8 AWG Wire: Ampacity, Uses & Specs | PES Supply

8 AWG Wire — Ampacity, Uses & Specifications

NEC Table 310.16 ampacity ratings, solar PV applications, voltage drop calculator, and installation guide for 8 AWG copper and aluminum conductors.

By PES Supply Technical Team — Last updated July 31, 2026

8 AWG Wire Overview

8 AWG wire is used for **larger PV source circuits, subpanel feeders, and EV charging circuits** at 40–50A. In solar installations, 8 AWG THHN/THWN-2 is commonly used for inverter AC output circuits, charge controller DC connections, and battery interconnect cables for mid-size systems. It is also standard for electric range circuits and larger water heater installations.

8 AWG wire has a cross-sectional area of 16.51 kcmil (8.37 mm²) with a conductor diameter of 0.1285 inches (3.264 mm). The copper weight is approximately 50.0 lbs per 1,000 feet, with a DC resistance of 0.628 Ω/1,000 ft for copper and 1.03 Ω/1,000 ft for aluminum at 75°C.

50A
75°C Copper Rating
55A
90°C Copper Rating
16.51
Area (kcmil)

8 AWG Wire Specifications

Specification Copper (Cu) Aluminum (Al)
AWG Size 8 8
Ampacity (60°C / 140°F) 40A 35A
Ampacity (75°C / 167°F) 50A 40A
Ampacity (90°C / 194°F) 55A 45A
Conductor Diameter 0.1285 in (3.264 mm) 0.1285 in (3.264 mm)
Cross-Sectional Area 16.51 kcmil (8.37 mm²) 16.51 kcmil (8.37 mm²)
DC Resistance (Ω/1000 ft @ 75°C) 0.628 1.03
Weight (lb per 1000 ft) 50.0 lbs 15.0 lbs
Wire Types Available THHN, THWN-2, XHHW-2, USE-2, PV Wire, NM-B (Romex), MC Cable, UF-B

NEC Table 310.16 — 8 AWG Ampacity Ratings

The following ampacity values are from NEC Table 310.16 (formerly Table 310.15(B)(16)), which provides allowable ampacities of insulated conductors rated up to 2000V. Ampacity is the maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.

Conductor Type 60°C (140°F) 75°C (167°F) 90°C (194°F)
Copper (Cu) 40A 50A 55A
Aluminum (Al) 35A 40A 45A

Insulation Types by Temperature Rating

Temp Rating Insulation Types Common Applications
60°C / 140°F TW, UF General wiring, direct burial (UF)
75°C / 167°F THW, THWN, XHHW, USE Commercial conduit, wet locations
90°C / 194°F THHN, THWN-2, XHHW-2, USE-2, PV Wire Solar PV, high-temp, dry & wet locations

Important: The 90°C ampacity column may only be used for derating purposes (e.g., temperature correction and conduit fill adjustment). The actual circuit ampacity is limited by the equipment terminal rating — typically 75°C for equipment rated 100A or greater, and 60°C for equipment rated less than 100A per NEC 110.14(C).

Solar PV Applications — NEC Article 690 Requirements

Solar photovoltaic (PV) installations are governed by NEC Article 690, which has specific requirements for conductor sizing, temperature correction, and overcurrent protection that go beyond general wiring rules. 8 AWG wire is commonly used in PV systems for source circuits, output circuits, and interconnection wiring.

NEC 690.8 — PV Circuit Current Sizing

For PV source and output circuits, NEC 690.8(A) requires that conductors be sized to carry not less than 125% of the continuous current. This accounts for the fact that PV circuits can operate at maximum current for extended periods:

  • PV Source Circuit Current: The rated Isc (short-circuit current) of the PV module × 1.25 (NEC 690.8(A)(1)(1))
  • PV Output Circuit Current: The rated Isc of the PV array × 1.25 (NEC 690.8(A)(1)(2))
  • Conductor Ampacity: Must be ≥ 125% of the calculated circuit current after applying all correction factors (NEC 690.8(B))

For example, if 8 AWG THHN-2/PV Wire is rated at 55A at 90°C, the maximum continuous PV circuit current is 55A × 0.80 = 44A (after applying the 125% continuous current factor).

Temperature Correction — NEC Table 310.15(B)(1)

PV conductors often operate in high ambient temperatures, especially on rooftops. NEC Table 310.15(B)(1) provides correction factors that reduce ampacity at elevated temperatures. For rooftop installations where conductors are within 0.5 inches of the roof surface, add 33°C (91°F) to the ambient temperature per NEC 310.15(B)(2).

