Designing a commercial solar PV system requires careful attention to multiple layers of technical, regulatory, and site-specific variables. One of the most important—yet often overlooked—elements in this process is the interconnection method between the solar array and the building’s existing electrical infrastructure. This choice can significantly influence the system’s performance, safety, cost, and approval timeline.
While breaker backfeed connections are commonly used in residential systems due to their simplicity and compatibility with standard panel sizes, they are not always suitable for larger commercial installations. In fact, many commercial solar projects benefit more from a line-side tap interconnection, especially in systems above 100 kW, or those involving backup power infrastructure such as generators or automatic transfer switches (ATS).
At One Place Solar, we help clients and EPCs navigate these decisions with confidence. Our integrated design and engineering services—including solar permit design, solar sales proposals, preliminary layout planning, and state-specific engineering-stamped plan sets—ensure that your interconnection is not only code-compliant but also tailored to your project’s long-term success.
In this article, we explain what a line-side tap is, why it’s beneficial, how we incorporate it into our solar permit designs, and how we used it to deliver a highly efficient and scalable solution in a recent commercial installation.
What is a Line-Side Tap?
A line-side tap, also known as a supply-side connection, refers to the method of connecting a solar PV system on the line side of the main service disconnect, typically between the utility meter and the main breaker in the electrical service equipment. In this setup, solar-generated power enters the electrical system directly—bypassing the main breaker panel entirely.
This approach contrasts with a load-side (or breaker-based) interconnection, where the solar output is fed into an existing breaker space within the main panel. While this method works for smaller systems, it often hits limitations in larger commercial or agricultural settings.
A line-side tap is recognized and permitted by NEC 705.12(A) and is particularly useful in overcoming panel limitations, avoiding costly upgrades, and enabling seamless integration with complex electrical environments.
Why Choose a Line-Side Tap for Commercial Solar?
In high-capacity systems like our 246.4 kW ground-mounted solar array installed at Special K Hog Farm in McLean, Illinois, a line-side tap was essential to achieving a compliant, scalable, and utility-ready system design. Here are the top reasons why a line-side tap is often the preferred interconnection method for commercial solar:
1. Bypasses Main Panel Limitations
One of the most common challenges in commercial installations is the 120% rule, outlined in NEC 705.12(D)(2), which restricts how much solar power can be backfed through a panel’s busbar. In many commercial panels, the available capacity for a backfed breaker is either nonexistent or insufficient for systems above 100 kW.
By using a line-side tap, the solar system feeds directly into the service entrance conductors, bypassing the busbar altogether. This eliminates the need for costly panel upgrades or utility service changes, saving time and budget.
2. Integrates Seamlessly with ATS and Backup Generators
Many commercial facilities already operate with automatic transfer switches (ATS) and backup generators to ensure power continuity. A load-side connection can conflict with these setups, especially when the solar system and generator are both feeding into the same panel.
A line-side tap resolves this conflict by delivering solar power upstream of the ATS, ensuring isolation between solar and generator circuits and maintaining compliance with both NEC and utility safety standards. This was especially important in our McLean project, where the existing electrical infrastructure included a 400A load center and an exterior ATS.
3. Simplifies Utility Interconnection Approvals
Some utilities actually prefer or require a line-side tap in larger installations due to the simplicity of load calculations and the avoidance of backfeed complications. By initiating utility coordination early in the project, our team ensures that the selected interconnection strategy aligns with local utility guidelines, helping clients avoid redesigns or extended approval delays.
In our experience, utilities are more likely to expedite Permission to Operate (PTO) when the interconnection method is clearly documented, NEC-compliant, and matches their expectations.
4. Provides Cleaner Power Distribution and Installation Flexibility
In a line-side tap configuration, the electrical path is more direct and requires fewer internal connections within the existing panel. This can result in:
- Reduced voltage drop, especially over longer distances
- Simplified wiring diagrams
- Improved inspection outcomes, as inspectors find this layout cleaner and easier to verify
Additionally, line-side taps offer more installation flexibility for electricians, particularly when working with custom-built or aging panels that cannot accommodate additional breakers.
How One Place Solar Supports Line-Side Tap Projects
Our team at One Place Solar has successfully delivered multiple commercial solar projects using line-side tap interconnections. In each case, our services cover everything from site analysis to final utility approval, ensuring clients receive a turnkey design package.
Our support includes:
- Solar Permit Design: Each plan set includes detailed NEC-compliant interconnection diagrams, panel schedules, and voltage drop analysis.
- Solar Sales Proposals and Prelim Layouts: Our preliminary packages help clients and sales teams visualize the system layout, inverter groupings, and electrical flow before committing to final engineering.
- Engineering-Stamped Plan Sets: We provide structural and electrical stamps in over 40 U.S. states, backed by full calculations and AHJ formatting.
- PTO Support: We coordinate with local utilities to submit interconnection applications, respond to reviewer feedback, and help close out PTO documentation.
Additional Services Beyond Solar PV
One Place Solar is more than a solar design company. We also provide engineering services for growing markets that often overlap with solar infrastructure:
- Telecommunication Tower Design: Structural analysis, foundation design, and antenna mounting layouts.
- EV Charging Station Design: Complete layout and load analysis for Level 2 and DC fast charging infrastructure.
- Hybrid Interconnection Support: We design and integrate battery systems, diesel generators, and solar in hybrid microgrids with appropriate ATS and control schemes.
Whether you’re building a solar-powered farm, data center, or EV-ready commercial plaza, we help you plan and connect your infrastructure with long-term reliability and compliance in mind.
Final Thoughts: Design Smart, Connect Confidently
For commercial solar clients, choosing the right interconnection method can make or break a project. The line-side tap provides a clean, scalable, and compliant path for high-capacity systems, especially when paired with professional electrical planning and utility coordination.
At One Place Solar, we help developers, EPCs, and contractors design smarter systems with fewer surprises. With a focus on solar permit design, prelim layouts, sales proposals, and engineering-stamped plan sets, we are committed to supporting your project from concept to commissioning.
If you’re planning a ground-mount or rooftop commercial solar project and want to explore whether a line-side tap is right for you, our team is ready to help.
Looking to simplify your interconnection process?
Reach out to One Place Solar for sample plan sets, pricing, or a no-obligation consultation.