Answer
A single-line diagram (SLD) is a simple drawing of how a solar system is wired, from the panels to the grid. Permit offices ask for module and inverter data, wire and conduit sizes, protection ratings, disconnects, grounding and rapid shutdown. Each office sets its own list, so check it first.
A permit office reads your single-line diagram (SLD) before it approves the job. A missing wire size or rating can send the whole package back, and every office keeps its own list of what must be on the drawing.
This guide lists what permit offices ask for on an SLD, using their own published checklists. It also covers string inverter, microinverter and battery drawings, and gives a self-check you can run before you submit.
Last updated: November 2026
Short answer
Permit offices want the SLD to show every main part of the system and its ratings. They also want wire sizes, conduit sizes, disconnects, grounding and rapid shutdown. The exact list changes by office and by code edition. Get the local checklist first.
What you will learn:
- What goes on a solar SLD, with the sources that ask for it
- How string inverter and microinverter drawings differ
- What batteries add to the drawing
- How SolarAPP+ and Arizona law affect the diagram rule
- A checklist to run before you submit
Keep the Drawing and the Design Data in Sync
See how string layout, equipment data and electrical workflow support sit together in one project.
Book a DemoChecking cost first? See the SurgePV pricing page · 20 minutes · No credit card required
What Is a Single-Line Diagram in Solar PV?
An SLD is a one-page schematic. A single line stands for each circuit, even when the circuit has several wires. Symbols stand for the equipment. The drawing follows the power from the PV modules, through the inverter, to the point where the system joins the grid.
A three-line diagram is different. It shows each phase wire on its own. Larger systems and some utilities ask for it. The electrical SLD glossary page covers the symbols. For a deeper look at symbols, read the solar single-line diagram guide.
Different people read the same drawing:
- The permit office (the authority having jurisdiction, or AHJ) checks the design against the code it has adopted.
- The fire reviewer looks at rapid shutdown and roof access.
- The utility looks at where and how the system connects.
What Do Permit Offices Ask For on the SLD?
Start with the checklist from your own office. These public documents show what offices ask for.
| Source | What it asks the one-line diagram to show |
|---|---|
| California Solar Permitting Guidebook, 4th edition (2019) | Main service or utility disconnect, modules per string and number of strings, inverter and combiner box make and model, grounding and bonding, conductor type and size, conduit type and size, and the number of conductors in each conduit. Batteries and their locations and venting, if used. |
| City of Longmont, Colorado, plans checklist | Number and wattage of modules, conductor sizes, wire lengths, insulation types, conduit sizes, fuses, breaker ratings, inverter type and ratings, AC and DC disconnect ratings, ground fault protection and PV arc-fault protection. Also the existing AC service, with panel rating and load calculations. |
| Jemena (Victoria, Australia), connection guidelines | Title block, the full system (existing and new), current and fault rating of devices, cable length and cable type from the point of supply to the inverter, and the point of supply to the network. |
Jemena is a utility in Victoria, Australia, not a US permit office. Its guideline covers larger systems: above 10 kVA single phase, and above 30 kVA up to 200 kVA three phase. It is included because its rules are published in full.
Longmont’s checklist also asks you to list the module’s short circuit current (Isc) and open circuit voltage (Voc). It asks for the math you used to size wires and breakers. Longmont wrote its checklist for the 2020 National Electrical Code (NEC), so the edition matters.
Title Block
Jemena asks for a title block with the drawing name, a drawing number, a version number, the designer, the date and the site address. A version number helps when the office reviews a second round. Even where an office does not ask for a title block, it costs you nothing to add one.
Conductor and Conduit Labels
Label each part of the circuit. The California guidebook asks for the conductor type and size, the conduit type and size, and the number of conductors in each conduit. Show the grounding conductor too. Longmont also asks for wire lengths.
Which Code Sections Matter?
The NEC is the US electrical code. Article 690 covers solar PV. Each state and city adopts a specific edition, and some add their own rules.
