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Commissioning and Troubleshooting Flashcards

7 cards from real NABCEP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. During PV system commissioning, you measure an open-circuit voltage significantly higher than the STC-rated Voc. What is the most likely cause?

    Answer: Ambient temperature is much lower than 25°C STC

    PV module Voc increases as temperature decreases below 25°C STC, so cold conditions yield higher-than-rated Voc readings.

  2. A string of 10 modules shows an Isc that is 15% lower than expected while all other strings test normally. What is the first diagnostic step?

    Answer: Inspect each module in the string for shading or soiling

    A proportionally low Isc in a single string commonly points to shading, soiling, or a failing module reducing current generation.

  3. When commissioning a battery-based off-grid system, what parameter must be verified to ensure the charge controller protects the battery bank?

    Answer: Maximum PV array open-circuit voltage vs. charge controller input rating

    The PV array Voc at minimum temperature must not exceed the charge controller's maximum input voltage rating to prevent damage.

  4. An inverter repeatedly faults with an 'AC voltage high' error during afternoon peak. What is the most probable cause?

    Answer: Utility grid voltage rises above the inverter's upper trip threshold

    Backfeed from distributed generation during low-load periods can raise local utility voltage, triggering AC overvoltage faults.

  5. During commissioning, an IR thermal scan of a module shows one cell running 20°C hotter than surrounding cells. What does this indicate?

    Answer: A localized cell defect such as a crack or hot spot

    An isolated hot cell in an IR scan is a classic sign of a cracked or defective cell creating a resistive hot spot.

  6. What is the correct procedure when an electrolytic capacitor is suspected of failing inside an inverter?

    Answer: De-energize the inverter, wait the manufacturer's specified discharge time, then inspect

    Capacitors store dangerous charge; the inverter must be de-energized and fully discharged before any internal inspection.

  7. A grid-tied PV system produces less energy than modeled but all electrical measurements appear normal. What non-electrical factor should be investigated?

    Answer: Actual site shading vs. design assumptions

    Discrepancies between modeled and actual energy production often stem from shading sources (trees, chimneys) not captured in the original design.