Abstract:
A cable bus system for the mounting and positioning of high amperature, from low to high voltage electrical power cables transmitting polyphase electrical current. The cable bus system included a ventilated enclosure used to protect electrical cables mounted therein. The enclosure is provided with multiple modular cable trays which are bolted together in a stacked arrangement to form a single multi-level cable raceway. The enclosure is further provide with ventilated top and bottom covers which are secured respectively to the top and bottom of the uppermost and bottommost calve trays to define the enclosed metal circuit. The cable bus system is capable of transmitting the same highest allowable “free air” cable amperature in both above and underground installations, effectively improving the transmission of electrical power from one end to the other end in installations where a transition of electrical power from on the ground is either necessary or economically preferable. For the underground portion, the cable bus is installed in the encasement that is uniquely offset vented or power cooled to meet the cable high amperage requirements. This cable bus system is also suitable for high vertical rise installations when utilizing anti cable slip mechanism or technique.

Description:
SCOPE OF THE INVENTION 
     The present invention relates to a cable bus system for use in the distribution of electric power, and more particularly an expandable cable bus system for the distribution and/or transmission of low, medium and high voltage, high amperage, polyphase alternating-current having amperatures ranging up to 8,000 Amps, and/or at voltages of up to 230,000 volts. 
     BACKGROUND OF THE INVENTION 
     In power generation and transmission, electrical generator coils or windings are used to produce alternating electric current. To effect the more economical transmission of produced electric current, polyphase transmission systems have been developed. Conventionally, most polyphase power transmission is effected in the form of three-phase power transmission where three alternating currents are produced. Three-phase electrical transmission systems are typically based on a three conductor construction, each conductor used to transfer individual alternating currents which are produced. The alternating currents are generated to reach respective instantaneous peak values at different times, with the second and third currents being delayed respectively by one-third and two-thirds of the current cycle time. 
     In electrical distribution equipment used to transmit high amperature electrical power from the grid to a load area, the generated polyphase power is supplied by way of electrically insulated stranded conductors or cables when installed near electrical grounds. As the amperature electric current to be delivered increases to higher values, the three conductor constructions become less economical and feasible to use due to the damaging mutual heating of the conductor insulation. Therefore, multiple single conductor cables spaced and strategically positioned apart, are provided for each separate phase as a means to effect equal current sharing, and prevent current varying along any one cable which could otherwise result in overheating. Where such multiple cable delivery systems are provided, it is necessary that the cables are arranged in a parallel format for each phase in a well spaced and oriented manner to avoid electrical current, as well as magnetic field imbalance. The specific cable spacing and orientation varies on an installation-by-installation basis, depending on a number of limitations on current carrying factors, such as the current amperature, cable size, as well as thickness and/or quality of cable conductor insulation. 
     In an effort to ensure optimal electrical power cable spacing and orientation, various cable bus systems have been developed to provide both mechanical protection and ensure the desired positioning of electrical cables. A prior art cable bus system  6  of the type sold under the name Superior Cable Bus™ by Superior Tray Inc. of British Columbia, Canada and MP Husky™ Cable Bus by MP Husky in Greenville, S.C., are shown in  FIG. 1 . In such conventional cable bus system  6 , a number of electrical cables  12  are housed within a metal enclosure  8 . The metal enclosure  8  is provided with parallel spaced C-channel sidewalls  16   a , 16   b  which are joined along the top and bottom edges respectively by a ventilated top panel  18  and a bottom panel  20  to define an interior raceway  22 . 
     Along each side of the raceway  22  opposing pairs of C-shaped rails  23  are provided at three foot intervals for each receiving and retaining therein in a series of split blocks  24  which must be locked together using bolts on each side. The split blocks  24  are used to secure the cables  12  in place with in the raceway  22 , in a sandwiched arrangement. Each split block  24  is formed as a series of chocks  26   a , 26   b , 26   c  which are approximately one inch in thickness. The chocks  26  are provided with a series of pre-drilled holes  28  which are centered along their abutting edges. The holes  28  are sized to receive respective cables  12  therein. The holes  28  are spaced and positioned across the block  24  at multiple levels to receive and support a number of electric cables  12  in a parallel relationship therein. 
     The applicant has appreciated that various limitations exist with prior art split block cable bus systems  6 . In particular, the use of split chocks  26   a , 26   b , 26   c  to support and position electrical cables  12  are both cumbersome and time consuming. In certain cases physical space constraints may prevent the installation of bolts necessary to lock the blocks together. Because it is not technically allowable or feasible to splice the parallel cables in each polyphase used in high amperature cable transmissions systems, it is necessary to physically draw full circuit lengths of cable in each layer of the electrical cables  12  successively over each chock  26   a , 26   b  at the site of installation. Because of the longitudinal length spacing between the sets of split blocks and the varying surface contour of each split block  24 , this in turn necessitates the use of labour intensive cable rollers to avoid cable damage, increasing both the time and cost of installation. 
     In addition, if the outside diameter of the cable insulation layer  13  varies relative to the diameter of preformed holes  28  as a result of manufacturing tolerances, the holes  28  formed in the cable support blocks  24  could be either too loose or too tight for proper cable mounting. The correction of hole sizes is both difficult and costly, if deemed possible, and therefore requires the manufacturing and replacement of the split blocks. 
