A technician is running a new 50A branch circuit to a range. They pull 8 AWG THHN copper wire through an attic where the ambient temperature reaches 120°F. During inspection, the installation fails. Why?
Answers
AThe wire gauge is too small after applying ambient temperature derating factors
BThe breaker must be upgraded to 60A to match the 8 AWG capacity
CTHHN is not permitted in residential attics
DA 50A circuit requires a minimum of 6 AWG regardless of temperature
Correct answer: A — The wire gauge is too small after applying ambient temperature derating factors
When ambient temperatures exceed 86°F (30°C), NEC requires ampacity derating. 8 AWG THHN at 50A will fall below the required capacity when derated for 120°F (49°C).
MIFOTRA exam practicealigned to NFPA 70 / IEC 60364·4 marks·Hard