Article 240 provides the requirements for overcurrent protection. Part I of this Article provides the usual scope, definitions, and “other Articles” information (240.1, 240.2, and 240.3, respectively) then it gets into protection of conductors in Sec. 240.4.
Section 240.4 does not cover flexible cords, cables, and fixture wires; those are covered in Sec. 240.5. Nor does it cover ungrounded conductors; those are covered in Sec. 240.15. So what exactly does it cover?
Normally, the OCPD provides both overload protection and short-circuit protection. In the case of motors, this function is separated, such that the OCPD protects the branch circuit from short-circuits and the motor overloads protect the motor from overload. But there’s another situation in which the OCPD provides only overload protection. That is when the interruption of the circuit would create a hazard [240.4(A)].
The NEC gives two examples of such hazards. One is a fire pump, and that seems obvious. The other is a material handling magnet. If the safety problem isn’t obvious to you, just think of a crane that magnetically picks up scrap automobiles.
