If you’ve been following the rise of solar over the past decade or so, you’ve likely noticed the massive role it’s playing in the United States’ renewable energy plans.

As the U.S. pushes for a completely renewable future, solar energy has become the focal point, comprising about 70% of the country’s planned utility-scale power capacity through 2025.

In 2023 alone, the U.S. added 32.4 GWdc of solar capacity to the grid, surpassing the 30 GWdc threshold for the first time. Solar also accounted for more than half (53%) of all new electrical capacity annually for the first time.

Today, over 5% of our electricity comes from solar, enough to power about 32.5 million homes. States like California, Texas, and Florida lead the way for solar development, weaning the country from traditional fossil fuels like coal. 

But even with the recent growth and excitement around solar, questions remain. What wire works for a solar installation? What qualities does photovoltaic wire offer that other types don’t? And how does copper PV wire compare to seemingly comparable wire types, like USE-2 cable?

Understanding how PV wire works and its applications across residential, commercial, and industrial applications is crucial to successful projects.

How Do Solar Arrays Work?

When we think about solar energy, the first thing that comes to mind are rows of giant solar panels.

As the sun shines, solar cells on the panels collect sunlight and convert it into electricity. Solar panel electricity is sent through PV wires to an inverter or combiner box, depending on whether it’s a residential or utility-scale installation, respectively. The electricity is then ready to use locally or added to the electrical grid. 

Generating solar energy is complex, and every component and wire used is critical.

Solar Wire: Small, But Important

In terms of the total cost of a project, PV wire is a small piece of the pie. But without wires connecting everything, the power the panels generate is useless.

Unfortunately, only specific wire types make sense in a solar application – solar PV wire and USE-2 cable. People generally prefer solar wire, but USE-2 could be a substitute in rare instances.

Checking the Codebook

The National Electrical Code (NEC) has a rule for every electrical project, and solar arrays are no exception.

Before starting any solar project, from residential to community- and utility-sized, consult the NEC guidebook. Articles 690, 691, and 705 each cover a specific part of the project, combining to ensure the job is safe.

Article 690 covers solar system construction, operation, and safety requirements and dictates who can install, maintain, and update installations. This section also has diagrams explaining what PV components are used, including illustrations explaining stand-alone, hybrid, and interactive solar configurations.

Article 691 covers PV installations with a generating capacity greater than 5,000kW (5 MW) and not under exclusive utility control. Generally, solar systems of this size are large commercial, community, or small utility-scale projects. The article also covers qualified workers, where to locate systems, and how to protect them.

Finally, Article 705 covers interconnected power production sources operating alongside other electricity sources. It covers more than just solar, stretching into wind power, fuel cells, battery storage, and direct current (DC) microgrids.

Essentially, Article 705 governs safe installation for any new electricity sources installed alongside existing ones.

Even the UL Has Rules

You didn’t honestly think the NEC would keep all the regulatory fun for itself, did you?

Underwriters Laboratories (UL) issued UL 4703 safety certifications for PV wires used in solar power systems. The certification awards wire meeting a long list of requirements, including sunlight resistance, UV protection, heat resistance up to 90°C, and other variables associated with surviving outside in the elements for 20+ years.

UL 4703 also covers aluminum PV wire, allowing for potential project cost savings.

PV Wire vs. USE-2

People once commonly used USE-2 (Underground Service Entrance) cable to connect solar panels outdoors. However, PV wire, which first appeared in the 2008 National Electrical Code, has largely replaced it.

Though the two cables look the same at first glance, key differences make PV wire the preferred choice for solar projects.

General Use: Installers use USE-2 wire for direct burial installations and to connect service equipment. However, it can work in grounded solar systems in a pinch.

PV wire works in grounded and ungrounded solar installations and in open-air installations.

Construction: USE-2 cable has thick insulation to help it survive underground but is not particularly flexible. Because it is primarily used underground, USE-2 doesn’t need to pass some flammability tests.

PV wire has even thicker insulation than USE-2, giving it more UV and sunlight resistance and better performance in colder temperatures. Despite the thicker insulation, PV wire is more flexible than USE-2.

Flexibility also comes into play when discussing the conductors. USE-2 conductors can be stranded or solid, but PV wire is always stranded for more flexibility.

Gauge Sizing: Though PV wire and USE-2 have many gauges, solar wire has more variety. Solar wire is available in sizes as small as #18 AWG.

Voltage Ratings: Both wires offer 600V options, and USE-2 has a 2kV rating. PV wire, though, has several varieties of wire available for whatever size project you need it for.

600V PV Wire – Generally used for residential solar systems mounted on rooftops or other small systems.

1000V PV Wire – Found on commercial and industrial-sized solar installations.

2kV PV Wire – Typically seen on utility-scale solar projects and can handle large amounts of power.

Temperature Ratings: USE-2 works in temperatures up to 90 degrees Celsius, wet or dry. PV wire, on the other hand, can be rated for temperatures as high as 150 degrees Celsius without damage.

Tests: PV wire undergoes flame and sunlight resistance tests, while USE-2 undergoes several abuse tests. USE-2 doesn’t need to meet the same sunlight resistance levels or flame retardance standards.

Most importantly, USE-2 does NOT meet UL 4703 certification requirements.

Don’t Skimp on Solar

Although there are situations where USE-2 is suitable for solar installations, PV wire exists for a reason.

If you’re working on a solar project, use either copper or aluminum PV wire to connect the system. It can survive in the elements, perform under pressure, and be under warranty for as long as your solar panels.

Renewable energy adoption is increasing as the U.S. aims for 100% carbon pollution-free energy by 2035. The effort is already showing results, with the Department of the Interior approving over 25GW of clean energy projects – enough to power about 12 million homes.

Overall, we’re all seeing what the power of a fully invested solar sector can do. Despite its small role, high quality PV wire is on the front lines, ensuring power gets where it needs to go safely and reliably.

Related Products