10 AWG UL4703 PV wire has a base ampacity of 40A at 90°C — but on a rooftop conduit in direct sun at 40°C ambient, that number drops to 23A after applying NEC derating factors. Choosing the right conductor starts with understanding ampacity, and this chart gives you the complete reference for every gauge we stock.
This guide covers base ampacity values for 6, 8, 10, and 12 AWG UL4703 copper PV wire, plus the NEC 690.8 derating calculations every installer needs before specifying cable for a project.
Contents
1. Base ampacity chart — UL4703 PV wire at 90°C
The values below are the base ampacity ratings per NEC Table 310.15(B)(16) for copper conductors with 90°C-rated insulation — the rating class of UL4703 PV wire. These are the starting values before applying derating factors.
| AWG | Cross-section (mm²) | Base ampacity at 90°C | Conductor resistance (Ω/1000ft) | Typical application |
|---|---|---|---|---|
| 12 AWG | 3.31 | 30 A | 1.93 | Module-to-module jumpers, short strings <50 ft |
| 10 AWG | 5.26 | 40 A | 1.24 | Standard residential and commercial string wiring |
| 8 AWG | 8.37 | 55 A | 0.778 | Long commercial runs, high-current strings, combiner feeds |
| 6 AWG | 13.3 | 75 A | 0.491 | Combiner-to-inverter feeder runs, utility-scale |
2. Temperature derating — NEC Table 310.15(B)(2)(a)
When ambient temperature exceeds 30°C, ampacity must be reduced by the correction factor from NEC Table 310.15(B)(2)(a). For 90°C-rated conductors like UL4703 PV wire, the correction factors are:
| Ambient temperature (°C) | Ambient temperature (°F) | 90°C conductor correction factor |
|---|---|---|
| 21–25°C | 70–77°F | 1.04 |
| 26–30°C | 79–86°F | 1.00 |
| 31–35°C | 88–95°F | 0.96 |
| 36–40°C | 97–104°F | 0.91 |
| 41–45°C | 106–113°F | 0.87 |
| 46–50°C | 115–122°F | 0.82 |
| 51–55°C | 124–131°F | 0.77 |
| 56–60°C | 133–140°F | 0.71 |
| 61–70°C | 142–158°F | 0.58 |
| 71–80°C | 160–176°F | 0.41 |
3. Conductor bundling derating — NEC Table 310.15(B)(3)(a)
When more than 3 current-carrying conductors share a raceway, ampacity must be reduced again. PV wire positive and negative conductors both count as current-carrying conductors.
| Current-carrying conductors in raceway | Ampacity adjustment factor |
|---|---|
| 1–3 | 1.00 (no derating) |
| 4–6 | 0.80 |
| 7–9 | 0.70 |
| 10–20 | 0.50 |
| 21–30 | 0.45 |
4. Conduit sun exposure — temperature adder
Per NEC 310.15(B)(3)(c), conduit exposed to direct sunlight on or above a rooftop must add a temperature correction to the ambient temperature before applying Table 310.15(B)(2)(a):
| Distance above roof | Temperature adder (°C) | Temperature adder (°F) |
|---|---|---|
| 0–90 mm (0–3.5 in) | +33°C | +60°F |
| Above 90 mm to 300 mm (3.5–12 in) | +22°C | +40°F |
| Above 300 mm to 900 mm (12–36 in) | +17°C | +30°F |
| Above 900 mm (36 in) | +0°C | +0°F |
5. Real-world calculation example
Scenario: commercial rooftop in Phoenix, AZ. Module Isc = 11A. Conduit runs within 90mm of the roof surface. 6 current-carrying conductors in conduit. Ambient temperature 40°C.
Step-by-step NEC 690.8 calculation
Step 1 — Minimum circuit ampacity:
Isc × 1.25 (irradiance factor) × 1.25 (continuous load) = 11A × 1.25 × 1.25 = 17.2A
Step 2 — Effective conduit temperature:
Ambient 40°C + rooftop adder (conduit within 90mm) +33°C = 73°C effective
Step 3 — Temperature derating factor:
At 73°C → correction factor = 0.58 (from Table 310.15(B)(2)(a))
Step 4 — Bundling derating factor:
6 conductors in raceway → adjustment factor = 0.80
Step 5 — Required ampacity:
17.2A ÷ (0.58 × 0.80) = 17.2A ÷ 0.464 = 37.1A required
Step 6 — Select conductor:
10 AWG base ampacity = 40A ≥ 37.1A required → 10 AWG UL4703 PV wire passes ✓
Use our free String Sizing Calculator
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Open Voltage Loss Calculator →6. Which AWG do you need?
Use this quick reference to select the right gauge before running the full NEC 690.8 calculation. These are general guidance values — always verify with the complete derating calculation for your specific site conditions.
| Module Isc | Run < 50 ft | Run 50–100 ft | Run 100–200 ft | Run 200+ ft |
|---|---|---|---|---|
| Up to 8A | 12 AWG | 12 AWG | 10 AWG | 10 AWG |
| 8–11A | 12 AWG | 10 AWG | 10 AWG | 8 AWG |
| 11–14A | 10 AWG | 10 AWG | 8 AWG | 8 AWG |
| 14–20A | 10 AWG | 8 AWG | 8 AWG | 6 AWG |
| 20–30A | 8 AWG | 8 AWG | 6 AWG | 6 AWG |
UL4703 Copper PV Wire — 6, 8, 10 & 12 AWG in Stock
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Browse UL4703 PV Wire →7. Frequently asked questions
What is the ampacity of 10 AWG PV wire?
The base ampacity of 10 AWG UL4703 PV wire is 40A at 90°C per NEC Table 310.15(B)(16). After applying temperature and bundling derating factors for a typical rooftop installation, the derated ampacity is typically 23–30A depending on site conditions.
What AWG PV wire do I need for a 400W solar panel?
A 400W panel typically has an Isc of 10–12A. Applying NEC 690.8 (Isc × 1.25 × 1.25 = 15.6–18.75A minimum circuit ampacity), then accounting for temperature and bundling derating, 10 AWG UL4703 PV wire is the correct specification for most residential and commercial installations. For runs over 150 ft, consider 8 AWG to keep voltage drop under 2%.
Does PV wire need to be derated for temperature?
Yes. NEC 310.15(B)(2)(a) requires ampacity derating whenever ambient temperature exceeds 30°C. For rooftop conduit in direct sun, an additional temperature adder of 17–33°C must be applied before selecting the derating factor. This is one of the most common calculation errors leading to inspection failures.
Can I use THHN wire instead of UL4703 PV wire?
No — not for DC string wiring. THHN wire is not listed for outdoor sunlight exposure or for use in ungrounded PV systems. NEC 690.31 requires PV Wire (UL4703) or USE-2 for exposed wiring in PV systems. THHN is permitted for AC wiring on the inverter output side within conduit.
What is the difference between 2000V and 600V UL4703 PV wire?
Both are certified to UL4703 but rated for different maximum system voltages. 2000V PV wire is required for most modern residential and all commercial/utility-scale systems where DC voltage exceeds 600V. See our 2000V vs 600V comparison guide for the full technical breakdown.
How much PV wire do I need for my solar project?
Calculate the total cable run per string (one-way distance × 2 for positive and negative conductors), multiply by the number of strings, and add 10–15% for field waste. Use our Voltage Loss Calculator to confirm gauge selection and get a reel estimate at the same time.
Questions about cable sizing for your project?
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