Code reference · NEC Table 310.16; 110.14(C); 240.4(D); 210.20(A); 210.19(A) IN
What size wire for a 15 amp breaker?
For a 15 A breaker, the minimum copper conductor is 14 AWG — set by NEC 240.4(D), which pairs 14 AWG copper with a maximum 15 A device. In aluminum, the minimum is 12 AWG (20 A at 75°C, 240.4(D) cap 15 A).
That answer assumes ≤3 current-carrying conductors, 30°C ambient, and a load that isn't continuous. A continuous load (3+ hours — EV charging, water heaters, most lighting) must be limited to 80% of the device: 12 A on this circuit (NEC 210.20(A)). Hot locations or bundled raceways derate the conductor further (310.15) and can push you up a size.
Distance is the other size driver. At 12 A load and 100 ft one-way on 14 AWG copper at 240 V, the computed voltage drop is 7.37 V (3.07%) — beyond the NEC's recommended 3% (210.19(A) Informational Note), so a longer run should be upsized even though the ampacity math passes.
Run the numbers yourself
Need this as a permit-ready document?
One Document Credit ($29) buys a full clause-cited compliance PDF — wire sizing, voltage drop, overcurrent protection, every value traceable to the section it came from.
Get your document →Every numeric value on this page is computed by the CircuitProof calculation engine — the same golden-tested code that renders our permit documents — not typed by hand. Code text is paraphrased and cited; always verify against your jurisdiction's adopted edition and a licensed professional before installation. Design documentation, not a stamped drawing.
More references: What size wire for a 20 amp breaker? · What size wire for a 30 amp breaker? · What size wire for a 40 amp breaker? · What size wire for a 50 amp breaker? · What size wire for a 60 amp breaker? · What size wire for a 70 amp breaker? · all 97 references