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The correct answer, 90°C (194°F), reflects the standard insulation temperature rating for feeder and branch circuit conductors located near a ballast. This is significant because ballasts, especially in fluorescent lighting systems, can generate significant heat during operation. Conductors that are in close proximity to heat sources, like ballasts, need to have a higher temperature rating to ensure safety and prevent insulation failure due to excessive heat.

Using conductors with a lower temperature rating could lead to a breakdown of the insulation, resulting in potential electrical hazards such as short circuits or fires. Therefore, the National Electrical Code (NEC) specifies that conductors in such applications must be rated to withstand higher temperatures, and the 90°C rating provides the necessary safety margin for reliable operation under these conditions.

Options that suggest lower temperature ratings are inappropriate for use near ballasts, as they do not provide enough thermal resistance to accommodate the heat generated. By adhering to the 90°C standard, electricians can ensure compliance with safety regulations and protect the integrity of electrical installations.