Test your knowledge with this question: What size conductor and protection device must you use for a 24A motor-compressor on a 240V circuit (Fig. 3)
Size the branch-circuit conductor per Table 310.16 and 440.32.
24A x 1.25 = 30A Per 110.14(C)(1)(a) and Table 310.16, you would select a 10 AWG conductor, rated 30A at 60°C.
Size the branch-circuit protection device per 240.6(A) and 440.22(A).
24A x 1.75 = 42A Selecting the next size down protection device yields a 40A device.
If a 40A protection device isn’t capable of carrying the starting current, you can size the protection device up to 225% of the equipment load current rating (24A x 2.25 = 54A, next size down 50A).
Size these branch-circuit conductors no smaller than the spec on the equipment nameplate. If the equipment doesn’t have a nameplate that specifies the branch-circuit conductors, size the conductors per 440.32.