What is the required insulation temperature rating for branch-circuit conductors within 3 inches of a ballast?

The required insulation temperature rating for branch-circuit conductors within 3 inches of a ballast is 90º C (194º F). This specification is crucial because ballasts, particularly in fluorescent lighting systems, can generate significant heat during operation. The National Electrical Code (NEC) recognizes that this heat can affect the conductors in close proximity, leading to potential overheating if the insulation rating is not adequate.

Insulation rated at 90º C provides the necessary thermal tolerance, ensuring that the conductors can safely operate without degrading their insulation or compromising their electrical integrity due to the elevated temperatures produced by the ballast's operation. This rating not only serves to protect the wiring but also enhances safety by reducing the risk of insulation breakdown and subsequent electrical failures.

Alternatives indicating lower temperature ratings, such as 70º C, 60º C, and 110º C, do not meet the specific requirements for this installation scenario. While 110º C insulation rating is robust, it is not the standard requirement for branch-circuit conductors near ballasts, making the 90º C rating the most appropriate choice in this context.