Ampacity Calculator
Calculate the safe current-carrying capacity of a wire.
How It Works
Adjusted ampacity = Base ampacity × conductor adjustment (4–6: 80%, 7–9: 70%, 10–20: 50%).
Example
12 AWG at 75°C with 5 conductors: 25 A × 0.8 = 20 A.
Frequently Asked Questions
What is ampacity?
The maximum current a conductor can carry continuously without exceeding its temperature rating.
Why does conductor count matter?
Bundled conductors trap heat, so NEC requires derating when more than 3 are in a raceway.
Which insulation rating is right?
Most modern wiring uses 90°C-rated THHN, but terminations often limit you to 60/75°C ampacity.