Solar PV System Installation: NEC Article 690 Complete Guide
Everything electricians need to know about NEC Article 690 requirements for photovoltaic installations. From rapid shutdown to conductor sizing, disconnects to grounding - ensure code-compliant solar installations.
NEC 2023 Updates
NEC 2023 includes significant updates to Article 690, particularly in rapid shutdown requirements, DC arc-fault protection, and energy storage integration. This guide covers current code requirements - always verify with your local AHJ for adopted code edition.
In This Guide
Article 690 Overview
NEC Article 690 - Solar Photovoltaic (PV) Systems covers the installation of solar PV systems including array circuits, inverter circuits, and storage batteries. It applies to all PV systems regardless of whether they are utility-interactive, stand-alone, or hybrid systems.
Article 690 Structure
- Part I (690.1-690.4) - General requirements and definitions
- Part II (690.7-690.9) - Circuit requirements including maximum voltage
- Part III (690.11-690.12) - Disconnecting means and rapid shutdown
- Part IV (690.31-690.35) - Wiring methods
- Part V (690.41-690.47) - Grounding and bonding
- Part VI (690.51-690.56) - Marking and labeling
- Part VII (690.71-690.72) - Connection to other sources
Article 690 works in conjunction with other NEC articles. Where requirements differ, Article 690 takes precedence for PV-specific installations. General wiring requirements from Chapters 1-4 still apply unless modified by Article 690.
PV System Components
PV Module (Solar Panel)
The smallest complete, environmentally protected assembly of photovoltaic cells. Typically 300-450W per module for residential installations. Each module has its own maximum voltage (Voc) and short-circuit current (Isc) ratings.
String
Modules connected in series to achieve the required voltage. String voltage must not exceed the inverter's maximum input voltage or NEC maximum system voltage limits.
Array
All PV modules and other equipment mechanically and electrically integrated to form a DC power-producing unit. Multiple strings may be combined in parallel at a combiner box.
Inverter
Converts DC power from the array to AC power for use by loads or export to the grid. Types include string inverters, microinverters, and power optimizers with central inverter.
Rapid Shutdown Equipment
Equipment that reduces PV system conductors and modules to safe voltage levels within the array boundary and outside the array boundary per NEC 690.12.
Rapid Shutdown Requirements (NEC 690.12)
Rapid shutdown is one of the most critical requirements for rooftop PV systems. It ensures firefighters and first responders can safely operate around solar installations by quickly reducing voltage levels.
NEC 2023 Rapid Shutdown Requirements
PV system circuits installed on or in buildings shall include a rapid shutdown function to reduce shock hazard for emergency responders.
Outside Array Boundary
Controlled conductors outside the array boundary shall be limited to not more than 30 volts within 30 seconds of rapid shutdown initiation.
Inside Array Boundary
Controlled conductors within the array boundary shall be limited to not more than 80 volts within 30 seconds of rapid shutdown initiation.
Array Boundary Definition
The array boundary is defined as 1 foot from the array in all directions. This includes:
- 1 foot from the outermost modules
- 1 foot below the mounting plane of the array
- Raceways and enclosures within this boundary must meet the 80V requirement
Rapid Shutdown Methods
| Method | Technology | Compliance |
|---|---|---|
| Microinverters | AC output at each module, DC contained within module | Inherently compliant |
| DC Optimizers | Module-level electronics reduce voltage when communication lost | Compliant when listed |
| Rapid Shutdown Boxes | External shutdown devices at array with initiation at inverter | Compliant when listed |
| String Inverter Only | No module-level shutdown capability | Does NOT comply |
Initiation Device Requirements
The rapid shutdown initiation device shall be located at a readily accessible location outside the building, or inside at the main service disconnect. It must be clearly marked and function shall be accomplished by a single action.
Conductor Sizing and Ampacity
Maximum System Voltage (690.7)
PV system DC voltage is calculated based on the coldest expected temperature. Use the module's open-circuit voltage (Voc) and apply temperature correction factors.
Voltage Calculation Formula
Max System Voltage = Voc × Number of Modules in String × Temperature Correction Factor
Temperature correction factors from NEC Table 690.7(A) range from 1.02 at 20C to 1.25 at -40C for crystalline silicon modules.
Conductor Ampacity (690.8)
PV source and output circuit conductors must have an ampacity not less than the maximum circuit current multiplied by 1.25 (125%).
Ampacity Calculation
- Maximum Circuit Current = Sum of parallel-connected module short-circuit currents (Isc)
- Minimum Conductor Ampacity = Maximum Circuit Current × 1.25
- Additional derating may be required for conduit fill and ambient temperature
| Circuit Type | Common Wire Size | Notes |
|---|---|---|
| Module to Module (String) | 10 AWG | USE-2 or PV Wire, typically pre-installed |
| String to Combiner | 10 AWG | THWN-2, USE-2, or PV Wire in conduit |
| Combiner to Inverter | 6-2 AWG | Size based on combined string currents |
| Inverter to Panel (AC) | 10-6 AWG | Based on inverter output current |
Important: PV Wire and USE-2 are rated for wet locations and direct sunlight exposure. Standard THHN/THWN should only be used inside conduit and not exposed to direct sunlight.
