NEC Code Reference for Solar Installers: Articles 690, 705, 625, 250, 310, 240
The National Electrical Code (NFPA 70) is the backbone of every safe solar installation. This reference distills the six NEC articles solar installers touch most often — 690, 705, 625, 250, 310, and 240 — into key requirements, sizing tables, and the changes arriving in the NEC 2026 cycle. Use it as a jobsite quick reference, then confirm specifics against your adopted code edition and AHJ.
Always verify the adopted editionNEC is updated every three years but adopted state-by-state. As of 2026, many states run NEC 2020 or 2023. Confirm which edition your AHJ enforces before final design.
Article 690 — Solar Photovoltaic (PV) Systems
Article 690 is the dedicated PV section. It governs array conductors, inverters, grounding, rapid shutdown, and overcurrent protection specific to solar.
Key requirements
- 690.7 — Maximum voltage. PV system voltage = corrected Voc × modules in series. Use the correction factors in Table 690.7(A) for cold temperatures (e.g. 1.25× at −10°C, 1.18× at 1°C to 10°C).
- 690.8 — Circuit sizing & current. PV circuit current = Isc × 1.25 (irradiance) then × 1.25 (continuous) = 1.56 × Isc. Size conductors and OCPD at this value.
- 690.11 — DC arc-fault protection. Required for PV systems on 1- and 2-family dwellings with max voltage >80V and >240W.
- 690.12 — Rapid shutdown. Conductors leaving the array boundary must reduce to <30V within 30s (1- and 2-family dwellings).
- 690.31 — Wiring methods. PV wire (RHH/RHW-2/PV) in sunlight-exposed runs; secure every 6 in on the array, every 24 in elsewhere.
- 690.43 — Equipment grounding. Exposed non-current-carrying metal parts of PV frames, rails, and equipment shall be grounded.
- 690.47 — Grounding electrode system. PV system grounding electrode requirements; a single electrode may suffice if bonded to building GES.
NEC 2026 changeProposed revisions refine rapid-shutdown boundaries for bifacial and building-integrated PV and clarify energy-storage interaction. Expect expanded guidance on DC-coupled battery conductors under 690/706.
Article 705 — Interconnected Electric Power Production Sources
Article 705 governs how a PV (or other) generator ties to the utility grid or a premises wiring system.
- 705.11 — Source connections. Connect at the service, feeder, or branch-circuit level with approved means; busbar/load calc per 705.12.
- 705.12 — Busbar/load calculations. Backfed breaker sum + load ≤ busbar rating, OR use the 120% rule: backfed OCPD ≤ busbar rating × 1.2 − main breaker. Common for residential supply-side/loads-side interconnects.
- 705.20 — Available fault current. Equipment SCCR must exceed available fault current at the interconnection point.
- 705.28 — Source conductors. Sized per 705.28 continuous current rules; similar 1.25× factor.
- 705.40 — Loss of primary source. Interactive inverter must disconnect (anti-islanding) per UL 1741.
Article 625 — EV Power Transfer Systems
Increasingly relevant as PV installers add EV charging. Key points:
- 625.40 — Branch circuit. EVSE is a continuous load; size branch circuit and conductors at 125% of rated current (e.g. 48A EVSE → 60A circuit, #6 Cu).
- 625.41 — Rating. EVSE rated 15A to 80A; level 2 residential is typically 32–48A.
- 625.50 — Fixed indoor EVSE. GFCI protection required for personnel protection.
- 625.54 — Receptacles. 125V/250V EV receptacles require GFCI.
Article 250 — Grounding and Bonding
Grounding bonds the system reference to earth; bonding keeps non-current-carrying metal at the same potential.
- 250.4 — General requirements. System grounded, equipment bonded, fault-current path has low impedance.
- 250.53 — Grounding electrode system. If a single rod reads >25Ω, drive a second rod (no further measurement required).
- 250.66 — GEC sizing. Size grounding electrode conductor by the largest ungrounded service conductor per the table below.
- 250.122 — EGC sizing. Size equipment grounding conductor by the OCPD ahead of the circuit per the table below.
- 250.194 — Grounding of PV systems. References Article 690 for PV-specific grounding.
Article 310 — Conductors for General Wiring
- 310.15 — Ampacity. Use Table 310.16 for ≤600V conductors; derate for ambient temperature and conduit fill (>3 current-carrying conductors).
- 310.15(B)(1) — Temperature correction. Multiply ampacity by correction factor for ambient (e.g. 0.82 at 41–45°C for 90°C insulation).
- 310.15(C)(1) — Adjustment. Derate 80% for 4–6 CCC, 70% for 7–9, etc.
- Insulation types: THWN-2 (90°C wet/dry), PV wire (90°C, sunlight-resistant, direct burial), RHH/RHW-2.
Article 240 — Overcurrent Protection
- 240.4 — Protection of conductors. OCPD rated ≤ conductor ampacity. Small-conductor rules: 15A for #14 Cu, 20A for #12, 30A for #10.
- 240.6 — Standard ampere ratings. 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150…
- 240.21 — Location. OCPD at conductor supply point; tap rules allow shorter unprotected runs.
- PV OCPD sized at 1.56 × Isc per 690.8 / 690.9.
Quick Reference Tables
Wire ampacity (NEC Table 310.16, 75°C column, Cu)
| AWG | Ampacity (Cu, 75°C) | Typical PV use |
|---|---|---|
| #14 | 20 A | Small string home runs (rare in PV) |
| #12 | 25 A | Residential string home runs |
| #10 | 35 A | Combined string / microinverter trunk |
| #8 | 50 A | Sub-array home runs |
| #6 | 65 A | Combiner output, EV charging |
| #4 | 85 A | Inverter AC output, large combiner |
| #2 | 115 A | Commercial inverter output |
| 1/0 | 150 A | Service entrance, large ESS |
Derate before you use theseApply temperature correction (310.15(B)(1)) and conduit-fill adjustment (310.15(C)(1)) to the 90°C column first, then cap at the 75°C rating when terminations are 75°C-rated.
EGC sizing (NEC Table 250.122)
| OCPD rating | Copper EGC | Aluminum EGC |
|---|---|---|
| 15 A | #14 | #12 |
| 20 A | #12 | #10 |
| 60 A | #10 | #8 |
| 100 A | #8 | #6 |
| 200 A | #6 | #4 |
| 400 A | #3 | #1 |
Grounding electrode conductor sizing (NEC Table 250.66)
| Largest ungrounded service conductor (Cu) | GEC (Cu) |
|---|---|
| #2 AWG or smaller | #8 |
| #1 or 1/0 | #6 |
| 2/0 or 3/0 | #4 |
| Over 3/0 to 350 kcmil | #2 |
| Over 350 to 600 kcmil | #1/0 |
What's New in NEC 2026
The 2026 cycle emphasizes energy storage integration and smart-inverter functionality:
- Article 706 (ESS) gains clarity on residential lithium battery installations, including listing (UL 9540/9540A) and NFPA 855 alignment.
- Rapid shutdown (690.12) provisions refined for building-integrated and bifacial arrays.
- DC-coupled battery conductors sizing harmonized between 690 and 706.
- EVSE + PV coordination guidance expanded under 625 and 705.
- Smart-inverter functions (volt-VAR, frequency-watt) referenced to IEEE 1547-2018 and Rule 21.
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Related Collections
Further Reading
- NEC Wire Sizing Guide: Ampacity Charts for Solar and Generator Installations
- NEC 2026 Code Changes: Top 10 Updates Affecting Solar Installers
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