Patent Abstract:
A cable tray has a pair of opposed side rails with a pair of aligned through bores. One or more stacked cable support blocks extend between the opposed side rails. A lower rung extends between the rails at the pair of aligned through bores. The lower rung has an upwardly opening channel extending along its length receiving the bottom edge of a lowermost one of the cable support blocks. The lower rung also has at least one opening extending through the lower rung in alignment with the pair of aligned through bores. A fastener extends through at least one opening of the lower rung and through at least one of the pair of aligned through bores in the side rails.

Full Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to cable trays for use with electrical cables. 
     Cable trays are used to support electrical cables which run through factories and other structures. Cable trays may have straight and (horizontally and vertically) curved sections to accommodate the installation requirements of a particular setting. 
     One type of known cable tray has a pair of parallel side rails or stringers that are interconnected with a plurality of transverse rungs at predetermined intervals along the length of the parallel side rails. Cables are laid on top of the rungs. The rungs are typically attached to the side rails by fasteners, or are welded to the side rails. The parallel side rails may be joined end-to-end by a splice plate or a connecting bar. However, since these cable trays generally do not secure the cables in spaced relation to each other, they may be unsuitable for use with high power cables where there may be a need to keep the cables cool, or to prevent the cables flailing in the event of a fault or short circuit. 
     A cable tray more suited to high power cables is disclosed in U.S. Pat. No. 3,618,882 to Podedworny. In Podedworny, two abutting support blocks with semi-circular cut-outs on adjacent faces provide a housing with cylindrical openings that confine the cables in spaced relation in the cable tray. The blocks are secured to each other and to a rung by bolts extending vertically through the blocks and into the rung. 
     To install the type of cable tray disclosed by Podedworny, lower support blocks may be placed on rungs with their semi-circular face facing upwardly and the lower support blocks may be temporarily held in place by bolts. Cables may then be laid into the semi-circular channels without risk of the support blocks shifting or falling over. Next, the bolts may be removed, the upper support blocks set in place and the bolts again inserted to complete the assembly. This manner of assembly is time consuming and may become difficult where the tray has a large vertical curve. More specifically, with a large vertical curve, as it becomes hard to keep a lower support block properly positioned while the bolts are inserted and there is also a risk of the lower support block shifting when the bolts are removed preparatory to installing the upper support blocks. 
     SUMMARY 
     The present invention seeks to provide a cable tray which is easier to install. 
     In accordance with an embodiment of the present invention, a cable tray has a pair of opposed side rails with a pair of aligned through bores. One or more stacked cable support blocks extend between the opposed side rails. A lower rung extends between the rails at the pair of aligned through bores. The lower rung has an upwardly opening channel extending along its length receiving the bottom edge of a lowermost one of the cable support blocks. The lower rung also has at least one opening extending through the lower rung in alignment with the pair of aligned through bores. A fastener extends through at least one opening of the lower rung and through at least one of the pair of aligned through bores in the side rails. 
     These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the figures which illustrate example embodiments of the invention: 
         FIG. 1  is a perspective view of a cable tray made in accordance with this invention; 
         FIG. 2  is a front view of the cable tray of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view along the lines  3 - 3  in  FIG. 2 ; 
         FIG. 3A  is a magnified view of  FIG. 3 ; 
         FIGS. 4 ,  5 , and  6  are exploded fragmentary views of a portion of the cable tray of  FIG. 1  illustrating assembly of the cable tray; 
         FIG. 7  is a cross-sectional view along the lines  7 - 7  in  FIG. 6 ; and 
         FIG. 8  is a fragmentary perspective view of a portion of a cable tray made in accordance with another embodiment of the invention. 
     
    
    
     DESCRIPTION 
     Referring to  FIG. 1 , a cable tray  10  has a pair of opposed side rails  12   a  and  12   b  to which are attached opposed pairs of lower and upper rungs  14 L,  14 U. A plurality of cable support blocks  26 ,  28  are held in place by each pair of rungs, and cables  32  extend through cylindrical openings formed by the support blocks. Vented covers  17  may be attached to the upper and lower rungs  14 U,  14 L. 
     Turning to  FIGS. 2 ,  3 , and  3 A, each of rungs  14 L and  14 U has a U-shaped profile which provides a central channel  16  along the length of each rung. An opening  34  extends along the length of each of the two side arms  19  of each rung. The lowermost support block  26 L is fitted into the central channel  16  of the lower rung  14 L and the uppermost support block  26 U is fitted into the central channel  16  of the upper rung  14 U. Each rung is positioned so that its openings  34  are aligned with aligned through bores  50  ( FIG. 4 ) in opposed side rails  12   a ,  12   b . A rod  18  runs through each opening  34  in the rungs and through the through bore  50  ( FIG. 4 ) in each of the side rails  12   a ,  12   b . The rods are threaded and a flange nut  20  is threaded to either end of each rod to attach the rungs to the side rails. 
