The quick answer
Choose PV wire whenever the cable will sit in the sun or connect panels on the roof. It is made for PV circuits and gives you more voltage headroom.
Choose USE-2/RHW-2 only when the run is 600V or less and the installation location permits it. It is most common for underground or conduit applications.
| Question | Short answer |
|---|---|
| Best for exposed rooftop runs? | Listed PV wire |
| Best for direct burial / underground? | Either; USE-2/RHW-2 common |
| Highest voltage rating? | PV wire (up to 2000V) |
| Permitted in PV circuits? | Both, with conditions |
| Can I use house wire (THHN) outside? | No |
Note
Ratings from UL 4703 and UL 854. Code conditions per NEC (NFPA 70) Article 690.
Choosing the wrong DC cable can increase cost, delay approval, or create installation risks. For installers, EPCs, and distributors, the decision should be based on cable location, system voltage, sunlight exposure, and what the local AHJ accepts.
Local regulations, grid connection rules, the adopted NEC edition, and installer requirements vary by country, state, utility, and project type.
Solar Wiring in 2 Minutes
Solar wiring starts with how the panels are connected. The connection method decides whether voltage or current increases.
| Wiring method | How panels connect | What adds up |
|---|---|---|
| Series | Positive connects to negative | Voltage |
| Parallel | Same terminals connect together | Current |
This difference is important because voltage affects the cable’s voltage rating, while current affects the required wire gauge. Solar cable also needs to withstand long-term outdoor exposure, including sunlight, heat, cold, rain, and ozone. Regular building wire is not designed for these rooftop conditions over a typical 25-year solar system life.
Meet the Two Cables: PV Wire & USE-2
PV wire and USE-2 are both single-conductor, weather-resistant cables, but they are designed for different installation needs. PV wire is made specifically for solar PV systems, while USE-2 is an underground service cable that was later used in some solar applications.
What Is PV Wire?
PV wire is the standard cable for solar PV circuits. It is designed for outdoor solar applications, where cables may be exposed to sunlight, moisture, temperature changes, and rooftop conditions.
PV wire is available in voltage ratings such as 600V, 1000V, and 2000V, making it suitable for many residential, commercial, and utility-scale solar projects. Its insulation and conductor design help improve durability and routing flexibility during installation.
What Is USE-2 Cable?
USE-2 cable stands for Underground Service Entrance cable. It was originally designed for underground power service applications and was commonly used in certain solar installations before PV wire became the more widely accepted standard. USE-2 cable is typically rated for 600V and 90°C in wet or dry locations, making it durable for underground runs, conduit installations, and outdoor electrical environments.
PV Wire vs. USE-2: Side-by-Side
PV wire is built for solar PV circuits and performs better in exposed, higher-voltage installations. USE-2/RHW-2 is tougher than regular building wire and can be used in some PV applications, but it is normally limited to 600V and depends more heavily on marking, location, and AHJ approval.
| Feature | PV Wire | USE-2 / RHW-2 |
|---|---|---|
| Standard | UL 4703 | UL 854 |
| Voltage rating | 600 / 1000 / 2000V | 600V |
| Dry temp rating | 90 / 105 / 125 / 150°C (by type) | 90°C |
| Wet temp rating | 90°C | 90°C |
| Sunlight / UV | Sunlight resistant; built for exposed PV use | Must be marked sunlight resistant if exposed |
| Conductor | Usually stranded | Stranded or solid |
| Flexibility | Higher | Lower |
| Where it fits | Grounded and ungrounded PV DC circuits where listed and permitted | Code-permitted exposed PV array locations, normally 600V max, subject to marking/listing/AHJ |
| Typical cost | Higher | Lower |
Based on our installation team’s real project experience, PV wire is the better choice for exposed rooftop runs and higher-voltage PV systems. Rooftop wiring faces direct sunlight, high heat, rain, wind, abrasion, and long-term insulation aging, so a PV-specific cable is better suited for these conditions. USE-2/RHW-2 should be used only when its rating, installation method, and application range are fully confirmed.
Which One Should You Use?
Pick the cable based on the location, system voltage, markings, and AHJ requirements.
Pick PV Wire When…
Choose PV wire when the cable will be exposed on the roof, connected between modules, used in an ungrounded array, or installed in a system above 600V. For most modern PV projects, PV wire is the safer default because it is built specifically for solar circuits, direct sunlight, and higher-voltage DC applications.
USE-2/RHW-2 Is OK When…
USE-2/RHW-2 can work for buried or conduit runs, and in some exposed PV array locations if the cable is sunlight-resistant, properly marked, rated for the system voltage, and accepted by the AHJ. Under NEC 690.31(C), exposed single-conductor DC conductors must be within the PV array and must be listed PV wire or sunlight-resistant Type USE-2/RHW-2.
Don’t Use THHN or House Wire
Standard building wire such as THHN is not suitable for exposed outdoor solar runs. It is not designed for long-term rooftop exposure, and its wet-location temperature rating and sunlight-resistance limitations can create both durability and code-compliance issues in exposed PV circuits.
