Journeyman Electrician Exam (NEC)Services, Feeders, and Branch CircuitsMedium
A commercial kitchen requires a feeder for a continuous load of 75 amperes and a noncontinuous load of 50 amperes. The feeder conductors are copper, rated 75°C. What is the minimum required rating of the overcurrent protective device (OCPD) for this feeder?
- A100 amperes
- B150 amperes
- C175 amperes
- D125 amperes
Show answer & explanationAnswer & explanation
Correct answer: B. 150 amperes
According to NEC 215.2(A)(1)(a) and 215.3, the feeder OCPD must be sized for 125% of the continuous load plus 100% of the noncontinuous load. Continuous load = 75 A * 1.25 = 93.75 A. Noncontinuous load = 50 A. Total calculated load = 93.75 A + 50 A = 143.75 A. The next standard OCPD size is 150 amperes (NEC 240.6(A)).
Why the other options are wrong
- A. 100 amperes is too small; it does not account for the 125% factor for the continuous load.
- C. 175 amperes is larger than the minimum required OCPD size.
- D. 125 amperes is too small; the calculation yields a higher value.
Feeder OCPD Sizing (Continuous/Noncontinuous)
Overcurrent protective devices for feeders supplying continuous loads must be sized at 125% of the continuous load plus 100% of the noncontinuous load, then rounded up to the next standard OCPD size if necessary.
- Continuous loads are multiplied by 125%.
- Noncontinuous loads are multiplied by 100%.
- Feeder OCPD must be sized to protect the conductors.
- NEC 215.3 and 240.6(A) apply.
Memory trick: Continuous loads need an extra boost, then pick the next standard fuse.