NEMA TC 9:2004

This standard defines general requirements including materials, trade sizes, dimensions, and workmanship for the following types of fittings for PVC plastic utilities duct used for the underground installation of communication and electrical wire and cable: a. Type EB - Designed for encased burial in concrete when installed in trenches underground. b. Type DB - Designed for direct burial in trenched underground without a requirement for encasement in concrete. Type DB may also be encased in concrete. NOTE - The values stated in U.S. customary units are to be regarded as the standard.