Every solar PV installation in the United States must comply with NEC Article 690 — the section of the National Electrical Code dedicated to photovoltaic systems. Whether you’re installing a 4 kW residential system in Texas or a 500 kW commercial project in New Jersey, the same core requirements apply: voltage limits, conductor sizing, rapid shutdown, ground fault protection, and disconnecting means.
This guide covers the sections that matter most to solar installers: what they require, how to calculate compliance, and what AHJs look for when reviewing permit packages.
Which NEC Edition Applies?
The applicable NEC edition is whichever version your state or local jurisdiction has adopted. As of 2026, most jurisdictions are on NEC 2020 or NEC 2017. California is on NEC 2020 (with California Electrical Code amendments). Check with your AHJ before starting design. The requirements described here align with NEC 2020 unless otherwise noted.
What Is NEC Article 690?
NEC Article 690 is the dedicated PV systems section of NFPA 70, the National Electrical Code. First added in 1984, it has been revised significantly with each NEC cycle as system voltage levels increased, string inverter designs changed, and module-level power electronics became standard.
Article 690 covers:
- System voltage limits (690.7)
- Circuit current and conductor sizing (690.8)
- Wiring methods and routing (690.31)
- Rapid shutdown requirements (690.12)
- Overcurrent protection (690.9)
- Ground fault detection and interruption (690.5)
- Disconnecting means (690.13–690.15)
- AC module and inverter requirements (690.6, 690.60)
- Energy storage systems (690.71–690.74 in NEC 2020; Article 706 in NEC 2023)
690.7 — Maximum Voltage
690.7 is the section that limits how many modules you can put in series. The maximum PV system voltage determines string length, and exceeding it is one of the most common permit rejection triggers.
Residential vs. Commercial Limits
| System Type | Maximum Voltage |
|---|---|
| One- and two-family dwellings | 600V DC |
| All other occupancies (commercial, industrial) | 1000V DC |
| Systems using listed 1500V equipment | 1500V DC |
For most residential string inverter designs, the 600V DC limit is the binding constraint. This is why most residential systems use 10–14 modules per string depending on module Voc.
Temperature-Corrected Voltage Calculation
690.7 requires calculating system voltage at the lowest expected ambient temperature at the installation site. Module Voc increases as temperature drops, so a cold morning in Minneapolis produces higher string voltages than a hot afternoon in Phoenix.
The calculation:
Vmax = Voc(STC) × modules_in_series × temperature_correction_factorTemperature correction factors are found in Table 690.7(A) of the NEC or in the module manufacturer’s temperature coefficient data:
| Lowest Temperature (°C) | Correction Factor |
|---|---|
| 0 to −4 | 1.10 |
| −5 to −9 | 1.12 |
| −10 to −14 | 1.14 |
| −15 to −19 | 1.16 |
| −20 to −24 | 1.18 |
| −25 to −29 | 1.20 |
| −30 to −34 | 1.21 |
Example calculation:
- Module Voc (STC): 45.3V
- Modules in series: 13
- Installation city: Denver, CO (record low −25°C)
- Temperature correction factor at −25°C: 1.20
Vmax = 45.3 × 13 × 1.20 = 706.7VThis exceeds the 600V residential limit. Reduce to 12 modules:
45.3 × 12 × 1.20 = 651.3VStill over. Try 11 modules:
45.3 × 11 × 1.20 = 597.96V ✓ (under 600V)Use the Module Datasheet Coefficient, Not the Table
NEC Table 690.7(A) gives conservative correction factors. If you use the module manufacturer’s published temperature coefficient of Voc (typically expressed as %/°C), you can calculate a more precise — and often less conservative — correction. Both methods are accepted by most AHJs, but confirm with yours before using the datasheet method.
690.8 — Circuit Current and Conductor Sizing
690.8 sets the minimum conductor ampacity for PV source circuits and PV output circuits. The key multiplier is 1.25× the module Isc.
The 690.8 Calculation
For PV source circuit conductors (from modules to combiner or inverter):
Minimum ampacity = Isc × 1.25For systems with multiple source circuits combined:
Minimum ampacity = (sum of all Isc values) × 1.25Example:
- Module Isc: 10.2A
- 2 strings combined at a combiner box
Minimum ampacity = (10.2 + 10.2) × 1.25 = 25.5ASelect conductors rated for at least 25.5A after all derating factors (temperature, conduit fill).
