Abstract:
A cable shield ground connector includes an inner part and outer part clamped together by means of a threaded stud carried by the inner part engaged by a nut. The inner part defines a smoothly tapered, arcuate, conductor-receiving trough portion configured for insertion between the conductors of a service cable and the cable shield. A threaded stud and tang project from the inner part in a direction opposite from the opening defined by the trough portion. A plurality of teeth project integrally from fillets of the outer part in parallel rows to define a jacket-gripping portion of the outer part. The channel-shaped outer part defines a guide for receiving the tang of the inner part. The stud passes through an aperture defined by the web of the outer part and the tang is received in the guide, thereby assuring longitudinal alignment of the inner and outer connector parts.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates generally to devices for implementing a ground connection between a metallic shield of a service cable and a common ground point. More particularly, the present invention relates to a two-part ground clamp connector which mounts to a buried service cable and includes an attachment point for connection of a flexible conductor to establish continuity with a common ground point.  
           [0003]    2. Description of the Related Art  
           [0004]    A number of devices have been employed for connecting a ground wire with the tubular ground shields of service cables. Most conventional devices employ clamp assemblies of various forms. In applications to which the present invention relates, the cables, clamping devices and associated interconnections are ordinarily positioned within a cabinet, housing or other enclosure to provide protection from the ambient environment. The service cables to which the present invention relates are buried service cables that enter the enclosure for the purpose of interconnection and/or grounding at specified intervals. A number of conventional designs are configured to secure the service cable rigidly or semi-rigidly to a ground point within the enclosure. For such designs, damage to the cables can occur when the enclosure is subject to intense environmental changes and the cables are fixedly positioned relative to the housing. For example, it is not uncommon for such enclosures to heave as a result of frost while the service cables are frozen in position in the ground.  
           [0005]    To avoid disruptions of the ground connection possibly caused by shifting of the enclosure relative to the buried cables, it has become common to establish a ground connection with a flexible wire between the cable and a common ground point. For example, U.S. Pat. No. 4,895,525 illustrates a two-part cable shield grounding clamp connector including a threaded stud to which such a flexible grounding wire can be attached. This particular cable shield grounding clamp connector utilizes arcuate inner and outer plates with the inner plate provided with teeth to scrape the inner surface of a metallic shield to establish improved electrical contact. The &#39;525 patent illustrates a tang projecting outwardly for longitudinally indexing the inner part of the illustrated grounding clamp connector relative to the cable jacket, but lacks means for longitudinally aligning the inner and outer connector parts. Further, the teeth provided on the inner part of the &#39;525 connector may interfere with installation by, for example, catching and crumpling the thin metallic shield.  
           [0006]    Another representative example is described in U.S. Pat. No. 4,571,013, which discloses a connector for cable shields in the form of a strip of metal bent into a U-shape with a stud extending through the legs to engage a nut that clamps the legs together. Teeth project inwardly from each of the inner and outer legs for gripping the cable shield and jacket to resist pull out. By forming the connector from a single bent strip of metal and passing the stud through both legs, the &#39;013 patent illustrates one approach to maintaining alignment between the inner and outer portions of a cable shield connector. The teeth on the inner leg may also catch the shield during installation. Additionally, once compressed by the nut and stud, the connector may prove difficult to remove without damage to the cable shield.  
           [0007]    An alternative approach is exemplified by U.S. Pat. No. 5,722,840 for a conductor protector and U.S. Pat. No. 6,322,378 for a conductor protector for ground clamp, both assigned to the assignee of the present invention. These patents disclose a ground clamp that surrounds a cable and a received conductor protector. The smooth, arcuate conductor protector is inserted beneath the cable jacket to establish conductive relationship with the ground shield and substantially surround the conductors to protect them from crushing when the clamp is secured around the service cable. These ground clamp assemblies have proven appropriate for their intended use and have been commercially successful. However, they can be costly to manufacture and time consuming to install. Further, the exterior portion of the clamp occupies significant space in what are typically confined enclosures.  
           [0008]    There is a need in the art for a less complicated and less costly connector for establishing a reliable electrical connection between a common ground point and the metallic shield of a buried service cable. The connector should be easily installed and removed with minimal damage to the metallic shield of the service cable. The connector should also preferably be of compact design.  
