Solar energy is booming in the United States for a good reason.

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In 2021, about 23.6 GWdc of solar power capacity was installed in the U.S., accounting for nearly half (46%) of new electricity-generating capacity. It was also the third consecutive year that solar held the largest share of new generating capacity. Of all electricity generated in the U.S. last year, almost 4% came from solar panel systems.

The United States has relied on the power of fossil fuels for decades, but there has been a concerted effort to make the energy we consume cleaner. Solar cells, also known as photovoltaic cells, are small but are packed together into solar panels, which convert sunlight into usable electricity. As more panels or modules are connected, they form arrays, and may eventually be connected to the power grid as part of a system.

Requirements for North American PV module interconnecting wires

Recently, the Underwriters Laboratories (UL) issued a brief overview of the solar panel market and the copper wire requirements needed to serve that industry. We took some time to brush up on the differences between PV and USE-2 wire in photovoltaic modules.

According to UL, “PV wire has superior sunlight resistance and low-temperature flexibility in addition to a thicker insulation or jacket and a proven level of flame resistance.”

Overall, only wires or cables highlighted in the National Electric Code (NEC) can be installed in modules sold in the U.S.

Single-conductor Type USE-2 cable and photovoltaic (PV) wire are both ok to use in exposed outdoor installations.

Because these installations are usually found in more extreme environmental conditions, insulation for these conductors must be sunlight resistant and rated for wet conditions. It also must be able to handle temperatures of up to 90°C.

The main differences between PV wire and USE-2 wire


  • PV wire is solely used for interconnecting PV modules and was developed to handle 90°C in wet conditions and 150°C in dry conditions.
  • USE-2 wire is usually used for connecting service equipment terminals and is mostly found underground. Therefore, it is only rated to handle 90°C in wet or dry conditions.
  • Both can be UL rated at 600V. However, PV wire can also be 1000V or 2000V rated if needed.
  • Both can be used in grounded PV arrays, but only PV wire can be used in ungrounded ones.


  • PV wires have thicker insulation for added protection.
  • USE-2 is often used in places that don’t require a high level of flexibility and can be made of either stranded or solid conductors.
  • Since PV is used only in solar panels, it needs to be flexible, so it is only made from stranded wires.
  • The smallest size available for USE-2 wire is 14 AWG, while PV can get as small as 18 AWG.


PV wire must go through a flame test and strict sunlight resistance tests, while USE-2 must pass several abuse tests that PV isn’t subject to. USE-2 does not need to go through a flame test because it isn’t typically installed where flames might be. USE-2 also doesn’t have to meet the same standards for sunlight resistance.

Both tests are part of the UL 4703 specification requirements.

Powering the Future of Solar Energy

As the country inches closer toward a greener future on the back of solar energy, we could start seeing our electricity supply shift dramatically. This makes the need for high-quality PV wire more vital than ever.

A recent study by the U.S. Department of Energy Solar Energy Technologies Office and the National Renewable Energy Laboratory suggested that solar could provide up to 40% of the country’s generated electricity by 2035.

However, solar installers will need to pick up the pace to hit those goals, with an estimated deployment rate of 60 GW between 2025 and 2030.

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