Section 240.21(C)(6) in the NEC® mentions the "25 foot rule". What does this rule require?

Section 240.21(C)(6) in the National Electrical Code (NEC) outlines specific requirements for the installation of secondary conductors related to their length and the ampacities they must maintain. According to this section, the "25 foot rule" establishes that secondary conductors can be a maximum of 25 feet in length and must adhere to designated ampacity requirements. This means that when secondary conductors are run for short distances, they can effectively handle a certain amount of current, ensuring safety and compliance with electrical standards.

The requirement aims to provide a balance between flexibility in installation while also mitigating risks associated with longer conductor runs, which could lead to overheating or performance issues if not properly sized according to the current they may carry. This reinforces the idea that even in shorter runs, the characteristics of the conductors—such as their capacity to carry electrical load without exceeding safe temperature limits—must be carefully considered. Thus, option C accurately captures the essence of the "25 foot rule" laid out in Section 240.21(C)(6), ensuring both compliance and safety in electrical installations.