Definition
Conductor ampacity is the maximum current (in amperes) a conductor can carry continuously under specified ambient and bundling conditions without exceeding its temperature rating. NEC Table 310.16 provides base ampacities for 60°C, 75°C, and 90°C insulations.
Ampacity by AWG (90°C insulation, NEC 310.16)
| AWG | Ampacity |
|---|---|
| 14 | 30 A |
| 12 | 40 A |
| 10 | 55 A |
| 8 | 75 A |
| 6 | 105 A |
| 4 | 140 A |
| 2 | 190 A |
| 1/0 | 260 A |
| 4/0 | 405 A |
Derating Sequence
- Base ampacity (NEC Table 310.16, 90°C column).
- × temperature factor (NEC Table 310.15(B)(2)(a)).
- × conduit-fill factor (NEC 310.15(B)(3)(a)).
- Not to exceed terminal rating (60°C or 75°C).
- Must satisfy 1.25 × Isc × 1.25 minimum.
Key Takeaways
- Conductor ampacity = max continuous current capacity.
- NEC Table 310.16 provides base values.
- Apply temperature + conduit-fill derating.
- Final ampacity capped by terminal temperature rating.
- Required ampacity for solar = 1.5625 × Isc (NEC 690.8).
Frequently Asked Questions
4 commonly searched questions about Conductor Ampacity.
What is conductor ampacity?
Maximum current a conductor can carry without exceeding its insulation temperature rating. Listed in NEC Table 310.16 by AWG/kcmil size and insulation rating.
What's PV Wire ampacity?
PV Wire is 90°C rated. 12 AWG: 30 A. 10 AWG: 40 A. 8 AWG: 55 A. 6 AWG: 75 A. Derated for ambient + conduit fill.
How is ampacity derated?
Temperature (NEC Table 310.15(B)(2)(a)): at 50°C ambient, 90°C conductors derate 0.82. Conduit fill (NEC 310.15(B)(3)(a)): 4–6 conductors × 0.80.
Terminal temperature limit?
Final ampacity may not exceed 60°C or 75°C column ampacity per NEC 110.14(C), based on terminal markings. Most equipment is 75°C-rated.
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