Public checklists point to these NEC items:
| NEC item | Where an office cites it | What to show |
|---|---|---|
| 690.11 (arc-fault protection) | Longmont checklist | PV arc-fault protection |
| 690.12 (rapid shutdown) | Longmont checklist and California guidebook (which cites the California Electrical Code) | The rapid shutdown method and the device that starts it |
| 690.45 (equipment grounding conductor size) | Longmont checklist | Grounding on the drawing, with the sizing math |
| Table 690.31(A) (temperature correction) | Longmont checklist | The temperature factors used in wire sizing |
| 705.12 (connection to the building supply) | California guidebook (California Electrical Code numbering) | Where the system connects, and the breaker and busbar ratings |
The California guidebook shows the busbar check in its standard plan. The inverter breaker plus the main breaker must not be more than 120% of the busbar rating. Its tables are based on the 2016 California codes, so read the current rule for your area. The NEC text is sold by NFPA, so confirm any section number in the edition your office adopted.
Check the code edition
Longmont’s checklist says plans must follow the 2020 NEC. Another office may use a newer or older edition. Rapid shutdown rules can differ between editions. Use the edition your office names, not a rule you remember.
String Inverter and Microinverter Drawings
The two layouts look different on paper.
String inverter. Most of the drawing is on the DC side. Show each string, the number of modules in it, and the string voltage and current. Show the combiner box, if you use one, and the DC disconnect. Then show the inverter, the AC disconnect and the connection to the panel. Show how the system meets rapid shutdown.
Microinverter. There is little high-voltage DC wiring to draw. Show each module with its microinverter. Then show the AC cable that joins them, the AC junction or combiner, the AC disconnect and the connection to the panel. Many microinverter systems have module-level shutdown built in. Check the product’s listing before you write that on the drawing.
DC optimizers with a string inverter. This sits between the two. Show the strings, and mark the optimizer at each module. Note how the optimizers help the system meet rapid shutdown.
| SLD element | String inverter | Microinverter |
|---|---|---|
| Array notation | Strings, with modules per string | Each module paired with its microinverter |
| DC wiring | Shown from strings to the inverter | Mostly inside the module and microinverter |
| AC wiring | Inverter to AC disconnect to panel | AC cable to junction to AC disconnect to panel |
| Rapid shutdown | Show the method and the device | Note the built-in method, if the listing supports it |
| Overcurrent protection | DC fuses or breakers, plus the AC breaker | AC breaker |
The microinverters vs string inverters guide compares the three designs. The rapid shutdown glossary page explains the term.
How Do You Add Battery Storage to the SLD?
A battery adds blocks to the drawing. The California guidebook asks you to include batteries in the diagram and show their locations and venting. Jemena asks you to show the battery inverter rating in kVA and the battery size in kWh.
Add these items:
| Item | What to show |
|---|---|
| Battery inverter or hybrid inverter | Make, model, kVA rating and kWh size |
| Battery | Make, model and capacity |
| Battery management system | A separate block, if it sits outside the battery |
| Backup load panel | The circuits the battery backs up (see the critical load panel page) |
| Transfer switch or backup device | Type and rating |
| Battery disconnect | A pad-lockable, labeled switch (Jemena asks for this) |
| Export control | How the system limits export, if the utility asks (Jemena asks for the export limit) |
Show how the battery is coupled. With DC coupling, the battery connects on the DC side to a hybrid inverter, so one inverter block has both PV and battery inputs. With AC coupling, the battery has its own inverter on the AC side, so the drawing has two inverter blocks. An unclear drawing invites questions from the reviewer.
The battery storage glossary page explains the basics.
Residential and Commercial SLDs
Both use the same core items. Larger systems add more.
| Topic | Residential | Commercial |
|---|---|---|
| Diagram type | Single-line diagram | Often a single-line and a three-line diagram |
| Transformer | Usually none | Shown, with its ratings |
| Engineer stamp | Depends on the office | Depends on the office and state |
| Studies | Rarely | Utility and protection studies, if the utility asks |
Engineer stamp rules vary. For example, Arizona law says a city may not require a professional engineer stamp on a solar PV system unless it decides one is needed. If it does, it must explain why in writing (Arizona Revised Statutes 9-468).
For the full package, not only the SLD, read the solar permit package checklist.
