Which statement best describes the maximum ampacity rating for #12 THWN wire?

Which statement best describes the maximum ampacity rating for #12 THWN wire?

• A. 25 amps
• B. 15 amps
• C. 30 amps
• D. 20 amps

Answer: (A)

Ampacity is the maximum current a conductor can carry safely, based on its gauge and insulation rating. For copper #12 with THWN insulation, the NEC ampacity table uses the 75°C rating, which shows 25 amperes. That means the wire can carry up to 25 A under standard conditions. The 60°C column would be 20 A, and higher-temperature ratings (like THWN-2 at 90°C) would only apply if that insulation is used, along with appropriate conditions. In typical practice, you’ll see #12 circuits protected by 20 A breakers, even though the conductor’s rating allows up to 25 A.

Ampacity is the maximum current a conductor can carry safely, based on its gauge and insulation rating. For copper #12 with THWN insulation, the NEC ampacity table uses the 75°C rating, which shows 25 amperes. That means the wire can carry up to 25 A under standard conditions. The 60°C column would be 20 A, and higher-temperature ratings (like THWN-2 at 90°C) would only apply if that insulation is used, along with appropriate conditions. In typical practice, you’ll see #12 circuits protected by 20 A breakers, even though the conductor’s rating allows up to 25 A.