     Another disadvantage is that the cables used are normally heavier, larger sized conductors with relatively thin insulation which can be readily ruptured and fail at the three foot interval support locations, as a result of commonly occurring and damaging electrical system fault forces. 
     Further, the positioning of split blocks  24  at approximate three foot intervals results in the formation of sectionalized compartments along the length of the raceway  22 . If ventilation openings in the top panel  18  are inadvertently covered by debris or the like, this disadvantageously may result in localized cable hot spots along the raceway  22  as a result of blockage of required airflow. 
     More problematic however, if cables  12  at a lower level require removal or replacement as a result of damage or failure, with prior art systems it is necessary to first completely remove and thereafter reinstall all overlying chock blocks  26   c , 26   d  and the upper cable layers from the raceway  22  at significantly increased time, cost and difficulty. 
     Another disadvantage of the prior art of cable bus systems are typically installed above ground level in order to ensure that free flowing air passing through the vented covers dissipates undesirable heat generated by cables away from the enclosure. Heat trapped within the vicinity of the high amperage cables will cause the ambient temperature to rise, causing premature failure of the cable installation or necessitating the substantial derating of the allowable cable amperature, which can become cost prohibitive. 
     Power cables of varying levels of amperage are commonly installed underground by either underground conduits encased within poured concrete, or alternately directly buried. Due to the slow rates of heat transfer away from the heat generating cables due to a lack of airflow, the amperage of cables installed in such mediums are restricted both technically and by industry standards to approximately one half of that allowable for cables which are continuously cooled by air movement. When a power cable circuit is conventionally installed partially underground with the balance of the circuit installed where there is open airflow, the allowable amperage for the cables in the total circuit length is restricted to the lower underground amperage values resulting in uneconomical installation practices. 
     SUMMARY OF THE INVENTION 
     The present invention provides a cable bus system for the mounting and positioning of electrical power cables used to conduct high amperature, polyphase electrical current up to 8,000 Amps. The cable bus system is configured to ensure that electrical impedance along each parallel conductor cable is identical to provide equal current load sharing, while minimizing phase impedance and the generation of cable mutual heating thereby. In the cable bus system, a predetermined number of electrical cables are fixed in position relative to each other to minimize the possibility of excessive heating of cable conductor insulation as a result of the heat generated by the transmission of electricity therealong. 
     A further object of this invention is to prove an underground cable bus system meets free or forced flowing air requirements necessary to maintain cooling of the power cables and thereby attain the maximum cable amperage throughout the circuit route. 
     Another object is to provide a subterranean cable transmission assembly in which a cable bus enclosure is provided in an underground encasement composed of concrete or other suitable material, and which is air vented in an offset manner that prevents entry of debris and soil materials into the enclosure at preselected locations along the encasement circuit length. 
     Another object of the present invention is to provide a cable bus system for use in the orientation of electrical power cables, and which allows for the simplified addition and/or removal of electrical cables as power supply and/or load requirements may change. 
     Another object of the invention is to provide a cable bus system enclosure for insulated electrical cables used in the transportation and/or transmission of high amperature electrical power, and preferably electrical power at amperatures of up to 8,000 Amps from a source to a load area, and which is constructed to provide for enhanced uninterrupted airflow longitudinally along the enclosure. 
     Another object of the invention is the use of high temperature power cables in the present invention to achieve a compact, highly efficient power feeder system for critical circuits required to remain in operating condition without failure during emergency fire situations. 
     Another object of the invention is to provide a cable bus system which incorporates one or more stackable modular metal cable trays for use in the assembly of a multi-layer metal cable enclosure used in the erection of a cable bus or raceway, and which are configured to support a number of electrical power cables at multiple spaced layers, while minimizing electrical impedance, maximizing ventilation of heat generated by current carrying cables and achieving the highest industry allowable free air power cable enable amperage. 
     A further object of the invention is to provide a cable bus system which is adapted to support electrical cables with minimized risk of cable insulation damage as a result of mechanical stresses at cable/support system contact points. 
     Another object of the invention is to provide auxiliary anti-slip gripping sleeve or grommet for positioning over the cable outer cover at strategically located cable clamp location in vertical cable bus installations. Although the cables in vertical arrays are usually clamped approximately every two to three feet in vertical installations, there is a high risk of cable slipperage particularly in vertical heights greater than approximate 30 feet due to downward forces exerted by gravitational weight during cable vibration or electrical fault forces. Typically the gripping sleeves are formed of an elastomeric or resiliently compressible material such as rubber Neoprene™ or plastic. Anti-slip gripping sleeves may advantageously serve as both a non-slip connection between the cable, clamp and enclosure cross-brace members and serve to additionally insulate the electrical cable from metallic cable bus support components. 
