How many second-level subdivisions are present in the first-level subdivision NEC 240.21(B)?

The correct choice indicates that there are four second-level subdivisions under the first-level subdivision NEC 240.21(B). In the National Electrical Code (NEC), the section focused on overcurrent protection and requirements around conductors involves various critical aspects that ensure safety and compliance in electrical installations.

The first-level subdivision NEC 240.21(B) specifically addresses the rules for conductor short-circuit protection. This section is essential for understanding how to appropriately safeguard conductors in various scenarios, detailing conditions under which conductors can be connected, the maximum lengths of different types of conductors, and the respective protection measures that must be instituted.

By analyzing this section closely, one can find that it branches into four distinct second-level subdivisions, which outline particular guidelines and parameters necessary for adhering to safe electrical practice. This division is crucial for professionals who must apply these standards in real-world situations, ensuring that all installations comply with the NEC.

Understanding the structure of these subdivisions helps practitioners navigate through the code efficiently and ensures that they can quickly locate specific regulations pertaining to overcurrent protection based on the parameters defined by this part of the NEC.