Solar one-line diagram: what to include

A one-line (or single-line) diagram represents each circuit with a single line, no matter how many conductors it has. It isn’t a wiring diagram and it isn’t drawn to scale. It shows what’s connected to what, in order, with the ratings a reviewer needs to check that every part is protected and the system connects to the utility safely.

Draw it from the source to the service: modules on one side, the utility on the other, everything in between in the order the power flows. Label every piece of equipment with its make, model and key ratings, and every conductor run with its size and type.

This guide is general. The electrical code edition, local amendments and utility rules vary. Confirm the details with your building department and your utility.

Show the module make, model and wattage, the total number of modules, and how they’re grouped. For a string inverter, show each string and how many modules are in it. Reviewers use the spec sheet values, like open-circuit voltage and short-circuit current, to check that the string voltage stays within the inverter’s limits in cold weather and that the conductors and overcurrent devices are sized correctly. Some departments want those values and calculations on the sheet.

• String inverter. DC circuits run from the strings to one central inverter, sometimes with module-level optimizers. Show the DC input circuits, the inverter’s ratings and its AC output.
• Microinverters. Each module (or pair) converts to AC right at the array. Show the AC branch circuits, how many microinverters are on each, and where they combine.
• Hybrid or battery inverter. Show both the PV input and the battery connection, plus any backup loads panel.

List the make, model, continuous AC output current and voltage. The output current drives the size of the breaker and conductors downstream.

The National Electrical Code requires PV systems on buildings to have rapid shutdown, so firefighters can de-energize conductors on the roof. Show how your system meets it (module-level electronics, or equipment listed for rapid shutdown) and where the initiator is, often the service disconnect or a dedicated switch. Include the rapid shutdown equipment’s spec sheet in your submittal.

Show every disconnecting means and every overcurrent device, with its rating:

• DC disconnect, often built into a string inverter
• AC disconnect, which many utilities require to be visible, lockable and near the meter
• Combiner for DC strings, or an AC combiner panel for microinverter branch circuits, with the breaker or fuse size for each circuit
• The PV breaker where the system connects to your panel, with its amp rating and position on the busbar

Tag every run between two pieces of equipment and describe it: the number of conductors, their size and insulation type, the equipment grounding conductor size, and the conduit type and size. Many plan sets use a conductor schedule keyed to the tags:

A format example only. Sizes depend on your equipment, run lengths and code calculations.

Show the equipment grounding conductors that run with each circuit, how the modules and racking are bonded, and how the system ties into the building’s grounding electrode system. If a new grounding electrode or electrode conductor is required, show it with its size.

The point of interconnection is where your solar connects to the building’s electrical system. There are two common approaches:

• Load-side connection. A breaker in the main panel (or a subpanel) is fed by the solar instead of feeding a load. This is the most common approach for small residential systems.
• Supply-side connection. A connection between the meter and the main disconnect. It usually needs specific equipment and utility approval.

For a load-side connection, the busbar matters. The NEC’s Article 705 includes what’s known as the 120% rule: when the solar breaker sits at the opposite end of the busbar from the main breaker, the main breaker rating plus 125% of the inverter’s continuous output current may not exceed 120% of the busbar rating.

Example: a panel with a 200 amp busbar and a 200 amp main breaker allows 240 amps in total. That leaves 40 amps for solar, which fits an inverter with up to 32 amps of continuous output (32 × 1.25 = 40).

If your system doesn’t fit, the usual options are a supply-side connection, a smaller main breaker where the load calculation allows it, or a panel upgrade. The code offers other methods too. Your electrician, utility and building department decide which works. Either way, show the main panel’s busbar rating, main breaker rating, and the solar breaker’s size and position on the one-line.

Show the utility meter and service, and a production meter if your utility requires one. If the system includes a battery (an energy storage system), show the battery and its inverter or charge controller, its disconnect and overcurrent protection, any backup loads panel, and how the system isolates from the grid during an outage.

The electrical code requires warning labels and placards on solar equipment: at the disconnects, on the rapid shutdown switch, at the service equipment to show there are two sources of power, and next to a backfed breaker. Many departments want a label sheet or a list of labels with their locations. Use the wording and formats your code edition requires.

In AI CAD PRO, the one-line diagram is built from the equipment you placed and the connections you explicitly defined. It doesn’t invent a utility service, meter, disconnect, battery connection or wiring you haven’t placed, so the diagram shows the system you actually plan to install.

Attach your spec sheets as PDFs so the assistant can work from real ratings. Drafting checks flag missing electrical connection or specification data before you export, and the Resolution center tells you what’s missing and where to find it. These are drafting checks, not a code review, and the app doesn’t supply complete engineering calculations. See solar plans and electrical plans for more.