         SUMMARY OF THE INVENTION  
         [0009]    A cable shield ground connector in accordance with one embodiment of the present invention comprises an inner part defining a longitudinally extending cable-receiving trough. A threaded stud is fixed to an opposite side of the inner part projecting generally perpendicularly and away from the cable-receiving trough. The trough narrows or converges to a point at one end to ease insertion of the inner part between the core conductors of the cable and the conductive shield. Longitudinally opposed to the point is a tang projecting away from the trough in a similar direction to the threaded stud. The trough is substantially smooth on its inner and outer surfaces as well as the edges leading to the point. The arcuate configuration of the trough enhances the rigidity of the inner part.  
           [0010]    A connector outer part includes an aperture for receiving the threaded stud and a guide for receiving the tang projecting from the connector inner part. The outer part is primarily in the form of a longitudinally extending channel, e.g., a substantially planar web connecting longitudinally extending fillets that project generally perpendicular to the web. The fillets strengthen the outer part such that it is substantially rigid along its length. A plurality of teeth extend integrally from each fillet at a jacket-gripping end of the outer part opposite the guide. The teeth are sharp and angled toward the guide to provide improved pull out resistance for the connector.  
           [0011]    In preparation for assembling the connector to a cable shield, the cable jacket and metallic shield are slit over a short distance to allow insertion of the connector inner part. The point of the conductor-receiving trough is inserted between the conductors (the core) of the service cable and the surrounding metallic shield, which is in turn surrounded by a thick plastic or rubber jacket. Electrical continuity is established between the conductive connector inner part as it contacts the inner surface of the metallic shield.  
           [0012]    A cable shield ground connector in accordance with the illustrated embodiment of the present invention is preferably inserted circumferentially opposite the slit. As a result, the connector is engaged with an intact portion of the metallic shield and cable jacket. The connector inner part is inserted into the cable until the stud contacts the end of the cable jacket. The connector outer part is then placed over the outwardly projecting stud and tang with the jacket gripping end teeth against the outside of the cable jacket. Together, the threaded stud and tang ensure longitudinal alignment of the connector inner part and outer parts. A nut engages the threaded stud to compress the connector outer part against the connector inner part. Tightening the nut causes the teeth projecting from the outer part to dig into the jacket of the service cable. The teeth are angled and pointed so that force exerted to pull the connector out of the cable actually causes the teeth to dig into the jacket. The compressed engagement between the outer and inner connector portions ensures that a large area of the metallic shield is in surface to surface contact with the received inner connector part. A flexible ground conductor is preferably affixed to the threaded stud prior to tightening the clamping nut.  
           [0013]    An object of the present invention is to provide a new and improved cable shield ground connector that is efficiently installed and removed.  
           [0014]    Another object of the present invention is to provide a new and improved cable shield ground connector that exhibits improved pull out resistance.  
           [0015]    A further object of the present invention is to provide a new and improved cable shield ground connector of efficient and economic design.  
           [0016]    A yet further object of the present invention is to provide a new and improved cable shield ground connector of compact configuration. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    These and other objects, features and advantages of the invention will become readily apparent to those skilled in the art upon reading the description of the preferred embodiment, in conjunction with the accompanying drawings, in which:  
         [0018]    [0018]FIG. 1 is a side view of one embodiment of an inventive cable shield ground connector;  
         [0019]    [0019]FIG. 2 is a top view of the cable shield ground connector of FIG. 1;  
         [0020]    [0020]FIG. 3 is a top view of the inner part of the cable shield ground connector illustrated in FIG. 1;  
         [0021]    [0021]FIG. 4 is a side view, partly in phantom, of the inner part of FIG. 3;  
         [0022]    [0022]FIG. 5 is a side view, partly in phantom, of the outer part of the cable shield ground connector of FIG. 1;  
         [0023]    [0023]FIG. 6 is an enlarged view of one tooth of the outer part illustrated in FIG. 5;  
         [0024]    [0024]FIG. 7 is a bottom view of the outer part of FIG. 5;  
         [0025]    [0025]FIG. 8 is a perspective end view of an embodiment of the inventive cable shield ground connector;  
         [0026]    [0026]FIG. 9 is a right end view of the inner part of FIG. 4;  
         [0027]    [0027]FIG. 10 is a left end view of the outer part of FIG. 5; and  
         [0028]    [0028]FIG. 11 is a perspective side view of the cable shield ground connector of FIGS. 1, 2 and  7  mounted to a service cable and a ground wire. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    An embodiment of a cable shield ground connector is illustrated in FIGS.  1 - 11  and is generally designated by the numeral  10 . The connector has an inner part  20  configured to be inserted between the conductive metallic shield and the conductors, or core of a service cable. When inserted, a conductor-receiving trough  26  of the inner part  20  surrounds a majority of the circumference of the core. An outer part  30  of the connector is configured to align longitudinally with the inner part  20  along the outside of the service cable. A stud  25  projects from the inner part through an aperture  35  in the outer part  30 . A nut  45  or other fastening means engages the stud  25  to clamp the outer part  30  to the inner part  20 . As will be more fully described below, the inner part  20  is in electrical contact with the cable shield, while the outer part  30  grips the cable jacket in a manner that resists forces acting to pull the inner part from inside the cable. The outer part  30  compresses the cable shield against the inner part  20  to ensure electrical continuity over a large area of a received portion (the conductor-receiving trough) of the inner part  20 .  
