Solar One Line Diagram (SLD) Requirements: Installer Guide
A solar one-line diagram (SLD) is a simplified electrical schematic showing how a PV system connects from the solar array through the inverter, disconnects, overcurrent protection, service equipment, and utility interconnection point. Solar installers submit SLDs as part of permit and interconnection packages so reviewers can verify electrical code compliance.
A missing callout, incorrect conductor calculation, mismatched breaker rating, or equipment model that does not match the cut sheet can trigger corrections and delay approval. This guide explains what belongs on a residential solar SLD, how key NEC requirements translate into diagram callouts, why one-line diagrams get rejected, and what changes when battery storage joins the scope.
GreenLancer prepares permit-ready solar permit design plan sets with complete one-line diagrams built to your AHJ's adopted code cycle. Sign up for free to get started.
What Is a Solar One-Line Diagram?
A solar one-line diagram is the electrical schematic of a PV system shown in simplified single-line notation rather than full wiring detail. SLD stands for single-line diagram, which is also commonly called a one-line diagram. Installers and plan reviewers generally use the terms interchangeably.
The drawing shows major PV equipment and the electrical path between components, typically including modules, strings, inverters, conductors, overcurrent protection, disconnects, service equipment, and the point of interconnection. It also gives reviewers the ratings and calculations needed to evaluate the design against the National Electrical Code and local requirements.
Is a Solar SLD the Same as a Wiring Diagram?
No. A solar SLD shows system topology, equipment ratings, protection, and major electrical connections in simplified notation. A wiring diagram usually provides more detailed conductor-to-terminal information for installation, commissioning, or troubleshooting.
One-Line Diagram vs. Three-Line Diagram
A one-line diagram represents a multi-conductor electrical system using simplified single lines. A three-line diagram shows individual phase conductors and provides more detailed wiring information.
Most residential PV permit packages use one-line diagrams. Three-line diagrams are more common on complex commercial, three-phase, or engineered projects, although the required drawing format ultimately depends on the AHJ, utility, and project scope.
Solar One-Line Diagram Example: What Reviewers Follow
A typical grid-tied residential solar SLD reads from the PV array toward the utility service. A reviewer should be able to follow the complete electrical path without having to infer how major components connect.
A typical sequence is:
PV modules and string configuration
DC conductors or module-level power electronics
Inverter or microinverter system
Required disconnecting means and overcurrent protection
AC output circuit
Main service panel or other distribution equipment
Point of interconnection with the premises wiring system
Utility meter and service connection, where shown
Each applicable circuit segment should include the conductor size and type, equipment ratings, OCPD information, and other callouts needed to verify the design.
Graphic opportunity: Add an annotated GreenLancer residential SLD with numbered callouts for the array, inverter, conductors, disconnects, service panel, backfed breaker, and point of interconnection.
What Must Be on a Residential Solar SLD?
Exact requirements vary by jurisdiction, but the following checklist covers information commonly reviewed on residential PV one-line diagrams. Use it as a pre-submittal check before the permit package leaves your hands.
DC Side Checklist
Module manufacturer, model, and quantity
String configuration, including the number of strings and modules per string
Maximum system DC voltage calculated using the applicable NEC 690.7 temperature correction
Module short-circuit current (Isc) and calculated maximum PV circuit current
PV source and output circuit conductor size, type, insulation rating, and wiring method
DC OCPD rating and listing, where required by NEC 690.9
DC disconnect location and rating, where applicable
Rapid shutdown initiator and system configuration
Equipment grounding conductor sizing and grounding or bonding details required for the system
Inverter Checklist
Inverter information should match the equipment documentation exactly. A model-number mismatch between the SLD and equipment cut sheet can lead to plan-review corrections.
