CSLB C-46 Solar ContractorPhotovoltaic System InstallationHard
A solar installer is preparing to connect a string inverter to the AC service panel. They need to ensure that the inverter's AC output circuit is properly sized and protected. The inverter has a continuous output current of 25A at 240V. According to NEC 690.8(A)(1) and 690.8(B)(1), what is the minimum required ampacity for the conductors connecting the inverter to the AC service panel?
- A25A
- B35A
- C31.25A
- D30A
Show answer & explanationAnswer & explanation
Correct answer: C. 31.25A
NEC 690.8(A)(1) requires continuous currents (like inverter output) to be multiplied by 125% for conductor sizing. So, 25A * 1.25 = 31.25A. The conductors must have an ampacity of at least 31.25A. The OCPD would then be the next standard size above 31.25A (e.g., 35A or 40A, depending on standard sizes and specific wire type/temperature ratings). The question specifically asks for *conductor ampacity*.
Why the other options are wrong
- A. 25A is the continuous current, but conductors must be sized for 125% of this value.
- B. 35A is a standard OCPD size that could protect a 31.25A conductor, but the question asks for the *conductor ampacity* itself, not the OCPD size.
- D. 30A is too low; 25A * 1.25 = 31.25A.
NEC 125% Rule (Conductor Ampacity)
For continuous currents in PV systems, the conductors must have an ampacity not less than 125% of the maximum continuous current.
- Applies to both DC and AC PV circuits that carry continuous current.
- Ensures conductors do not overheat under prolonged load.
- Calculated ampacity must then be matched to appropriate wire gauge.
Memory trick: Conductor Sizing: Continuous Current * 1.25