bore centers, wherein the thread center is slightly offset from the elongated passageway diameter and the elongated passageway being just slightly larger than the stud to be received. Furthermore, the elongated passageway includes more than one thread size milled into the offset bore diameter. 
   To that end there is provided an electrically conductive transformer stud connector comprising, a body with an elongated passageway centered at a first point, for receiving a transformer stud having threads of a particular root distance, a first thread corresponding to the transformer stud threads of a particular size within the elongated passageway wherein the elongated passageway is centered at a second point that is vertically offset from the first point by a distance equal to the root distance. 
   The present invention further provides a method of making an electrically conductive transformer stud connector comprising forming a cylindrical elongated passageway within a connector body centered at a particular point for receiving a stud of a predetermined root distance, forming a first threaded region corresponding to a predetermined thread size and pitch centered at a point that is vertically offset from the particular point, forming a second threaded region overlapping the first threaded region corresponding to a second predetermined thread size and pitch wherein the first threaded region and the second threaded region overlap along a single line of tangency. 
   As shown by way of a preferred embodiment herein, the connector of the present invention includes a single elongated passageway with an offset bore cradle for accommodating more than one thread size which is easy to install and remove. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a perspective view of a portion of the connector according to the present invention. 
       FIG. 2  is a cross-sectional drawing of a connector according to the present invention. 
       FIG. 3  is a cross-sectional drawing of a connector according to the present invention having a stud installed. 
       FIG. 4  is a cross-sectional drawing of a connector according to the present invention having an alternate stud installed. 
       FIG. 5  is a schematic drawing of the threaded hole of the connector according to the present invention depicting the thread arrangement. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , there is shown a perspective view of the connector according to the present invention. Shown is connector body  10  having a longitudinal bore  12  including threads  14  disposed along the inner diameter. Set screws  16  protrude from the top of connector body  10  and can be screwed into connector body  10  to contact transformer stud (not shown). As shown in  FIG. 1 , and which will be further described with respect to  FIG. 2 , threads  14  are helically disposed about a portion of the circumference of longitudinal bore  12 . In a preferred embodiment, the threads  14  are helically disposed around up to approximately 130° of longitudinal bore  12 , but threads  14  may also be disposed in a parallel or non-helical arrangement. There is further shown side surface  18  of the connector body  10 , which, when mounted to a transformer stud faces the transformer. 
   The connector body  10  is an integrally formed metallic member, preferably formed of aluminum or other material, having high electrical conductivity. Transformer stud connector body  10  includes central, generally elongate cylindrical bore  12 . The central bore  12  is internally threaded to accommodate the extending, externally threaded transformer stud (not shown). The length of bore  12  need only be approximately the length of the extending portion of the stud so that when the body is placed over the stud, the stud and the bore extend generally the same distance. 
   Transformer stud connector body  10  will typically include conductor-accommodating ports  11  for receiving conductors located on the cantilevered step portions  13  of connector body  10 . In this way, additional conductor accommodating ports  11  can be added without extending the length of connector body  10 . 
   Each conductor port will also include a securement device such as a set screw  17  for securing the conductor. Each set screw aperture is in communication with the respective conductor receiving port so that set screws  17  may be inserted therein to mechanically and electrically secure the ends of the conductors within the stud connector body  10 . In a typical arrangement, each of the ports extends from one side surface of the connector body  10 . The conductor ports are generally positioned on similarly facing surfaces so that conductors inserted into the ports can be inserted from the same direction. 
   Referring now to  FIG. 2 , the transformer stud connector body  10  is depicted as having a central region with a longitudinal bore  12 , and two cantilevered step portions  13 . The longitudinal bore  12  includes an aperture  20  for receiving at least one particular size stud. In the particular example described with respect to  FIG. 2 , the longitudinal bore  12  is drilled to accept at maximum, a 1 inch stud. In the case of a 1-inch diameter stud, the aperture  20  is drilled to a diameter of 1.060 inches. 
   In accordance with the present invention, to accommodate the stud, once aperture  20  is drilled, the threads for a particular size thread are tapped into aperture  20 . In the exemplary embodiment of the present invention described, two threads, a larger diameter thread  22  having a center point  23  and a smaller diameter thread  24 , are tapped into aperture  20 . The location of the larger diameter thread  22  is located with respect to the aperture center  21 . The larger diameter thread  22  center  23  is offset from the aperture center  21  by a distance  26  that corresponds to the root distance between the valley and crest of the stud thread that is received into the larger diameter thread  22 . The third center  28  of the smaller diameter thread  24  is located such that the smaller thread crest is tangent to the larger diameter thread crest at a point  25  along the base of aperture  20 . By offsetting the center  23  of larger diameter thread  22  a cradle  27  is formed at the base of aperture  20 . 
