Practice Test Geeks(NABCEP) North American Board of Certified Energy Practitioners Solar Practice Test
← All NABCEP Flashcard Decks

Inverter Systems 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 Inverter Systems flashcards as text

  1. A grid-tied inverter displays a 'Ground Fault' error and shuts down. What is the most likely cause?

    Answer: An unintended current path exists between a current-carrying conductor and ground

    A ground fault error indicates that current is flowing through an unintended path to ground, typically caused by insulation failure or wiring errors in the DC array.

  2. What is 'frequency-watt' (Freq-Watt) control mode in a grid-tied inverter?

    Answer: A grid support function that reduces inverter output power when grid frequency rises above threshold

    Frequency-Watt (or Freq-Watt) control reduces inverter active power output as grid frequency increases above a set threshold, helping stabilize grids with excess generation.

  3. For a transformerless grid-tied inverter, NEC requires which of the following to reduce leakage current risk?

    Answer: Ground fault protection device (GFPD) integrated into or paired with the inverter

    NEC 690.5 requires ground fault protection for ungrounded PV systems (common with transformerless inverters) to detect and interrupt ground fault currents that could cause fires or shock hazards.

  4. A string inverter has two independent MPPT inputs. How does this benefit the system designer?

    Answer: It permits strings with different orientations or shading conditions to be optimized independently

    Dual independent MPPT inputs allow strings facing different directions (e.g., east and west) or with different shading profiles to each operate at their individual maximum power points rather than compromising to a single point.

  5. What is 'volt-VAR' (Volt-VAR) control in advanced grid-interactive inverters?

    Answer: Reactive power (VAR) output adjusted in response to local grid voltage to help regulate voltage

    Volt-VAR control allows inverters to absorb or inject reactive power (VARs) in response to grid voltage deviations, helping utilities maintain voltage within acceptable limits on distribution feeders.

  6. An off-grid inverter/charger is rated for 4,000W continuous AC output. A customer wants to run a 3-ton central air conditioner with a 5,400W LRA (locked rotor amperage) starting current. What is the key specification to check?

    Answer: The inverter's surge capacity rating to handle motor starting current

    Motor starting (LRA) can require 3-6× the running current for 1-3 seconds; the inverter's surge/peak capacity rating must exceed the motor's LRA to successfully start the load without shutdown.

  7. According to UL 1741-SA (Supplement A), what capability must inverters have to qualify for use in Hawaiian Electric and California Rule 21 interconnection?

    Answer: Advanced grid support functions including voltage and frequency ride-through and reactive power control

    UL 1741-SA certifies inverters for advanced grid support functions required by Hawaiian Electric and California Rule 21, including voltage/frequency ride-through, volt-VAR, and volt-watt controls.