These requirements cover cellular metal floor raceway systems intended to be installed as an integral part of the building structure and constructed for the installation of wires and cables in accordance with the National Electrical Code (NEC)@ NFPA 70. These requirements do not cover rigid or flexible conduit@ surface metal raceways and fittings@ underfloor raceways and fittings@ or other products of a similar nature. These requirements do not cover the structural aspects or properties of cellular metal floor units ?C their load-carrying and fire-resistant capabilities or their physical dimensions with relation to mechanical strength. Cellular metal floor raceways consist of the hollow spaces in cellular metal floors and associated fittings that serve as enclosures for wires and cables. A duct or cell is a single enclosed tubular space in a cellular floor unit with a longitudinal axis parallel to the longitudinal axis of the floor units. Header duct is an enclosed transverse wire raceway that@ by providing access to predetermined cells of a cellular metal floor@ facilitates the installation of wiring from a distribution center to the cells. Cellular metal floor raceway is always installed with concrete poured over the raceway and may be installed on top of a concrete slab. Trench header is a transverse wire raceway that provides access to all cells of the cellular floor units it crosses. Trench header allows lay-in wiring along its length by providing removable cover plates at its top surface. Trench header may be the bottomless type allowing direct access for wiring into cells with factory punched holes or it may incorporate a bottom pan requiring field cut entry holes into cells.