![]() 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. 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 post mentioned that there were spare ducts in the duct banks so I used table B310.6 and Figure B310.1 to interpolate a new cable capacity. The process begins with the crew digging the trench.Ģ. Re: Concrete encasement for duct banks Charlie I agree with you statement regarding using Annex B for cable ratings. 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. For example, smoother select fill dirt would be used as back-fill and there are no above-ground applications for Direct Burial PVC Conduit. Duct banks in loose back fill or low strength CDF/FTB may flex instead of fracturing.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. A low resistance ground grid is desired in a facility because it (1) helps maintain an equal ground potential throughout the facility, (2) helps keep the voltage on equipment lower during lightning strikes, and (3) establishes a low resistance path for ground faults (to ensure tripping of. There seemed to be some concern that inadequately reinforced concrete duct banks could facture during earth movements. If this is in a facility the concrete encased conductor helps establish a low resistance ground grid. I have heard various discussions from civil engineers about which duct protection approach is best for handling movement from earthquakes. In some applications red dye is also added as an attempt to discourage dig-ins. Sand and pea gravel have horrible thermal properties, so these materials are only used for conduits carrying instrumentation cables or power cables with negligible thermal loading.įTB and CDF both provide some protection again accidental dig-ins, while still allowing some ability to expose conduits if needed. FTB is very similar to CDF but is specifically designed to have good thermal transfer. ![]() Depending on the thermal properties of the native soil, we may require the use of Fluidized Thermal Backfill (FTB) for installations with thermal constraints. For large power cables, thermal considerations are really important. One important distinction is thermal constraints.
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