Journeyman Electrician Exam (NEC)Equipment and DevicesMedium
A journeyman electrician is installing a 277-volt LED luminaire in a commercial warehouse. What is the maximum continuous load permitted on a 20-ampere branch circuit supplying this luminaire?
- A24 amperes
- B25 amperes
- C16 amperes
- D20 amperes
Show answer & explanationAnswer & explanation
Correct answer: C. 16 amperes
For continuous loads, the maximum overcurrent device rating must not exceed 125% of the continuous load. Conversely, the continuous load must not exceed 80% of the branch-circuit rating. For a 20-ampere circuit, 20 A * 0.80 = 16 amperes.
Why the other options are wrong
- A. This exceeds the 80% continuous load limit for a 20-ampere circuit.
- B. This exceeds the 80% continuous load limit for a 20-ampere circuit.
- D. This represents the full rating of the branch circuit, which is only allowed for non-continuous loads or if the overcurrent device is rated for 100% continuous operation.
Continuous Load Limit for Branch Circuits
For continuous loads (expected to operate for 3 hours or more), the maximum load current must not exceed 80% of the branch circuit's overcurrent device rating, unless the overcurrent device assembly is listed for 100% continuous operation.
- Continuous load is 3 hours or more.
- Load must not exceed 80% of OCPD rating.
- This rule applies to the branch circuit conductors and overcurrent device.
Memory trick: Long loads need a smaller share of the circuit's power.