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
Frequently Asked Questions
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