Additional Derating Factors
690.8 requires applying all applicable correction and adjustment factors from NEC Article 310:
| Factor | When It Applies |
|---|---|
| Temperature derating | Conductors in rooftop conduit exposed to sun; add 17°C to ambient per most interpretations |
| Conduit fill adjustment | More than 3 current-carrying conductors in a conduit |
| Conductor length | Not an NEC factor, but relevant for voltage drop calculations |
Rooftop Conduit Temperature Is a Common Failure Point
Conductors in conduit strapped directly to a roof surface in direct sun regularly exceed 75°C ambient — well above the 30°C NEC standard assumption. Most solar installers add a 17°C adder (total 47°C) or use the ASHRAE 2% design temperature plus 40°C. Undersized conductors in hot rooftop conduit are a common reason for failed inspections.
690.12 — Rapid Shutdown
Rapid shutdown is the most impactful change in recent NEC cycles for residential installers. It exists to protect firefighters from energized conductors when fighting a rooftop fire.
The Requirement
For building-mounted and building-integrated PV systems (NEC 2017 and later):
Conductors inside the array boundary must be reduced to 30V or less within 30 seconds of initiating rapid shutdown.
The “array boundary” is defined as 1 foot from the array in all directions.
How to Meet 690.12
Three common approaches:
Module-Level Power Electronics (MLPEs)
Microinverters and DC optimizers with rapid shutdown capability automatically de-energize modules when the system shuts down. Most major MLPE manufacturers (Enphase, SolarEdge, APsystems) produce systems that meet 690.12 as a listed product. This is the most common residential approach.
Listed Rapid Shutdown System (MRSS)
For string inverter designs that don’t include MLPEs, a Module-level Rapid Shutdown System (MRSS) can be added. These devices clamp module output voltage to safe levels when shutdown is initiated. Products from Tigo, SolarBOS, and others serve this use case.
Conduit-in-Conduit (Legacy Approach)
Under NEC 2014, rapid shutdown only required reducing conductors outside the array boundary to 30V within 10 seconds. If your AHJ is on NEC 2014 (rare in 2026), string inverter systems with conductors in conduit may qualify. Verify with your AHJ.
Ground-Mount Exemption
Rapid shutdown does not apply to ground-mounted systems that are 5 feet or more from any building. If a ground-mount array is within 5 feet of a structure, consult your AHJ — some require rapid shutdown, others exempt it.
690.31 — Wiring Methods
690.31 specifies which wiring methods are permitted for PV systems. Key rules:
| Location | Permitted Wiring Methods |
|---|---|
| Module-to-module (within array) | Listed PV wire (sunlight resistant, wet location rated) |
| Exposed roof runs | Listed PV wire or USE-2 in conduit |
| Inside building | Conductors in conduit (EMT, rigid, or PVC per 690.31(G)) |
| Rooftop conduit | EMT, rigid conduit; PVC conduit allowed if approved by AHJ |
Key rule from 690.31(G): Wiring systems installed on or in a building interior must use conduit from the first readily accessible enclosure to the building exterior. This prevents exposed PV wire (which is not permitted inside buildings) from entering through roof penetrations without protection.
Roof Penetrations
All roof penetrations must be:
- Sealed watertight (typically with a listed roof mount flashing kit)
- Protected against chafing where conductors pass through the roof decking
- Inspected by the AHJ as part of the rough-in inspection
690.9 — Overcurrent Protection
Every PV source circuit and PV output circuit must have overcurrent protection sized per 690.9.
| Circuit | OCP Sizing Rule |
|---|---|
| PV source circuit | Not less than 1.25 × Isc; not greater than the lowest-rated component |
| PV output circuit | Sized per 690.8 current × 1.25; coordinated with inverter input |
| DC combiner | Coordinated with string fuses and combiner box ratings |
DC-rated fuses and breakers only. Standard AC breakers are not rated for DC current interruption and must never be used in DC PV circuits.
AHJ Submission Checklist
Most AHJs require the following for a residential solar permit package:
Site Plan
Scaled drawing showing the property, roof outline, array location, module layout, azimuth, and setbacks. Include north arrow and scale bar. Some AHJs require a satellite image overlay.
