If the duct bank is 100 feet, then the total volume of concrete needed is 3.215 square feet times 100 feet, which equals 321.5 cubic feet of concrete. Now multiply this number by the total length of the duct bank. By dividing 462.96 by 144, the result is 3.215 square feet. This is the cross-sectional area occupied by the concrete alone.Ĭonvert the cross-sectional area occupied by the concrete from square inches to square feet by dividing that number by 144. So, 576-square inches minus 113.04 square inches equals 462.96 square inches. Subtract this number from the total cross sectional area of the duct bank. He says that Annexes are not mandatory (90.3). I told him that one must (should) use table B310.7. For a three-by-three, that is 3.14 times 4 times 9, which equals 113.04 square inches. I had a contractor tell me that the ampacity of 5 sets 4-500kcmil in a duct bank was determined from table 310.16. The conduit area is pi times the radius squared times the number of conduits. The conduit area would be the cross-sectional area of one conduit times the number of conduits. Now subtract from this number the total area occupied by the conduit. In this three-by-three example, that would equal 24 inches times 24 inches or 576 square inches. Multiply the total width and total height. Since this is a three-by-three duct bank, its height will also be 24 inches.Ĭalculate the cross-sectional area of the duct bank. Repeat step 2 using the number of vertical conduits instead of the number of horizontal conduits. Once all the runs of conduit are in place and properly connected, the crew fills the trench with cement and the ends of the pipe are directed into and terminate in approved electrical devices or boxes.Calculate the total height of the duct bank. Once more, CANTEX PVC Pipe Solvent Cement needs to be applied with a dauber in between each run.Ĥ. Once again, the entire installation process needs to be repeated for every 10 or 20 feet, depending upon the length of the conduit.ģ. See the CANTEX Full Product Line Catalog for determining the NEC 70 spacer requirements for the necessary trade size of the spacers and the required separation space. The rows of CANTEX PVC Intermediate Spacers are connected for every row of pipe. The amount of spacers coordinates with how many rows of conduit are being installed. Once the trench is completed, CANTEX PVC Base Spacers must be placed in rows in the trench. The process begins with the crew digging the trench.Ģ. Once again, the process for encasing Direct Burial and Encased Burial PVC Utility Duct in cement is basically the same as the cement encasement process for Schedule 40 and 80 PVC Pipe. Once all the runs of PVC DB Conduit are in place and properly connected, the crew fills the trench with dirt.ĭB Direct Burial & EB Encased Burial Cement Installation This process is repeated every 10 to 20 feet, depending upon the length of the conduit.ĥ. The pipe is twisted slightly to secure it. Once the pipe is smooth, the correct type of CANTEX PVC Solvent Cement gets applied to the inside of the belled end and the outside of the spigot or “straight” end of the conduit with a dauber.Ĥ. If the pipe has been cut, a reamer tool must be used to remove burrs or debris before cementing. In between each run of pipe, the belled end of the conduit gets cemented to the straight end. A crew begins by digging a trench for the conduit.Ģ. Consequently, the ends of the DB PVC Conduit runs are directed into and terminate in approved electrical devices or boxes. By dividing 462.96 by 144, the result is 3.215 square feet. For example, smoother select fill dirt would be used as back-fill and there are no above-ground applications for Direct Burial PVC Conduit. DB Direct Burial PVC Utility Duct InstallationĪlthough the direct burial installation for DB PVC Utility Duct is very much the same as it is for Schedule 40 and Schedule 80 PVC Pipe, there are some differences in back-fill requirements and performance capabilities.
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