Abstract:
A universal ground clamp having a clamping strap having a series of holes to facilitate the installation of the clamp onto a wide range of structures of various shaped and sized cross-sections. A metal stud, through which the clamping strap is secured, includes a terminal portion adapted to accommodate and have secured therein a ground wire. In one form, a pair of curved plates supported upon the stud are used to form a tight clamping action of the strap about the structure to be grounded, without subjecting the strap to localized stresses or tearing, but permitting the strap to tightly encircle the structure. One of the curved plates is captivated on the strap with stops. In another form, projections extend from the strap at the hole through which the stud is inserted in order to allow the stud to be readily inserted into the hole and prevent the stud from being inadvertently separated from the strap.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 09/654,249, filed Sep. 1, 2000 now U.S. Pat. No. 6,559,387, which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to electrical grounding devices and, more particularly, to an universal clamp used in coupling rods, pipes or other structures of various cross-sections to ground mechanisms. 
     BACKGROUND OF THE INVENTION 
     In many instances, there is a need to provide an electrical coupling to structures of various sized and shaped cross-sections for grounding purposes. These instances include grounding of pipes, conduit, and other structures of mechanical and/or electrical systems to dissipate electrical charge to protect the systems and/or individuals who may come in contact with the components of such systems. Grounding clamps are commonly employed for these purposes. 
     Grounding clamps come in a variety of configurations and use various means for forming a conductive attachment. One type of clamp includes a metal strap with a plurality of holes, a metal stud, and conventional nuts to secure the strap about the periphery of the structure. More specifically, the metal strap encircles the structure and the threaded stud is inserted through two of the holes to secure the metal strap tightly around the periphery of the structure. The metal strap is drawn tightly around the periphery of the structure as the nut is tightened on the bolt. The clamp typically includes a ground terminal to which a wire is attached for connecting the clamp to a conventional ground mechanism, such as a ground rod. Strap type clamps accommodate different diameters of pipes or conduits or cross-sections of other shaped structures, such as boxes. This adaptability to a variety of structures eliminates the need for an inventory of grounding clamps that are specifically designed for a specified structure. 
     Strap-type clamps typically use nuts with sharp edges. These sharp edges are known to gouge the metal strap as the metal strap is tightened at the stud. This gouging causes creases and areas of weakness which severely shortens the overall life of the strap and can limit the effectiveness with which it conducts electricity. 
     One solution to gouging, or otherwise providing a non-destructive tightening of the strap, is disclosed in my U.S. Pat. No. 4,626,051, which discloses the use of two nuts, each having a smooth curved surface for engaging the strap. The curvature of the surface better accepts the angle of the metal strap as it leaves the various structures and attaches to the stud. While this advancement successfully prevents the gouging of the strap by eliminating the sharp edges of the engagement, one of the nuts must be removed from the stud during installation, and this leads to the possibility of losing the nut and/or lost time retrieving (if even possible) the lost nut. This situation is compounded by the fact that many installations are made in awkward and sometimes dangerous locations, such as those to suspended systems requiring installers to use scaffolding, catwalks and/or ladders to reach the suspended structures. 
     Another problem associated with existing strap-type grounding clamps is that the stud must be thread through the initial hole it is fed through in the metal strap in order to prevent the stud from coming apart from the strap, (e.g., in order to prevent the stud from becoming lost). Unfortunately, the threading of the stud through the hole of the strap increases installation time and keeps the installer in the awkward or dangerous positions required to install the clamp, (e.g., scaffolding, catwalks, ladders, etc.), longer than he or she need be. Alternatively, existing strap-type grounding clamps may be provided with holes through which the stud easily passes; however, such configurations are unacceptable because they increase the likelihood that the stud will be lost and/or increase installation time due to lost time retrieving (if possible) the lost stud. 
