The Underwriters Laboratories (UL) recently put out 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 current standards for our own PV wire products, and the distinction between PV wire and USE-2 wire in photovoltaic modules. We thought you might be interested.
In summary, UL says “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 that will be sold in the US.
Requirements for North American PV module interconnecting wires
- 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, the insulation for these conductors must be sunlight resistant and rated for wet conditions, and 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 be able to handle 90°C in wet conditions and 150°C in dry conditions.
- USE-2 wire is usually used for connecting terminals of service equipment, and is mostly found underground, and is therefore only rated to handle 90°C in wet or dry conditions.
- Both can be UL rated at 600V. However, PV wire can also be rated 1000V or 2000V if needed.>
- Both wires 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 movement out of the wire, and can therefore be made out of either stranded or solid conductors.
- However, since PV wire is used only in solar panels, it needs to be flexible, so is only made from stranded wires.
- The smallest size available for USE-2 wire is 14 AWG, however PV can get as small as 18 AWG.
- PV wires must go through a flame test, USE-2 does not (since it isn’t usually installed in places where flames would be found). On the other hand, USE-2 must go through various abuse tests that PV wires aren’t subject to.
- PV wire must go through more strict sunlight resistant tests.
- Both of these tests are part of the UL 4703 specification requirements.
You can find out more about the solar market on the first page of the report, “Designing UL Compliant Photovoltaic Wire” (.pdf format).