     To at least partially achieve some of the aforementioned objects, the present invention provides a cable bus system which includes a ventilated enclosure suitable for use in the protection of unarmoured or armoured electrical cables mounted therein. Although not essential, the enclosure is most preferably provided with a modular design and consisting of one or more multiple single level cable trays which maybe bolted in a stacked arrangement in the formation of a single or multi-level cable raceway. In such an embodiment, the addition or removal of individual cable trays may thus be used in the erection of a larger or smaller capacity cable bus system depending on the power distribution requirements. Further, the use of modular cable trays allows existing cable bus systems to be upgraded in future with ease, allowing the addition of more cables as consumption requirements at a load and/or site may change. 
     The cable bus system is typically provided with ventilated top and bottom covers which are screwed, bolted or welded respectively to the top and bottom of the uppermost and bottommost cable trays to define the enclosed metal circuit. 
     In a simplified construction, each metal cable tray includes a pair of longitudinally extending vertical side panels, which are joined in a fixed orientation by a series of transversely extending connecting runs or cross-brace members. The connecting runs are screwed, welded or bolted at each end to a respective side panel and serve as both cross-brace members and a lower support for an associated array of electrical cables resting thereon. In optimum construction, the cross-brace members are provided with a generally flat and smooth uppermost surface which is selected to allow the cables of each associated array to be drawn longitudinally thereacross and along the raceway during straight cable pulling operations, without the requirement of cable support rollers. 
     One or more clamp members are provided to secure the cables of each array to an upper face of the associated cross-brace member. In one simplified construction, the clamp members may consist of an elongated metal bar which is provided with a series of spaced keepers which are configured for fitted placement over the upper peripheral portion of cables. The clamp members may be secured in a variety of manner, but most preferably are fixed in place by way of screws or bolts, which allows for later removal in the event cable repair and/or replacement may be required in future. 
     Most preferably, the cross-brace members of each cable tray are longitudinally off-set relative to the cross-brace members of a next, and more preferably each remaining modular tray in the cable bus system. It is to be appreciated that such an offset configuration allows vertical access to each cable array from a topside of the raceway without requiring the complete disassembly of the cable bus system. 
     Accordingly, in one aspect the present invention resides in a cable bus system comprising: a longitudinally extending raceway comprising, at least one longitudinally extending cable tray, each cable tray including: a pair of generally parallel longitudinally extending side beams, and a plurality of laterally extending cross supports, the cross supports spanning between and being coupled to each said side beam and defining a cable support surface, a ventilated bottom cover secured to a lowermost one of said cable trays, at least one electrical cable array disposed in an interior of said raceway and associated with a corresponding one of said cable trays, each said cable array comprising a plurality of insulated high amperature electrical cables disposed in a generally parallel spaced operable position in supporting contact with the cross supports of the associated said cable tray, at least one clamping member for securing said cables substantially against movement from said operable position in said raceway. 
     In another aspect the present invention resides in a high amperage electric cable bus system comprising: a longitudinally extending raceway comprising, a plurality of longitudinally extending cable trays, each cable tray having a generally modular construction and including a pair of generally parallel longitudinally extending side members, and a plurality of laterally extending cross supports, the cross supports spanning between and fixedly coupled to each said side beam, the cable trays being positioned in a generally stacked orientation with the side beams of an a first said cable tray being secured in substantially aligned juxtaposition with the side members of a next lower cable tray, arrays selected for the distribution of high amperature polyphase electrical current disposed in an interior of said raceway, each cable array being associated with a respective one of said cable trays and comprising a plurality of generally parallel spaced electrical cables disposed in supporting contact with the cross supports of the associated said cable tray, clamping members for securing said electrical cables of each cable array against movement relative to said associated cable tray. 
     In a further aspect, the present invention resides in a longitudinally extending cable raceway section for use in a cable bus system, the raceway section including: a plurality of longitudinally extending cable trays, each cable tray including an opposing pair of longitudinally extending side members, and a plurality of laterally extending cross-brace members, the cross-brace members each defining a generally smooth cable-support surface and spanning between and being coupled to each said side member, a ventilated bottom panel secured to a lowermost one of said cable trays and extending laterally substantially between each said side member to define a lower extent of the raceway section, a plurality of electrical cable arrays disposed in an interior of said raceway, each said cable array associated with a respective one of said cable trays and comprising a plurality of generally parallel spaced electrical cables, mounted in said position in supporting contact with cross supports of the associated said cable tray, a plurality of clamping members for securing said cables in said mounted position and substantially against movement in said raceway. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference may now be had to the following detailed description taken together with the accompany drawings, in which: 
         FIG. 1  shows a partial perspective exploded view of a prior art cable bus system used in the transmission of high amperature electrical current; 
         FIG. 2  shows a partial perspective view of multi-tray cable bus system in accordance with a preferred embodiment of the invention; 
         FIG. 3  shows a schematic sectional end view of the cable bus system shown in  FIG. 2 ; 
         FIG. 4  shows a perspective view of a bottom most modular cable tray used in the cable bus system of  FIG. 2  prior to the mounting of electrical cables therein; 
         FIG. 5  shows a perspective view of the bottom tray of  FIG. 4  illustrating the initial placement of a first cable array therein; 
         FIG. 6  illustrates a perspective view of the bottom tray of  FIG. 4  showing the coupling of the first cable array in an operational position; 
         FIG. 7  illustrates a perspective view of the one piece contoured clamp used in securing electrical cables to the modular tray; 
         FIG. 8  illustrates the positioning of a second upper modular cable tray used in the positioning of a second cable array in the cable bus system of  FIG. 2 ; 
         FIG. 9  shows a schematic sectional end view of a cable bus system in accordance with a further embodiment of the invention which shows the positioning of further neutral wires identified as N; 
         FIG. 10  shows a schematic side view of an above-ground power distribution system which incorporates a cable bus system in accordance with a preferred embodiment of the invention; 
         FIG. 11  shows a schematic side view of a cable bus system installed as a part of a subterranean power distribution system in accordance with another embodiment of the invention; 
         FIG. 12  shows a cross sectional view of the subterranean power distribution system shown in  FIG. 11 , taken along  12 - 12 ′; 
         FIG. 13  shows an enlarged side view of vertical air vent used in the subterranean power distribution system of  FIG. 11 ; 
         FIG. 14  shows a cross sectional view of the air vent shown in  FIG. 11 , taken along  14 - 14 ′; and 
         FIG. 15  shows a schematic side view of cable bus systems installed as a part of a subterranean power distribution system in accordance with another embodiment of the invention. 
