Master Electrician Exam (NEC)Services, Feeders, and Branch CircuitsMedium
A master electrician is installing a new 20A, 120V branch circuit for a bathroom receptacle in a dwelling unit. The circuit conductors will be 12 AWG copper with 75°C insulation. What is the maximum continuous load permitted on this circuit?
- A16 Amperes
- B24 Amperes
- C12 Amperes
- D20 Amperes
Show answer & explanationAnswer & explanation
Correct answer: A. 16 Amperes
For a continuous load, the maximum current is limited to 80% of the branch circuit's overcurrent device rating. A 20A branch circuit allows a maximum continuous load of 20A * 0.80 = 16A. The conductor's ampacity must also be considered, but 12 AWG copper is rated for 25A at 75°C, which is sufficient.
Why the other options are wrong
- B. This exceeds the 80% continuous load limit for a 20A circuit.
- C. This is 60% of the circuit rating, which is too conservative.
- D. This is the total rating of the circuit, not the maximum continuous load.
Continuous Load on Branch Circuits
A continuous load is one where the maximum current is expected to continue for 3 hours or more.
- Overcurrent devices and conductors must be rated for 125% of the continuous load.
- This means the continuous load cannot exceed 80% of the overcurrent device rating.
- Applies to branch circuits and feeders.
Memory trick: Continuous load means 80% capacity.