Ambient Temp Range 60°C Rating 75°C Rating 90°C Rating
21–25°C (70–77°F) 1.00 1.00 1.00
26–30°C (79–86°F) 1.00 1.00 1.00
31–35°C (88–95°F) 0.91 0.94 0.96
36–40°C (97–104°F) 0.82 0.88 0.91
41–45°C (106–113°F) 0.71 0.82 0.87
46–50°C (115–122°F) 0.58 0.75 0.82
51–55°C (124–131°F) 0.41 0.67 0.76
56–60°C (133–140°F) — 0.58 0.71
61–70°C (141–158°F) — 0.33 0.58
71–80°C (159–176°F) — — 0.41

Example: A 8 AWG THHN-2 PV Wire rated at 55A at 90°C, installed on a rooftop at 40°C ambient + 33°C rooftop adder = 73°C, has a correction factor of 0.58. Adjusted ampacity = 55A × 0.58 = 31A. After the 125% continuous current requirement: maximum PV circuit current = 25A.

Wire Types for PV Applications

NEC 690.31(C) requires that PV source and output circuit conductors use one of the following wire types:

  • USE-2 — Underground Service Entrance cable, 90°C wet/dry, sunlight-resistant
  • PV Wire — Specifically rated for PV applications, 90°C wet/dry, 600V or 2000V, sunlight-resistant, direct burial, improved flame resistance
  • XHHW-2 — Cross-linked polyethylene, 90°C wet/dry, may be used in raceways
  • THWN-2 — Thermoplastic heat and moisture resistant nylon, 90°C wet/dry, may be used in raceways

PV Wire and USE-2 are the preferred types for exposed rooftop wiring, as they are rated for sunlight resistance and the harsh thermal environment near solar modules. THHN/THWN-2 is acceptable when installed in conduit.

Installation Requirements — NEC Articles 300 & 310

Proper installation of 8 AWG conductors requires compliance with NEC Article 300 (Wiring Methods) and NEC Article 310 (Conductors for General Wiring). These articles cover conduit fill, bending radius, support spacing, and physical protection requirements.

Conduit Fill Calculations — NEC Chapter 9

NEC Chapter 9 Table 1 specifies maximum conduit fill percentages: 53% for 1 conductor, 31% for 2 conductors, and 40% for 3 or more conductors. The following table shows typical EMT conduit sizes for 8 AWG THHN/THWN-2 conductors:

Number of Conductors Min. EMT Conduit Size Fill % Used
1 conductor 1/2" ~30%
2 conductors 3/4" ~25%
3 conductors 3/4" ~35%
4 conductors 1" ~38%

Note: Conduit fill values are approximate for THHN/THWN-2 copper conductors in EMT. Always verify with NEC Chapter 9 Tables 4 and 5 for your specific wire type and conduit material. When more than 3 current-carrying conductors are installed in the same conduit, ampacity must be derated per NEC Table 310.15(C)(1).

Bending Radius — NEC 300.34

NEC 300.34 requires that conductors not be bent to a radius less than 8 times the overall diameter of the conductor or cable. For 8 AWG wire with an approximate diameter of 0.1285" (stranded), the minimum bending radius is:

  • Single conductor: 8 × 0.1285" = 1.03" minimum bend radius
  • In conduit: The conduit bending radius must meet NEC Table 2 (Chapter 9) requirements based on conduit size, which is typically more restrictive than the conductor bending radius

Support Spacing — NEC 300.11 & 330.30

Conductors in raceways are supported by the conduit system itself. For cable assemblies (such as MC cable or NM-B in 8 AWG), support spacing requirements include:

  • MC Cable: Secured every 6 feet and within 12 inches of each box, fitting, or termination (NEC 330.30)
  • NM-B (Romex): Secured every 4.5 feet and within 12 inches of boxes (NEC 334.30)
  • Conduit (EMT): Supported every 10 feet and within 3 feet of boxes/terminations (NEC 358.30)
  • Conduit (RMC): Supported every 10 feet and within 3 feet of boxes/terminations (NEC 344.30)

Physical Protection — NEC 300.4

NEC 300.4 requires physical protection of conductors and cables:

  • Through studs/joists: Bored holes must be at least 1.25 inches from the edge of the framing member, or protected with a steel plate at least 1/16 inch thick
  • Exposed to damage: Cables passing through floor/ceiling must be protected by guard strips at least as tall as the cable
  • Underground: Direct-buried conductors must be at the depths specified in NEC Table 300.5 — minimum 24 inches for direct-burial cables (18 inches for residential branch circuits with GFCI protection)
  • In wet locations: Raceways must be arranged to prevent moisture entry; drain points should be provided at low points in the run

Conductor Derating — NEC 310.15(C)(1)

When more than 3 current-carrying conductors are installed in the same raceway or cable, the ampacity must be reduced per NEC Table 310.15(C)(1) (formerly 310.15(B)(3)(a)):

  • 4–6 conductors: 80% ampacity
  • 7–9 conductors: 70% ampacity
  • 10–20 conductors: 50% ampacity
  • 21–30 conductors: 45% ampacity
  • 31–40 conductors: 40% ampacity
  • 41+ conductors: 35% ampacity

Neutral conductors carrying harmonic currents (non-linear loads) are counted as current-carrying conductors. Equipment grounding conductors are not counted.

