CSLB C-46 Solar ContractorPhotovoltaic System InstallationMedium
A solar installer is connecting a new grid-tied string inverter to a residential service panel. The inverter has a maximum continuous output current of 25A. According to NEC 690.8(A)(1), what is the minimum required ampacity for the conductors carrying the inverter's AC output?
- A35A
- B30A
- C25A
- D31.25A
Show answer & explanationAnswer & explanation
Correct answer: D. 31.25A
NEC 690.8(A)(1) requires that PV system circuit conductors be sized to carry a continuous current of not less than 125% of the maximum current. For an inverter with a maximum continuous output current of 25A, the minimum required ampacity is 25A * 1.25 = 31.25A.
Why the other options are wrong
- A. 35A is higher than the minimum required, which is acceptable but not the minimum.
- B. 30A is too low; the calculated minimum is 31.25A.
- C. 25A is the inverter output, not the minimum required ampacity after applying the 125% rule.
NEC 690.8(A)(1) (PV Conductor Sizing)
Requires PV system circuit conductors to have an ampacity of at least 125% of the maximum continuous current they are expected to carry.
- Applies to both DC and AC PV circuits.
- Accounts for continuous operation and potential variations in current.
- Ensures conductors do not overheat, preventing fire hazards and insulation degradation.
Memory trick: For PV wires, multiply by one-point-two-five, to keep the circuit alive!