     Thus, the present invention addresses the need for an entirely self contained universal clamp that eliminates loose parts and the need for a more efficient method and apparatus for installing universal grounding clamps. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view of an universal ground clamp embodying features of the present invention and being attached to a structure with a circular cross-section by way of example; 
     FIG. 2 is an exploded perspective view of the universal ground clamp of FIG. 1; 
     FIG. 3 is a bottom perspective view of the sliding nut of the universal ground clamp of FIG. 1; 
     FIG. 4 is a cross-sectional view of the sliding nut taken along line  4 — 4  of FIG. 3; 
     FIG. 5 is a side elevational view of the sliding nut captivated along the strap of the universal ground clamp of FIG. 1; 
     FIG. 6 is a plan view of the sliding nut captivated along the strap of the universal ground clamp of FIG. 1; 
     FIG. 7 is a partial cross-sectional view of the sliding nut captivated along the strap and taken along line  7 — 7  of FIG. 6; 
     FIG. 8 is an end elevational view of the strap of FIG. 5; 
     FIG. 9 is a plan view of the curved nut of the universal ground clamp of FIG. 1; 
     FIG. 10 is a cross-sectional view of the curved nut taken along line  10 — 10  of FIG. 9; 
     FIG. 11 is a side elevational view of an alternate universal ground clamp embodying features of the present invention showing a stud and sliding nut captivated along the strap thereof; 
     FIG. 12 is a plan view of the strap and curved strap engaging plate of alternate universal ground clamp of FIG. 11; and 
     FIG. 13 is an exploded perspective view of the alternate universal ground clamp of FIG.  11 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the present invention is shown embodied in an universal ground clamp  10  used as a coupling for attaching a ground to mechanical and/or electrical systems comprising conduits, pipes or other structures with various cross-sectional shapes and sizes having conductive capacity. The purpose of attaching a ground clamp  10  is to aid in dissipating electrical charge from structural components of a system, primarily for the safety and protection of the system components not intended to carry electrical charge and those coming in contact with such components. 
     The universal ground clamp  10  includes a stud  12 , a curved nut  14  on the stud  12 , a terminal ground wire assembly  15  at the stud  12 , a strap  16  with end stops  11 , and a sliding nut  13  captivated on the strap  16  between the stops  11 . The end stops  11  prevent the nut  13  from sliding off the strap  16 , and, thus, eliminates the possibility of losing the nut  13  during installation of the clamp  10 . 
     Referring to FIGS. 1 and 2, the strap  16  is elongated to cover a range of different cross-sectional shapes and sizes. These shapes and sizes include circular, oval and even rectangular or square cross-sections. The length of the strap depends on the particular range of shapes and sizes to be accommodated. For example, with a reference to a circular cross-section, a strap length of about six inches covers a diameter range of three-eighths of an inch to two inches, a strap length of about twelve inches covers a diameter of three-eighths of an inch to three and five-eighths inches, and a strap length of about fourteen inches covers a diameter range of about three-eighths of an inch to four inches. For diameters larger than four inches, a longer strap can be used or two or more straps can be joined together to form one ground clamp. 
     The strap is made of any conductive material and suitable thickness that is sufficiently malleable to conform to the various shapes and sizes of the items to which the clamp may be secured. For example, both thirty-two thousandths of an inch dead soft fully annealed copper and twenty-five thousandths of an inch pre-galvanized steel are both suitable thicknesses and materials to effectively conform to the various structures. 
     To accommodate different shapes and sizes, the strap  16  includes a plurality of spaced holes along a longitudinal centerline, as illustrated in FIGS. 2 and 6. The diameter of each hole may vary depending on the diameter of the shank portion  25  of the stud  12 . For example, the diameter of the holes may be about two hundred sixty-six thousandths of an inch to accommodate an outer diameter of the stud shank of about two hundred fifty thousandths of an inch. 
     The holes  67  are generally spaced at equal distances from each other. The number of holes in the strap depends on the length of the strap. As the strap length is increased, the number of holes is increased. For example a strap having a length of about six inches may have fourteen holes, a strap having a length of nine and one-half inches may have twenty-three holes, and a strap having a length of twelve inches may have twenty-nine holes. 
