NEC 690

Quick Facts

What is NEC 690?

Formal definition

NEC Article 690 (titled “Solar Photovoltaic (PV) Systems”) is the article of the National Electrical Code that covers PV system equipment, circuits, and disconnects. It is published by NFPA as part of NFPA 70.

Engineering definition

NEC 690 specifies the design rules for safe installation of PV power sources: voltage limits, current calculations, overcurrent protection, grounding, conductor identification, disconnects, arc-fault and ground-fault protection, rapid shutdown, and equipment labeling.

Industry definition

Solar designers and electrical engineers reference “690” as shorthand for the entire body of electrical code that applies to a solar project. “Is this 690 compliant?” is the universal question on every plan review.

Permitting definition

AHJs use NEC 690 as the checklist for plan review. SolarApp+ automated permitting systems are built around NEC 690 compliance rules. Permit rejections almost always cite a specific 690.x subsection.

NEC 690 Explained Simply

For installers: NEC 690 tells you what wires you can use, how big they need to be, where disconnects go, what labels to apply, and how rapid shutdown must work. Memorize the 690.7, 690.8, 690.12, 690.13, and 690.56 numbers and you’ve covered 80% of field requirements.

For homeowners: This is the electrical safety code that ensures your solar system is wired the same as every other professionally installed PV system in America. Firefighters, electricians, and inspectors all share the same rulebook.

For junior designers: Open the code book to 690 and read every paragraph at least once. Make a habit of citing the exact subsection in every design note. Plan reviewers will too.

For new engineers: NEC 690 is one of seven articles covering distributed energy (690, 691 utility-scale, 692 fuel cell, 694 wind, 705 interconnection, 706 ESS, 710 stand-alone, 712 DC microgrids). Understand the inter-article relationships.

Analogy: NEC 690 is the building code for solar PV — every wire, breaker, disconnect, and label is governed by it. Designers who don’t internalize 690 produce systems that fail inspection or, worse, fail dangerously.

Why NEC 690 Matters

Safety. First-responder safety (rapid shutdown), fire prevention (arc fault), shock prevention (grounding + disconnects), and ongoing maintenance safety all derive from NEC 690.

Code compliance. Plan-review checklists everywhere in the US are organized around 690 subsections. Non-compliance = no permit.

Engineering decisions. Conductor type, OCPD rating, EGC size, inverter selection, rapid-shutdown device choice — every component on the SLD is constrained by 690 requirements.

Project cost impact. Code-compliant equipment (PV Wire, MLPE for rapid shutdown, UL 1741-SB inverters) costs more than non-compliant alternatives. Designers who minimize compliance cost without violating code provide measurable value.

Permitting impact. A 690-compliant SLD passes review in days. A 690-incompliant SLD bounces 3+ times, delaying construction.

Key Subsections — What Each Covers

NEC 690.4 — General Installation Requirements

Source circuit installation rules; equipment listing requirements; module-level voltage and current limits.

NEC 690.7 — Maximum Voltage

• (A) Maximum system voltage (Voc at coldest expected temperature × series modules).
• (C) 600 V limit for one-/two-family dwellings unless specific exceptions met.
• Use ASHRAE-extreme low ambient or local-historic-low for temperature correction.

NEC 690.8 — Circuit Sizing & Current

• (A) Calculation of maximum circuit current: 1.25 × Isc.
• (B) Conductor ampacity sizing including 1.25 continuous-duty factor.
• (B)(2) OCPD sizing.

NEC 690.9 — Overcurrent Protection

• Required only where the source could be overcurrented.
• Source-circuit OCPDs sized per 690.9(B).
• Inverter output OCPD per Article 240 plus 690.9.

NEC 690.11 — Arc-Fault Circuit Protection

DC circuits operating ≥80 V require listed AFCIs. Most modern inverters include integrated DC AFCI.

NEC 690.12 — Rapid Shutdown of PV Systems on Buildings

• (B)(1) Outside array boundary: ≤80 V within 30 seconds.
• (B)(2) Inside array boundary: ≤30 V within 30 seconds OR ≤80 V if PV hazard controlled equipment listed to UL 3741.
• Initiator: located outside the building per AHJ requirements.
• Equipment options: MLPE (microinverters or DC optimizers), UL 3741 PV Hazard Control Systems, or central rapid shutdown devices.