         FIG. 16  shows a cross-sectional view of a power distribution system which incorporates a cable bus system in accordance with a preferred embodiment, installed above grade; 
         FIG. 17  shows a power distribution system which incorporates a cable bus system in accordance with a preferred embodiment, installed directly on grade in accordance with an alternate embodiment; 
         FIG. 18  illustrates a schematic side view of a cable system installed as part of a subterranean power distribution system in accordance with a further possible construction; 
         FIG. 19  shows a schematic side view of a cable bus system installed as part of a power distribution system for high rise applications; 
         FIG. 20  illustrates a partial perspective view of a cable sleeve used in the vertical securement of electrical cables in a vertically oriented cable bus system in accordance with a preferred embodiment; 
         FIG. 21  is a perspective view of a vertically oriented cable bus system used in the vertical securement of electrical cables in the power destruction system shown in  FIG. 19 , with the top cover removed; 
         FIG. 22  illustrates an exploded perspective view of a fastener and anchor bar construction used in securing electrical cables within the cable bus system in accordance with a further embodiment of the invention; and 
         FIG. 23  illustrates a partial cross-sectional end view of the fastener and anchor bar shown in  FIG. 22  in an assembled configuration. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is made to  FIGS. 2 and 3  which illustrate a cable bus system  10  in accordance with a preferred embodiment of the invention used in the distribution and transmission of three-phase electrical power. As will be described, the cable bus system  10  is formed having one and preferably a number of aluminum (or other metal) enclosures  14  which define a longitudinally extending raceway  22  used to house and protect a series of insulated electrical cables  12 . 
       FIG. 2  shows best each of the electrical cables  12  as comprising high amperature, low, medium and high voltage electrical cables which are provided in an electrically conductive core  11  layer which is typically formed of stranded copper wire, and an electrically insulating outer coating or sheath  13 . In the embodiment shown, the cables  12  are longitudinally aligned in two vertically stacked, lower and upper cable arrays  30   a , 30   b , each consisting of six cables  12  in parallel. As shown schematically in  FIG. 3 , the current of each phase A,B,C is divided equally between the paralleled electrical cables  12 . The electrical cables  12  of each array  30   a , 30   b  are further staggered and offset laterally relative to each other to optimize inter-cable spacing to achieve balanced electromagnetic field selected to minimize mutual heating amongst the cables  12  and to maximize the transfer of heat away therefrom. 
       FIGS. 2 and 3  show best the metal enclosure  14  as including a pair of vertically stacked cable trays  32   a , 32   b , a ventilated bottom cover  34  and a ventilated top cover  36  which, in assembly, define the longitudinally extending raceway  22 . Although not essential, most preferably at least one of the cable trays  30   b  is used to mount and is electrically connected to a grounding lead  100  serving as a ground path for stray voltage and/or in the event of electrical fault currents. 
     Each of the cable trays  32   a , 32   b  are normally formed from aluminum, or other suitable metal materials and are provided with a modular construction which allows for their use interchangeably. As shown best in  FIGS. 3 and 4  the cable tray  32  includes a pair of longitudinally extending and parallel spaced sidewall members  38   a , 38   b  which are joined in a fixed, parallel spaced arrangement by a series of transversely extending cross-brace members  40   a , 40   b , 40   c . The side members  38   a , 38   b  are shown as having a generally I-beam construction, with each including a longitudinally extending planar rectangular web  42 , 42 ′, having generally transversely oriented planar flanges  44   a , 44   a ′, 44   b , 44   b ′ joined along upper and lower edges thereof. 