     Alternate spacing may also be used to space the holes adjacent the ends of the strap. For example, the spacing between the end holes can be larger. That is, the distance between the first hole  61  and the second hole  62  and the distance between the last hole  69  and the next-to-last hole  68 , is larger. This enables the strap to be designed to fit a particular cross-section size at the lower end of the range for the particular clamp. In addition, for mid-range sizes, the first segment of the strap is usually about the structure, and thus, there is no need for a hole in this area. For example, the spacing between the first hole  61  and second hole  62  may be about one-half of an inch, which may be the same as the distance between the second-to-last hole  68  and the last hole  69 , which may also be about one-half of an inch. The spacing between each intermediate hole  67  may be about four hundred thousandths of an inch. 
     The spacing of the holes is also related to the length of the stud  12 . In other words, the distance between each intermediate hole cannot be greater than the length of the shank portion  25  of the stud  12 . This relationship between the stud and the strap enables the clamp to accommodate intermediate cross-sections between the hole spacings. 
     As seen in FIG. 2, the stud  12  includes a hexagonally shaped head  27  and a shank portion  21 , which includes a short, non-threaded shank portion  23  and the longer threaded shank portion  25 . The non-threaded shank portion  23  is located adjacent the base  24  of the hexagonally shaped head  27 . The non-threaded shank portion, however, is optional. The threaded shank portion  25  extends below the non-threaded shank portion  23  and axially along the longitudinal axis of the stud  12 . The hexagonally shaped head  27  defines an internally threaded hole  28  coaxial with the longitudinal axis of the stud  12 , as part of the terminal ground wire assembly  15 . 
     The terminal ground wire assembly  15  includes a ground wire stud  51  with external threads configured to mate with internal threads  29  lining the threaded bore  28 . The head  27  of the stud  12  also defines a bore  80  that extends perpendicular to the longitudinal axis of the stud  12  and passes completely through the head  27 . The bore  80  is shaped to accept a stranded or solid ground wire  18  of various gauges, such as those in at least the range of fourteen to six AWG. The bore  80  may be round or elongated to accommodate larger diameter wires. 
     The threaded hole  28  forms a “T” with bore  80 . Thus, when the ground wire  18  is inserted into the bore  80 , the ground wire stud  51  is threaded into the threaded hole  28  until it engages the ground wire  18 . The combination of the ground wire stud  51 , the head  27  of the metal stud  12 , and the “T” configured bores  28  and  80  result in the use of compressive forces to secure the ground wire  18  to the stud  12 . By tending to eliminate the stresses, such as those applied when the ground wire is wrapped around a ground post, the conductive capacity of the ground wire  18  is less likely to be reduced because of the reduced chance for the wire to be frayed or split. 
     With reference to FIGS. 5-8, the strap  16  includes end stops  11  to captivate the sliding nut  13  to prevent inadvertent loss during installation of the clamp  10 . Although the strap  16  is illustrated with stops  11  at both ends, only the stop at the free end  11   a  of the strap (FIG. 2) is necessary. The use of stops at both ends, however, facilitates ease of assembly of the clamp because then the stud can be positioned at either end, and there will be no potential for the sliding nut to become separated from the strap during installation. 
     As illustrated, the stops  11  take the shape of a raised partial dimple. More specifically, each of the stops has a center portion  91  symmetrically curved about the longitudinal centerline of the strap  16  with a major radius of curvature  95  and a pair of smoother curved segments  96  extending from the center portion  91  to the sides of the strap  92  with a second radius of curvature. For example, the center portion may have a radius of the curvature of about one hundred thousandths of an inch and a depth of about one hundred thousandths of an inch (dimension Z). The secondary curved portions  96  may have a radius of curvature of about thirty-one thousandths of an inch. The foregoing described stop is only one example of a stop shape contemplated by the present invention. For example, the stop may be formed with a constant radius of curvature. The stop also may include multiple dimples. Although the dimple-type configuration is formed integral from the strap, such as by conventional stamping or metal bending techniques, the stops can also be formed using separate components. For example, small protrusions, rivets, screws, tabs, studs or any other obstruction at the end of the strap to prevent the release of the sliding nut could be used in accordance with the present invention. 
