CSLB C-10 Electrical ContractorEquipment and InstallationMedium
A 3-phase, 4-wire feeder supplies a panelboard with a continuous lighting load of 150 amperes and a non-continuous receptacle load of 40 amperes. What is the minimum required ampacity for the feeder conductors before any temperature correction or adjustment factors?
- A190 amperes
- B150 amperes
- C227.5 amperes
- D187.5 amperes
Show answer & explanationAnswer & explanation
Correct answer: C. 227.5 amperes
Per NEC 215.2 and 210.19(A), continuous loads must be multiplied by 125%: 150A x 1.25 = 187.5A. Add the non-continuous load of 40A: 187.5 + 40 = 227.5A minimum feeder ampacity.
Why the other options are wrong
- A. Incorrectly adds only 100% of continuous load plus a rounded amount.
- B. Uses only the continuous load, ignoring the non-continuous portion.
- D. Only accounts for the continuous load at 125%, omitting the 40A non-continuous load.
Continuous + Non-Continuous Feeder Sizing
Feeder conductors must be sized at 125% of continuous loads plus 100% of non-continuous loads.
- Continuous load = operates 3+ hours
- 125% factor applies only to continuous portion
- Add non-continuous load at 100% to get total minimum ampacity
Memory trick: Continuous loads get a 25% cushion; non-continuous loads stay as-is.