Overcurrent Protection (NEC 690.9)
PV source circuits and PV output circuits require overcurrent protection when the maximum circuit current exceeds the ampacity of the conductors.
When OCPD is Required
Overcurrent protection is required when the sum of available fault currents from parallel sources exceeds the conductor or module ampacity:
- • More than 2 strings in parallel typically require string fusing
- • Fuse or circuit breaker rating shall not exceed module Isc × 1.56
- • Module backsheet typically lists maximum series fuse value
DC Arc-Fault Circuit Protection (690.11)
PV systems with DC source circuits, DC output circuits, or both operating at 80 volts or greater shall be protected by a listed arc-fault circuit interrupter (AFCI).
- Arc-fault protection can be at inverter or external device
- Must detect and interrupt arcing faults
- Shall disable inverter or disrupt operation of system
- Annunciation required to indicate arc-fault detection
Disconnect Requirements (NEC 690.13-690.15)
PV System Disconnecting Means
A means shall be provided to disconnect all conductors of a PV system from all other conductors in a building or structure.
DC Disconnect
- • Required between array and inverter
- • Shall be listed for DC at system voltage
- • Suitable for current available
- • Accessible and within sight of inverter (or lockable)
AC Disconnect
- • Required at point of connection to premises wiring
- • Typically at main panel or dedicated breaker
- • Shall disconnect ungrounded conductors
- • Can be integral to inverter if listed
Utility-Interactive Disconnects
Per NEC 690.13(B), the inverter output disconnect for utility-interactive systems shall be accessible by the utility and may be required to be lockable by utility requirements.
Grounding and Bonding (NEC 690.41-690.47)
System Grounding
PV systems may be grounded or ungrounded. Most residential grid-tied systems with string inverters use ungrounded (floating) DC arrays with ground-fault detection.
Ground-Fault Protection (690.41(B))
Grounded DC PV arrays shall be provided with ground-fault protection that complies with 690.41(B). Ungrounded arrays shall comply with 690.41(A) and use listed equipment marked for ungrounded PV arrays.
Equipment Grounding (Bonding)
All exposed non-current-carrying metal parts of PV equipment shall be grounded (bonded) per NEC 690.43:
- Module frames
- Mounting structure/racking
- Inverter enclosures
- Combiner boxes
- Junction boxes and conduit
Module Grounding Methods
- • WEEB (Washer Electrical Equipment Bond) - Star washer that pierces anodized coating
- • Grounding lugs - Listed grounding lugs with proper hardware
- • Bonding clips - Listed clips that bond frame to rail
- • Lay-in lugs - UL-listed for grounding/bonding applications
Equipment Grounding Conductor Sizing
EGC size per NEC 690.45 based on the rating of the overcurrent device or maximum circuit current:
| OCPD Rating (A) | Copper EGC | Aluminum EGC |
|---|---|---|
| 15 | 14 AWG | 12 AWG |
| 20 | 12 AWG | 10 AWG |
| 30 | 10 AWG | 8 AWG |
| 60 | 10 AWG | 8 AWG |
| 100 | 8 AWG | 6 AWG |
Labeling Requirements (NEC 690.51-690.56)
Proper labeling is essential for inspector approval and first responder safety. Missing or incorrect labels are common inspection failures.
690.53 - DC PV Power Source
A permanent label at DC disconnect or junction box indicating: Maximum Power Point Current (Imp), Maximum Power Point Voltage (Vmp), Maximum System Voltage, and Short-Circuit Current (Isc).
690.54 - Interactive System Point of Connection
Label at AC disconnect location indicating: Rated AC output current, Nominal operating AC voltage.
690.56(C) - Rapid Shutdown
Rapid shutdown switch must be marked: "PHOTOVOLTAIC SYSTEM RAPID SHUTDOWN SWITCH" in capital letters. Mark shall be reflective red with white letters, minimum 3/8 inch height.
690.31(G) - DC Conductor Routing
Where DC conductors are run inside a building, the conduit or raceway shall be marked every 10 feet with "WARNING: PHOTOVOLTAIC POWER SOURCE" using red background with white letters.
Common Code Violations
1. Non-Compliant Rapid Shutdown
Using string inverters without module-level rapid shutdown equipment. Systems installed after NEC 2017 adoption require rapid shutdown both inside and outside array boundary.
2. Missing or Incorrect Labels
Common issues: missing rapid shutdown label at service, missing DC source label, incorrect voltage/current ratings, labels not durable for outdoor use.
3. Improper Conductor Type
Using THHN exposed to sunlight or weather. USE-2 or PV Wire required for exposed rooftop applications. THWN-2 acceptable in conduit.
4. Inadequate Module Grounding
Using unlisted grounding clips, missing grounding of every module frame, or improper bonding between rails. Each module must be bonded to grounding system.
5. Backfed Breaker Issues
Solar breaker not listed for backfeed, exceeding 120% bus rating without proper calculation, or backfed breaker not at opposite end from main.
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