Copper vs Aluminum Wire: Resistance, Ampacity & Cost (2026)
One ratio drives every other difference on this page: aluminum’s resistivity is 21.2 Ω-cmil/ft at 75 °C versus copper’s 12.9, so aluminum has 1.64× the resistance of copper at the same cross-section. NEC Chapter 9, Table 8 shows it directly — 12 AWG solid copper is 1.93 Ω per 1,000 ft, 12 AWG aluminum is 3.18 Ω (3.18 ÷ 1.93 = 1.65). At 4/0 it’s 0.0608 Ω vs 0.100 Ω, the same 1.65 ratio. What that costs you in practice: a 20 A load at the end of a 100 ft run on 12 AWG copper drops 2 × 1.93 × 0.1 × 20 = 7.72 V, or 6.4% of a 120 V circuit. The same run in 12 AWG aluminum drops 2 × 3.18 × 0.1 × 20 = 12.72 V, or 10.6%. Aluminum fixes this by going up two AWG sizes, which restores both ampacity and resistance to within about 3% of copper — 2/0 copper is 0.0967 Ω/1000 ft, 4/0 aluminum is 0.100 Ω. Aluminum wins on the two things that scale with size: it weighs 30.4% of copper per unit volume (0.0975 vs 0.3212 lb/in³), and raw copper traded near $6.20/lb in mid-July 2026 against roughly $1.42/lb for aluminum — a 4.4× metal spread on top of a 3.3× density spread. Copper wins on everything that scales with the number of terminations. That single trade-off explains why the 2026 US market runs aluminum service entrances into copper branch circuits, and why the debate almost never turns on conductivity alone.
| Factor | Copper | Aluminum |
|---|---|---|
| Resistance per 1,000 ft (same gauge, 75 °C) | NEC Ch. 9 Table 8: 12 AWG solid 1.93 Ω, 10 AWG 1.21 Ω, 8 AWG 0.764 Ω, 2 AWG 0.194 Ω, 4/0 0.0608 Ω. Resistivity constant K = 12.9 Ω-cmil/ft. Stranded runs slightly higher than solid (12 AWG stranded = 1.98 Ω) because of lay length. | 12 AWG 3.18 Ω, 10 AWG 2.00 Ω, 8 AWG 1.26 Ω, 2 AWG 0.319 Ω, 4/0 0.100 Ω. K = 21.2 Ω-cmil/ft. Every pair works out to 1.64–1.65× copper: 3.18/1.93 = 1.647, 0.100/0.0608 = 1.645. Treat 1.65× as the rule of thumb and it will be right to within 1% at any size. |
| The “two gauge sizes larger” equivalence rule | Baseline 75 °C ampacities (Table 310.16): 4 AWG = 85 A, 2 AWG = 115 A, 1/0 = 150 A, 2/0 = 175 A, 4/0 = 230 A. | Step up two AWG sizes and you land within ~5% on ampacity and ~4% on resistance. 2 AWG Cu (115 A, 0.194 Ω) ≈ 1/0 Al (120 A, 0.201 Ω). 2/0 Cu (175 A, 0.0967 Ω) ≈ 4/0 Al (180 A, 0.100 Ω). NEC Table 310.12 codifies it for single-phase dwelling services: 100 A = 4 Cu or 2 Al; 150 A = 1 Cu or 2/0 Al; 200 A = 2/0 Cu or 4/0 Al; 400 A = 400 kcmil Cu or 600 kcmil Al. |
| Ampacity at the same size | Table 310.16, 75 °C column: 12 AWG 25 A, 10 AWG 35 A, 8 AWG 50 A, 6 AWG 65 A, 2 AWG 115 A, 1/0 150 A, 4/0 230 A, 250 kcmil 255 A. Small-conductor rule 240.4(D) still caps 14 AWG at 15 A, 12 AWG at 20 A, 10 AWG at 30 A regardless of the table. | 12 AWG 20 A, 10 AWG 30 A, 8 AWG 40 A, 6 AWG 50 A, 2 AWG 90 A, 1/0 120 A, 4/0 180 A, 250 kcmil 205 A — consistently 77–86% of copper at the same size, most commonly about 80% (20/25 = 80%, 90/115 = 78.3%, 180/230 = 78.3%, 205/255 = 80.4%). 240.4(D) caps 12 AWG aluminum at 15 A and 10 AWG at 25 A, one step below copper. |
| Weight per 1,000 ft (bare conductor) | Density 0.3212 lb/in³. 12 AWG ≈ 19.8 lb per 1,000 ft (0.0198 lb/ft); 2/0 ≈ 403 lb; 4/0 ≈ 641 lb (0.64 lb/ft). A 300 ft pull of three 4/0 copper conductors is roughly 576 lb of metal before insulation. | Density 0.0975 lb/in³ — 30.4% of copper. 12 AWG ≈ 6.0 lb per 1,000 ft; 4/0 ≈ 195 lb (0.195 lb/ft), a 3.3× reduction at the same gauge. Even after upsizing two steps for equal ampacity, 4/0 aluminum at 195 lb/1,000 ft is still 2.1× lighter than the 2/0 copper it replaces (403 lb). That difference is why utility and long-feeder work went aluminum. |
