Input tax credit on ducts and manholes in optical fiber networks allowed as plant and machinery, ITC not barred. Ducts and manholes used in optical fiber cable networks serve as necessary conduits and network nodes for transmission of telecommunication signals and, under the Explanation to Section 17, fall within the definition of plant and machinery. They are not specifically excluded as land, building, other civil structures, telecommunication towers or certain pipelines. Consequently, input tax credit on such ducts and manholes is not barred by the immovable-property exclusions in sub-section (5) of Section 17 and is available to taxable persons providing telecommunication services.