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Photovoltaic (PV) Wire and USE-2 for Solar

PV wire and USE-2 are both single-conductor cables seen in solar installations, but they are built and listed differently. This sheet compares them, explains sunlight resistance and covers what to check before quoting wire for DC solar circuits.

Ref EL-0014NEC 690UL 4703

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

PV wire (also printed as PV cable or photovoltaic wire) is single-conductor cable listed to UL 4703 for photovoltaic systems. It has thicker insulation and jacketing than most building wire, is sunlight resistant and is rated for wet locations and the temperatures found on rooftops and under arrays. It is made in 600 V, 1000 V and 2000 V ratings. USE-2 is underground service entrance cable listed to UL 854. It is rated for wet locations and direct burial but is not necessarily rated for exposed outdoor use in sunlight. Many cables are multi-rated, for example PV wire also marked RHW-2 and USE-2. NEC Article 690 sets which wiring methods are allowed in each part of a PV system.

How to identify

Read the print. Look for "PV wire" or "photovoltaic wire," the voltage rating, temperature rating, "sunlight resistant," and any other type letters. A cable marked only USE-2 is not PV wire. Check the stranding class too. Connectors such as MC4-style connectors are rated for a range of conductor sizes and insulation diameters.

PV wire and USE-2 compared

Feature	PV wire (UL 4703)	USE-2 (UL 854)
Main purpose	Exposed PV source and output circuits	Underground and service entrance
Voltage ratings available	600 V, 1000 V, 2000 V	600 V
Sunlight resistance	Required for the listing	Only if separately marked
Insulation	Thicker; often XLPE or similar	Thermoset insulation
Direct burial	Often also rated; check marking	Yes
Use in exposed array wiring	Permitted where 690 allows	Check NEC 690 for the edition in force

Key points

The installer must follow NEC 690 for conductor types, sizing and circuit requirements. Ampacity and overcurrent sizing are code calculations, not counter choices.
System voltage on many arrays is above 600 V. Confirm the wire's voltage rating matches the system.
Connector compatibility matters. Use connectors listed with the wire and from compatible families. Mismatched connectors are a known fire cause.
Wire management on arrays uses clips and ties rated for UV and outdoor service.
Conduit runs on roofs are subject to added temperature rules in the NEC.

Common mistakes

Selling USE-2 for exposed module wiring because it is rated for wet locations.
Quoting 600 V wire for a 1000 V system.
Mixing connector brands that are not listed together.
Using plain cable ties that break down in sunlight.

Governing standards: NEC Article 690 (solar photovoltaic systems); UL 4703 (photovoltaic wire); UL 854 (service entrance cables). The adopted NEC edition.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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