Bring a Permit Package to a Demo
SurgePV supports roof modeling, layout, electrical workflow support and bill of materials output. Bring a recent permit job and see how those steps connect.
Book a Free DemoWant the price? Read the SurgePV pricing page · Guided demo · No credit card required
Why Do Permit Offices Send an SLD Back?
No public source ranks the reasons by how often they happen, so this list does not claim one. These are the problems that office checklists and rules point to:
- Missing wire sizes. Longmont and the California guidebook both ask for conductor sizes. Longmont asks for the sizing math.
- Missing conduit or cable details. Offices ask for conduit size and type, the number of conductors, and (in Jemena’s case) cable length and type.
- Wrong or missing ratings. Longmont asks for breaker, fuse, inverter and disconnect ratings.
- Rapid shutdown not shown. Both Longmont and the California guidebook cite the 690.12 rule.
- Grounding left off. Longmont asks for all grounding on the one-line diagram.
- Wrong code edition. Longmont names the 2020 NEC. Use the edition your office names.
- A drawing that does not match the application. Jemena rejects drawings that disagree with the online application form.
- Hand-drawn sketches. Jemena does not accept them.
- Wrong project details. Jemena rejects drawings with the wrong address or a previous project’s data.
Pro Tip
Before you draw, download your permit office’s current submittal checklist and tick it against the self-check below. Put the office’s name and the code edition it adopts in the title block, so the reviewer can see you worked from the right list.
Self-Check Before You Submit
DC side
- Module make, model, Voc, Isc and power shown
- Modules per string and number of strings shown
- Combiner box and fuse ratings shown, if used
- DC disconnect shown with ratings
- Conductor size and type labeled on every DC run
- Conduit size and type labeled
Inverter
- Inverter make, model and AC and DC ratings shown
- Rapid shutdown method and start device shown
- PV arc-fault protection noted, if your office asks
AC side
- AC disconnect shown with rating and location
- Breaker size and panel busbar rating shown
- Busbar check shown (the California guidebook uses the 120% rule)
- Meter location shown
- Conductor size and type labeled on every AC run
Grounding
- Grounding electrode conductor shown and sized
- Equipment grounding conductors shown and sized
- Racking bonding method noted
Title block and match
- Site address, designer and date shown
- Drawing number and version shown
- Code edition named, matching your office
- Drawing matches the application and the equipment sheets
- Battery coupling and backup circuits shown, if used
Local rules differ
This list is a base. Offices add their own rules, such as site plan details or utility meter notes. Download your office’s current submittal document before you finalize the package.
How to Buy Solar Electrical Engineering Services
Define the electrical boundary before you ask for a quote. The scope should state system capacity and type, voltage levels, the point of connection, the equipment, any available fault and service data, the rules that apply, the utility’s needs, required studies, the deliverables, file formats, and who signs the work.
A provider may deliver more than an SLD. Examples are string schedules, wire and voltage-drop calculations, overcurrent protection, grounding and bonding, equipment schedules, labels, cable routing, three-line diagrams and interconnection documents. Ask the provider to list what it leaves out and who checks and approves regulated work. Check any required license with the licensing authority.
A qualified reviewer should compare ratings and equipment names across the calculations, schedules, drawings and datasheets. Remote design does not replace a site check, utility approval, installation supervision, testing or commissioning, unless the quote says it does. The solar design services buyer’s guide gives a wider scorecard.
Disclosure: SurgePV is promoting Heaven Designs through a commercial relationship. Apply the same license check, sample review, paid-pilot and qualified QA process to every provider.
Review the Heaven Designs detailed engineering service, visit the Heaven Designs website, and request an electrically relevant sample before you ask for a quote.
When Is a Three-Line Diagram Needed?
A single-line diagram shows a three-phase system with one line. That is often enough to show the design, support a permit and review the connection. A three-line diagram shows each conductor or phase on its own. It is a different deliverable when you must work out phase-specific connections, current transformers, metering, protection, switchgear or terminal details.