NEC 690.13 — DC Disconnect

• (A) Means of disconnect from all current-carrying conductors.
• (B) Marking: “PHOTOVOLTAIC SYSTEM DC DISCONNECT” + voltage + current.
• (C) Rating: ≥ Voc and ≥ 1.25 × Isc.
• (D) Readily accessible.

NEC 690.14 — Grounding & Bonding

Equipment grounding requirements; system grounding (typically functionally grounded inverters today).

NEC 690.31 — Conductor Methods & Materials

• Permitted conductor types: PV Wire, USE-2 (DC source/output), THHN, XHHW-2 (interior AC).
• 690.31(D) labeling and color coding.
• Module interconnect cables (single-conductor exposed wire) per 690.31(C).

NEC 690.41 — System Grounding

Requirements for functionally grounded PV systems (most modern transformerless inverters).

NEC 690.43 — Equipment Grounding & Bonding

Module-to-module bonding, racking bonding, EGC to all metal components.

NEC 690.45 — Equipment Grounding Conductor (EGC)

Sized per Table 250.122 or NEC 690.45(B) larger requirement.

NEC 690.46 — Array Equipotential Bonding

Required for arrays meeting specific criteria.

NEC 690.56 — Identification of Power Sources

• (B) “PHOTOVOLTAIC SYSTEM” plaque on the service entrance.
• (C) Rapid shutdown placard with location of initiator.

NEC 690.71 — Energy Storage Systems

Cross-references NEC 706 for ESS integration.

NEC 690.72 — Self-regulated PV Charge Control

Rules for off-grid charge controllers.

Engineering Deep Dive — Worked Calculations

Maximum system voltage (690.7)

Module Voc = 41.8 V, β_Voc = −0.27 %/°C, site cold ambient = −10 °C, 22 modules in series.

Voc_temp = 41.8 × [1 + (−0.0027)(−10 − 25)]
         = 41.8 × 1.0945
         = 45.75 V/module
Vmax_string = 45.75 × 22 = 1,006.5 V → violates 1,000 V limit
Solution: reduce to 21 modules → 960.8 V

Conductor ampacity (690.8)

Module Isc = 13.5 A.

• Max circuit current per 690.8(A) = 1.25 × 13.5 = 16.875 A
• Continuous-duty adjustment per 690.8(B) = 1.25 × 16.875 = 21.09 A
• Minimum ampacity needed: 21.09 A → 12 AWG PV Wire (rated 30 A at 90 °C, derated to 24 A at 50 °C ambient).

OCPD sizing (690.9)

For the 13.5 A Isc above, the source-circuit fuse must be ≥ 1.25 × 13.5 = 16.875 A → standard 20 A fuse.

NEC 2023 Notable Changes

• Clarified rapid shutdown is required on all rooftop systems including ground-mounted arrays attached to buildings.
• Expanded UL 3741 PV Hazard Control System path for compliance.
• Refined arc-fault requirements for higher voltages.
• Aligned ESS requirements with updated NEC 706.
• New section addressing PV bidirectional inverter operation (Article 705 alignment).

Design Considerations

• Voltage margin. Design Voc at 90% of NEC 690.7 limit for thermal and measurement margin.
• Conductor temperature. Use 90 °C conductor type (PV Wire, XHHW-2) for ampacity headroom.
• EGC sizing. Apply NEC 250.122 unless 690.45(B) demands larger.
• Equipment listing. All combiner boxes, disconnects, inverters must be UL listed.
• Labels. Maintain a label schedule sheet referencing every 690.x label.
• Inspection. Document calculations directly on the SLD for AHJ verification.

Permitting Implications

NEC 690 is the master checklist. Common rejection reasons:

1. String Voc > 690.7 limit.
2. Wire ampacity < 690.8(B) requirement.
3. Missing rapid shutdown initiator location.
4. EGC undersized.
5. Conductor type not listed per 690.31 (e.g., using THHN outdoors).
6. DC disconnect not “readily accessible.”
7. Missing or incorrect 690.56 labels.