Inverter manufacturer and model
Applicable UL 1741 listing information
Maximum DC input voltage and applicable DC current ratings
Nominal AC output voltage and frequency
Maximum continuous AC output current
Applicable utility-interactive or grid-support listing information
AC Side Checklist
AC output conductor size, type, and wiring method
AC OCPD sized for the inverter output circuit under the applicable NEC requirements
AC disconnect location and rating, where required
Interconnection method and applicable NEC section
Backfed breaker size where a breaker interconnection is used
Busbar rating and service-panel main OCPD rating shown separately
Available load-side interconnection capacity where NEC 705.12 applies
Supply-side connection details where NEC 705.11 applies
General Notes and Title Block
Applicable NEC edition and relevant local amendments
Project address
AHJ or jurisdiction information
Installer or design firm information
Drawing scale or “not to scale” notation
Revision date and version number
How to Create a Solar One-Line Diagram
Solar SLDs can be created manually in drafting software, generated through solar design software, or prepared as part of a professional permit design package. Regardless of the tool, the design process should follow the electrical path systematically.
Document the PV array. Identify modules, string configuration, module ratings, and calculated maximum system voltage.
Add DC-side equipment. Show combiner equipment, DC disconnects, conductors, OCPDs where required, and module-level electronics.
Add the inverter. Confirm the exact equipment model and relevant input and output ratings.
Size the AC output circuit. Document conductors, OCPD, disconnecting means, and wiring method.
Show the service equipment. Identify the panel busbar rating, main OCPD, and other equipment relevant to the interconnection.
Document the point of interconnection. Show whether the system uses a load-side, supply-side, or other approved interconnection method.
Add grounding, bonding, and rapid shutdown information. Include the applicable equipment and notes required for the design.
Cross-check the SLD against the equipment sheets. Model numbers, ratings, breaker sizes, conductor sizes, and equipment listings should agree throughout the permit package.
Verify the adopted code cycle. NEC references and plan notes should match the edition and amendments enforced by the AHJ.
NEC Requirements That Shape a Solar SLD
AHJs and utilities determine what documentation they require for a solar permit or interconnection application, but much of the electrical information shown on an SLD comes from NFPA 70, the National Electrical Code.
NEC Article 690 covers photovoltaic systems, while Article 705 addresses interconnected power production sources. Other NEC articles can also apply depending on the equipment, wiring method, energy storage system, and project configuration. The IAEI's overview of 2023 NEC changes for PV systems is a useful reference when updating solar design templates for newer code cycles.
NEC 690.7: Maximum DC Voltage
Maximum PV system DC voltage must be calculated using the applicable temperature correction rather than simply copying the module open-circuit voltage from the data sheet. The calculated maximum voltage affects equipment ratings, conductor insulation, system configuration, and other design decisions.
PV DC circuits on or in one- and two-family dwellings are limited to 600V. Higher-voltage PV systems may be permitted in other applications under NEC 690.7, subject to circuit location, system configuration, equipment ratings, and other applicable requirements.
NEC 690.8: Circuit Current and Conductor Ampacity
For the standard module Isc calculation method, maximum PV circuit current is generally based on 125% of module short-circuit current, multiplied by the number of parallel source circuits where applicable.
That is not the end of conductor sizing. Conductors must also satisfy the applicable ampacity checks under NEC 690.8(B), including temperature correction and adjustment factors for the number of current-carrying conductors where they apply.
Raceway fill is a separate calculation and should not be confused with conductor ampacity adjustment. Our NEC 690.8 solar conductor sizing guide explains the conductor ampacity checks in more detail. The IAEI's guide to photovoltaic system electrical calculations also provides worked examples of PV circuit calculations.
NEC 690.9: Overcurrent Protection
Where overcurrent protection is required, the SLD should identify the OCPD rating, location, and applicable equipment information. DC overcurrent devices used in PV circuits must be properly rated and listed for the application.
Separate overcurrent protection is not required on every PV source circuit. Some system configurations satisfy NEC 690.9 without individual source-circuit OCPDs because the available current cannot exceed the applicable conductor or equipment limits. The SLD and supporting calculations should reflect the actual design rather than assuming every DC circuit requires a fuse or breaker.
NEC 690.12: Rapid Shutdown
For systems subject to NEC 690.12, the SLD should identify the rapid shutdown initiator and provide enough information to show how the system meets the applicable controlled-conductor and voltage-limit requirements.
