What does ampacity mean in relation to a conductor?

• A. The voltage rating of a conductor
• B. The insulation thickness rating
• C. The resistance of a conductor at 25 C
• D. The maximum current a conductor can carry continuously under the conditions of use

Answer: (D)

Ampacity is the maximum current a conductor can carry continuously under the specified conditions without the insulation heating beyond its rated limit. This rating takes into account how much heat I squared R produces, as well as the insulation type, conductor size, installation method, and ambient temperature. Engineers use ampacity values to size conductors so they won’t overheat in actual service. It isn’t about the voltage a conductor can withstand, nor about how thick the insulation is, and it isn’t the conductor’s resistance at a standard temperature—the resistance affects heating, but ampacity defines the safe current limit.