NABCEP PVSI cheat sheet

NEC Article 690 governs PV systems; 690.12 requires rapid shutdown for conductors outside the array boundary to be reduced to ≤30 V within 30 seconds of shutdown (2017/2020 NEC).

NEC 690.7(A) voltage correction: module Voc at lowest expected ambient temperature = Voc(STC) × [1 + (Tmin − 25 °C) × βVoc/100], where βVoc is the Voc temperature coefficient in %/°C (typically −0.3%/°C).

NEC 690.8(A) maximum current: Isc × 1.25 for continuous current; 690.8(B) conductor ampacity must be ≥ 1.25 × 1.25 × Isc (125% for continuous plus 125% for irradiance) unless using listed combiner/fuse ratings.

NEC 690.9 requires overcurrent protection (OCPD) on PV source and output circuits when the sum of parallel module Isc × 1.25 exceeds the conductor ampacity or module series fuse rating.

NEC 690.13 disconnecting means must be a lockable, manually operable switch that opens all ungrounded conductors of the PV system; 690.15 requires disconnects for each PV source circuit or group.

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

NEC 690.31(C) requires PV source and output conductors to be protected from physical damage; 690.31(D) allows DC PV conductors inside buildings only if in metal raceway or listed for the application.

NEC 705.12(B)(2) 120% rule for busbar: (main breaker rating + PV breaker rating) ≤ 1.2 × busbar rating, or use a dedicated PV breaker at the opposite end of the busbar.

NEC 690.4(C) requires qualified persons to install PV systems; 690.6 requires PV modules to be listed to UL 1703 or UL 61730 and inverters to UL 1741.

PV module: nameplate STC ratings (Pmax, Voc, Isc, Vmp, Imp), temperature coefficients (Pmax, Voc, Isc), and maximum series fuse rating; verify these match the design string sizing.

String inverter: DC input window (min/max MPPT voltage, max DC voltage), AC output rating, efficiency curve, and required DC/AC disconnects; confirm max input current per MPPT.

Microinverter and DC optimizer: verify compatibility with module wattage and voltage window; check the manufacturer's compatibility list and rapid-shutdown capability.

Combiner box: fuse or breaker rating per string (≥1.25 × Isc), busbar ampacity, and enclosure NEMA rating for the installation environment.

Racking: rail and clamp load ratings (psf or Pa), attachment spacing per structural engineer, and corrosion resistance (e.g., mill-finish aluminum, stainless hardware).

Conductors: PV Wire (UL 4703) or USE-2 for outdoor DC; THWN-2 in conduit; verify ampacity per NEC 310.15 and 690.8 after derating for temperature and conduit fill.

Overcurrent devices: DC-rated fuses/breakers with voltage rating ≥ system Voc (including cold-temperature correction) and interrupt rating ≥ available fault current.

Monitoring and communications: revenue-grade or production meter, CT placement, data logger, and communication gateway; verify signal path and power source.

Rapid shutdown device: initiator and transmitter/receiver components listed to UL 1741; verify the system reduces conductors to ≤30 V within 30 seconds.

Arc-flash risk: calculate DC arc-flash energy using module Isc and string voltage; label per NEC 110.16 and NFPA 70E; DC arcs do not self-extinguish at low current.

Shock hazard: PV conductors are energized whenever illuminated; treat all DC conductors as live, use appropriately rated PPE (class 0 gloves for ≤1000 V DC), and verify with a CAT III/IV meter.

Ground-fault protection: verify GFDI (ground-fault detection and interruption) per NEC 690.5 for grounded systems or 690.35 for ungrounded; test per manufacturer procedure.

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.

Insulation resistance test: use a megohmmeter at 500 V or 1000 V DC; compare readings to manufacturer's minimum (often ≥1 MΩ per module or per 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 10% deviation indicates a fault.

Thermal imaging: scan modules, connections, and combiners under load; a temperature rise >10 °C above neighboring components indicates a high-resistance connection.

String current comparison: measure each string's operating current with a clamp meter; a deviation >10% from the string average indicates a fault or shading issue.

Emergency shutdown procedure: document the location of the AC disconnect, DC disconnect, and rapid-shutdown initiator; post signage per NEC 690.56(C).

Title block: verify project address, drawing scale, revision number, and date; confirm all sheets are the current revision before field work.

Site plan: check array layout, setbacks from property lines and ridges, access paths, and equipment pad locations against the actual site.

Single-line diagram (SLD): trace the power path from modules → strings → combiner → inverter → AC disconnect → main panel; verify component ratings and conductor sizes match the schedule.

Structural drawings: verify roof framing, attachment spacing, and load calculations; confirm the racking layout matches the structural engineer's stamped plans.

Electrical panel schedule: confirm the PV breaker size, busbar rating, and available space; verify the 120% rule calculation is documented.

String sizing table: compare the design string length and voltage window to the cold- and hot-temperature limits; flag any string outside the inverter MPPT window.

Equipment schedule: cross-check model numbers, ratings, and quantities against the delivered equipment; note any substitutions and verify they are approved.

As-built documentation: record any field changes (conductor routing, equipment relocation) on the plans and obtain approval before energizing.

Pre-inspection checklist: verify permits, approved plans, equipment listings, and manufacturer installation manuals are on site before starting the inspection.

Visual inspection: check module orientation, tilt, torque on connections, conduit support spacing (≤10 ft per NEC 334.30), and weather sealing at penetrations.

Electrical inspection: verify conductor sizes, OCPD ratings, grounding/bonding, and disconnect locations against the approved plans and NEC 690.

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

Documentation: photograph all components and labels, record serial numbers, and note any deficiencies with location and severity.

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