Patent Publication Number: US-2010126950-A1

Title: Cable tray

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of all applicable priority, including the application filing date, from Provisional Application Ser. No. 61/118,270 filed on Nov. 26, 2008, and that application is incorporated by reference herein in its entirety for all purposes. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     Electrical system conductors are always part of the construction of virtually any building whether the building is residential, business, or even a storage building. In most applications, local construction codes and building techniques dictate the use of metallic conduit mounted to various surfaces of the building. The necessary electrical system conductors are then drawn through the metallic conduit to terminate at the various control points designed within the electrical system. 
     With the increase in electrical and signaling technology, there has also been an increase in the variety of cables used to interconnect electrical and electronic equipment. While the electrical industry still makes extensive use of copper and sometimes aluminum electrical conductors disposed within cables, the use of optical cables has also become widespread and there is every indication that the use of optical cables may surpass the current percentage of use of copper or aluminum conductor cables. 
     With the widespread use of a virtually endless variety of electronic equipment and devices, there has also been a constant and steady increase in the use of specialized electrical system conductors in raceways and mechanical areas that do not use normal metallic conduit. Instead, cable trays are first installed within the raceways and mechanical areas. Thereafter, the electrical system conductors and cables are placed into the cable trays where the electrical system conductors remain until they must be serviced or remodeled. 
     One standard type of cable tray is made from an assembly of wire rods. These rods are welded together at various angles to result in what is usually a channel-shaped trellis that can be used as a cable tray. These channel-shaped cable trays are installed within the raceways and mechanical areas such that the two opposing sides of the channel are generally vertical while the web connecting the two opposing sides is mounted to face upward against gravity. The electrical system conductors are placed within the channel-shaped cable tray by simply locating the length of the wires parallel to the longitudinal axis of the channel-shaped cable tray and allowing the electrical system conductors to rest directly upon the metal used to fabricate the channel-shaped tray. 
     While this type of cable tray offers a simple and generally strong design for mounting loose electrical system conductors, the direct contact of the electrical system conductors onto the wire rods of the channel-shaped tray can introduce high areas of mechanical stress on the underside of the electrical system conductors that can, over time and use, cause fatigue fractures to occur in the electrical system conductors. Such cracks not only cause severe operational problems with the electrical devices interconnected using the electrical system conductors, such cracks also present a serious fire hazard. 
     The increased use of optical cables also presents additional reasons for use of a cable tray that does not bend or fracture the delicate optical fibers within the optical cable. Such fractures can be easily caused by high stress point loads on an optical cable when the optical cable is resting on the wire rods of a standard cable tray. Such pressure points can fracture the optical fibers, but the sensitivity of optical fibers is such that even excessive pressure on the optical fibers can affect many of the key performance characteristics of the optical cable such as the optical fiber&#39;s transmission signal speed, the operable bandwidth of the optical fiber, and the general performance integrity of the optical cable. In severe cases, these excessive pressures can also affect these same performance characteristics for copper data cables. 
     Various embodiments of the present invention described herein include features and characteristics that tend to reduce the probability and frequency of such fatigue cracks or high stress points that can reduce the overall performance of both metallic and optical cables. 
     SUMMARY OF THE INVENTION 
     This invention relates to an apparatus for installing electrical system conductors, and more specifically to the installation of electrical system conductors by placement of those electrical system conductors within a uniquely designed cable tray. More specifically and in accordance with the various embodiments of the present invention, a cable tray is disclosed that is made from an assembly of interconnected metallic rods. Various embodiments of the present invention utilize different shaped rods to provide combinations of concentrated strength, better rigidity, and reduction of stress concentration points between the outer surface of the various shaped rods and the electrical system conductors disposed within the cable tray. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings which form part of the specification: 
         FIG. 1  is a perspective view of one embodiment of the present invention showing one cable tray made from an assembly of wire rods. 
         FIG. 2  is a vertical section view of one embodiment of the present invention. 
         FIG. 3  is a top view of one embodiment of the present invention. 
         FIG. 4  is a left elevation view of one embodiment of the present invention. 
         FIG. 5  is a right elevation view of one embodiment of the present invention. 
         FIG. 6  is a vertical cross section of the bottom portion of one embodiment of the present invention as shown in  FIG. 3 . 
