Electrical Line Diagrams

Electrical Line Diagrams are schematic representations that illustrate how electrical components in a solar PV system are interconnected. They show the flow of power from solar modules through combiner boxes, inverters, disconnects, breakers, meters, transformers, and finally to the grid or load.

These diagrams are required for permitting, engineering review, system installation, utility interconnection, and safety compliance. They help designers, AHJs, utilities, EPCs, and installers understand how energy moves through the system — and ensure that everything is wired according to electrical codes (NEC), AHJ rules, and manufacturer specifications.

In modern workflows, line diagrams are generated automatically inside platforms like Solar Designing, and updated dynamically when changes are made to stringing, inverter selection, or system size.

Electrical Line Diagrams are foundational documents in solar design, often used alongside Stringing & Electrical Design, Inverters, and Electrical Single-Line Diagrams for full plan set preparation.

Key Takeaways

Electrical Line Diagrams clearly show how a solar PV system is wired from modules to the grid.
Required for permitting, utility interconnection, engineering, and safety compliance.
Include DC strings, AC connections, grounding, OCPD, and disconnects.
Essential for accurate installation and inspection processes.
Modern design platforms automatically generate line diagrams tied to real-time system changes.

What Are Electrical Line Diagrams?

Electrical Line Diagrams are simplified electrical schematics that show how different parts of a PV system connect in terms of wiring, current flow, voltage levels, and component relationships.

They typically illustrate:

Solar modules and strings
String connections to combiners
DC disconnects
Inverters
AC breakers
Grounding conductors
Rapid shutdown devices
Utility meter
Main service panel

For permitting or engineering purposes, Electrical Line Diagrams must reflect actual design choices — string count, string length, DC/AC ratio, conductor sizes, OCPD ratings, grounding methods, and interconnection type.

They serve as a universal communication tool that allows all stakeholders — installers, utility companies, engineering teams, and inspectors — to understand the PV system’s electrical structure quickly and accurately.

How Electrical Line Diagrams Work

1. Identify All System Components

Diagrams begin by listing every electrical component in the system, such as modules, inverters, breakers, and disconnects.

2. Map Component Connections

Lines represent conductors that connect components:

DC strings → combiner → DC disconnect → inverter
Inverter AC output → AC disconnect → panel/main service → meter → grid

This defines how power travels from the array to the building or grid.

3. Assign Voltage Levels and Circuit Ratings

Voltage, amperage, OCPD values, and wire sizes are added to ensure compliance with NEC and utility requirements.

4. Add Grounding & Bonding

Grounding conductors, equipment grounding, and bond points must be shown to ensure system safety.

5. Add Safety Devices

Rapid shutdown devices, AFCIs, GFCIs, and disconnect switches are shown clearly for inspector review.

6. Validate Against Electrical Codes

The diagram is checked for NEC compliance, including conductor sizing, overcurrent protection, system grounding, and inverter interconnection rules.

7. Export for Permitting

Final Electrical Line Diagrams feed into plan sets, often generated through the Solar Project Planning Hub.

Types / Variants of Electrical Line Diagrams

1. DC Line Diagrams

Show:

Module strings
Combiner boxes
DC disconnects
Inverter DC input
Voltage and current calculations

Used heavily for string inverter and central inverter systems.

2. AC Line Diagrams

Illustrate:

Inverter AC output
AC disconnects
Breakers and service panel connections
Metering setups
Utility-tie configurations

3. Single-Line Diagrams (SLDs)

A type of Electrical Line Diagram showing the entire system using simplified “one-line” representations.

(See Electrical Single-Line Diagram.)

4. Three-Line Diagrams

Used for commercial or three-phase systems where each AC phase conductor is shown separately.

5. Rapid Shutdown Diagrams

Highlight module-level rapid shutdown devices and conductors required for NEC 690.12 compliance.

How Electrical Line Diagrams Are Measured or Evaluated

While not measured numerically, diagrams are evaluated based on:

Accuracy

Must match the physical design and actual electrical configuration.

NEC Compliance

Codes for conductor sizing, OCPDs, grounding, and interconnection.

Completeness

Includes all required components for permitting.

Clarity

Easily readable by installers, engineers, and inspectors.

Buildability

Reflects real-world installation practices, not just theoretical wiring.

Typical Values / Ranges Shown in Diagrams

DC Values

String voltage: 300V–1500V
String current: 8A–15A
DC/AC ratio: 1.1–1.3

AC Values

Residential: 120/240V single-phase
C&I: 208V / 400V / 480V three-phase
Utility-scale: 600V–35kV via transformers

OCPD Ratings

DC fuses: 10A–20A
AC breakers: 20A–250A

These values vary by project type, component choice, and jurisdiction.

Practical Guidance for Solar Designers & Installers

1. Always match diagrams to the actual stringing design

If module count or string lengths change, update the diagram.

2. Use automated tools for accuracy

SurgePV auto-updates diagrams based on real-time design changes in Solar Designing.

3. Include all disconnects and safety devices

Missing disconnects are a top reason for AHJ rejections.

4. Label grounding and bonding clearly

Poor grounding documentation slows down utility approval.

5. Show correct conductor sizes and OCPD ratings

Align with calculations from tools like the Voltage Drop Calculator.

6. Confirm interconnection type

Load-side vs. supply-side must be clearly shown.

7. Coordinate with installers

Ensure the diagram matches real field routing.

Real-World Examples

1. Residential Rooftop PV System

A 7 kW system includes 2 strings feeding a string inverter.

The line diagram shows DC strings → inverter → 240V AC output → main panel → utility meter.

2. Commercial Flat Roof

Multiple inverters connect to a three-phase 480V panel.

Line diagrams display three-phase conductors, AC disconnects, and transformer connections.

3. Utility-Scale Solar Plant

Central inverters connect through medium-voltage transformers.

Line diagrams show MV switchgear, grounding grids, and utility tie-points.