     Referring to FIGS. 1,  3  and  4 , the sliding nut  13  has a multiple curved shape with a first curved portion  32 , a second curved portion  36 , and a third generally straight portion  31 . The first curved portion  32  defines a threaded bore  33  that cooperates with the threaded shank portion  25  of the stud  12 . The straight portion  31  includes a slot  35  through which the strap  16  extends to allow the sliding nut  13  to slide along the strap  16 . The second curved portion  36  positions the slot  35  such that the strap  16  is above the bore  33  of the first curved portion  32 . This positioning enables a straight alignment with the holes of the strap  16 . 
     More specifically, the radius of curvature of the first curved portion  32  of the sliding nut  13  must be generous enough to contact the strap  16  coming off the structure in a manner to ensure a smooth transition so as not to create any localized stress points on the strap, such as sharp bends creating points of weakness. For example, the radius of curvature of the first curved portion may be two hundred fifty thousandths of an inch for circular cross-sections. 
     The bore  33  of the first curved portion  32  is centered about the peak. The internal threads  34  of the bore  33  extend between the convex side  37  to the concave side  38  and mate with the external threads  26  of the stud  12 . The slot  35  formed in the straight portion  31  extends between the sides  93 ,  94  of the nut  13 . The slot width (dimension X) is to be greater than the thickness of the strap  16 , but less than the height of the stops  11  to allow the sliding nut  13  to slide freely along the strap  16 , but to prohibit passage of the stops  11 . For example, using a twenty-five thousandths of an inch or a thirty-two thousandths of an inch thick strap, the slot height may be about eighty thousandths of an inch, where the stops have a height of about one hundred thousandths of an inch. The length (dimension Y) of the slot depends on the width of strap (dimension W). For example, the slot length may be seven hundred sixty thousandths of an inch for a strap with a width of about six hundred thousandths of an inch. 
     With references to FIGS. 1,  2 ,  9  and  10 , the curved nut  14  remains on the stud  12 . The curved nut  14  defines a central bore  45  to receive the shank portion  25  of the stud  12 . The curved nut  14  is placed on the stud  12  prior to the manufacturing of the stud  12 . Thus, the curved nut  14  is captivated longitudinally along the shank portion  25  at the non-threaded portion  23  of the stud  12  because the diameter of the central bore  45  is less than the outer diameter of the threaded shank portion  25 . The curved nut  14  is free to rotate about the non-threaded portion  25  to properly approach the strap  16  during installation. Alternatively, the central bore  45  may have internal threads  44  that mate with the external threads  26  of the stud  12  to thread the nut  14  onto the shank portion  25  until it is in position at the non-threaded portion  23  for free rotation. 
     The curved nut  14  also includes a generally flat side  41  and a generally curved side  42 . The nut  14  is threaded onto the threaded shank portion  25  into position with the flat side  41  adjacent to the bottom  24  of the hexagonally shaped head  27 . When the flat side  41  of the curved nut  14  is adjacent to the bottom side  24  of the head  27  of the stud  12 , the curved nut  14  is free to rotate independently of the stud  12 . The curved side  42  facilitates the same smooth transition with the strap  16  as the first curved portion  32  of the nut  13 . The diameter of the curved nut  14  is large enough to reach the outer perimeter of the hexagonally shaped head  27  portion of the stud  12 . For example, the curved nut  14  may have a diameter of about two hundred fifty thousandths of an inch at the flat side where the maximum cross dimension of the head  27  of the stud  12  is about one-half of an inch. If the curved nut  14  is substantially smaller than the head  27  of the stud  12 , then there is a possibility that the strap may be pinched or gouged during the transition from the pipe  17  to the stud  12 . 