     Cable support blocks  26 L and  26 U are identical in configuration but oriented oppositely. Thus, each of the support blocks  26 L,  26 U has one straight face  42  (which for block  26 L is the lower face and which for block  26 U is the upper face) and one face  44  with four semi-circular cut outs  45  (which for block  26 L is the upper face and which for block  26 U is the lower face). It is the straight face  42  of each block  26 L,  26 U which is fitted into the channel  16  in a rung  14 L,  14 U. 
     Cable support blocks  26 L,  26 U sandwich cable support blocks  28 L,  28 U. Cable support blocks  28 L and  28 U are identical in configuration but oriented oppositely. Thus, each of support blocks  28 L and  28 U has one face  70  with four semi-circular cut outs  45  (which for block  28 L is the lower face and which for block  28 U is the upper face) and an opposite face  72  with five semi-circular cut outs  45  (which for block  28 L is the upper face and which for block  28 U is the lower face). As best illustrated in  FIG. 3A , the faces  44 ,  70 , and  72  are radiused at the semi-circular cut-outs to prevent cutting or chafing of the cable insulation. The semi-circular cut-outs in adjacent blocks align to form offset rows of cylindrical openings  60  for receiving cables. 
     Turning to  FIG. 4 , side rails  12   a ,  12   b  have opposed inwardly facing channels  46  at the ends of each rung  14 L which receive the ends of the support blocks  26 ,  28 . In this regard, as illustrated in  FIG. 7 , the cable support blocks  26 ,  28  have a length greater than the spacing between the opposed side rails  12   a ,  12   b  but less than the spacing between the bottoms of opposed channels  46  of the side rails. 
     A pair of inwardly facing depressions  52  extend along each side rail  12   a ,  12   b  from each end of each side rail. In consequence, the depressions of a side rail  12   b  line up with like depressions in a side rail  12   b ′ placed end-to-end with side rail  12   b , resulting in extended length depressions. Within each depression  52  of a side rail, a through bore  54  extends through the side rail. A splice plate  22  has a pair of protuberances  56  of complementary width to that of the extended length depressions, with longitudinally extending slots  58  extending through the splice plate at the protuberances. These protuberances of the splice plate may be fit into the extended length depressions with the slots  58  aligning with through bores  54 . Bolts  24  (with lock washers—not shown) and grommet nuts  30  may then be joined through each of the aligned through bores  54  and slots  58  to join the splice plate to the side rails  12   b ,  12   b ′. The bores  54  may be positioned such that when the end-to-end side rails are joined by a splice plate, there is a gap between the side rails. This gap between the side rails, along with the longitudinally extending slots  58  allows for thermal expansion. 
     To assemble cable tray  10 , with reference to  FIGS. 3A and 4 , lower rungs  14 L are first joined to side rails  12   a ,  12   b  by positioning each lower rung so that rods  18  may be inserted through a pair of adjacent through bores  50  in one side rail, through C-shaped openings  34  in the lower rung and out the pair of through bores  50  in the opposite side rail. Flange nuts  20  may then be threaded to the ends of the rods. Next, for each installed lower rung, a lower cable support block  26 L may be slid down opposed channels  46  of the side rails  12   a ,  12   b  and into channel  16  of the lower rung. Optionally, at this stage, cover sections  17  ( FIG. 1 ) could be installed on the bottom of the partially assembled cable tray. The cable tray, thus far assembled, may then be moved to its installed position and secured in position in any suitable fashion. This may be repeated with an adjacent section of cable tray and the adjacent section joined to the first section by splice plates  22 . 
