NABCEP Solar Energy System Design & Installation 2 — Questions and Answers
Question 1: What is the primary purpose of a combiner box in a large PV array?
- To convert DC power to AC power
- To combine multiple string outputs into a single feed to the inverter (Correct answer)
- To regulate voltage output from individual modules
- To monitor individual panel performance
Correct answer: To combine multiple string outputs into a single feed to the inverter
A combiner box aggregates the outputs of multiple PV strings into a single DC feed, simplifying wiring runs to the inverter.
Question 2: Which NEC article primarily governs the installation of solar photovoltaic systems?
- Article 690 (Correct answer)
- Article 702
- Article 705
- Article 480
Correct answer: Article 690
NEC Article 690 covers solar photovoltaic systems, including wiring methods, overcurrent protection, and disconnecting means.
Question 3: A PV system produces 8 kWp DC. If the inverter has a CEC efficiency of 96%, what is the approximate AC output at peak?
- 7.68 kW (Correct answer)
- 8.33 kW
- 7.20 kW
- 8.00 kW
Correct answer: 7.68 kW
Multiplying 8 kWp by 0.96 efficiency yields 7.68 kW AC output at peak conditions.
Question 4: What is the minimum required ground clearance for conductors on a residential rooftop PV system under NEC requirements?
- The NEC does not specify rooftop conductor ground clearance (Correct answer)
- 3 feet above the roof surface
- 18 inches above the roof surface
- Conductors must be in conduit when on rooftops
Correct answer: The NEC does not specify rooftop conductor ground clearance
The NEC addresses clearances for service drops and overhead conductors, but does not specify a minimum ground clearance for conductors already on a rooftop.
Question 5: Which factor most directly reduces the output of crystalline silicon PV modules on a hot summer day compared to STC ratings?
- Increased UV radiation
- Elevated cell temperature reducing Voc and Pmax (Correct answer)
- Higher irradiance exceeding STC levels
- Reduced atmospheric pressure at high temperatures
Correct answer: Elevated cell temperature reducing Voc and Pmax
Crystalline silicon has a negative temperature coefficient for power; as cell temperature rises above 25°C, both Voc and Pmax decrease.
Question 6: In a grid-tied PV system, what is the function of anti-islanding protection?
- Preventing the inverter from back-feeding power during a utility outage (Correct answer)
- Limiting the number of modules in a single string
- Protecting modules from reverse-current flow
- Ensuring balanced three-phase output
Correct answer: Preventing the inverter from back-feeding power during a utility outage
Anti-islanding protection causes the inverter to shut down when utility power is lost, preventing hazardous energization of a de-energized grid.
Question 7: When sizing DC conductors for a PV source circuit, NEC 690.8 requires the conductor ampacity to be at least what percentage of the module's rated Isc?
- 100%
- 125%
- 156% (Correct answer)
- 80%
Correct answer: 156%
NEC 690.8 requires DC source-circuit conductors to be rated at 156% of the module's Isc (125% × 125% for continuous current under sunlight).
NABCEP Solar Energy System Design & Installation 2
What is the primary purpose of a combiner box in a large PV array?