     To install the ground clamp  10 , the strap  16  is wrapped around the structure, such as the illustrated conduit  17  in FIG.  2 . It is manually tightened around the structure until one of the holes of the strap  16  lines up with the stud  12 . The sliding nut  13  is then slid into position under the aligned hole. The stud  12  is then inserted through the hole and turned into the threaded hole  33  of the sliding nut  13  to draw the strap  16  tightly around the structure  17 . A conventional tool, such as a wrench, pliers, vice grips, or the like may be used with the head  27  of the stud  12  as necessary to obtain the appropriate degree of tightness for the strap  16  about the structure. Next, the ground wire stud is turned to allow space for a ground wire to be inserted into bore  80  of the head  22  of the stud. After insertion of the ground wire, the ground wire stud  15  is tightened down by rotation to clamp the wire in the bore  80  by compressive force. The ground wire is attached to an acceptable ground mechanism. 
     In FIGS. 11-13, an alternate ground clamp is illustrated embodying features of the present invention. In this embodiment, the alternate ground clamp has a unique configuration designed to reduce the possibility of the stud becoming separated from the clamp assembly. For convenience, features of the alternate embodiments illustrated in FIGS. 11-13 that correspond to features already discussed with respect to the embodiments of FIGS. 1-10 are identified using the same reference numeral in combination with an apostrophe (′) merely to distinguish one embodiment from the other, but otherwise such features are similar. 
     Turning now to FIGS. 11-13, there is illustrated an alternate ground clamp, hereinafter referred to as  10 ′, which includes a stud securing mechanism  100 . More particularly, the portion of the strap  16 ′ which defines first hole  61 ′ contains projections, such as tabs  102  and  104 , which extend inward toward the center of the hole  61  and serve to engage at least a portion of the threads  26 ′ of stud  12 ′, thereby forming stud securing mechanism  100 . This stud securing mechanism  100  prevents the stud  12 ′ from coming apart from the strap  16 ′ and, thus, reduces the likelihood of losing the stud  12 ′ during installation of the clamp  10 ′. 
     In a preferred embodiment, the hole  61 ′ of strap  16 ′ has a diameter of about two hundred sixty-six thousands of an inch into which each of the tabs  102  and  104  projects by approximately twenty-three thousandths of an inch. Thus, the distance between tabs  102  and  104  (dimension V) is approximately two hundred twenty thousandths of an inch. The tabs  102  and  104  of the stud securing mechanism are preferably about one hundred twenty-five thousandths of an inch long (dimension U) and one hundred thousandths of an inch wide (dimension T). Thus, the opposing sides of tabs  102  and  104  cut into the metal strap  16 ′ by about one hundred two thousandths of an inch. The tabs  102  and  104  are preferably formed integral to the strap  16 ′ and, like the holes  61 ′,  62 ′  68 ′ and  69 ′ (FIG.  12 ), may be cut out of the metal strap  16 ′ via any conventional cutting or stamping process. In alternate embodiments, however, the tabs  102  and  104  may be formed using separate components or materials. 
     By cutting the tabs  102  and  104  out of a portion of the metal strap  16 ′, the clamp  10 ′ provides an amount of tab movement which allows the stud  12 ′ to be rapidly inserted through the hole  61 ′, rather than having to be threaded through the hole  61 ′, which reduces the amount of time needed to install the clamp. More particularly, the tabs  102  and  104  are of a sufficient length and thickness to allow for the deflection of one or more of the tabs  102  and  104  when the stud  12 ′ is pressed through hole  61 ′ and continue to engage at least a portion of the stud  12 ′ so that the stud  12 ′ will be retained on the strap  16 ′. 
