Wire size and breaker size from a load
Enter a load in amps, or watts and volts, and get the breaker and the minimum copper or aluminum conductor, with every step shown so an electrician can check it. Works for generator feeders, subpanels, EV and appliance circuits. It does not do voltage drop: use the voltage drop calculator for long runs.
Basis
2023 NEC. Continuous loads: 125% (210.19(A)(1), 215.2(A)(1)). Device: next standard size in 240.6(A). Conductor: Table 310.16 (as published), the insulation column corrected with Table 310.15(B)(1) and 310.15(C)(1) must carry the device rating, and the lower of the conductor and terminal columns must too (110.14(C)); 240.4(D) limits small conductors. Treat 14, 12 and 10 AWG as protected at 15, 20 and 30 A. A neutral that carries only unbalanced current is not counted; harmonic loads and other cases need an electrician. Equipment grounding conductor: Table 250.122. Results round to the safe side. Stops at 500 kcmil single conductors.
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