Ampacity Calculator
Standard is 30°C (86°F)
What is Ampacity?
Ampacity is the maximum current a conductor can carry continuously without exceeding its temperature rating. It is determined by the conductor material, size, insulation type, and installation conditions.
NEC Ampacity Table 310.16
The National Electrical Code provides ampacity tables based on:
- Conductor material (copper or aluminum)
- Insulation temperature rating (60°C, 75°C, or 90°C)
- Ambient temperature correction factors
Temperature Ratings
60°C (140°F): TW, UF wire
75°C (167°F): THW, THWN wire (most common)
90°C (194°F): THHN, XHHW wire (often used for derating)
Correction Factors
When ambient temperature exceeds 86°F (30°C), ampacity must be reduced using correction factors from NEC Table 310.15(B)(1).
Common Ampacities (Copper, 75°C)
- 14 AWG: 20A (limited to 15A by NEC 240.4(D))
- 12 AWG: 25A (limited to 20A by NEC 240.4(D))
- 10 AWG: 35A (limited to 30A by NEC 240.4(D))
- 8 AWG: 50A
- 6 AWG: 65A
- 4 AWG: 85A
- 2 AWG: 115A
- 1/0 AWG: 150A
- 4/0 AWG: 230A
About Ampacity Calculator
Ampacity Calculator - Calculate Current Carrying Capacity
Calculate the maximum current (ampacity) a wire can safely carry. Based on NEC Table 310.16 for copper and aluminum conductors with ambient temperature correction.
What is Ampacity?
Ampacity is the maximum current a conductor can carry continuously without exceeding its temperature rating. This is determined by:
- Conductor material (copper or aluminum)
- Wire size (AWG or kcmil)
- Insulation temperature rating
- Ambient temperature
- Installation conditions
NEC Table 310.16 Ampacity Values
Common copper conductor ampacities at 75°C (167°F):
| Wire Size | 60°C Rating | 75°C Rating | 90°C Rating |
|---|---|---|---|
| 14 AWG | 15A | 15A | 15A |
| 12 AWG | 20A | 25A | 30A |
| 10 AWG | 30A | 35A | 40A |
| 8 AWG | 40A | 50A | 55A |
| 6 AWG | 55A | 65A | 75A |
| 4 AWG | 70A | 85A | 95A |
| 2 AWG | 95A | 115A | 130A |
| 1/0 AWG | 125A | 150A | 170A |
| 4/0 AWG | 195A | 230A | 260A |
Ambient Temperature Correction
When ambient temperature exceeds 30°C (86°F), ampacity must be reduced:
- 31-40°C (86-104°F): 0.91 correction factor for 60°C, 0.88 for 75°C, 0.87 for 90°C
- 41-50°C (104-122°F): 0.82 correction factor for 60°C, 0.80 for 75°C, 0.80 for 90°C
- 51-60°C (122-140°F): 0.71 correction factor for 60°C, 0.71 for 75°C, 0.71 for 90°C
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