CSLB C-46 Solar ContractorPhotovoltaic System InstallationHard
A solar technician is installing a string inverter that requires dedicated AC overcurrent protection. The inverter's maximum continuous output current is 40A. According to the National Electrical Code (NEC), what is the MINIMUM standard overcurrent protection device (OCPD) rating required for this inverter circuit?
- A50A breaker
- B40A breaker
- C60A breaker
- D48A breaker
Show answer & explanationAnswer & explanation
Correct answer: A. 50A breaker
According to NEC 690.8(B)(1), AC circuits from inverters must have overcurrent protection sized at not less than 125% of the maximum continuous current. For a 40A continuous current, 40A * 1.25 = 50A. A 50A breaker is the minimum standard size that meets this requirement.
Why the other options are wrong
- B. 40A is equal to the continuous current, not 125% of it, which would lead to nuisance tripping for continuous loads.
- C. 60A would be permissible but is not the 'minimum' required; it provides more headroom than necessary.
- D. 48A is 120% of 40A, which is insufficient. Also, 48A is not a standard OCPD size.
NEC 125% Rule (Continuous Loads)
For continuous loads (operating for 3 hours or more), the overcurrent protective device must be sized at not less than 125% of the maximum continuous current.
- Applies to AC output circuits of inverters.
- Prevents nuisance tripping and ensures safety for sustained operation.
- Conductors are also sized to account for continuous loads.
Memory trick: Inverter's AC output needs 125% 'safety buffer' for continuous flow!