NEC Section 400.12 covers all things not permitted for flexible cords or cables. Line item 5 does not allow a flexible cord or cable to be installed where concealed by walls, floors, or ceilings or located above suspended or dropped ceilings. In Oregon, the code language for line item 5 was amended to read as follows:

Exception No. 1 to (5): Flexible cord and flexible cable shall be permitted if contained within an enclosure for use in other Spaces Used for Environmental Air as permitted by 300.22(C)(3).

Exception No. 2 to (5): In other than spaces used for environmental air, cord sets and power-supply cords shall be permitted above accessible suspended or dropped ceilings, if part of a listed assembly, other than a luminaire, and the cord length does not exceed 1.8m (6 ft).

Oregon amendments to the 2023 NEC^® are located in “Table 1-E” of the Oregon Electrical Specialty Code (OESC) which can be seen using the following link or the OESC PDF file located near the bottom of the screen: 2023 OESC