     As shown best in  FIG. 4  the cross-brace members  40   a , 40   b , 40   c  are welded to the web  42  of each side member  38   a , 38   b , in position spaced a marginal distance above the lower flanges  44   b . Although not essential, this configuration advantageously allows for the positioning of the ventilated bottom cover  34  in supported contact resting on top of the lower flanges  44   b , 44   b ′ of the members  38   a , 38   b . Preferably, the cross-brace members  40   a ,  40   b ,  40   c  are electrically conductive so as to carry any possible electrical fault current to instantly trigger circuit breaker activation. Although not essential, in the embodiment shown, the cross-brace members  40   a , 40   b , 40   c  are secured to the side members  38   a , 38   b  at staggered approximately one foot intervals with respect to a next tray  32   b  along the longitudinal length of the enclosure  14 . The applicant has appreciated that the offset longitudinal spacing of the cross-brace members  40   a , 40   b , 40   c  relative to the enclosure ends allows the positioning of the next cable tray  32   b  in a stacked orientation thereon, and with the cross-brace members  40  of the next adjacent upper cable tray  32  being non-aligned from those of tray  32   a . The non-alignment of the cross-brace members  40  of successively stacked cable trays  32  advantageously allows vertical axis to the cable arrays  30   a , 30   b  of both cable trays  32   a , 32   b  by simply removing the top cover  36 , and without necessitating significant disassembling the enclosure  14 . 
     In a simplified construction, the bottom cover  34  is normally formed as having a predetermined number of openings serving as vents to allow the heat produced by the cables  12  to flow out of the enclosure. The ventilated cover  34  has a lateral width which could be selected marginally less than the lateral distance separating the webs  42 , 42 ′ of each side member  38   a , 38   b . The bottom panel  34  may be screwed, bolted or riveted to the sidewall member flanges  44   a , 44   b ′ in place, or in an alternate configuration secured in position by weldments. 
     The cross-brace members  40  function as a support base for the electric power cables  12  in the assembly of the cable bus system  10 . The cross-brace members  40   a , 40   b , 40   c  are most preferably formed as upwardly open square C-shaped channels, with the top surface  46  of each cross-brace member  40  presenting a substantially smooth, burr-free horizontal surface. The applicant has appreciated that in ensuring the top surface  46  is provided without barbs, sharp projections, or other roughened features, allows the electrical cables  12  to be pulled longitudinally through the enclosure  14  while resting directly on the cross-brace members  40   a , 40   b , 40   c , without concern of damage to the cable insulating layer  13 . In addition, the uninterrupted length of the raceway  22  advantageously provides enhanced longitudinal airflow along the raceway  22  itself, minimize the potential for local hot spots. 
     References made to  FIG. 5  which illustrates the initial positioning of the first cable array  30   a  within the lower cable tray  32 . In particular, following the securement of the ventilated bottom cover  34 , the cables  12  of the cable array  30  are drawn along the raceway  22 , along the longitudinal length of the enclosure  14 . As each cable  12  is drawn, it moves over and is supported by the top surface  46  of the cross-brace members  40   a . 40   b , 40   c . It is to be appreciated that because the raceway  22  is substantially unobstructed in its longitudinal direction, the cables  12  may be pulled directly across the cross-brace members  40   a , 40   b , 40   c , without necessitating the use of cable rollers and other secondary support systems. 
     Following initial positioning of the first cable array  30   a , the cables  12  are secured in place relative to the cable tray  32   b  by the use of series of one piece clamping bars  50 . As shown in  FIGS. 6 and 7 , in a preferred construction, the clamping bars  50  are cut or stamped from an elongated bar of aluminum stock. Most preferably, the clamping bars  50  have an overall longitudinal length which is marginally less than the lateral spacing separating the side webs  42 , 42 ′ of the cable tray sidewall members  38   a , 38   b . Each clamping bar  50  is provided with six downwardly open U-shaped keeper pockets  58 . The keeper pockets  58  have a lateral width which has a dimension D, and which corresponds generally to the diameter of the insulating sleeve  13  of each electrical cable  12 . More preferably, the keeper pockets  58  are formed on respective centres which are separated by a distance  2 D, selected at twice the insulating sleeve  13  diameter from the next adjacent pocket  58 . It is to be appreciated that the lateral spacing of the keeper pockets  58  relative to each other advantageously ensures that the cables  12  in each cable array  30   a , 30   b  are maintained with an optimum spacing to balance electromagnetic fields, to minimize mutual heating amongst the cables  12  and to maximize the transfer of heat away from the cables  12  to the exterior of the cable bus system  10 . 
     Although not essential, most preferably, the clamping bars  50  is asymmetrically formed. In this construction, the clamping bars  50  extend from a first end  60   a  to a second end  60   b  with a first keeper pocket  58   a  spaced by a distance D x  from the end  60   a , and the second other endmost keeper pocket  58   b  spaced from the second end  60   b  by a distance D y . The applicant has appreciated that by selecting the distance D y  at approximately half that of D x , the clamping bars  50  may advantageously be used to orient the cables  12  of cable array  30   a , 30   b  in the desired laterally offset orientation relative to each other simply by reversing the orientation of the cable bars  50  when securing each successive cable array  30   a . 30   b  for each adjacent level in the raceway  22 . By providing one end  60   a  of the clamping bar  50  with an extension longer that the other end  60   b  in an ideal triangular electrical place conductor configuration may be achieved by reversing the clamping bars  50  on each adjacent level. Cable electrical impedance may thus be reduced, lowering system power losses. 