         [0030]    [0030]FIGS. 1, 2 and  7  illustrate an embodiment of the cable shield ground connector  10  as an assembly. The inner part  20  extends from a pointed insertion tip  22  to a tang  28  projecting generally parallel to the threaded stud  25 . The tang  28  projects to an outward end  29  that interacts with the connector outer part  30  as will be discussed below. The inner part  20  is inserted between the shield and the core of a cable until the stud  25  contacts the cable jacket. The threaded stud  25  provides a connection point for a flexible ground conductor. The stud  25  also serves as an anchor for clamping the outer part  30  to the inner part  20 .  
         [0031]    The inner part  20  flares from the tip  22  to define a conductor-receiving trough  23 . The flared portion  26  of the inner part  20  has an arcuate, or semi circular configuration when viewed in section, as best illustrated in FIGS. 7 and 9. This arcuate configuration generally matches the sectional shape of a service cable and enhances the longitudinal rigidity of the inner part  20 . The matched sectional configuration ensures maximum surface to surface contact between the cable shield and the outside surface of the flared portion  26  of the inner part  20 . The flared portion  26  inside and outside surfaces, as well as the edges  24  are substantially smooth. The edges  24  meet at an acute angle to define the insertion point  22 . This configuration ensures ease of insertion and minimizes the chances that the inner part  20  will catch or crumple the cable shield during insertion.  
         [0032]    The connector outer part  30  is configured to grip the jacket of the service cable and force the metallic shield into contact with the outside surface of the flared portion  26  of the inner part  20 . The outer part  30  is generally channel-shaped in cross section along most of its length, as best illustrated in FIGS. 7 and 10. The term “channel-shaped” is used to describe the shape of a member having a generally planar web  33  connecting longitudinally extending fillets  36 . This configuration is commonly used in structural steel members, in part because of its rigidity, or stiffness.  
         [0033]    One end of the outer part  30  is configured as a guide  38  for receiving the tang  28  projecting from the inner part  20 . To form the guide  38 , the fillets  36  end and the generally planar web  33  is cut and bent to form arms  39  that extend back along the web  33  in spaced relationship from and generally parallel to the web  33 . The arms  39  are laterally separated by a gap configured to closely receive the lateral width of the tang  28 . The arms  39  are connected by a web portion  41  that is generally perpendicular to the main web  33  of the outer part  30 . This web portion  41  also acts as a longitudinal end of the guide  38 . Thus, the guide  38  retains a received tang  28  laterally between the arms  39  and longitudinally adjacent the web portion  41 .  
         [0034]    As best illustrated in FIG. 1, the outer part  30  is longitudinally aligned with the inner part  20  at the threaded stud  25 /aperture  35  engagement and the tang  28 /guide  38  engagement. These two points of alignment simplify assembly and installation of the connector  10  by resisting mis-alignment while the nut  45  is tightened.  
         [0035]    [0035]FIG. 1 also illustrates that the tang end  29  engages the web  33  at the guide  38  to define a pivot point for the outer part  30  relative to the inner part  20 . Force exerted on the outer part  30  by tightening the nut  45  over the stud  25  forces the jacket gripping portion  32  of the outer part  30  toward the cable jacket and received trough portion  26 , with the outer part pivoting about the tang end  29 /web  33  contact point. This motion of the outer part  30  relative to the received trough portion  26  of the inner part ensures that the teeth  34  dig into the jacket and also forces the jacket and shield into contact with the outside surface of the received trough portion  26 . Without the tang end  29 /web  33  pivot point, the inner and outer parts would pivot about the stud  25 /nut  45  point of contact, producing a less predictable and therefore less reliable engagement between the connector  10  and a cable jacket/cable shield.  
