DC Electrical Calc: Wire Size

Wire sizing, voltage drop and ampacity for 12 V, 24 V and 48 V DC systems — offline, on site. Choosing a conductor means satisfying three rules at the same time: voltage drop, ampacity, and the small-conductor overcurrent limits in NEC 240.4(D). Most calculators check one of them and stop. Enter the current, the one-way distance and the system voltage. DC Electrical Calc returns the smallest conductor that satisfies all three at once, then tells you in one sentence which rule is actually limiting the answer: "Limited by voltage drop — not by ampacity. A smaller conductor would carry this current, but its drop would exceed the limit you set." When no size satisfies the constraints it says so, instead of returning the nearest one. Where the underlying table has no published value — 18 AWG and 16 AWG copper at 75 °C, for example — those sizes are treated as failing rather than guessed at.…