What does ampacity measure?

• A. The maximum current a conductor or device can safely carry under specified conditions.
• B. The maximum voltage a conductor can withstand.
• C. The minimum temperature at which a conductor operates.
• D. The average resistance of a conductor in normal use.

Answer: (A)

Ampacity is the maximum current a conductor or device can safely carry under specified conditions. It reflects how much electrical current the insulation and conductors can handle without overheating due to I^2R heating. The specified conditions include factors like ambient temperature, insulation temperature rating, conductor size, and installation method (free air vs. in a raceway or cabinet). If you exceed the ampacity, the heat generated can damage insulation or create a fire hazard. This concept is distinct from voltage rating, which is about the maximum voltage the insulation can withstand, or from temperature or resistance measures, which are not what ampacity describes.