         FIGS. 6A ,  6 B,  6 C, and  6 D are vertical cross sections similar to the cross section of  FIG. 6 , but which show various geometric shapes for the longitudinal rods that can be used in various embodiments of the present invention. 
     
    
    
     Corresponding reference numerals indicate corresponding steps or parts throughout the several figures of the drawings. 
     While one embodiment of the present invention is illustrated in the above referenced drawings and in the following description, it is understood that the embodiment shown is merely one example of a single preferred embodiment offered for the purpose of illustration only and that various changes in construction may be resorted to in the course of manufacture in order that the present invention may be utilized to the best advantage according to circumstances which may arise, without in any way departing from the spirit and intention of the present invention, which is to be limited only in accordance with the claims contained herein. 
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
     A set of preferred embodiments of the cable tray A of the present invention are illustrated in  FIG. 1  through  FIG. 6D . An example of the physical configuration of a preferred embodiment of the present invention is shown in  FIG. 1  where the cable tray A comprises a plurality of U-shaped transverse members  1  and a plurality of longitudinal members  2 . As is readily apparent, the plurality of U-shaped transverse members  1  are disposed substantially perpendicular to the plurality of longitudinal members  2  at a general spacing of about 3.9 inches on center. The longitudinal members  2  of the present embodiment are generally spaced about 2.0 inches on center. 
     Upon the positioning of the plurality of U-shaped transverse members  1  and the plurality of longitudinal members  2  it will be understood by those skilled in the art that at substantially each point where a single U-shaped transverse member  1  intersects with a single longitudinal member  2 , the U-shaped transverse member and the longitudinal member are welded together. 
     This is typical throughout the entire construction of the present embodiment of the invention with the exception of the longitudinal members  2 A. The other longitudinal members  2  are positioned such that the outer radius of the longitudinal member is welded against the outer radius of the adjacent U-shaped transverse member  1 . In contrast, each of the two longitudinal members  2 A is generally located at an end  3  of the plurality of U-shaped transverse members  1 . The longitudinal members  2 A are then welded in that position on the end  3  of the plurality of U-shaped members  2 . 
     It will be appreciated by those skilled in the art that when the present embodiment of the cable tray A is fully constructed, the cable tray is in the general shape of a channel having plurality of openings disposed between the framework of the assembled plurality of U-shaped transverse members  1  and the plurality of longitudinal members  2 . It will also be appreciated that when fully assembled, the outside dimension of the cable tray A of the present embodiment has a width of about 3.5 inches and a height of about 1.5 inches. In alternative embodiments of the present invention, the width and height can be readily adjusted to fit the dimension into which the cable tray A will be installed. In most instances the width and height of the assembled cable tray A will comparable to the width and height dimensions of standard wood construction framing material. 
     It will also be understood that while preferred embodiments of the present invention as described herein show the cable tray A as being generally channel-shaped and that the transverse members are U-shaped, the intended scope of this invention is not to be limited to only those embodiments that have channel shapes or U-shaped components. For example, other embodiments of the present invention include cable trays A that have a bottom and two sides where the two sides may be not be perpendicular to the bottom. 
     Other embodiments of the present invention include cable trays A where the two sides may be flared away from the longitudinal center of the bottom or flared toward the longitudinal center of the bottom, thereby making the interior angle formed by the sides and the bottom of each such embodiment either obtuse or acute respectively. This is to say, the angular placement of the sides of the present cable tray A in relation to the bottom of the cable tray may be adjusted as needed for specific applications and still remain within the intended scope of the present invention. 
     In a preferred embodiment, the overall length of the cable tray A is about 10 feet, however, the length of the cable tray A can be any other length while still remaining within the intended scope of the present invention. 
     Those skilled in the art will appreciate that the plurality of U-shaped transverse members  1  and the plurality of longitudinal members  2  may be of any type of material strong enough to support the weight to which the cable tray A is expected to support. In a preferred embodiment, the plurality of U-shaped members  1  and the longitudinal members  2  are made from a galvanized wire in accordance with ASTM A641. The zinc plating of the present embodiment is electrodeposited zinc having a Type III Finish and Service Condition One in accordance with ASTM B633. Alternatively, the finish of the material may also be a polyester powder coating having a general thickness of about 1.2 mils to about 3.0 mils. In yet other alternative embodiments of the present invention, the plurality of U-shaped transverse members and the plurality of longitudinal members  2  are made from either carbon steel Brite Basic Wire in accordance with A510, Grade 1008, or alternatively, 304 &amp; 306 Stainless Steel. To ensure that the assembled cable tray A shown in some preferred embodiments has a generally consistent geometric shape and balance, the angular formations within the assembled cable tray should not vary by more than about ±3 degrees; the overall camber should not exceed 0.5 inches over each ten foot length of cable tray; and, the twist should not exceed 0.5 inches over each ten foot length of the cable tray. 