| Cost per foot (mid-July 2026, single-conductor building wire) | 4/0 THHN/THWN-2 copper runs about $8.64/ft; 2/0 THHN about $5.72/ft. Copper cathode traded near $6.20/lb on COMEX on July 17, 2026, so the metal alone in 1,000 ft of 4/0 is roughly 641 lb × $6.20 ≈ $3,970. | 4/0 XHHW-2 aluminum runs about $2.19/ft — 3.9× cheaper than 4/0 copper, a $6.45/ft gap. Compared on the equal-ampacity pair that actually matters, 4/0 Al at $2.19/ft vs 2/0 Cu at $5.72/ft is still 2.6×. On a 200 A service with three 100 ft conductors that is $657 vs $1,716 — about $1,059 saved. Aluminum ran near $1.42/lb in July 2026, so the metal in 1,000 ft of 4/0 is ~195 lb × $1.42 ≈ $277, roughly 1/14 of copper’s metal cost. |
| Terminations, torque & antioxidant | Lands on any listed terminal, including CU-only lugs and standard 15/20 A back-wire or screw-terminal devices. Torque per NEC 110.14(D) still applies, but a slightly loose copper connection degrades far more slowly. | Requires terminals listed for aluminum — AL7CU/AL9CU or CU/AL on lugs and breakers, and specifically CO/ALR on 15/20 A receptacles and switches (a CU/AL mark does not qualify for 15/20 A devices). NEC 110.14(D) requires the manufacturer’s indicated torque be achieved by an approved means; the 2023 NEC widened “calibrated torque tool” to include shear-bolt and breakaway devices. Torque values live on the equipment label and range from roughly 20 in-lb on small setscrews to over 300 in-lb on large mechanical lugs. Wire-brushing and an oxide-inhibiting compound is standard practice per 110.3(B) manufacturer instructions — many AL-rated lugs ship pre-filled, and code does not impose a blanket paste requirement. |
| Safety history & the AA-8000 change | No comparable failure history in branch circuits. Copper’s oxide is conductive enough that a marginal joint tends to fail gradually rather than run away thermally. | The bad reputation is real but dated and specific. Pre-1972 branch circuits used AA-1350 alloy developed for transmission lines. A Franklin Research Center survey for the CPSC found homes wired with that pre-1972 aluminum were 55 times more likely to have a connection at an outlet reach “fire hazard conditions” (cover-plate screws at 149 °C / 300 °F, or sparking) than copper-wired homes. Alcoa patented the first 8000-series conductor alloy in 1972, followed by AA-8030 (1973) and AA-8176 (1975/1980). AA-8000 alloys mechanically behave like copper and retain tensile strength after the current-cycle and current-cycle-submersion tests. The NEC has required AA-8000 for building wire since 1987 — now NEC 310.3(B) (310.106(B) in older editions), covering solid aluminum 12, 10 and 8 AWG plus stranded aluminum 8 AWG through 1000 kcmil in RHH, RHW, XHHW, THW, THHW, THWN, THHN and SE Style U/R. |
| Thermal expansion & creep | Coefficient of linear expansion ≈ 16.5–17.1 × 10⁻⁶ /°C. Higher creep resistance means clamping force in a properly torqued joint holds through years of load cycling. | ≈ 23.1–23.8 × 10⁻⁶ /°C, about 35–40% more movement per degree. Aluminum also creeps (cold-flows) faster and at lower temperature than copper, so a compressed conductor slowly relaxes out from under a setscrew. Both effects reduce contact pressure, which raises joint resistance, which raises temperature — the runaway loop behind aluminum connection failures. Modern AA-8000 alloy plus AL-rated, torqued terminations is the engineered answer; the physics of expansion has not changed. |
