What rating should branch circuit conductors have if they are within 3 inches of a ballast?

The appropriate rating for branch circuit conductors that are placed within 3 inches of a ballast is indeed 90°C (194°F). This is essential because ballasts can generate significant heat during operation. Therefore, the temperature rating of the conductors must be high enough to safely accommodate the increased thermal environment that proximity to a ballast creates.

Conductors rated for 90°C are designed to handle higher temperatures without degrading their insulation or compromising safety. This ensures that the conductors can operate reliably and help prevent overheating, which could lead to insulation breakdown or potential fire hazards.

In contrast, using conductors with a lower temperature rating—such as those rated for 60°C (140°F) or 75°C (167°F)—would not provide adequate margin against the heat produced by the ballast, thereby increasing the risk of failure.