     In this simplified construction, a series of boreholes  62  are formed adjacent each end of the clamping bars  50 . The boreholes  62  are sized to receive therein screw fasteners  66  in the securement of each clamping bar  50  to selected cross-brace member  40   a , 40   c  with the cables  12  of the cable array  30   a  sandwiched in a friction fit therebetween. Most preferably, the screw fasteners comprise spring loaded bolts which engage hand tightenable wing wiring nuts to eliminate the need of a difficult to use power tools. 
     Preferably, following the securement of the cables  12  of the cable array  30   a  in the lower tray  32   a , the upper cable tray  32   b  is positioned. The upper cable tray  32   b  is stacked on top of, and secured to the lower cable tray  32   b  to provide the enclosure with multiple levels ( FIG. 8 ). In assembly, the cable tray  32   a  is oriented so that the lower flanges  44   b , 44   b ′ of the side members  38   a , 38   b  are positioned aligned in juxtaposed contact with the upper flanges  44   a  of the side members  38   a , 38   b  of the lower cable tray  32   a . More preferably, the cable tray  32   b  is oriented in position in a reverse longitudinal orientation relative to cable tray  32   a  so that the cross-brace members  40  of both cable trays  32   a , 32   b  do not vertically aligned. The cable trays  32   a , 32   b  are coupled to each other by the insertion of bolts  70  or other mechanical fasteners through the juxtaposed flanges  44   a , 44   b  and  44   a ′, 44   b′.    
     Following the securement of the cable tray  32   b , the electrical cables  12  of the upper cable array  30   b  are then drawn through the raceway  22  positioned and clamped to the cross-brace members  40   a , 40   c  of the upper cable tray  32   b , by the use of clamping bars  50  which are oriented in the reverse and staggered manner from those used to secure the lower cable array  30   a.    
     In the present invention, the length of the clamping bars  50  is further selected to advantageously act as a spacer to maintain the cables  12  a preferred spacing from the sidewalls webs  42 , 42 ′ and from each other. 
     In the preferred construction shown, the top cover  36  is secured to the top flanges  44   a , 44   a ′ of the topmost cable tray  32   b  by way of screws or other fasteners allowing for future easy removal. 
       FIGS. 2 and 3  show the top cover  36  as including both a flat and peaked ventilated cover panels  88 , 90 . It is to be appreciated that the peaked cover panel  90  advantageously may be used to provide for the enhanced shedding of snow, water and other debris which may accumulate on the upper surface of the metal enclosure  14 . Although not essential, the flat cover panel  88  may be provided in areas where debris or fallen material will not accumulate to restrict the ventilation. 
     Following the securement of the upper cable array  30   b , the cover panels  88 , 90  are screwed or bolted to the upper flanges  44   a , 44   a ′ of the upper cable tray  32   b  to complete the metal enclosure  14 . 
     Although the detailed description describes the use of a clamping bar  50  to secure electrical cables  12  against movement, the invention is not so limited. It is to be appreciated that other clamping arrangements including, without restriction, the use of individual cable clamps may also be used, and will now become apparent. 
     It is to be appreciated that with the modular construction of the cable trays  32   a , 32   b , if power delivery requirements increase in future, the cable bus system  10  may be easily expanded. For example, to increase electrical transmission capacity, the top cover  36  is removed, and a third level or more cable trays  32  used to secure additional cable arrays may easily be secured over the upper cable tray  32   b  in the same manner as its attachment to cable tray  32   a . Following installation of the desired number of additional cable trays, the top cover  36  is reinstalled. 
     In addition, the present invention advantageously allows for the simplified servicing and replacement of one or more electrical cables  12 . In the event cable replacement is required, the top cover  36  is removed. Because the cross-brace members  44   a , 44   b , 44   c  of the lower cable tray  32   a  are non-aligned with those of the upper cable tray  32   a , it is possible to directly access and remove the clamping bars  50  used to secure the lower cable array  30   a  in place without requiring disassembly and/or removal of the cable array  30   b.    
     Although the detailed description describes the cable bus system  10  as including a pair of cable arrays  30   a , 30   b , which each include six electrical cables  12 , the invention is not so limited. It is to be appreciated that the present invention is equally suited for use in the mounting of fewer or greater numbers of cable arrays  30 , having fewer or greater numbers of individual electrical cables  12 . Reference may now be had to  FIG. 9 , which shows an electrical cable bus system  10  in accordance with an alternate embodiment of the invention, and in which like reference numerals are used to identify like components. In  FIG. 9 , the cable enclosure  14  is provided as housing three electrical cable arrays  32   a , 32   b , 32   c , of cables  12 , and which are mounted respectively in cable trays  30   a , 30   b , 30   c.    
     In  FIG. 9 , the cable trays  30   a , 30   b , 30   c  are each configured to support and mount a cable array which includes up to 18 high amperature, high voltage electrical cables  12 . The electrical cables are secured in place by clamping bars  50  which have a number of keeper pockets  58  modified accordingly to the number of cables  12  to be secured. 
     Optionally the enclosure  14  may be provided with a number of electrical receptors, neutral conductors (N) or null spacing or voids which, for example, allow the future expansion of the cable bus system  10  to include additional power cables, in each array  30   a , 30   b , 30   c  should electric transmission or distribution demands increase. It is be appreciated that in assembly neutral conductors (N) will vary, depending on type of electrical system that is being corrected. 
