Master Electrician Exam (NEC)General Electrical KnowledgeEasy
A master electrician is installing a new 120V, 15A branch circuit to supply a continuous load. According to NEC Article 210.20(A), what is the maximum continuous load permitted on this circuit?
- A15 Amperes
- B12 Amperes
- C18.75 Amperes
- D20 Amperes
Show answer & explanationAnswer & explanation
Correct answer: B. 12 Amperes
For continuous loads, the branch-circuit overcurrent device rating must not be less than 125% of the continuous load. Conversely, the continuous load must not exceed 80% of the overcurrent device rating. Therefore, 15A * 0.80 = 12A.
Why the other options are wrong
- A. This is the rating of the overcurrent device, not the maximum continuous load permitted.
- C. This value (125% of 15A) would be the minimum overcurrent device size if 15A were the continuous load, which is incorrect for this question.
- D. This is a common next standard overcurrent device size, but not the correct answer for a 15A circuit's continuous load.
Continuous Load
A load where the maximum current is expected to continue for 3 hours or more. NEC requires overcurrent devices for continuous loads to be sized at 125% of the continuous load.
- Load operates for 3 hours or more.
- Overcurrent device must be sized at 125% of the continuous load.
- Continuous load cannot exceed 80% of the overcurrent device rating.
Memory trick: Continuous loads are a '25% more' commitment for protection.