Generally, you must install a fuse or circuit breaker at the point where the conductors receive their supply [240.21]. But under seven different conditions described in the nearly three pages of 240.21(A) through (H), you don’t have to.
With so much text and so many exceptions, things can get confusing in a hurry. Let’s examine the first exception:
Branch-circuit conductors that meet the requirements of 210.19 can have overcurrent protection per 210.20 [240.21(