UL 4703 PV Wire vs USE-2 vs THHN: What the Jacket Markings Mean

Pull a reel of solar cable off a supply house shelf and the jacket will carry a string of listings: PV WIRE, UL 4703, USE-2, RHH, RHW-2, 2000V, 90°C, SUN RES. Each one tells an inspector something different. Here is what they mean and why it matters for the wire you run on an array.

UL 4703 PV Wire

UL 4703 is the product standard for photovoltaic wire: single-conductor cable built for the exposed, sunlit, thermally cycled environment of a PV array. Compared with ordinary building wire, PV wire has thicker insulation, a cross-linked polyethylene (XLPE) or similar thermoset compound, sunlight resistance testing, and cold-bend performance down to −40 °C. It is listed at 600 V, 1000 V or 2000 V.

NEC Article 690 is where PV wire becomes mandatory. For exposed single-conductor wiring in the array, the code calls for listed PV wire or cable, and the requirements have tightened with each edition as ungrounded and functionally grounded systems took over the market. Check the edition your AHJ enforces, but PV wire is the safe default for anything outdoors and exposed.

USE-2

USE-2 is underground service-entrance cable rated 90 °C wet. It is sunlight resistant and allowed for direct burial, but it is not PV wire and does not carry the same insulation thickness or test regime. Older grounded arrays commonly used it. A cable marked both PV wire and USE-2 can be used either way.

RHH and RHW-2

These are building wire listings under UL 44 for thermoset-insulated conductors: RHH for 90 °C dry locations, RHW-2 for 90 °C wet locations. A PV wire that also carries RHH/RHW-2 can be pulled through conduit inside the building to the inverter without a splice to THHN, which saves a junction box and a termination on long runs.

600 V, 1000 V or 2000 V

The voltage rating on the jacket has to meet or exceed the maximum system voltage, which NEC 690.7 calculates from the string's open-circuit voltage corrected for the coldest expected temperature. Commercial and utility strings now design to 1500 V, which makes 2000 V cable the practical choice. Note that an assembly is only rated as high as its weakest part: our MC4 jumpers use 2000 V cable, but the connector limits the assembly to 1500 V DC.

THHN does not belong in the array

THHN/THWN-2 is fine inside raceway, but it is not sunlight resistant as a single exposed conductor and is not PV wire. It shows up in failed inspections when it is used to extend module leads or run exposed under racking.

Copper or aluminum

Copper PV wire is standard for source circuits and anything that terminates in an MC4 connector. Aluminum PV wire (for example 500 kcmil, 2 kV) is used on utility-scale feeders where conductor cost dominates; it needs aluminum-rated or dual-rated lugs and the right oxide inhibitor, never copper-only compression lugs.

What we stock and build

Our solar assemblies use US-made copper PV wire listed UL 4703, USE-2, RHH/RHW-2, 2000 V, XLPE insulated. We build it into 10 AWG and 12 AWG MC4 jumpers and 8 AWG and 6 AWG lugged leads. For sizing, see the PV wire size guide.

Listings and code requirements change between NEC editions. Confirm with the authority having jurisdiction.