Journeyman Electrician Exam (NEC)General Electrical Knowledge and Plan ReadingHard
A client is installing a new electric vehicle (EV) charger in a detached garage. The charger is rated for 48A continuous load. The supply conductors from the main panel in the house to a subpanel in the garage are 75 feet long. Assuming copper conductors are used and sized for 75°C terminals, what is the minimum standard AWG size required for the feeder conductors to the subpanel, according to NEC 210.19(A)(1) and 215.2(A)(1)?
- A2 AWG
- B4 AWG
- C6 AWG
- D8 AWG
Show answer & explanationAnswer & explanation
Correct answer: C. 6 AWG
EV charging is considered a continuous load. Per NEC 210.19(A)(1) and 215.2(A)(1), conductors supplying continuous loads must be sized for 125% of the continuous load. So, 48A × 125% = 60A. Referring to NEC Table 310.16 (75°C column for copper), the minimum conductor size for 60A is 6 AWG. Voltage drop would also need to be checked, but the question only asks for the minimum size based on ampacity for continuous load.
Why the other options are wrong
- A. 2 AWG copper is rated for 115A at 75°C, which is significantly larger than the minimum required.
- B. 4 AWG copper is rated for 85A at 75°C, which is larger than the minimum required.
- D. 8 AWG copper is rated for 50A at 75°C, which is insufficient for a 60A (125% of 48A) continuous load.
Continuous Load Conductor Sizing
Conductors supplying continuous loads (expected to operate for 3 hours or more) must be sized to carry at least 125% of the continuous load current.
- NEC 210.19(A)(1) for branch circuits and 215.2(A)(1) for feeders.
- This factor accounts for heat buildup over extended operation.
- The overcurrent protective device must also be sized for 125% of the continuous load.
Memory trick: Continuous: 125% for safety, then check the table.