Confused about 230V Air Compressor Wiring
You are in the wrong section, 440 is refer equipment, you need too roll back to section 430, Motors, Motor circuits, and Controllers.
Part III Motor and Branch circuit protection
Then look at label:
Continuous duty motor, Section 430.32.
More than 1 HP, Paragraph (A).
Thermally Protected, (2) A thermal protector integral with the motor, check, now we're looking at the right section: under 9A, shall not exceed 170%.
Table 430.248 FLA 1Ø AC, 5 hp, 28A, times 1.7, shall not exceed 47.6, so 45A from table 240.6(A). This is maximum, a 40A breaker would likely work fine and be acceptable by code.
Wire size, minimum 125% of 21.1 is 26.4, table 310.15 or 310.16 depending on year of code book, shows #10 wire, but with a **. So 240.4 says overcurrent protection for #10 conductors after any corrections can't exceed 30A, so you got to upsize to #8 AWG.