Underground conduit Large diameter (more than 2 inch/50 mm) conduit may be installed25L1005MC underground between buildings to allow installation of power and communication cables. An assembly of theseSTP60NE06-16 conduits, often called a duct bank, may either be directly buried in earth or encased in concrete. A duct bank will allowSTR6556A replacement of damaged cables between buildings or additional power and communications circuits to be added, without the expense of re-excavation of aNCP1396 trench. While metal conduit is occasionally used for burial, usually PVC, polyethylene or polystyrene plastics are now used due to lower cost.Formerly, compressed asbestos fiberPAC007 mixed with cement (such as Transite) was used for some underground installations. Telephone and communications circuits were typically installed in fired-clay conduit.