         [0036]    The illustrated embodiment of the jacket-gripping portion  32  of the outer part  30  includes two parallel rows of fang-like, piercing teeth  34 . Each row of teeth  34  integrally projects from a longitudinally extending fillet  36 . FIGS. 5 and 6 best illustrate the configuration of the teeth  34 . Each tooth  34  extends from a root  37  to a terminal point  31 . The point  31  is offset toward the guide end of the outer part relative to the root  37  producing an acute angle A between the guide-edge of the tooth and the fillet  36 . The teeth are preferably aggressively shaped, e.g., sharp, with an acute internal angle B of between 15° and 50 °. Another preferred aggressive feature of the teeth  34  is that they project from the fillet  36  a distance H 2  at least approximately twice the height H 1  of the fillet  36 . Since the teeth  34  are located only on the outer part  30 , they can be far more aggressively configured than teeth located on a received portion of a cable shield ground clamp connector.  
         [0037]    Teeth so configured have exceptional pull-out resistance due to the fact that they will actually dig in and actively engage the cable jacket in response to force exerted to pull the connector  10  from its installed position (as illustrated in FIG. 11). However, upon loosening of the nut  45 , the jacket-gripping portion  32  is easily disengaged from the cable jacket  54 , in part because of the two part configuration of the connector  10 .  
         [0038]    As is best shown in FIGS.  8 - 10 , the outer part  30  is generally rectangular or channel shaped in cross-section while the inner part  20  is generally arcuate in cross-section. FIGS. 7 and 10 illustrate the lateral width W 2  between the inside edges of the two rows of teeth  34  making up the jacket-gripping portion  32  of the outer part  30 . FIG. 9 illustrates the lateral width W 1  of the trough portion  26  of the inner part  20 . W 1  is less than W 2 , which produces the functional relationship (best illustrated in FIG. 8) that the jacket-gripping portion  32  of the outer part fits over the trough portion  26  of the inner part  20 . It should be noted that the fillets  36  need not be precisely perpendicular to the web  33  of the outer part  30 . An angle of the fillets  36  relative to the web  33  of at least approximately 90° will provide adequate stiffness to the outer part  30 .  
         [0039]    When the connector  10  is assembled to a service cable as shown in FIG. 11, the jacket-gripping portion  32  engages the jacket  54  and the cable shield inside to stretch them over and against the outside surface of the trough portion  26 . The relative positions of the longitudinally opposed ends of the inner part  20  and outer part  30  are determined by the tang end  29 /web  33  pivot point so that the jacket-gripping portion  32  and received trough portion  26  are forced together when the nut  45  is tightened. The shapes and relative relationships described ensure intimate surface to surface contact between the outside surface of the trough portion  26  and the cable shield over a large surface area. Such contact helps ensure reliable electrical continuity between the cable shield and a ground wire  60  fixed to the assembled connector  10 .  
         [0040]    With specific reference to FIGS. 1, 3,  4  and  11 , the connector inner part  20  comprises a tapered arcuate conductor-receiving trough portion  26  for insertion between the conductors  52  and the metallic shield  56  of a service cable  50 . In this position, the trough portion  26  is configured to surround a majority of the circumference of the received conductors. In other words, the trough portion  26  is configured to have an arcuate extent of at least approximately 180°. This configuration improves the longitudinal stiffness of the inner part  20  and affords some protection to the conductors as they emerge from the service cable. Longitudinally opposite from the trough portion  26 , the inner part  20  becomes channel-shaped in section as best seen in FIG. 9. Intermediate the trough portion  26  and tang  28 , the inner part supports a rigidly fixed threaded stud  25 . Other means for clamping the inner part  20  to the outer part  30  may occur to one of skill in the art. Further, means other than a threads on the stud  25  and a complementary nut  45  may occur to those skilled in the art for engaging the stud as an anchor point for the assembled connector  10 .  
         [0041]    While a preferred embodiment of the foregoing invention has been set forth for purposes of illustration, the foregoing description should not be deemed a limitation of the invention herein. Accordingly, various modifications, adaptations and alternatives may occur to one skilled in the art without departing from the spirit and the scope of the present invention.