Standardization of conduit construction

The growing use of metallic conduit for the installation of wires in buildings, and the frequent tendency to use conduits of too small interior diameter, have led the National Electrical Contractors Association to prepare data in regard to the proper size of conduit to be used in installing wire and cables. The result of the investigation of this subject by the Association is embodied in six charts showing in full size the proper sizes of conduits to be used for the installation of numerous combinations of wires and cables. These charts were officially adopted at the 12th annual meeting of the National Electrical Contractors Association.