Ferrous metal raceways and related hardware can be installed in environments subject to severe corrosive influences only when they are ______ approved for the condition.

Ferrous metal raceways are vulnerable to corrosion, especially in environments where they are exposed to moisture, chemicals, or other corrosive substances. To ensure durability and longevity in such conditions, materials used for raceways must meet specific material requirements that are suitable for corrosive environments. This is why the correct answer emphasizes that for ferrous metal raceways and their hardware to be utilized in these severe conditions, they must be made of materials specifically approved for those corrosive circumstances.

Using raceways that are constructed from materials unsuitable for the environment would likely lead to deterioration, safety hazards, and potential failure in electrical systems. Hence, a focus on using appropriately formulated materials that are certified for such environments is essential to maintain the integrity and safety of electrical installations.