Which statement correctly describes the relationship between wire diameter and ampacity?

Which statement correctly describes the relationship between wire diameter and ampacity?

• A. Small diameter wire has a smaller ampacity than large diameter wire
• B. Small diameter wire has a larger ampacity than large diameter wire
• C. They have equal ampacity
• D. Ampacity is independent of diameter

Answer: (A)

Ampacity is the maximum current a conductor can carry without overheating its insulation. When a wire is thicker, it has more cross-sectional area to carry current and to dissipate heat. This lowers the resistance per length and allows the heat generated by I^2R losses to spread out over a larger area, reducing temperature rise. So a thicker (larger diameter) wire can carry more current safely than a thinner (smaller diameter) one. That’s why the statement that small diameter wire has a smaller ampacity than large diameter wire is correct. In practice, ampacity also depends on insulation, ambient temperature, and installation conditions, but the general relationship remains: increasing diameter increases ampacity.

Ampacity is the maximum current a conductor can carry without overheating its insulation. When a wire is thicker, it has more cross-sectional area to carry current and to dissipate heat. This lowers the resistance per length and allows the heat generated by I^2R losses to spread out over a larger area, reducing temperature rise. So a thicker (larger diameter) wire can carry more current safely than a thinner (smaller diameter) one. That’s why the statement that small diameter wire has a smaller ampacity than large diameter wire is correct. In practice, ampacity also depends on insulation, ambient temperature, and installation conditions, but the general relationship remains: increasing diameter increases ampacity.