System Maintenance & 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.
Read the first 7 System Maintenance & Troubleshooting flashcards as text
A microinverter-based system's monitoring portal shows one microinverter reporting zero production for three consecutive days while all others are normal. The FIRST field action should be to:
Answer: Verify AC circuit continuity at the affected branch circuit and check for tripped GFCI or breaker
Before replacing hardware, verify that AC power is present and the branch circuit is not open, which is the most common cause of a single microinverter going offline.
Electroluminescence (EL) imaging is BEST used during maintenance to detect:
Answer: Invisible cracks, inactive cell areas, and delamination not visible to the naked eye
EL imaging applies a forward current to modules and captures emitted near-infrared light, revealing micro-cracks and inactive cell regions invisible under normal conditions.
An installer notices that string fuses in a combiner box have blown repeatedly after replacement. The MOST likely root cause is:
Answer: A ground fault in one string is causing backfed current from parallel strings to exceed fuse rating
Repeated fuse failure usually indicates excessive backfed fault current from parallel strings flowing through the faulted string, which exceeds the fuse's continuous current rating.
A flooded lead-acid battery bank in an off-grid system shows specific gravity readings that vary significantly between cells in the same battery. This condition is BEST corrected by:
Answer: Performing an equalization charge at the manufacturer-specified voltage
An equalization charge applies a controlled overcharge that stirs the electrolyte and balances cell state-of-charge, correcting specific gravity stratification and imbalance.
After a hailstorm, a technician visually inspects a PV array and finds no broken glass. However, output is down 15% compared to pre-storm data. The MOST appropriate next diagnostic tool is:
Answer: Infrared thermography or EL imaging to identify impact-induced micro-cracks
Hail can cause micro-cracks that are invisible to the naked eye but significantly reduce cell performance; IR or EL imaging reveals these sub-surface defects.
During commissioning verification of a new grid-tied system, the measured short-circuit current (Isc) at the combiner box is noticeably lower than the calculated value. Which factor should be checked FIRST?
Answer: Actual irradiance level at time of measurement compared to STC irradiance
Isc is directly proportional to irradiance; measurements taken at less than 1000 W/m² will yield lower Isc values than STC-rated specifications, which is normal.
A grid-tied string inverter's display shows an 'Isolation Fault' error. This indicates:
Answer: The DC resistance between the PV array conductors and ground has dropped below the minimum threshold
An isolation fault means the impedance between ungrounded DC conductors and earth ground has fallen below the inverter's minimum threshold, indicating a potential ground fault in the array.