The rules for protecting flexible cords [240.5] differ from those for protecting conductors [240.4]. You must protect a flexible cord in one of two ways.
The first way is you protect it with an overcurrent device based on its ampacity as specified in Table 400.5(A)(1) and Table 400.5(A)(2). That’s right, you’re also using Art. 400 for this. But if it’s fixture wire, use Table 402.5 (yep, Art. 402). You can use supplementary overcurrent protection, as covered in Sec