Journeyman Electrician Exam (NEC)Wiring Methods and MaterialsEasy
A residential electrician is installing a new 120-volt, 15-amp branch circuit for a bedroom using NM cable. What is the minimum size copper conductor required for this circuit, assuming it is not part of a bundle exceeding 24 inches in length and the ambient temperature is 30°C (86°F)?
- A8 AWG
- B12 AWG
- C10 AWG
- D14 AWG
Show answer & explanationAnswer & explanation
Correct answer: D. 14 AWG
For a 15-amp branch circuit, 14 AWG copper conductor is the minimum size permitted by the NEC, assuming standard conditions and no derating factors apply that would require a larger size. Article 240.4(D) permits 14 AWG for 15-amp overcurrent protection.
Why the other options are wrong
- A. 8 AWG copper is rated for 40 or 50 amps and is significantly oversized.
- B. 12 AWG copper is rated for 20 amps and is larger than necessary for a 15-amp circuit.
- C. 10 AWG copper is rated for 30 amps and is much larger than necessary.
Minimum Conductor Size
The smallest gauge of conductor permitted by the NEC for a given overcurrent protective device rating, ensuring safe current carrying capacity.
- Minimum size for 15A circuit is 14 AWG copper.
- Minimum size for 20A circuit is 12 AWG copper.
- Minimum size for 30A circuit is 10 AWG copper.
Memory trick: Small wires for small amps, big wires for big amps, remember the 'AWG current rule'.