NABCEP PVSI flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

NEC 690.12 rapid shutdown

Requires PV conductors outside the array boundary to be reduced to ≤30 V within 30 seconds of shutdown; applies to rooftop and ground-mounted systems per the 2017 and 2020 NEC.

Cold-temperature Voc correction

Module Voc at the lowest expected ambient temperature equals Voc(STC) × [1 + (Tmin − 25 °C) × βVoc/100], where βVoc is the Voc temperature coefficient in %/°C.

NEC 690.8 conductor ampacity

PV source and output circuit conductors must have ampacity ≥ 1.25 × 1.25 × Isc (125% for continuous current and 125% for irradiance) unless using listed combiner or fuse ratings.

120% busbar rule

NEC 705.12(B)(2) permits the sum of the main breaker and PV breaker ratings to be ≤120% of the busbar rating, or the PV breaker may be placed at the opposite end of the busbar.

NEC 690.13 disconnecting means

Requires a lockable, manually operable switch that opens all ungrounded conductors of the PV system; the disconnect must be clearly labeled and accessible to the AHJ.

NEC 690.47 grounding electrode

DC grounding electrode conductor sized per NEC 250.166; 690.47(C) permits a common DC/AC grounding electrode for inverters listed to UL 1741 with integrated DC grounding.

Module nameplate STC ratings

Standard Test Conditions (1000 W/m², 25 °C cell temperature, AM 1.5) ratings for Pmax, Voc, Isc, Vmp, and Imp; used for string sizing and system design calculations.

String inverter DC input window

The MPPT voltage range and maximum DC input voltage of a string inverter; the designed string voltage must remain within this window across all expected temperatures.

Maximum series fuse rating

The maximum overcurrent protection device rating permitted in series with a PV module, listed on the module nameplate; exceeding it voids the module listing and creates a fire hazard.

PV Wire vs USE-2

PV Wire (UL 4703) is rated for outdoor, exposed, and wet locations; USE-2 is rated for underground service entrance. Both are common for DC PV source circuits.

Combiner box fuse rating

The DC fuse or breaker rating per string must be ≥1.25 × Isc and ≤ the module maximum series fuse rating; the busbar must be rated for the total combined current.

Rapid shutdown device

A UL 1741-listed initiator and transmitter/receiver that reduces PV conductors outside the array boundary to ≤30 V within 30 seconds of shutdown per NEC 690.12.

DC arc-flash hazard

DC arcs do not self-extinguish at low current and can sustain at system voltage; arc-flash energy is calculated from module Isc and string voltage, and labels are required per NEC 110.16.

GFDI test procedure

Ground-fault detection and interruption must be tested per the manufacturer's procedure; for grounded systems per NEC 690.5 and ungrounded systems per NEC 690.35.

Insulation resistance test

Use a megohmmeter at 500 V or 1000 V DC to measure conductor-to-ground resistance; compare to the manufacturer's minimum (often ≥1 MΩ per module or string) and record values.

I-V curve trace

Compare measured Pmax, Voc, Isc, and fill factor to expected values at the measured irradiance and cell temperature; a deviation of 10% or more indicates a fault.

Thermal imaging inspection

Scan modules, connections, and combiners under load; a temperature rise greater than 10 °C above neighboring components indicates a high-resistance connection or failing component.

String current comparison

Measure each string's operating current with a clamp meter; a deviation greater than 10% from the string average indicates a fault, shading issue, or mismatched module.

Rapid shutdown test

Measure voltage at the inverter or combiner within 30 seconds of initiating shutdown; confirm ≤30 V at the array boundary per NEC 690.12 and record the result.

Title block verification

Confirm the project address, drawing scale, revision number, and date on the title block; ensure all sheets are the current revision before beginning field work.

Single-line diagram trace

Trace the power path from modules through strings, combiner, inverter, AC disconnect, and main panel; verify component ratings and conductor sizes against the equipment schedule.

String sizing table check

Compare the design string length and voltage window to the cold- and hot-temperature limits; flag any string outside the inverter MPPT window or exceeding maximum DC voltage.

Electrical panel schedule

Confirm the PV breaker size, busbar rating, and available space; verify the 120% rule calculation is documented and the breaker is placed correctly on the busbar.

Structural drawing review

Verify roof framing, attachment spacing, and load calculations; confirm the racking layout matches the structural engineer's stamped plans and local snow/wind loads.

Equipment schedule cross-check

Compare model numbers, ratings, and quantities on the equipment schedule to the delivered equipment; note any substitutions and verify they are approved by the designer.

As-built documentation

Record any field changes such as conductor routing or equipment relocation on the plans and obtain approval before energizing the system.

Pre-inspection checklist

Verify permits, approved plans, equipment listings, and manufacturer installation manuals are on site before starting the inspection; missing documents can delay the inspection.

Conduit support spacing

NEC 334.30 requires conduit to be supported at intervals not exceeding 10 ft and within 3 ft of boxes; verify supports are secure and properly spaced during inspection.

Labeling inspection

Confirm all required labels are present and legible: rapid shutdown, DC/AC disconnects, PV system warning, and arc-flash labels per NEC 690.56 and 110.16.

Functional testing

Perform the rapid-shutdown test, verify inverter startup and grid-tie, and confirm monitoring communication; record results with timestamps and test conditions.

Deficiency report

List each finding with the applicable code reference, a description, and a required corrective action; classify as critical (safety) or non-critical.

Final inspection report

Include the inspection date, inspector name, scope, test results, deficiency list, and sign-off; deliver to the AHJ and system owner.