     While the detailed description describes and illustrates the cable tray  32   b  as being positioned vertically on top of the cable tray  32   a , the invention is not so limited. It is to be appreciated that although illustrated in a horizontal orientation, the metal enclosure  14  could also be mounted vertically and/or in an inclined position depending on the site of installation and the intended direction of the electrical raceway  22 . 
     Reference is now made to  FIGS. 10 ,  11  and  15  which show assembled power distribution systems  200 , 300 , 400  which incorporate a cable bus system  10  in accordance with the present invention, and in which like reference numerals are used to identify like components. 
       FIG. 10  shows an above-ground power distribution system  200  in which a cable bus system  10  is provided for the power between a power sending end  102  and a power receiving end  104 . As the cable bus system  10  is positioned within the open air, any heat generated within the cables  12  flows both perpendicularly as well as longitudinally along the raceway  22  throughout the circuit length, ensuring against potential hot spots. 
       FIGS. 11 and 14  show respectively alternate power distribution systems  300 , 400  which are adapted for below ground installation in transmitting and conducting electricity from power sending end  102  to the power receiving end  104 . 
     As shown best in  FIGS. 11 to 13 , the subterranean power distribution system  200  is formed having a concrete vault or enclosure  110  which is sized to house the cable bus system  10  therein. Most preferably, the enclosure  110  has a generally rectangular cross sectional profile housing with a closed top, bottom and sidewall  112 , 114 , 116 , 118 . The enclosure  110  most preferably has a maximum width of less than about 1 meter and a height of less than about 1 meter. The enclosure  110  defines an internal cavity  120 , which extends longitudinally from the sending end  102  to the power receiving end  104  with the cable bus system  10  extending lengthwise therein. As shown best in  FIG. 12 , the top of the enclosure  110  is sealed. To provide a more economical construction, the cable bus system  10  may be provided without the top cover  36  for increased air circulation. 
     As shown in  FIGS. 13 and 14 , where longer enclosures  110  are necessary, the power distribution system  300  may be provided with one or more vertical air vents  122 . The air vents  122  include an air vent shaft  124  which extends vertically downwardly from a surface grate  126 . The bottom  130  of the shaft  124  is preferably open and lined with gravel  128  allowing for the drainage of any water which accumulates therein outwardly by way of underlying drainage tile  131 . Most preferably, the sidewall aperture  132  is spaced vertically above the bottom  130  of the air vent shaft  124 . As shown best in the cross-sectional view of  FIG. 13 , each vertical air vent  122  allows for airflow and communication from the interior  120  of the enclosure  110  by way of a sidewall aperture  132  formed through the sidewall  116 , and which opens into the vent shaft  124 . Most preferably the air vent grate is positioned a vertically spaced distance above the bottom  130  of the air vent shaft  124  by a distance selected to prevent any water, leaves or any other debris which may accumulate within the shaft  124  from blocking the aperture  132  and/or flowing into the enclosure interior  120 . Although not essential, preferably the air vent shaft  124  and aperture  132  are each provided with mesh screening  126 , 138  to for safety and to prevent ingress by rodents and other pests. 
     It is be to appreciated that the subterranean power distribution system  300  shown in  FIG. 11  advantageously allows for maximum enhanced free air flow along the length of the enclosure  110  and about the cable bus system  10 , to allow for the electrical transmission of maximum cable amperage. In particular, in the construction shown, air may freely flow both vertically through the air vents  122 , as well as longitudinally along the enclosure  110  to exhaust any cable generated heat. 
     Although  FIG. 11  illustrates the power distribution system  300  as including two vertical air vents  122 , it is to be appreciated that the number of vents  122  will change depending on air flow requirements. 
     Reference may be had to  FIG. 15  which shows schematically a subterranean power distribution system  400  in accordance with a further embodiment of the invention, and in which like reference numerals are used to identify like components. In  FIG. 15 , increased airflow into the concrete enclosure  110  is provided by way of a periscope-type air vent  140  which cooperate with in-ground offset vertical air vents  122  to provide enhanced longitudinal air flow. In particular, the airflow vent  140  extends upwardly through the top wall  112  of the enclosure to a raised vent outlet  142 . The height of the vent outlet  142  is positioned to avoid possible obstruction by snow or other debris. As shown best in  FIG. 15 , a power fan vent unit  150  is provided to assist exhausting any warm air from within the enclosure interior  120 . The power fan vent unit  150  includes a thermostat control  152  temperature sensor  154  and power fan  156 . The thermostat control  152  is operable to preselect a desired ambient temperature surrounding the cables  12 . The temperature sensor  154  attached to the thermostat  152  is positioned at a selected high temperature location along the length of the underground enclosure  110 . When temperature within the enclosure interior  120  exceeds the a preselected threshold, the power fan  156  is activated to blow cool air downwardly into the enclosure  110 , forcing any warmer air therein to be exhausted through the offset vertical air vents  122 . 
