Wire Size Calculator
NEC double-check: ampacity (310.16) and 3% voltage drop. The bigger of the two wins.
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How it works
- Ampacity check — NEC Table 310.16 (75°C column, THHN). Continuous loads sized at 125% per NEC 210.19(A)(1). Small conductors capped per 240.4(D): 14 AWG → 15A, 12 AWG → 20A, 10 AWG → 30A.
- Voltage-drop check — drop must stay ≤ 3% (NEC 210.19(A) informational note).
- The larger of the two results wins — long runs often need bigger wire than ampacity alone suggests.