When is it required that conductors be derated?

• A. When There Are Two Current-Carrying Conductors and One Grounded Conductor
• B. When There Are Three Current Conductors and One Grounded Conductor
• C. When Ambient Temperature Exceeds 40°C
• D. When Conductors Are in Damp Locations

Answer: (B)

Derating is required when more than three current-carrying conductors share the same raceway, cable, or enclosure. The neutral (grounded conductor) counts toward that total if it carries current. In this scenario, there are three current-carrying conductors plus a neutral that is part of the circuit, so the number of current-carrying conductors exceeds three, triggering the derating requirement. The other conditions—having only two current-carrying conductors, or factors like ambient temperature or damp locations—do not by themselves define the derating trigger in this context.