What does the term ampacity refer to, and how would ambient temperature affect it?

• A. Ampacity is the maximum current a conductor can safely carry; higher ambient temperature reduces ampacity.
• B. Ampacity is the voltage rating of a conductor; temperature has no effect.
• C. Ampacity is the resistance of a conductor; temperature has no effect.
• D. Ampacity is the length of the conductor; temperature increases length.

Answer: (C)

Ampacity is the maximum current a conductor can safely carry continuously without the insulation overheating beyond its rating. Ambient temperature affects this because hotter surroundings make it harder for the conductor to shed heat. When temperatures rise, the allowable current must be reduced (derated) to keep the conductor within its temperature limit. Cooler ambient conditions allow a bit more current, up to other design limits.

This concept isn’t about voltage rating, resistance, or length. Those are different properties of a conductor, while ampacity specifically concerns how much current can be carried safely given heat considerations.