Journeyman Electrician Exam (NEC)Equipment and DevicesHard
A journeyman electrician is installing a 277-volt LED luminaire in a commercial warehouse. The luminaire is rated for 150 watts. The branch circuit supplying the luminaire is protected by a 20-ampere circuit breaker. According to NEC 210.23(A)(1), what is the maximum continuous load permitted on this 20-ampere branch circuit for luminaires?
- A24 amperes
- B12 amperes
- C16 amperes
- D20 amperes
Show answer & explanationAnswer & explanation
Correct answer: C. 16 amperes
NEC 210.23(A)(1) states that where a branch circuit supplies luminaires or other utilization equipment, the continuous load shall not exceed 80 percent of the branch-circuit rating. 1. The branch circuit rating is 20 amperes. 2. Continuous load limit = 20 A * 80% = 16 A. 3. This means the total continuous current drawn by the luminaires on this circuit cannot exceed 16 amperes.
Why the other options are wrong
- A. 24 amperes exceeds the branch circuit rating and the continuous load limit.
- B. 12 amperes is less than the maximum permitted continuous load.
- D. 20 amperes is the total circuit rating, but not the maximum for continuous loads.
Continuous Load Limit for Branch Circuits
The maximum current that a branch circuit can carry continuously (3 hours or more) without exceeding 80% of the circuit's overcurrent device rating, as required by the NEC.
- NEC 210.23(A)(1) and 210.20(A) specify the 80% rule.
- Applies to most branch circuits with continuous loads.
- Protects against excessive heat buildup in conductors and devices.
Memory trick: Branch Circuit: Continuous Load, Eighty Percent Safe.