Journeyman Electrician Exam (NEC)Equipment and DevicesMedium
A technician is installing a 20-ampere, 120-volt general-purpose branch circuit in a commercial building. The circuit will supply receptacles. What is the minimum continuous load permitted on this branch circuit, assuming it is protected by an overcurrent device rated for 100% continuous operation?
- A20 amperes
- B12 amperes
- C16 amperes
- D24 amperes
Show answer & explanationAnswer & explanation
Correct answer: C. 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. Conversely, 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.
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.
- B. This represents 60% of the OCPD rating, which is lower than the maximum permitted continuous load.
- D. This value exceeds the branch circuit's capacity, even with a 100% rated OCPD, as the OCPD itself would be 20A.
Continuous Load Limit for Branch Circuits
The maximum amount of current a branch circuit can continuously carry, limited to 80% of the overcurrent device rating unless the overcurrent device and its assembly are specifically listed for 100% continuous operation.
- A load is continuous if it operates for 3 hours or more.
- Protects conductors and OCPDs from overheating.
- NEC 210.20(A) and 215.2(A)(1) specify this requirement.
Memory trick: Eighty percent power, for hours and hours!