If you order a three-line diagram, give the provider the utility and service setup, phase and voltage data, grounding, equipment and terminal data, protection and metering needs, conductor data and the drawing standard. Keep device tags and ratings the same across the SLD, the three-line diagram, the schedules and the calculations. Ask the utility, the permit office, the owner or the engineer of record if one is required. Do not order one only because it looks more detailed.
SolarAPP+ and the Single-Line Diagram
SolarAPP+ is an online platform that checks code compliance for eligible homes and issues a permit and inspection checklist. The US Department of Energy funded it, and the National Laboratory of the Rockies (formerly NREL) first developed it. The SolarAPP Foundation now manages it. See the SolarAPP+ help center.
SolarAPP+ builds a schematic diagram for the inspector from the data the contractor enters when submitting the design, as the SolarAPP+ help article on schematic diagrams explains.
SolarAPP+ only covers some systems. Its help center lists these limits:
| Item | SolarAPP+ limit |
|---|---|
| Building type | One- and two-family homes, and townhomes up to three stories |
| Service rating | 400 A or less |
| Service disconnect and busbars | 225 A or less |
| System size | 38.4 kW or less, if it meets certain install rules |
| Single battery | 20 kWh or less |
| Not covered | Ground-mount, multi-family, commercial, utility-scale, ballasted and homeowner-installed systems |
These four limits come from the SolarAPP+ eligibility article cited below, last updated 16 October 2026. They apply to SolarAPP+ review only, not to every permit office.
Source: SolarAPP+ eligibility article, last updated 16 October 2026.
Arizona has a state rule on this. It says cities must ask for a one-line or three-line diagram. Then it adds that no diagram is needed when a qualified online automated permitting platform is used to check code compliance. It defines that platform as a web portal that automates plan review and issues permits for residential solar in real time (Arizona Revised Statutes 9-468). Outside Arizona, check the local rule before you assume the SLD is waived.
Where Does Design Software Help?
Drawing an SLD by hand takes care. A wrong wire size or a missing label can still cause a correction. Design software can keep the equipment list, string layout and bill of materials in one place, so the drawing and the data match.
SurgePV’s solar design software covers roof modeling, layout, shading, yield modeling, financial modeling, electrical workflow support and bill of materials output. The same project data can feed solar proposals. SurgePV is sold per user per year, and you see it in a guided demo. Pricing is on the pricing page.
Software does not replace the review by the responsible engineer or approval by the permit office or utility. Set up the string layout first, using the solar stringing and wiring guide, so the numbers on the drawing are right. For code changes in your area, read NEC 2026 solar changes. To see how the design data feeds the drawing on a live project, book a SurgePV demo.
Frequently Asked Questions
What is a single-line diagram for solar PV?
A single-line diagram (SLD) is a simple drawing of a solar system’s wiring. One line stands for each circuit, and standard symbols stand for the equipment. It runs from the PV modules, through the inverter, to the point where the system connects to the grid. Permit offices use it to check the design before they issue a permit.
Do I need a single-line diagram for a solar permit?
Often, yes. The California Solar Permitting Guidebook and city checklists such as Longmont, Colorado, ask for a one-line diagram. Arizona law says cities must ask for a one-line or three-line diagram. It makes one exception: no diagram is needed when a qualified online automated permitting platform checks the code. Check your own permit office.
Does SolarAPP+ replace the single-line diagram?
Not always. SolarAPP+ checks code compliance for eligible homes and builds its own schematic diagram from the data you enter. Arizona’s law drops the diagram rule when a qualified online platform checks the design. Other places may still ask for a diagram, so check the local rule before you submit.
How do I show battery storage on a solar SLD?
Add the battery and its inverter to the drawing. Show the battery inverter rating in kVA and the battery size in kWh. The California guidebook also asks for battery locations and venting. Make clear whether the battery is DC-coupled or AC-coupled, and mark which circuits it backs up.
What is rapid shutdown and how do I show it on an SLD?
Rapid shutdown (RSD) is a safety feature that lowers the voltage on rooftop wiring when someone triggers it. Show the RSD method and the device that starts it. The voltage limits and timing depend on the NEC edition your area uses, so check that edition before you draw.
Where this fits
This article is part of SurgePV's Solar Design hub, which works through the topic from first principles to the decisions a project team actually has to make.