     Although  FIG. 15  illustrates a most preferred embodiment of the invention in which a power fan vent unit  150  is provided for cooling the cable bus system  10 , the invention is not so limited. It is to be appreciated that in an alternate possible construction, the power fan unit could be provided in conjunction with or as part of an air conditioning unit to further facilitate cable cooling, where for example, still increased high amperages per cable are desired. In particular, for every 10° C. of enclosure cooling, cable amperage may be increased by approximately 10%. It is to be appreciated that if increased amperature for the system is required, particularly on an intermittent basis, it may be substantially less costly to increase the amperature to existing cables  12  by air conditioning, rather than retrofitting or replacing the entire cable bus system  10 . In embodiments where an air conditioning unit is provided in place of the power fan vent unit  150 , any offset vertical vents  122  could be omitted, and a suitable air conditioner, cooling coil and fan would be provided. 
     It is to be appreciated that the cable bus system  10  of the present invention advantageously is adapted for installation in both above and underground applications. By way of non-limiting example, as shown in  FIG. 16 , where underground rock formations  175  are encountered which prohibit the economic installation of the cable bus system  10  below grade, the cable bus system  10  may be gradually diverted upwardly aboveground and over any obstacles and top covered with a suitable berm. If necessary, the cable bus system  10  may then be returned back below ground, either directly on grade as shown in  FIG. 17  with or without a covering enclosure  110 , or re-buried by covering with a suitable fill, or the like as shown in  FIG. 12 . 
     Although the detailed description describes the clamping bar  50  and the enclosure  14  is made of aluminum, the invention is not so limited. Both the clamping bar  50  and/or enclosure  14  could be made of a variety of materials including other types of metals, cellulose based materials, wood, as well as plastics and polycarbonate-based compounds. 
     Reference may be had to  FIG. 18  which shows schematically a subterranean distribution system  500  in accordance with a further embodiment of the invention and in which like reference numerals are used to identify like components. 
     In  FIG. 18 , the top wall  112  of the enclosure  110  is provided with an outwardly open U-shaped profile along its vertical extent: In the preferred construction shown the sides of the U-shaped cover portion  112   a  act as a bollard which provide additional structural protection for the power fan vent unit  150 . The power distribution system  500  shown in  FIG. 18  is envisioned for the transmission for electrical power from a power sending end  102  such as a transformer to the power receiving end  104 . 
     Reference may be had to  FIG. 19  which illustrates a power distribution system  600  used to transmit power from a power sending end such as a transformer  102  to a vertically displaced power receiving end  104 , as for example, is found in high-rise applications. In  FIG. 19 , like reference numerals are used to identify like components. 
     In addition to the subterranean vault or enclosure  100 , the cable bus system  10  extends vertically above grade to the height of a desired target building floor  190 . As shown best in  FIGS. 20 and 21 , where the cable bus system  10  extends vertically, a serious of anti-slip sleeves or grommets  210  are provided to assist in the vertical securement of the electrical cables  12 . In particular, the grommets are formed from an elastomeric material such as suitable plastic, rubber or Neoprene are characterized by a split cylindrical side wall  212  which extends axially and which integrally formed at an end thereof, a pair of radially projecting tabs  214   a , 214   b.    
     As shown best in  FIG. 20 , the sleeve  210  has a radial diameter R d  which is selected marginally less than the cables  12 . The sleeves  210  may advantageously be positioned about the cables  12  at the point of their attachment to the cross-brace members  40 , so that the tabs  214   a , 214   b  are bearing contact with the upward-most surfaces of cross-brace members  40  and clamping bars  50 . It is to be appreciated that the securement of the sleeves  210  interposed between the clamping bar  50  and cross-brace  40  provides increased frictional as well as mechanical clamping force to the cables  12 , minimizing the likelihood that the cables  12  may sag vertically under their weight. 
     Reference may be had to  FIGS. 22 and 23  which illustrates a most preferred fastener bolt assembly  220  used in the securement of the clamping bars  50  to each cross-brace member  40 . The bolt assembly  220  includes a spring biased anchor bolt  222 , and a wing nut  224 . The anchor bolt  222  includes a threaded shaft  226 , seating plate  228  and a compressible helical spring  240 . 
     It is to be appreciated that the shaft  226  is configured for threaded engagement by the wing nut  224 . 
     As shown in the exploded view, the seating plate  228  preferably includes a pair of locating guide grooves  230   a , 230   b  which are spaced for engagement with the sides of the cross-brace member  40  which define the open channel  24   a  therein. The plate  228  is provided with a dimension selected to allow its insertion into the channel  24   a  in a first orientation, while preventing its removal therefrom when rotated to align the grooves  230   a , 230   b  transversely relative thereto. The spring  240  has a length selected to resiliently bias the seating plate  228  into engaging contact with the underside of the channel top surface  46  to assist in maintaining desired positioning as the wing nut  224  is tightened along the shaft  226 . 
     While the preferred embodiments disclosure the use of the cable bus system  10  as used in the transmission and distribution of three-phase high amperature electric power, it is to be appreciated that the invention is equally suited for other polyphase or mono-phase power distribution and/or transmission, depending on load and power generation requirements. 
     Although the detailed description describes and illustrates various preferred aspects, the invention is not so limited. Many modifications and variations will now occur to persons skilled in the art. For definition of the invention, reference may be had to the appended claims.