     Although the general characteristics of the cable tray A are substantially described and disclosed above, variations in the geometric shape of the plurality of U-shaped transverse members  2  provide a variety of preferable strength characteristics and resistance to combat fatigue cracking and abrasion of the electrical system conductors. 
     More specifically, when electrical system conductors are installed in a prior art style cable tray having round or square U-shaped transverse members, the geometry of those member shapes causes the outer surface of the electrical system conductor to rest upon a relatively sharp corner or small radius. This results in the weight of the electrical system conductor being transferred onto the cable tray at the sharp corner or small radius of the round or square shaped transverse rod. This generates a mechanical rise in the stress load at those very concentrated points and can more easily result in chaffing or fatigue cracks in the metallic electrical conductor, the optical fiber within the cable, or the cable&#39;s insulation. Various embodiments of the present invention tend to reduce this stress concentration area by incorporating alternative geometric shapes for the plurality of U-shaped transverse members  2 . 
     For example, the embodiment of the cable tray A as shown in  FIG. 1 ,  FIG. 2 ,  FIG. 3 ,  FIG. 4 ,  FIG. 5 , and  FIG. 6  show the plurality of U-shaped transverse members to be generally obround in shape ( FIG. 6 ), having a height of about 3.5 mm and a width of about 6.5 mm. When the obround shape is used, a flat portion  4  of each of the plurality of U-shaped transverse members  1  rests upon the outer radius of each of the longitudinal members  2 . This orientation of the obround U-shaped transverse member  1  positions the opposite flat face  5  of the obround shape upward to face the bottom of the electrical system conductors when the electrical system conductors are placed within the cable tray A. As can be seen, the point load between the electrical conductor and the transverse members  1  is significantly lower in the present embodiment than the old art embodiment because the surface area of the obround flat surface  5  reduces the loading per square inch against the bottom of the electrical conductor. 
     In this same manner, the plurality of U-shaped transverse members  1  can be made using rods that provide yet other geometric shapes that tend to reduce the point loading between the electrical system conductors in the cable tray A and the plurality of U-shaped transverse members  1  of the cable tray. For example, the plurality of u-shaped transverse members  2  may be elliptically shaped as shown in  FIG. 6A . In other embodiments of the present invention, the plurality of transverse U-shaped members may be in the shape of a square having substantially rounded corners as shown in  FIG. 6B . In yet other embodiments of the present invention, the plurality of U-shaped transverse members may be in the shape of an extremely flattened elliptical as shown in  FIG. 6C . Finally, in yet another embodiment of the present invention, the plurality of U-shaped transverse members may be in the shape of an elliptical rod that has been halved as shown in  FIG. 6D . It is appreciated that the U-shaped transverse member may be of yet other geometric shapes while still remaining with the intended scope of this invention and act to reduce the point loading on the electrical system conductors placed in the cable tray, with the primary limiting factor for the chosen geometric shape, and the dimension of that shape, being the shape&#39;s ability to provide the structural integrity to carry the weight of the number of electrical system conductors to b disposed within the cable tray A. 
     In each of the above geometric shapes it is understood that a goal is to select a shape that proffers the flattest surface area to the bottom surface of the electrical conductor to thereby reduce the point loading between the cable tray A and the electrical conductor residing within the cable tray. Thus, in each shape identified for the present invention, the intent is to generate a structural system where the contact point load on an electrical conductor placed within the cable tray such that the surface of the U-shaped transverse members contacts the electrical conductor placed within the cable tray is less than the contact point load of a cable tray having U-shaped members that are in the shape of one of either a substantially sharp cornered square, a substantially sharp cornered rectangle, a substantially sharp cornered triangle, or a circle. 
     While the above description describes various embodiments of the present invention, it will be clear that the present invention may be otherwise easily adapted to fit any configuration where a cable tray is required. Additionally, as various changes could be made in the above constructions without departing from the scope of the invention, it is also intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. The scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.