Journeyman Electrician Exam (NEC)General Electrical Knowledge and Plan ReadingMedium
A technician is installing a new 480Y/277V, 3-phase, 4-wire feeder to supply a lighting panel. The panel has a total non-continuous lighting load of 150A per phase. What is the minimum required ampacity for the feeder overcurrent protective device (OCPD), assuming no demand factors or other loads?
- A225 A
- B150 A
- C200 A
- D187.5 A
Show answer & explanationAnswer & explanation
Correct answer: B. 150 A
Since the lighting load is specified as 'non-continuous,' the 125% rule for continuous loads (NEC 215.3 for feeders) does not apply. Therefore, the overcurrent protective device must be sized at least 100% of the non-continuous load. The minimum required ampacity for the OCPD is simply the total non-continuous load, which is 150A.
Why the other options are wrong
- A. This is an incorrect calculation or unrelated standard size.
- C. This is a common standard OCPD size, but the calculated minimum is 150A. A 200A OCPD would be permitted if higher than the minimum, but 187.5A is not the minimum.
- D. This would be 125% of 150A (187.5A), which is incorrect for a non-continuous load.
OCPD Sizing for Non-Continuous Loads
Overcurrent protective devices (OCPDs) for non-continuous loads must have an ampacity not less than 100% of the load served.
- Non-continuous loads operate for less than 3 hours at a time.
- This contrasts with continuous loads, which require OCPDs sized at 125% of the load.
- NEC Articles 210.20(A) for branch circuits and 215.3 for feeders govern OCPD sizing.
Memory trick: OCPD: Continuous 125%, Non-continuous 100%.