   By offsetting the tapped threads from the center  21  of aperture  20 , the majority of the inside circumference of aperture  20  remains smooth, i.e., without threads. Therefore, it is easier to slip connector  10  onto the transformer stud since there is a smaller area of the inner circumference that is covered by threads that may catch onto the threads of the stud during installation or removal of the connector  10 . In addition, aperture  20  can be drilled to a smaller dimension. In the example described, the aperture is only 0.060″ larger than the stud size to be accommodated whereas it normally would be oversized at least ⅛″ and typically ¼″. Further, the size of the larger diameter thread  22  is the same size as the stud to be accommodated, it is not oversized. Due to the large diameter thread  22  being the same size as the stud diameter and the center  23  of the large diameter thread  22  being only slightly offset from the aperture center  21 , the arc  29  for the larger diameter thread  22  spans up to about 130° of the aperture  20  inner circumference depending on thread profile. Therefore, because the radius of the large diameter thread  22  matches the stud diameter the contact surface in cradle  27  between the connector threads  14  and the stud is maximized, resulting in enhanced electrical conductivity. 
   Turning again to  FIG. 2 , connector  10  includes a set screw  16  for securing the connector to the threaded stud. The set screw  16  is received into the connector body in a threaded bore  34  and can thus be raised or lowered by rotating the set screw  16 . In this way, the set screw  16  can be adjusted to contact a threaded stud within longitudinal bore  12 . 
   In a preferred embodiment of the present invention, the connector  10  is produced by forming the longitudinal bore  12  by drilling into the connector body  10  to create a void or aperture  20 . Thereafter, a first tap or milling operation is performed to form the larger diameter thread  22 , which in the preferred embodiment may be a 1-14 thread. Once the large diameter thread  22  is formed, a milling operation is performed to form the small diameter thread  24 , which in the preferred embodiment may be ⅝-11 thread. As will be further shown and described with respect to  FIG. 5 , the threaded regions are positioned within the connector body  10  by offsetting the large diameter thread center  23  from the aperture center  21  by a distance equal to the root distance between the valley and crest of the larger thread size chosen. The third center  28  of the smaller diameter thread  24  is located such that the smaller diameter thread crest is tangent to the larger thread crest at a point  25  along the base of aperture  20 , which is typically directly opposite the set screw  16 . In a three dimensional frame of reference with respect to the two threads  22  and  24 , multiple points  25  would extend along a tangent line within cradle  27 . 
   Removal of the overlapping thread sections could be done by a milling/threading/tapping operation on the side of aperture  20  where interlocking of the second stud in desired, typically opposite the set screw  16 . Alternately, the overlapping thread sections can be formed at other locations around the entire inner diameter of longitudinal bore  12 . 
   While the preferred embodiment of the connector according to the present invention is described with respect to a particular large and small thread pitch. It would be clear to one skilled in the art that any standard or non-standard thread pitches could be overlapped in the manner described. Likewise the present invention need not be limited to overlapping two particular thread pitches, but may include more than two particular thread pitches that are formed within aperture  20 . 
   Turning now to  FIG. 3 , there is shown a transformer stud  30  installed within aperture  20 , which has a diameter slightly smaller than aperture  20 , such that the connector  10  can be slipped over stud  30  without the stud and connector threads becoming engaged. Once the stud is fully inserted within the connector, set screw  16  is rotated to bear against stud  30 , thereby causing the threads on stud  30  to engage the complementary pitch threads  14  within aperture  20  and thus secure the connector  10  to the stud. It should be noted that while a standard flat tip set screw is depicted, to minimize thread distortion, a saddle typed stud clamping screw can be used. The saddle type screw utilizes a saddle piece featuring the same type of thread pattern to allow for normal fit over the stud thread, therefore avoiding any thread damage and providing a more positive mechanical and electrical connection. 
   Turning now to  FIG. 4 , there is shown a transformer stud  40  installed within aperture  20 , which has a diameter smaller than aperture  20 , such that the connector can be slipped over stud  40  without the stud and connector threads becoming engaged. Once the stud is fully inserted within the connector, set screw  16  is rotated to bear against stud  40 , thereby causing the threads on stud  40  to engage the complementary pitch threads  14  within aperture  20  and thus secure the connector to the stud. Stud  40  engages the small diameter threaded region  24  of aperture  20  which are overlapped with the large diameter threads  22  that are engaged by stud  30  of  FIG. 3  along the various tangent points  25  in thread cradle  27 . 
   Turning now to  FIG. 5 , there is shown a side view of an exemplary stud thread  50  shown depicting the thread pitch of a one inch diameter stud. In the view depicted the stud thread crest  52  and valley  54  are shown. The crest  52  and valley  54  are separated by a root distance  56  that corresponds to the offset distance between aperture center  21  and large diameter thread center  23 . It should be recognized by one skilled in the art that the stud  50 , root distance  56  and offset distance  26  can be varied to suit a particular stud size. However, regardless of the size of the root distance  56 , the offset  26  and root distance  56  are preferably equal, for a connector designed for a particular stud size. 
   Various changes to the foregoing described and shown structures would now be evident to those skilled in the art. Accordingly, the particularly disclosed scope of the invention is set forth in the following claims.