With the rapid development of the photovoltaic (PV) industry in the Americas, selecting the right cables for projects has become a top concern for investors, EPC contractors, and construction teams. As the "veins" of the PV system, cables not only carry electricity but also directly affect the system's safety, lifetime, and investment returns.
In the American market, PV cables must comply with UL standards. Among them, UL44 series cables are widely used due to their excellent heat resistance, weather resistance, and insulation performance. In addition to the well-known XHHW-2 and RHW-2, cables such as PV Wire, USE-2, THHN, THWN-2, MV-90, and MV-105 also play important roles at different stages of PV projects.
This article systematically analyzes the cable requirements of each PV station stage - from modules → combiner box → inverter → distribution → grid interconnection - and introduces the most commonly used UL44 series cables in detail.
Why Cable Selection Is Critical in PV Projects?
Cables are the key to long-term stable operation of PV systems:
- Safety: Cable insulation aging, overheating, or short circuits can directly cause fires.
- Efficiency: Excessive resistance or mismatched cables can cause energy losses.
- Lifetime: High-quality cables can last 25–30 years, matching PV module lifespans.
Compliance: In the Americas, almost all large-scale PV projects require cables certified under UL44, UL4703, and UL1072 standards.
Thus, each stage of the PV system requires the right cable type to ensure performance and reliability.
UL Cable Applications Across PV Project Stages
For a quick overview, see the following table:
| PV Stage | Common Cable Types | Standard/Certification | Voltage Rating | Application Features |
|---|---|---|---|---|
| Module → Combiner Box (DC) | PV Wire, USE-2 | UL4703, UL44 | 600V / 1000V / 2000V | Outdoor DC wiring, UV/weather resistant |
| Combiner Box → Inverter (DC) | PV Wire, USE-2, RHW-2 | UL44 | 600V / 2000V | Suitable for direct burial or conduit |
| Inverter → Distribution (AC) | XHHW-2, RHW-2, THWN-2, THHN | UL44 | 600V | AC wiring, conduit or tray installation |
| Distribution → Transformer | XHHW-2, RHW-2, MV-90, MV-105 | UL44 / UL1072 | 600V / 5kV / 15kV | Low-voltage and medium-voltage applications |
| Transformer → Grid | MV-90, MV-105 | UL1072 | 5kV / 15kV / 25kV / 35kV | Medium-voltage grid tie, long-term use |
PV Wire & USE-2: Modules → Combiner Box (DC Side)
Cables between PV modules and from modules to the combiner box are the capillaries of the DC side.
- PV Wire
Standard: UL4703 (PV-specific, based on UL44)
Voltage rating: 600V / 1000V / 2000V
Advantages: UV, weather, and moisture resistance for long-term outdoor use
Applications: Module-to-module, module-to-combiner box connections
- USE-2
Standard: UL44
Voltage rating: 600V / 1000V
Advantages: Suitable for direct burial, UV resistance, cost-effective
Applications: Module strings, module-to-combiner box connections
Comparison: PV Wire vs USE-2
| Feature | PV Wire | USE-2 |
|---|---|---|
| Standard | UL4703 | UL44 |
| Voltage rating | 600V / 1000V / 2000V | 600V / 1000V |
| Weatherproof | Excellent | Good |
| Application | Module interconnections | Module interconnections |
| Cost | Slightly higher | Lower |
RHW-2: Combiner Box → Inverter (DC Trunk Cables)
This stage carries larger DC currents, demanding high safety and durability.
- RHW-2
Full name: Rubber-insulated Heat and Water-resistant
Standard: UL44
Temperature rating: 90°C / 105°C
Advantages: Thick insulation, heat and moisture resistance, suitable for burial or conduits
Applications: Main DC trunk cables from combiner box to inverter
XHHW-2 & RHW-2 & THHN/THWN-2: Inverter → Distribution Panel (AC Side)
Inverter AC output typically uses 600V low-voltage cables, with common types including:
- XHHW-2: XLPE insulation, 90°C / 600V; heat, moisture, and oil resistant
- RHW-2: EPR insulation, 105°C / 600V; flexible, highly durable
- THHN / THWN-2: PVC insulation + nylon jacket; low-cost, widely available, THWN-2 supports 90°C wet/dry
Comparison: XHHW-2 vs RHW-2 vs THHN/THWN-2
| Feature | XHHW-2 | RHW-2 | THHN / THWN-2 |
|---|---|---|---|
| Insulation | XLPE | EPR | PVC + Nylon |
| Temperature | 90°C | 105°C | 90°C |
| Flexibility | Medium | High | General |
| Cost | Medium | Slightly higher | Low |
| Applications | Industrial/PV AC | High-reliability AC | General AC distribution |
Low-Voltage & Medium-Voltage Cables: Distribution Panel → Step-up Transformer
At this stage, both low-voltage and medium-voltage cables may be used:
- Low voltage: XHHW-2, RHW-2
- Medium voltage: MV-90, MV-105
- MV-90: Max conductor temp 90°C
- MV-105: Max conductor temp 105°C, suitable for high-temperature or dense installations
- Voltage levels: 5kV, 15kV, 25kV, 35kV
MV90 & MV105: Transformer → Grid Interconnection (Medium Voltage)
This is the main artery connecting the PV plant to the grid:
- MV-90: Lower cost, suitable for standard conditions
- MV-105: Higher temperature rating, ideal for harsh or hot environments
- Voltage levels: Typically 15kV, 25kV, 35kV
Comparison: MV-90 vs MV-105
| Feature | MV-90 | MV-105 |
|---|---|---|
| Conductor Temp | 90°C | 105°C |
| Insulation | XLPE/EPR | Higher-grade XLPE/EPR |
| Voltage Range | 5–35kV | 5–35kV |
| Cost | Lower | Higher |
| Applications | General use | Harsh/hot environments |
In American PV projects, UL44 series cables are widely used across all electrical stages:
DC side: PV Wire, USE-2, RHW-2
AC low-voltage side: XHHW-2, RHW-2, THHN, THWN-2
Medium-voltage side: MV-90, MV-105
Proper cable selection ensures not only 25–30 years of safe, stable operation but also reduces O&M costs and increases project profitability.
If you are in the design or bidding phase of a PV power plant project, this guide can help you choose the most suitable UL44 cable solution according to UL standards, project environment, budget, and schedule.
Why Choose Dongguan Greater Wire & Cable Co., Ltd.?
As more EPC contractors in the Americas seek cost-effective and reliable cable suppliers, many are turning to China. At Dongguan Greater Wire & Cable Co., Ltd., we have become a trusted partner for PV projects worldwide.
✅ Certified Products: UL, IEC, TUV certifications for global compliance
✅ Full Product Range: XHHW-2, RHW-2, USE-2, PV Wire, THWN-2, MV-90, MV-105
✅ Reliable Logistics: On-time delivery with secure export packaging
✅ Strong Support: Fast response, professional technical support, and tailored solutions
📞 Contact Us Today for Your Next PV Project
Dongguan Greater Wire & Cable Co., Ltd.
WhatsApp/WeChat: +86 135 1078 4550 / +86 136 6257 9592
Email: manager01@greaterwire.com
👉 Let's power your solar future together with cables you can trust.