One-Line Electrical Diagram
Show all major components: modules, inverter(s), disconnect switches, meters, load panel, utility connection point. Label every component with make, model, and rating. Include wire sizes, conduit types, and breaker ratings for all circuits.
Voltage and Current Calculations
Show the 690.7 Vmax calculation with temperature correction. Show the 690.8 conductor sizing with all derating factors applied. Include the rapid shutdown system product specification.
Equipment Cut Sheets
Include UL listing pages for: solar modules, inverter(s), rapid shutdown equipment, AC and DC disconnects, and any combiner boxes. Some AHJs also require cut sheets for roof mounts and conduit fittings.
Structural Assessment
Most AHJs require a structural letter or calculation showing the roof can support the additional dead load of the array (typically 3–5 lbs/sq ft). Some jurisdictions accept a simple prescriptive table for certain framing configurations; others require a PE-stamped letter.
Use SurgePV to Generate Code-Ready One-Lines
SurgePV’s solar design tool automatically generates NEC-compliant electrical diagrams with correct voltage and current calculations pre-filled. The one-line outputs in DXF and PDF formats accepted by most AHJs. Book a demo to see the permit package workflow.
Common Inspection Failures
These are the most frequent NEC 690 violations that trigger failed inspections or correction notices:
| Violation | Section | How to Avoid |
|---|---|---|
| String voltage exceeds 600V residential limit | 690.7 | Always calculate with lowest record temperature for the site location |
| Conductors undersized for rooftop conduit temperatures | 690.8 | Add 17°C (or use ASHRAE method) when sizing conductors in exposed roof conduit |
| No rapid shutdown on roof-mounted array | 690.12 | Use listed MLPEs or MRSS for all roof-mounted systems |
| PV wire inside building without conduit | 690.31(G) | Use conduit from first accessible enclosure through all interior runs |
| AC breaker used in DC circuit | 690.9 | Use only DC-rated fuses or breakers listed for PV in all DC circuits |
| Missing or unmarked disconnect | 690.13 | Label all disconnects with “Solar PV System Disconnecting Means” per 690.13(E) |
| No ground fault protection on ungrounded systems | 690.5 | Verify inverter includes listed GFDI function; document in permit package |
NEC 690 vs. NEC 2023 Changes
NEC 2023 introduced significant changes to Article 690. If your jurisdiction has adopted NEC 2023:
- Article 706 now covers energy storage systems (moved from 690.71–690.74)
- 690.12 rapid shutdown language was clarified for array boundary definitions
- 1500V DC systems have clearer provisions for commercial-scale installations
- Wiring method requirements in 690.31 were reorganized for clarity
Check your jurisdiction’s adoption status before assuming any specific edition applies.
Run NEC 690 Voltage and Current Checks in SurgePV
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Frequently Asked Questions
What is the difference between NEC 690 and NEC 705?
NEC Article 705 covers “Interconnected Electric Power Production Sources” — it’s the article that governs how your PV system interconnects with the utility grid, including the load side tap rule (705.12) and backfeed breaker sizing. Article 690 covers the PV system itself. Both apply to a grid-tied solar installation.
Can I use a 1000V inverter on a residential system?
No. For one- and two-family dwellings, NEC 690.7 limits the PV system voltage to 600V DC regardless of the inverter’s rated input voltage. If your inverter is rated to 1000V input but the system is on a residence, you are still limited to 600V.
How do I know which temperature correction factor to use?
Use the lowest expected ambient temperature for the installation location. NFPA 70 allows using the temperature from the ASHRAE Handbook of Fundamentals (2% annual design temperature). Alternatively, use the temperature data from the module manufacturer’s instructions if provided. The NEC table (690.7(A)) provides correction factors for given temperature ranges.
Is a rapid shutdown initiator required inside the building?
Yes. NEC 690.12 requires a rapid shutdown initiator at an accessible location outside the PV array boundary — typically at the service panel or at the utility disconnect location. The initiator is typically a labeled switch that triggers the MRSS or MLPE shutdown signal.
What if my jurisdiction hasn’t adopted the 2017 or 2020 NEC?
Some jurisdictions are still on NEC 2014 or earlier. The rapid shutdown requirements in NEC 2014 are less stringent (only require reducing conductors outside the array boundary, not within). If your AHJ is on NEC 2014, confirm the applicable requirements before designing the rapid shutdown system.