| Availability in small gauges | Manufactured from 18 AWG up (and far finer for electronics and flexible cord), solid or stranded, in NM-B, THHN, MC, UF and tinned marine grades. Anything below 8 AWG is copper by default in the US market. | Building wire is made in stranded AA-8000 from 8 AWG through 1000 kcmil — that is the exact size range NEC 310.3(B) names. The code’s minimum permitted aluminum size is 12 AWG (vs 14 AWG for copper), but 12 and 10 AWG aluminum branch wire is effectively not stocked, and NEC 310.3(C) requires 8 AWG and larger in a raceway to be stranded anyway. Practical floor: 8 AWG, most commonly seen at 6 AWG and up in SER, SEU, URD and XHHW-2. |
| Typical applications | Branch circuits and receptacle/switch wiring (15–20 A, many terminations, small gauges). All low-voltage DC: 12 V and 24 V systems, solar array and battery cabling, automotive, and anything where a 3% drop budget on a low source voltage leaves no headroom. Marine and RV: ABYC E-11 calls for stranded copper conductors, with tinned copper per UL 1426 the norm — solid conductor is out because it work-hardens and fractures under vibration. | Service entrance and service laterals (SER, SEU, URD, XHHW-2), subpanel feeders, long distribution runs, utility drops, and large commercial feeders where the conductor count is low, the run is long, and every pound and dollar per foot compounds. AA-8000 branch circuits are code-legal with CO/ALR devices but rarely worth the termination discipline in residential work. |
Our Verdict
Split it by termination count, not by preference. Aluminum belongs on service entrances and feeders. On a 200 A residential service, NEC Table 310.12 lets you use 4/0 aluminum where 2/0 copper would otherwise be required, and at mid-July 2026 pricing that is roughly $2.19/ft against $5.72/ft — about $1,059 saved on three 100 ft conductors, at 195 lb per 1,000 ft instead of 403 lb. A service entrance has perhaps six terminations total, all in AL-rated lugs, all torqued to a label value, all inspectable. That is exactly the environment where aluminum’s weaknesses are managed and its 2.6× cost advantage is fully banked. The same logic carries to subpanel feeders and any long run where you are buying pounds of metal rather than connections. Copper belongs on branch circuits. A 1,500 sq ft house has hundreds of device terminations, and each one is a spot where 23.8 × 10⁻⁶ /°C expansion and cold flow can slowly back a conductor out from under a screw. Aluminum branch wiring is legal in AA-8000 with CO/ALR-marked 15/20 A devices, and AA-8000 is genuinely a different material from the AA-1350 that earned the 55×-fire-hazard-conditions finding in the Franklin Research Center survey for the CPSC. But the savings on 12 and 14 AWG are trivial while the termination discipline required is not, and 12 AWG aluminum is capped at 15 A by 240.4(D) versus 20 A for copper. Copper is the default and should be. Copper is also the only sensible choice for every low-voltage DC system — solar, battery banks, 12/24 V vehicle and house wiring — because on a 12 V source a 3% drop budget is 0.36 V, and aluminum’s 1.65× resistance eats that immediately unless you upsize two gauges into cable that will not fit the terminals it needs to land on. For boats specifically, ABYC E-11 calls for stranded copper (tinned copper per UL 1426 in practice) and rules out solid conductor entirely for vibration resistance, so aluminum never enters the conversation. Same for RVs and any mobile installation. The short version: buy aluminum by the pound, buy copper by the connection.