Wire Derating Calculator
Stack ALL NEC derating factors — temperature, conduit fill, continuous load — into one combined result
Base Wire Selection
Ambient Temperature Correction
NEC Table 310.15(B)(1) — correction factors for ambient temperatures other than 30°C (86°F)
Conduit Fill Derating
NEC Table 310.15(C)(1) — adjustment factors for more than 3 current-carrying conductors
Continuous Load Adjustment
NEC 210.20(A) — continuous loads (3+ hours) require 125% conductor sizing
Combined Derating Results
Final Derated Ampacity
35.0A
10 AWG Cu @ 75°C
Base Ampacity
35A
NEC 310.16
Temp Factor
×1.000
30°C ambient
Conduit Factor
×1.00
3 conductors
Combined Factor
×1.000
0.0% total derating
Calculation
35A × 1.000 × 1.00 = 35.0A
✓ No derating required — conditions at or better than standard rating
NEC 310.16 — Copper Ampacity Reference
Base ampacity at 30°C ambient, ≤3 current-carrying conductors in raceway
| Gauge | 60°C | 75°C | 90°C | Derated |
|---|---|---|---|---|
| 14 AWG | 15A | 20A | 25A | 20.0A |
| 12 AWG | 20A | 25A | 30A | 25.0A |
| 10 AWG | 30A | 35A | 40A | 35.0A |
| 8 AWG | 40A | 50A | 55A | 50.0A |
| 6 AWG | 55A | 65A | 75A | 65.0A |
| 4 AWG | 70A | 85A | 95A | 85.0A |
| 3 AWG | 85A | 100A | 115A | 100.0A |
| 2 AWG | 95A | 115A | 130A | 115.0A |
| 1 AWG | 110A | 130A | 145A | 130.0A |
| 1/0 AWG | 125A | 150A | 170A | 150.0A |
| 2/0 AWG | 145A | 175A | 195A | 175.0A |
| 3/0 AWG | 165A | 200A | 225A | 200.0A |
| 4/0 AWG | 195A | 230A | 260A | 230.0A |
| 250 kcmil | 215A | 255A | 290A | 255.0A |
| 300 kcmil | 240A | 285A | 320A | 285.0A |
| 350 kcmil | 260A | 310A | 350A | 310.0A |
| 400 kcmil | 280A | 335A | 380A | 335.0A |
| 500 kcmil | 320A | 380A | 430A | 380.0A |
| 600 kcmil | 350A | 420A | 475A | 420.0A |
| 700 kcmil | 385A | 460A | 520A | 460.0A |
| 750 kcmil | 400A | 475A | 535A | 475.0A |
NEC Table 310.15(B)(1) — Temperature Correction Factors
Factors for ambient temperatures other than 30°C
| Ambient °C | 60°C | 75°C | 90°C |
|---|---|---|---|
| 10°C (50°F) | 1.29 | 1.20 | 1.15 |
| 15°C (59°F) | 1.22 | 1.15 | 1.12 |
| 20°C (68°F) | 1.15 | 1.11 | 1.08 |
| 25°C (77°F) | 1.08 | 1.05 | 1.04 |
| 30°C (86°F) | 1.00 | 1.00 | 1.00 |
| 35°C (95°F) | 0.91 | 0.94 | 0.96 |
| 40°C (104°F) | 0.82 | 0.88 | 0.91 |
| 45°C (113°F) | 0.71 | 0.82 | 0.87 |
| 50°C (122°F) | 0.58 | 0.75 | 0.82 |
| 55°C (131°F) | 0.41 | 0.67 | 0.76 |
| 60°C (140°F) | — | 0.58 | 0.71 |
| 65°C (149°F) | — | 0.47 | 0.65 |
| 70°C (158°F) | — | 0.33 | 0.58 |
| 75°C (167°F) | — | — | 0.50 |
| 80°C (176°F) | — | — | 0.41 |
NEC Reference Notes
310.15(B)(1): Ambient temperature correction factors — apply when ambient temperature differs from 30°C (86°F)
310.15(C)(1): Conduit fill adjustment — apply when more than 3 current-carrying conductors in a single raceway or cable
310.15(E): Neutral conductors carrying harmonic currents (3rd harmonic and multiples) count as current-carrying conductors
110.14(C): Wet or damp locations limit termination temperature to 75°C, regardless of conductor insulation rating
210.20(A): Continuous loads require conductor ampacity ≥ 125% of continuous load (applied as ÷1.25 to ampacity)
Multiple factors: When both temperature correction and conduit fill apply, multiply all factors together against the base ampacity