Voltage Drop Reference (8 AWG Copper, 240V, 50A)

Voltage drop is a critical consideration in conductor sizing. The NEC recommends a maximum voltage drop of 3% on feeders and 5% total (feeder + branch circuit) for efficient operation. For solar PV circuits, voltage drop directly affects system yield — every 1% of voltage drop represents approximately 1% power loss.

Distance (ft) Voltage Drop (V) % Drop Status
25 ft 1.57V 0.7% ✓ Good
50 ft 3.14V 1.3% ✓ Good
75 ft 4.71V 2.0% ✓ Good
100 ft 6.28V 2.6% ✓ Good
150 ft 9.42V 3.9% ⚠ Marginal
200 ft 12.56V 5.2% ✗ Upsize
300 ft 18.84V 7.8% ✗ Upsize
400 ft 25.12V 10.5% ✗ Upsize

Calculations based on copper conductor resistance of 0.628 Ω/1000 ft at 75°C operating temperature. Values assume single-phase AC or DC circuits (2 conductors). For three-phase circuits, multiply voltage drop by 0.866.

Interactive Voltage Drop Calculator

Calculate voltage drop for 8 AWG copper wire based on your specific circuit parameters. This calculator uses the standard voltage drop formula: VD = 2 × R × I × L ÷ 1000, where R is conductor resistance per 1000 ft, I is current in amps, and L is one-way circuit length in feet.

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Don't see what you need? We stock THHN, THWN-2, XHHW-2, USE-2, PV Wire, MC Cable, and bare copper in all AWG sizes. Browse all wire & cable → or contact our team for custom quotes.

Frequently Asked Questions

What is the ampacity of 8 AWG copper wire?
The ampacity of 8 AWG copper wire depends on the temperature rating of the insulation. Per NEC Table 310.16: 60°C rated insulation (TW, UF) is rated at 40A, 75°C rated insulation (THW, THWN, XHHW) is rated at 50A, and 90°C rated insulation (THHN, THWN-2, XHHW-2) is rated at 55A. The actual circuit ampacity is limited by the temperature rating of the equipment terminals — typically 75°C for most equipment rated 100A or more, and 60°C for equipment rated less than 100A.
What size breaker do I need for 8 AWG wire?
For 8 AWG copper wire, the maximum breaker size depends on the insulation temperature rating and equipment terminal ratings. At 75°C (the standard for most equipment), 8 AWG copper is rated at 50A. The breaker should not exceed the ampacity of the conductor at the lowest temperature rating in the circuit. For continuous loads (including most solar PV circuits), the conductor must be sized at 125% of the continuous load current per NEC 210.19(A)(1).
Can I use 8 AWG wire for solar PV installations?
Yes. For solar PV installations per NEC Article 690, 8 AWG wire must be rated for the environment. PV source and output circuits require USE-2 or PV Wire (90°C wet-rated, sunlight-resistant) per NEC 690.31(C). The conductor must be sized at 125% of the PV circuit continuous current per NEC 690.8(A). Temperature correction factors from NEC Table 310.15(B)(1) must be applied based on the highest ambient temperature the conductor will experience. For rooftop installations where conductors run within 0.5 inches of the roof surface, add 33°C to the ambient temperature per NEC 310.15(B)(2).
How far can I run 8 AWG wire before voltage drop becomes a problem?
Voltage drop depends on current, length, and system voltage. For 8 AWG copper wire (resistance 0.628 Ω/1000 ft), the general rule is to keep voltage drop under 3% for feeders and under 5% total. Use the interactive calculator above to determine exact values for your circuit. As a quick reference at 50A and 240V, 8 AWG copper stays within 3% voltage drop at approximately 114 feet one-way.
What conduit size do I need for 8 AWG wire?
For THHN/THWN-2 8 AWG conductors in EMT conduit, typical minimum conduit sizes are: 1 conductor → 1/2", 2 conductors → 3/4", 3 conductors → 3/4", and 4 conductors → 1". These values are based on NEC Chapter 9 Table 1 (40% fill for 3+ conductors). Always verify with NEC Chapter 9 Table 5 (conductor area) and Table 4 (conduit area) for your specific wire type and conduit material. When conductors are bundled or installed in high ambient temperatures, derating factors may require upsizing the conduit.

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Disclaimer: This guide is for informational purposes and is based on the 2023 National Electrical Code (NEC). Always consult the current NEC and local codes, and work with a licensed electrician. Ampacity values reference NEC Table 310.16. PES Supply is not liable for installation errors or code violations.