What is the maximum insulation temperature rating for feeder and branch circuit conductors within 3 inches of a ballast?

The maximum insulation temperature rating for feeder and branch circuit conductors that are installed within proximity to a ballast is specified by the National Electrical Code (NEC). When conductors run near equipment that generates heat, such as ballasts for lighting fixtures, it’s crucial to ensure that the insulation can withstand elevated temperatures.

In this case, the correct rating for conductors placed within 3 inches of a ballast is 90°C. This temperature rating is designed to provide a higher threshold for heat exposure, thus ensuring the safe operation of the electrical system under conditions where heat is a factor. This means that conductors with a 90°C rating can operate safely in environments where ambient temperatures might be increased due to heat dissipation from the ballast.

Conductors rated for lower temperatures, such as 70°C or 80°C, would not be appropriate in this situation because they would not be able to handle the increased temperature without the risk of insulation failure or degradation. The higher rating not only accommodates the potential rise in temperature due to the ballast but also ensures compliance with the NEC and enhances the overall safety and longevity of the electrical installation.