Journeyman Electrician Exam (NEC)Services, Feeders, and Branch CircuitsMedium
A panelboard in a commercial occupancy contains overcurrent devices, with the highest continuous load on any given circuit being 30 amperes. What is the maximum percentage of the total overcurrent device ampere rating that the continuous load is permitted to exceed, according to NEC 215.2(A)(1) and 230.42(A)(1) for feeders and services?
- A125 percent
- B100 percent
- C80 percent
- D150 percent
Show answer & explanationAnswer & explanation
Correct answer: C. 80 percent
NEC 215.2(A)(1) and 230.42(A)(1) specify that where a feeder or service supplies continuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125% of the continuous load. This means that a continuous load can only constitute 80% of the overcurrent device's rating (1 / 1.25 = 0.80 or 80%). Therefore, the continuous load is permitted to exceed 80% of the overcurrent device's rating.
Why the other options are wrong
- A. 125 percent is the multiplier *applied to* the continuous load, not the percentage of the OCPD rating it can be.
- B. 100 percent would imply no derating for continuous loads, which is incorrect.
- D. 150 percent is not a relevant factor in this calculation.
Continuous Load OCPD Sizing
Overcurrent devices protecting conductors supplying continuous loads must be sized at 125% of the continuous load, meaning the continuous load cannot exceed 80% of the OCPD rating.
- Applies to continuous loads (3 hours or more).
- OCPD rating must be at least 125% of continuous load.
- Equivalent to continuous load not exceeding 80% of OCPD rating.
Memory trick: Continuous heat needs extra circuit strength.