Depending on the equipment and system design, compliance may rely on module-level power electronics, inverter-integrated equipment, or a listed PV Hazard Control System.
Our solar rapid shutdown requirements guide covers NEC 690.12 requirements, equipment configurations, and marking considerations in more detail.
NEC 690.13: PV System Disconnecting Means
The PV system disconnecting means should be shown with its rating, location, and applicable equipment information.
Where disconnect equipment is accessible to unqualified persons and operates above the applicable voltage threshold, NEC 690.13 includes requirements that restrict access to energized parts, such as an enclosure that requires a tool or lock to open.
The disconnect configuration shown on the SLD should also agree with the site plan, equipment layout, and other sheets in the permit package.
NEC 705.11 and 705.12: Utility Interconnection
The SLD should clearly identify how the PV system connects to the premises wiring system.
NEC 705.12 applies to load-side source connections and includes requirements for busbars, conductors, panelboards, and other distribution equipment.
NEC 705.11 addresses supply-side source connections. Supply-side and load-side interconnections are documented differently, so simply labeling a connection “solar tie-in” is usually not enough for a permit-ready drawing.
Why Solar One-Line Diagrams Get Rejected at Plan Check
Many SLD corrections involve specific documentation, coordination, or calculation problems rather than a complete system redesign. Catching these issues before submittal can reduce correction cycles.
DC-Side Corrections
Maximum system voltage shown as module Voc without the required temperature correction
Temperature correction or ampacity adjustment factors missing from conductor calculations
DC OCPD shown where equipment ratings or system configuration do not support the selected device
Required OCPD omitted from a circuit
Conductor type or wiring method does not match the installation
String quantity or module count differs between the SLD, layout, and equipment schedule
AC-Side Corrections
Load-side interconnection calculations are a common source of corrections. Our 120% rule for solar guide explains one of the most frequently used NEC 705.12 busbar methods.
AC output OCPD does not match the inverter output circuit requirements
Backfed breaker size conflicts with the available busbar interconnection capacity
Main breaker rating and busbar rating are treated as the same value when they are different
Interconnection method is shown without enough information to verify the applicable NEC pathway
The SLD interconnection method does not match the actual service-panel configuration
Rapid Shutdown Corrections
Rapid shutdown initiator is not identified
System configuration does not clearly demonstrate compliance with NEC 690.12
Equipment shown on the drawing does not match the listed rapid shutdown solution
Required rapid shutdown markings do not match the adopted NEC edition
Grounding and Equipment Grounding Conductor Corrections
PV grounding and bonding requirements vary with circuit configuration and equipment. NEC 690.45 addresses equipment grounding conductor requirements for PV source and output circuits, while Article 250 contains the broader grounding and bonding rules used throughout the system.
Missing EGC sizing, inconsistent grounding details, or grounding information that conflicts between sheets can lead to corrections. NEC 690.47 also addresses grounding electrode system requirements applicable to PV systems.
General Documentation Corrections
Equipment model numbers on the SLD do not match the submitted cut sheets
NEC edition referenced in the notes does not match the code adopted by the AHJ
Breaker ratings differ between the SLD and panel schedule
Equipment shown on the roof or site plan is missing from the SLD
Required source identification, directory, or marking information is missing or outdated
The U.S. Department of Energy's rooftop solar permitting and inspection resource explains how permitting and inspection processes contribute to solar soft costs and why streamlined review matters.
A resubmittal costs installers time on every project. GreenLancer's permit design team checks SLDs against the project configuration, equipment documentation, and applicable AHJ requirements before submittal.
Solar SLD Software vs. Professional Permit Design
Solar design platforms can automate parts of the one-line diagram process. The exact electrical-design capabilities vary by software, project type, equipment, geographic market, and subscription level.
Aurora Solar offers U.S. residential plan-set services that can produce electrical diagrams as part of a permit package, including single-line and three-line options. Enphase Solargraf and OpenSolar also provide electrical design or SLD capabilities. Installers may also build diagrams manually using drafting tools such as AutoCAD or Visio.
