Where is NM cable allowed to be installed?

NM cable, or Non-Metallic sheathed cable, is primarily designed for interior use in residential applications. It is most appropriate for installation in areas that are protected from moisture, physical damage, and environmental factors that can deteriorate the cable.

The correct installation area, which pertains to the highlighted answer, is that NM cable can be run on top of ceiling joists located 6 feet from an attic access opening. This is acceptable because the cable is less likely to be subjected to physical damage when it is secured properly and positioned safely above accessible areas. Moreover, this installation method helps maintain necessary clearances and minimizes the risk of damage from attic activity.

In contrast, NM cable would not be appropriate for installation in exterior walls, as these areas are subject to more extreme weather conditions and potential moisture exposure. Additionally, running NM cable on the floor joists of a crawl space is also not advisable due to the risk of moisture accumulation and possible exposure to pests, which can compromise the cable's integrity. Finally, installing NM cable inside concrete ceilings is not permissible as the conduit would not provide the necessary protection against physical damage, and the concrete's moisture retention could affect the cable over time.