Picking the Right Size (Wire Gauge)
Wire gauge is not chosen by panel voltage. It is chosen by maximum circuit current, NEC correction factors, and voltage drop over the cable run. Start with the required ampacity, then increase the conductor size if the DC run is long.
| Step | What to do |
|---|---|
| 1 | Enter the circuit current |
| 2 | Add the cable run length |
| 3 | Check voltage drop |
| 4 | Compare recommended wire sizes |
| 5 | Choose the safer gauge before ordering |
A small sizing mistake can mean wasted cable, higher losses, or a failed inspection. That is why the calculation should happen before the purchase order, not after installation.
Check before you commit
Use the solar wire size calculator and voltage drop calculator to find the right cable gauge now.
Before You Order: Size AWG/mm² Alone Is Not Enough
From APS project experience, many solar cable issues start with a request that only gives the size, such as “10 AWG PV wire” or “4mm² solar cable.” Size is only one part of the specification. The same conductor size may work in one project and fail in another if the voltage rating, installation method, ambient temperature, cable grouping, or required standard is different.
Before confirming production, APS normally checks the system voltage and current, cable run and voltage-drop target, installation environment, required standard such as UL 4703, USE-2/RHW-2, EN 50618, or IEC 62930, and connector or terminal requirements.
Takeaway
Confirm the full application before ordering. When required, APS can support the order with datasheets, conductor-resistance checks, insulation-resistance records, voltage test records, and batch traceability documents.
Outdoor Install Checklist
Even the right solar cable needs proper installation to perform safely outdoors. Before finishing the job, check the key points below.
| Checkpoint | What to confirm |
|---|---|
| Connectors | Use rated connectors, such as MC4, and crimp them correctly |
| Cable support | Secure cables so they do not hang, rub, or pull on terminals |
| Bend radius | Avoid sharp bends and follow the cable’s minimum bend radius |
| Labeling and routing | Label and support DC conductors as required by NEC 690.31 |
| Polarity and torque | Double-check polarity and torque on every connection |
| Permits and grid tie-in | Use proper permits and a licensed electrician for panel or grid connection |
Need Help Specifying Solar Cable for a Project?
For installers, EPCs, and distributors, getting the cable spec right is part of controlling project risk and avoiding rework. Anpu Cable Group (APS Cable) manufactures H1Z2Z2-K solar cable to EN 50618 / IEC 62930 for DC interconnection in rooftop, ground-mount, and off-grid systems, with per-batch electrical, insulation-resistance, and safety testing and traceable records. If you are scoping conductor type, voltage class, and gauge, the APS technical service team can support sizing and compliance review.
Scoping conductor type, voltage class, and gauge for a solar project? Get a spec and compliance review from our cable engineers.
Talk to a cable expert →FAQs
Is PV wire or USE-2 better for a rooftop install?
Listed PV wire, in most cases. It has the strongest sunlight resistance, higher voltage ratings, and works in grounded and ungrounded arrays. Exposed USE-2/RHW-2 runs must be sunlight-resistant and within the array.
Can I use USE-2 instead of PV wire? Is it allowed by code?
Sometimes, with conditions. NEC Article 690 permits sunlight-resistant USE-2/RHW-2 in code-permitted PV locations, capped at 600V. Check the cable marking, the location, and the NEC edition your AHJ enforces.
Can I use regular THHN or house wire for solar panels outside?
No. THHN is generally limited to 75°C wet and is not built for long-term UV exposure. Use listed PV wire or sunlight-resistant USE-2/RHW-2 as required.
What gauge wire do I need, and how do I avoid voltage drop?
Size by the circuit’s maximum current plus NEC factors, then upsize on long runs. Keeping DC voltage drop low (often a 2% to 3% target) reduces power loss. A wire size and voltage drop calculator confirms it.
Why is solar cable more expensive than normal wire? Is it worth it?
PV wire uses thicker UV-rated insulation and tougher construction to last the life of an array. On a 25-year-plus install, compliant cable avoids early failures and code issues.
Related Articles
- Solar Cable Selection Guide: PV Wire vs USE-2
- H05VV-F Cable: Complete Guide to Specifications, Uses, and Applications
- EGC Ground Wire Sizing Chart: 2026 NEC Guide
- BVVB Flat Cable Guide: Specs, Applications, and Installation
References
- UL Standards & Engagement, UL 4703 – Photovoltaic Wire (scope and ratings)
- NFPA, NFPA 70, National Electrical Code (NEC), 2026 edition
- Eland Cables, Photovoltaic H1Z2Z2-K Cable to EN 50618 (superseding PV1-F)
Need support for your cable project? View ANPU Cable’s PV1-F / H1Z2Z2-K 1500V DC Solar Cable product page for specifications, customization options and quotation support, or contact our team for project-based cable selection.