Some utilities publish their own simplified SLD templates for specific interconnection configurations. Southern California Edison, for example, provides a simplified SLD template for certain Rule 21 PV configurations.
Utility templates can be useful for straightforward projects, but installers still need to verify that the template applies to the current tariff, interconnection program, system size, and equipment configuration. More complex projects and systems with battery storage may require a project-specific electrical drawing.
Regardless of the platform or template, the completed SLD must match the actual equipment, system configuration, adopted NEC edition, utility requirements, and AHJ expectations.
When a Professional Permit Design Service Makes Sense
Automated tools can work well for repeatable residential systems in familiar jurisdictions. Professional permit design becomes especially useful when projects involve:
Battery energy storage
Service equipment modifications
Supply-side connections
Complex load-side interconnections
Commercial or three-phase systems
Unfamiliar AHJs
PE-stamped electrical drawings
Large project volumes or tight turnaround requirements
Preparation and engineering requirements vary by jurisdiction and project type. A designer or contractor can prepare an SLD in many cases, while other projects require review and sealing by a licensed professional engineer.
How SLD Requirements Change for Solar Plus Storage
Adding battery storage can significantly change the one-line diagram. The exact configuration depends on whether the ESS is AC-coupled, DC-coupled, or integrated through a hybrid inverter or other listed system architecture.
AC-Coupled Battery SLDs
In an AC-coupled system, the battery inverter connects to the AC electrical system separately from the PV inverter. The SLD should show the ESS as another source where it can export power to the premises wiring system.
Applicable ESS conductors, OCPDs, disconnecting means, equipment ratings, and interconnection details should be shown. Treating an AC-coupled battery inverter only as a load can result in an incomplete interconnection analysis.
DC-Coupled Battery SLDs
In a DC-coupled system, the battery connects on the DC side through a hybrid inverter, charge controller, or other listed equipment. The battery does not necessarily appear as a separate AC source.
The SLD should document the DC-side equipment, battery connection, applicable ratings, disconnecting means, and how the combined PV and ESS system connects to the premises wiring system.
How Storage Affects Load-Side Interconnection Calculations
Where PV and an AC-coupled ESS can both contribute power to the same busbar, the load-side interconnection analysis must account for the applicable contribution from both sources.
An approved energy management system, power control system, or other listed control strategy can affect the maximum current used in the interconnection calculation when permitted by the applicable NEC provisions and equipment listings. The simple 120% rule should not be applied to every solar-plus-storage configuration without evaluating how the ESS operates.
What to Add to a Solar Plus Storage SLD
Battery or ESS manufacturer and model
Applicable UL 9540 listing information
Battery inverter or hybrid inverter manufacturer and model
Applicable UL 1741 listing information
ESS conductors and OCPD where applicable
ESS disconnecting means required by the applicable NEC provisions
Updated point of interconnection showing the PV and ESS configuration
Energy management or power control system information when used as part of the compliance strategy
Backup-load panel, transfer equipment, or microgrid interconnection device where applicable
Battery permitting also involves requirements outside the SLD itself. Fire-code provisions such as NFPA 855 and product safety standards such as UL 9540 can affect equipment location and installation. UL provides additional information on energy storage system testing and certification.
Our solar battery storage permit guide covers ESS permitting and interconnection requirements in more detail.
How Solar SLD Requirements Vary by AHJ
The NEC provides the electrical framework for PV design, but solar permitting remains highly decentralized in the United States. Local AHJs can adopt different NEC editions, amendments, checklists, drawing conventions, and engineering requirements.
NREL's residential rooftop PV permitting guide highlights the significant variation in permitting practices among U.S. jurisdictions. Installers entering a new market should verify both AHJ and utility requirements rather than relying on a standard template developed for another jurisdiction.