     For example, in the embodiment illustrated in FIGS. 11-13, the stud  12 ′ may be readily pressed through the hole  61 ′, causing the tabs  102  and  104  to flex or deflect during the insertion of the stud  12 ′ (see FIG.  11 ). Once the insertion force on the stud  12 ′ is removed, the tabs  102  and  104  remain biased against the stud  12 ′ to engage the threaded portion  25 ′ of the stud  12 ′. This prevents the stud  12 ′ from becoming inadvertently or accidentally separated from the strap  16 ′. More particularly, the tabs  102  and  104  bend in the direction the stud is inserted into the hole  61 ′ and form a one way locking mechanism which allows the stud  12 ′ to continue to travel into the hole in the insertion direction but prevents the stud  12 ′ from traveling through the hole  61 ′ in the opposite direction unless forced to do so, such as by reverse threading therethrough. Thus, once the stud  12 ′ is inserted into the hole  61 ′ and engages the stud securing mechanism  100 , the component  10 ′ becomes an entirely self contained universal clamp. 
     The projections of the stud securing mechanism  100  are of a sufficient length that they can bend away from the strap  16 ′ to allow stud  12 ′ to be readily inserted there through, and remain in contact with at least a portion of the stud  12 ′ in order to prevent the stud from being removed from the hole  61 ′ in the opposite direction. The projections may be lengthened to extend further in toward the center of hole  61 ′ so that they may provide additional resistance against movement of a stud  12 ′ (once inserted) in a direction opposite the initial insertion direction. In a preferred embodiment, however, the projections will not extend very far in toward the center of the hole  61 ′ in order to facilitate a fair balance between ease of insertion and resistance against unintentional removal. 
     In alternate embodiments of the universal ground clamp, additional holes defined by the strap may be provided with projections so that the stud can be readily inserted through any one of the additional holes and prevented from being moved in a direction opposite the direction of insertion in a manner similar to that discussed above. For example, in one embodiment of the clamp, all of the holes illustrated in FIGS. 12-13 may include projections such as tabs  102  and  104 . In yet another embodiment, all of the holes except the initial hole  61 ′ may include projections for preventing the stud  12 ′ from being inadvertently separated from the strap  16 ′. Thus, with such a configuration, an entirely self contained universal clamp and a more efficient method and apparatus for installing universal ground clamps is provided. 
     Since the stud  12 ′ and strap  16 ′ are self contained via the stud securing mechanism  100 , a preferred embodiment of the universal ground clamp  10 ′ may be provided with only one end stop  11 ′. For example, in the embodiment illustrated in FIGS. 11-13, the universal ground clamp  10 ′ may be provided with only one end stop, end stop  11   a ′, which is located on the free end of the strap  16 ′ and keeps the curved nut  13 ′ captivated on the strap  16 ′ between itself and the stud  12 ′. Thus, the present invention addresses the need for an entirely self contained universal clamp that eliminates loose parts and the need for a more efficient method and apparatus for installing universal grounding clamps. 
     The stud  12 ′ may then be rapidly inserted into the first hole  61 ′, flexing the tabs  102  and  104  against the threaded portions of the stud to prevent the stud from being inadvertently removed from the strap. The strap  16 ′ may then be wrapped about the object to be electrically grounded and the threaded end of the stud  25 ′ aligned and rapidly inserted into a second hole defined by the strap  16 ′. In a preferred embodiment, a nut such as the curved nut  13 ′, is connected to the portion of the threaded end  25 ′ extending through the second hole beyond the strap  16 ′ so that the stud and nut may be used to tighten the clamp about the object to be grounded. In alternate embodiments, however, projections such as tabs  102  and  104  may be formed at the second hole as discussed above and may be used effectively alone as a nut for the stud so that the clamp may be tightened and secured about the object to be grounded. 
     While the invention has been described in the specification and illustrated in the drawings with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments illustrated by the drawings and described in the specification as the best modes presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the description of the appended claims.