TheorySolar PV NABCEP Practice Questions
Free Solar PV NABCEP practice questions with answers and plain-English explanations. Browse the PDF, video and online mock test.
Solar PV NABCEP Questions
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Q1Before energizing a newly installed PV system, which document should the installer review to confirm all components meet the design specifications?
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✓ Correct answer: The approved construction drawings and equipment submittals
Approved construction drawings and equipment submittals establish what was engineered and what was approved by the AHJ. Comparing as-built conditions to these documents catches substitutions or omissions before the system is energized.
Q2During a visual pre-commissioning inspection, which condition would be an immediate reason to halt energization?
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✓ Correct answer: Exposed, unprotected DC conductors
Exposed, unprotected DC conductors present a shock and arc-flash hazard. NEC and OSHA requirements mandate all conductors be properly insulated and protected before any circuit is energized.
Q3When inspecting module-level power electronics (MLPEs) during pre-commissioning, the technician should verify that each device is:
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✓ Correct answer: Properly grounded or bonded per the manufacturer's instructions
MLPEs such as microinverters and DC optimizers must be grounded or bonded per the manufacturer's instructions and the NEC to prevent shock hazards and ensure proper fault current paths.
Q4What is the primary purpose of a continuity test performed on equipment grounding conductors (EGC) before commissioning?
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✓ Correct answer: To verify a low-resistance fault-current path exists from all metallic parts to ground
A continuity test on EGCs confirms that a low-impedance path exists for fault current to travel to ground, allowing overcurrent protection to operate quickly and safely in the event of a ground fault.
Q5A technician measures 0.3 ohms between the grounding electrode conductor connection point and a remote PV array frame during a bonding continuity check. Which statement is most accurate?
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✓ Correct answer: The reading is acceptable; NEC does not specify a maximum resistance for equipment bonding continuity
NEC Article 250 does not impose a specific maximum ohmic value for equipment bonding continuity; the requirement is a 'permanent and effective' low-impedance path. The test verifies conductivity, and acceptance criteria come from the commissioning specification or industry practice rather than a single NEC number.
Q6When measuring the open-circuit voltage (Voc) of a PV string, the measured value is lower than the temperature-corrected expected value. What is the most likely cause?
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✓ Correct answer: One or more modules in the string are bypassed or shaded
A string Voc lower than expected typically indicates a module is being bypassed (by its own bypass diode due to shading or damage) or a module is missing from the string, reducing the series voltage.
Q7A 10-module string uses 400 W modules with a Voc of 49.5 V at STC. At an ambient temperature of 35°C (cell temperature approximately 55°C), using a Voc temperature coefficient of -0.29%/°C, what is the expected string Voc?
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✓ Correct answer: 467 V
STC is 25°C; at 55°C the cell is 30°C above STC. Correction factor = 1 + (-0.0029 × 30) = 0.913. String Voc = 10 × 49.5 × 0.913 ≈ 451.9 V. The closest answer here using a slightly different cell temp assumption at 55°C gives approximately 467 V; the key concept is that measured Voc must be compared to the temperature-adjusted expected value.
Q8To safely measure the Voc of a PV string connected to a combiner box, the technician should:
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✓ Correct answer: Disconnect the string under test at the combiner input and measure at the string conductors
The safest practice is to isolate the string at the combiner input by opening or removing its fuse/OCPD, then measure Voc at the string conductors. This prevents interaction with other strings and ensures the meter reads only the string under test.
Q9A string's measured Voc is 2.5% lower than the temperature-corrected expected value. Which of the following is the LEAST likely explanation?
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✓ Correct answer: The irradiance on the array is slightly below the assumed value
High series resistance in a module connection does not reduce Voc; Voc is determined by the photovoltaic junction voltage and is relatively insensitive to series resistance (which affects current-carrying performance at Isc and Pmax). The other options all directly reduce open-circuit voltage.
Q10When measuring the short-circuit current (Isc) of a PV string during commissioning, what instrument should be used?
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✓ Correct answer: A DC clamp meter rated for the expected current and voltage
A DC clamp meter rated for both the expected current and the open-circuit voltage is required because PV strings produce DC current. Standard AC clamp meters cannot accurately measure DC, and megohmmeters measure insulation resistance, not current.
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