Submit calculations and label schedules with every SLD. PE stamp validates 690 compliance.

Utility Interconnection Impact

NEC 690 governs the PV side; NEC 705 governs interconnection. Together they define everything from the array to the utility connection. Utility interconnection studies confirm 705 compliance and rely on a 690-compliant array drawing.

UL 1741-SB inverters (required by many state grid codes) implement IEEE 1547-2018 grid-support functions that the NEC 690 framework anticipates.

India Regulatory Context

India does not enforce NEC 690 directly. Indian solar code references:

• IS 14286 — Crystalline PV module standard.
• IS 16170 / IS 16221 — PV inverter performance and safety.
• IS 3043 — Earthing code.
• CEA Connectivity Regulations — Grid interconnection.
• MNRE Technical Specifications — Bankable plant requirements.

International EPCs operating in both markets typically design to NEC 690 as a baseline and overlay India-specific requirements where stricter.

Software Applications

Most string-sizing tools (PVsyst, Helioscope, Aurora, SMA Sunny Design, Sungrow Solution Designer) include built-in NEC 690.7 checks. Conductor sizing tools (e.g., Bluebeam plugins, Calcpad, NREL Wire Sizer) help verify 690.8.

Real-World Examples

Residential — 690 compliance audit

A 9.5 kW San Diego system. SLD shows 22 modules × 1 string. Voc(STC) = 41.4 V. ASHRAE 99.6% min = 5 °C.

• Voc(5°C) = 41.4 × 1.054 = 43.6 V. String Voc = 22 × 43.6 = 959 V. Compliant with 690.7(A) 1000 V.
• Isc = 13.5 A; OCPD = 20 A; conductor 10 AWG PV Wire ampacity 40 A → 24 A after derating. Compliant.
• Rapid shutdown via SolarEdge optimizers — UL listed, integrated initiator on the inverter exterior. Compliant with 690.12.

Commercial — common 690 violation

1 MW Boston rooftop. Designer used average annual minimum temperature instead of ASHRAE extreme low. Voc check passed at average min but exceeded 1,000 V at the actual record-low −22 °C. Permit rejected; redesign required.

Common Mistakes

1. Using STC Voc without temperature correction.
2. Sizing conductors to Imp instead of 1.25 × Isc.
3. Forgetting the second 1.25 continuous-duty multiplier in 690.8(B).
4. Routing PV Wire through interior conduit (use THWN-2 inside the building).
5. Missing the rapid-shutdown placard.
6. Specifying a non-listed inverter.
7. Mixing NEC editions in the design notes (always cite the AHJ’s adopted edition).
8. Treating ground-mount as 690-exempt — NEC 690 still applies; rapid shutdown is what differs.

Best Practices

• Always cite the NEC edition adopted by the AHJ (varies by state — California is on NEC 2023, Texas on NEC 2020, etc.).
• Provide voltage and conductor calculation worksheets on every SLD.
• Use AHJ-published label schedules where available.
• Validate inverter and module models against AHJ approved-equipment lists.
• Cross-reference every design note to a specific 690.x subsection.

Standards & Certifications

• NEC / NFPA 70 — National Electrical Code; Article 690 is the PV section.
• NFPA 1 — Fire Code; references rapid-shutdown placards.
• UL 1703 / UL 61730 — Module safety listing.
• UL 1741 / UL 1741-SB — Inverter listing.
• UL 3741 — PV Hazard Control System listing (alternate 690.12 compliance path).
• UL 9540 — ESS listing.
• IEEE 1547 — DER interconnection.
• IBC / IRC — Cross-referenced for structural fire setbacks.

Key Takeaways

• NEC Article 690 governs every solar PV electrical design decision in the United States.
• Core sections: 690.7 (voltage), 690.8 (current), 690.9 (OCPD), 690.11 (AFCI), 690.12 (rapid shutdown), 690.13 (disconnect), 690.31 (conductors), 690.41–46 (grounding), 690.56 (labels).
• NEC editions adopted by each state vary — always cite the AHJ’s adopted edition.
• Compliance is verified through the SLD plus accompanying calculations and label schedules.
• NEC 690 works alongside NEC 705 (interconnection) and NEC 706 (energy storage).