Before finalizing an SLD for a new jurisdiction, verify:
Which NEC edition the AHJ currently enforces
Whether local electrical-code amendments affect the project
Whether the AHJ publishes a solar permit checklist or standard SLD format
Whether specific equipment ratings or calculations must appear directly on the one-line diagram
Whether the utility requires a separate SLD for interconnection
Whether the jurisdiction accepts SolarAPP+ for qualifying residential projects
Whether electrical sheets require review or sealing by a licensed professional engineer
The IREC National Solar Licensing Database is another useful starting point for checking state-level solar licensing requirements before entering a new market.
GreenLancer's permit design team produces complete, permit-ready plan sets with SLDs built to your AHJ's adopted code cycle. Whether it's a standard residential job or a solar plus storage submittal, we handle the documentation so you can stay focused on the field.
Complete the form below to get started.
FAQ: Solar One-Line Diagram Requirements
What is a solar one-line diagram?
A solar one-line diagram is a simplified electrical schematic showing how a PV system connects from the modules through the inverter, electrical protection, service equipment, and point of interconnection. It gives permit reviewers and utilities the information needed to evaluate the system's electrical design.
What does SLD stand for in solar?
SLD stands for single-line diagram. It is also commonly called a one-line diagram. Both terms describe the simplified electrical drawing used in solar permit and interconnection packages.
Is a single-line diagram the same as a one-line diagram?
Yes. Single-line diagram and one-line diagram generally refer to the same type of simplified electrical drawing, and SLD is a common abbreviation. In solar permitting, you may also see terms such as solar SLD, PV one-line diagram, solar one-line diagram, electrical one-line diagram, or single-line electrical diagram.
Is a solar SLD the same as a wiring diagram?
No. An SLD shows the major system components, electrical path, ratings, protection, and interconnection in simplified form. A wiring diagram usually provides more detailed information about individual conductor and terminal connections.
What should a solar one-line diagram include?
A residential solar SLD commonly includes the modules and string configuration, inverter, conductors, applicable OCPDs, disconnecting means, grounding information, service equipment, busbar and main-breaker ratings, rapid shutdown information, and point of interconnection. Exact requirements vary by AHJ and utility.
What NEC sections apply to solar one-line diagrams?
NEC Article 690 is the primary PV article and includes requirements for maximum voltage, circuit sizing, overcurrent protection, rapid shutdown, and disconnecting means. NEC Article 705 covers interconnected power sources, including load-side and supply-side connections. Other NEC articles can apply depending on the system configuration.
Why do solar one-line diagrams get rejected at plan check?
Common corrections include missing temperature correction for maximum DC voltage, incomplete conductor ampacity calculations, incorrect OCPD sizing, equipment model numbers that do not match the cut sheets, inconsistent breaker or busbar information, and interconnection details that do not match the actual service equipment.
Does a solar plus storage system need a different SLD?
Yes. An AC-coupled ESS typically appears as another power source with its own conductors, protection, disconnecting means, and equipment ratings. A DC-coupled ESS is represented differently because the battery connects through a hybrid inverter, charge controller, or other DC-side equipment.
Does a solar one-line diagram need a PE stamp?
It depends on the jurisdiction and project scope. Many standard residential rooftop projects do not require a PE seal on the electrical SLD, while some AHJs require engineering review for commercial systems, complex interconnections, service modifications, or other project conditions.
What software do solar installers use to create one-line diagrams?
Solar design platforms such as Aurora Solar, Enphase Solargraf, and OpenSolar provide electrical design or one-line diagram capabilities. Some installers also use general drafting software such as AutoCAD or Visio. Features and supported project types vary by platform.
Who can draw a solar one-line diagram?
Preparation requirements vary by jurisdiction. Designers, contractors, or solar design firms can prepare SLDs for many projects, while some jurisdictions or project types require review and sealing by a licensed professional engineer. GreenLancer prepares one-line diagrams as part of complete solar permit plan sets and can provide PE review when required.
Do all AHJs require the same solar one-line diagram format?
No. Required callouts, drawing formats, code editions, engineering requirements, and submittal procedures vary by jurisdiction. Installers should verify current AHJ and utility requirements before finalizing the design.
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