     With all of the sections of cable tray secured in position, a first row of cables  32  may be laid into the cable trays such that each cable is received by the semi-circular cut  45  outs of the lower block  26 L. Turning to  FIG. 5 , a cable support block  28 L may then be slid down opposed channels  46  in the side rails at each lower rung into abutment with block  26 L. In this position, the semi-circular cut outs  45  in block  28 L form, with semi-circular cut outs  45  in block  26 L, cylindrical openings  60  which confine each cable  32  in the first row of cables. Turning to  FIG. 6 , a second row of cables  32  may then be laid into the semi-circular cut outs  45  in the top face of block  28 L. Thereafter, a cable support block  28 U may then be slid down opposed channels  46  in the side rails at each lower rung and into abutment with block  28 L. In this position, the semi-circular cut outs  45  in block  28 U form, with semi-circular cut outs  45  in block  28 L, cylindrical openings  60  which confine each cable  32  in the second row of cables. A third row of cables may then be laid into the semi-circular cut outs  45  in the top face of block  28 U. Thereafter, a cable support block  26 U may be slid down opposed channels  46  in the side rails at each lower rung and into abutment with block  28 U. In this position, the semi-circular cut outs  45  in block  26 U form, with semi-circular cut outs  45  in block  28 U, cylindrical openings  60  which confine each cable  32  in the third row of cables. Lastly, for each block  26 U, an upper rung  14 U is positioned so that the top face  42  of block  26 U is received by the channel  16  of the upper rung. The upper rung is then joined to side rails  12   a ,  12   b  by inserting rods  18  through a pair of adjacent through bores  50  in one side rail, through openings  38  in the upper rung and out the pair of through bores  50  in the opposite side rail. Flange nuts  20  may then be threaded to the ends of the rods. The result is that the support blocks  26 ,  28  are clamped in place between the rungs  14 L,  14 U and the blocks  26 ,  28  hold the cables in place. Lastly, cover sections  17  ( FIG. 1 ) may be installed. 
     As is apparent from  FIG. 2 , adjacent rows of cables are staggered in a trefoil formation which balances the electromagnetic fields produced by the power cables thereby lowering system impedance and reducing power losses in addition to optimizing load sharing amongst the cables. Further, this improves heat dissipation of the assembly and reduces the prospects of a flailing cable impacting (and shorting to) another cable. The radiusing of the edges of the openings  60  also help to prevent cable damage. 
     It will be apparent from the foregoing that cable trays according to this invention ease installation in the field. For instance, assembly does not require any step of partial disassembly and the support blocks will stay in place even in vertically curved cable tray sections. 
     Numerous modifications may be made without departing from the spirit of the invention. 
     For example, with wider side rails, a greater number of blocks  28  could be used to increase the number of rows of cables. Also, with narrow side rails, only blocks  26 L,  26 U could be used to construct a cable tray with one row of cables. Indeed, in a relatively low power application where there is little concern for flailing cable in the event of an electrical fault and where only one row of cables is needed, it may be possible to install only the lower rungs  14 L and lower support blocks  26 L and simply set the one row of cables into the semi-circular cut outs of the top face of the lower support blocks  26 L. 
     While not preferred, the joining wall of the U-shaped rungs could be thickened and be provided with a single opening in place of openings  38  in the side arms  19  of the rungs. In such instance, the rungs would have a tendency to rotate until stabilized by a support block  26 L or  26 U being fitted into their central channels  16 . 
     The rungs could have other profiles which provide a channel to support the support blocks and openings to receive the rods. 
     While the openings  38  have been described as C-shaped, they could have other shapes and could, for example, be cylindrical bores through the rungs. However, a drawback with long bores through the rungs is that any foreign material that found its way into the long bores could jam the rods during installation. 
     While rods  18  have been described as threaded at both ends to receive nuts, the rods could equally be in the nature of long bolts such that nuts need be threaded to only one end of the rods. Further, a nut with a lock washer could be substituted for the described flange nuts. Alternatively, the rods could clamp the side rails with other mechanisms, such as cams. 
     In the alternate embodiment the rungs  14 L,  14 R do not have openings  34  and the long rods  18  are not used. Instead, as shown in  FIG. 8 , the rungs  114 L have ears  190  at each end with through bores  192 . Each through bore  192  aligns with a bore  50  ( FIG. 4 ) in a side plate and a bolt  194  extends through the bore  50  ( FIG. 4 ) and the aligned bore  192  and is held in place by a flange nut  196 . Top rung is similarly configured. Alternatively, vertical slots could be cut into rungs  14 L,  14 R proximate their ends so that the modified rungs could be used with bolts  194  and nuts  196 . However, these options considerably complicate installation of the top rung, especially where, as is often the case, the cable tray is proximate the ceiling. Further, this reduces the strength of the assembly. Yet further, in an industrial setting subject to significant vibration, any necessary re-tightening of the nuts  196  as preventative maintenance would be difficult. 
     Other modifications will be apparent to those skilled in the art and, therefore, the invention is defined in the claims.

Technology Classification (CPC): 7