What is the allowable ampacity for each 10 AWG copper THHN conductor in a conduit with 2 sets of circuits supplying fluorescent lighting?

The allowable ampacity for a 10 AWG copper THHN conductor in a conduit with multiple circuits is impacted by factors such as the number of conductors, the type of conductors, and environmental conditions. In the context of this question, it is important to consider not only the standard ampacity for a single conductor but also the potential de-rating that occurs due to the grouping of conductors.

For 10 AWG copper wire, the standard ampacity is generally around 30 to 35 amps under typical conditions. However, when multiple conductors are placed together in a conduit—such as in this scenario with "2 sets of circuits"—the National Electrical Code (NEC) mandates that the ampacity must be reduced to prevent overheating. This de-rating applies when there are more than three conductors in a conduit, necessitating a look at the NEC tables for guidance.

In this situation, the significant number of conductors, combined with the fluorescent lighting and the heat generated under load, leads to a de-rated capacity for the conductors involved. When calculated with the appropriate correction factors for conductor grouping and ambient temperature, the allowable ampacity for each 10 AWG copper THHN conductor in this specific installation environment would be 28