CSLB C-46 Solar ContractorPhotovoltaic System InstallationMedium
A solar installer is connecting a new 7.6 kW string inverter to a 240V, 30A dedicated circuit in a residential service panel. According to NEC 690.8(A)(1), what is the minimum required ampacity for the conductors connecting the inverter's AC output to the overcurrent protective device?
- A20 Amperes
- B40 Amperes
- C25 Amperes
- D30 Amperes
Show answer & explanationAnswer & explanation
Correct answer: B. 40 Amperes
NEC 690.8(A)(1) requires that the ampacity of conductors for PV inverter output circuits be at least 125% of the maximum current. For a 7.6 kW inverter at 240V, the maximum current is 7600W / 240V = 31.67A. Applying the 125% rule: 31.67A * 1.25 = 39.59A. Therefore, a 40A conductor ampacity is required.
Why the other options are wrong
- A. 20A is too low for the calculated current.
- C. 25A is too low and does not meet the 125% rule.
- D. 30A is the breaker size, not the conductor ampacity, and is insufficient for the 125% rule.
NEC 690.8(A)(1) 125% Rule
For PV inverter output circuits, the conductor ampacity must be at least 125% of the maximum inverter output current.
- Applies to continuous loads.
- Ensures conductors can safely handle sustained current.
- Calculated current is multiplied by 1.25.
Memory trick: Current's high, so multiply by one point twenty-five (1.25) to size the wire right.