What materials must ferrous metal raceways be made of when installed in corrosive areas?

Ferrous metal raceways, when installed in corrosive areas, must be comprised of approved materials that can resist corrosion. The NEC specifies that when selecting raceways for potentially corrosive environments—such as areas exposed to moisture or chemicals—materials should be chosen based on their ability to withstand such conditions effectively. This typically includes coatings or treatments that enhance their resistance to corrosion.

Choosing "approved materials" ensures compliance with the NEC standards, which helps prevent failures that could arise from corrosion over time. It allows for the use of ferrous materials that have been protected or evaluated for use in these harsh environments, ensuring safety and longevity of the electrical installation.

Other choices do not specify materials that adhere to NEC standards under corrosive conditions. For instance, while plastic and concrete composites might be suitable in some instances, they do not directly relate to ferrous metal raceways. Non-ferrous metals could be acceptable in corrosive situations but do not address the requirement specifically for ferrous materials. Thus, only the choice of approved materials accurately reflects the NEC’s intent and guidelines for use in corrosive areas.