Wire Ampacity Chart — Copper & Aluminum

Pick the table for your conductor material — copper or aluminum — then find the wire size on the left and read across to the temperature-rating column. The temperature rating that governs is the lowest one in the circuit — and in practice that's usually the termination, not the insulation. Breakers, lugs, and receptacles are typically rated 60°C or 75°C, so a 90°C wire like THHN or XHHW-2 is normally applied at the 75°C column even though its insulation could run hotter.

The 90°C column still earns its keep: when you derate for high ambient temperature or for more than three current-carrying conductors in a raceway, you're allowed to start the math from the 90°C value (if the wire is 90°C-rated) — as long as the final answer doesn't exceed the termination-rated ampacity. Our ampacity & derating calculator runs that chain for you.

For the three smallest branch-circuit sizes, NEC 240.4(D) caps the overcurrent device below the table value: 14 AWG copper → 15 A, 12 AWG copper → 20 A, 10 AWG copper → 30 A (and 12 AWG aluminum → 15 A, 10 AWG aluminum → 25 A). So even though the chart shows 12 AWG copper at 25 A in the 75°C column, you still protect it at 20 A in ordinary branch-circuit work. The table values remain the correct starting point for derating.

The chart assumes 30°C (86°F) ambient air and no more than three current-carrying conductors together in a raceway or cable. Hotter ambients need the correction factors of NEC 310.15(B)(1); four or more current-carrying conductors need the adjustment factors of NEC 310.15(C)(1). Long runs may be governed by voltage drop before ampacity — check with the voltage drop calculator, using the circular-mil column here. And always verify against the code edition your jurisdiction actually enforces.