A journeyman electrician is installing a new 277-volt LED luminaire in a commercial warehouse. The luminaire is rated for a continuous operation of 5.5 amperes. The branch circuit supplying this luminaire is protected by a 20-ampere circuit breaker. What is the minimum continuous load permitted on this branch circuit?
- A20 amperes
- B16 amperes
- C5.5 amperes
- D4.4 amperes
Show answer & explanationAnswer & explanation
Correct answer: B. 16 amperes
According to NEC Section 210.20(A), the overcurrent device rating shall not be less than the noncontinuous load plus 125% of the continuous load. This means the continuous load on a branch circuit should not exceed 80% of the overcurrent device rating. For a 20-ampere OCPD, the maximum continuous load is 20 A * 0.80 = 16 amperes. The question asks for the minimum continuous load *permitted* on the branch circuit, which is effectively asking the maximum it can handle. The luminaire's rating of 5.5A is simply the actual load, which is well within the 16A limit.
Why the other options are wrong
- A. This would be the total load if it were entirely noncontinuous, or if the OCPD was rated for 100% continuous use AND the circuit was designed for that.
- C. This is the actual continuous load of the luminaire, but the question asks about the *minimum continuous load permitted on the branch circuit*, implying its capacity.
- D. This is 80% of the actual luminaire load, not the circuit capacity.
Continuous Load Capacity of Branch Circuits
The maximum continuous current a branch circuit can safely carry, which is limited to 80% of the overcurrent protective device rating, unless the OCPD and its assembly are specifically listed for 100% continuous operation.
- A load is considered continuous if it operates for 3 hours or more.
- Protects conductors and overcurrent devices from excessive heat buildup.
- NEC 210.20(A) and 215.2(A)(1) are the governing sections.
Memory trick: 80 percent rule: For loads that stay, 16 amps lead the way!