Required minimum ampacity
100 A
The conductor must be rated for at least the 100 A load current at the selected 75°C column.
NEC Table 310.16 · NEC 310.15(B)(16) equivalent
Calculator 06 / NEC 310
Wire size from load amps
Enter a load current and get the smallest copper conductor gauge per NEC Table 310.16 ampacity, with the citation behind the answer.
Conductor inputs
Conductor temperature rating
Table 310.16 ampacities assume not more than 3 current-carrying conductors; derate per NEC 310.15(C)(1) when more are present. Verify termination ratings (typically 75°C) before relying on the 90°C column.
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Smallest conductor (copper)
3 AWG (100 A)
Smallest 75°C column size with ampacity ≥ 100 A: 3 AWG at 100 A — 0 A of margin.
NEC Table 310.16 · NEC 310.15(B)(16) equivalent
Row context — selected gauge vs required
Selected (75°C)
3 AWG
100 A
Required
100 A
load current
Margin
+0 A
100 − 100
Same row in the other columns for reference: 60°C → 1 AWG (110 A) · 90°C → 3 AWG (115 A). Termination ratings (typically 75°C) may restrict which column is usable.
How this was calculated
- Required minimum ampacity = load current = 100 A.
- Read the copper 75°C column of NEC Table 310.16 (equivalent to 310.15(B)(16)) from smallest to largest gauge.
- Select the first gauge with ampacity ≥ 100 A — 3 AWG at 100 A.
- Derate per NEC 310.15(C)(1) if more than 3 current-carrying conductors are bundled, and confirm terminations allow the column temperature rating.
Engineering disclaimer: Ampacity tables reflect conductor alone; final sizing must also account for voltage drop (NEC 210.19(A) note), ambient temperature correction (NEC 310.15(B)(2)), continuous-load factors (NEC 210.19(A)(1)), and the authority having jurisdiction. Rule data is transcribed from NEC Table 310.16 for reference — always verify it against the current licensed copy of the NEC.