CSLB C-46 Solar ContractorPhotovoltaic System InstallationHard
A solar installer is connecting a new 7.6 kW string inverter to a 240V, 30A dedicated circuit breaker in the main service panel. The inverter's maximum continuous output current is 31.67A. According to NEC 690.8(A)(1) and 690.8(B)(1), what is the minimum continuous current rating the overcurrent protection device (OCPD) should have for this inverter output circuit?
- A40A
- B60A
- C50A
- D30A
Show answer & explanationAnswer & explanation
Correct answer: C. 50A
NEC 690.8(A)(1) states that continuous current for PV system circuits is calculated at 125% of the maximum current. So, 31.67A * 1.25 = 39.5875A. According to NEC 690.8(B)(1), the OCPD must be rated for this calculated continuous current. The next standard OCPD size above 39.5875A is 50A.
Why the other options are wrong
- A. 40A is too low; 31.67A * 1.25 = 39.5875A, which exceeds 40A.
- B. 60A would be permissible but is not the minimum required size; 50A is sufficient.
- D. 30A is too low; it does not account for the 125% continuous current factor.
NEC 125% Rule for PV OCPD
For continuous PV system currents, the current used to determine the minimum overcurrent protection device (OCPD) rating must be multiplied by 125%.
- Applies to continuous currents (3 hours or more).
- Ensures OCPD does not trip prematurely.
- Calculated current determines the minimum standard OCPD size.
Memory trick: NEC Sizing: Continuous Current + 125% = OCPD