Ampacity by temperature rating
| Temperature rating | Ampacity | Typical insulation |
|---|---|---|
| 60°C | 40 A | — |
| 75°C | 50 A | THW |
| 90°C | 55 A | THHN / THWN-2, XHHW-2 |
Reference tables · Copper ampacity
2023 NEC · Table 310.16
8 AWG copper wire ampacity
At a 75°C termination rating, 8 AWG copper carries 50 A under the published table's basis conditions — 30°C ambient, no more than three current-carrying conductors.
What 8 AWG copper is used for
8 AWG copper carries 50 A at 75°C, making it a common choice for 40 A and 50 A circuits — ranges, larger water heaters, EV charging equipment, and hot tubs. It typically pairs with a 50 A overcurrent device.
Terminations usually decide the practical answer. Breakers and equipment are typically listed for 60°C or 75°C, so even 90°C-rated insulation on this conductor is normally limited to the 50 A column at the terminals. Check the equipment's listing rather than assuming.
Derating
Ampacity in real conditions
| Ambient | 3 conductors | 4 conductors | 7 conductors | 10 conductors | 21 conductors |
|---|---|---|---|---|---|
| 20°C | 55.5 A | 44.4 A | 38.9 A | 27.8 A | 25 A |
| 30°C | 50 A | 40 A | 35 A | 25 A | 22.5 A |
| 40°C | 44 A | 35.2 A | 30.8 A | 22 A | 19.8 A |
| 50°C | 37.5 A | 30 A | 26.3 A | 18.8 A | 16.9 A |
Properties
| Circular mils | 16,510 |
|---|---|
| DC resistance | 0.778 Ω per 1000 ft |
| Ampacity at 75°C | 50 A |
| Overcurrent ceiling | Set by ampacity |
| Largest standard breaker | 50 A |
| Area, THHN / THWN-2 | 0.0366 in² |
| Area, XHHW-2 | 0.0437 in² |
| Area, THW | 0.0556 in² |
Voltage drop over distance
Single-phase 240 V, carrying 50 A on 8 AWG copper.
| One-way distance | Drop | Within 3%? |
|---|---|---|
| 25 ft | 0.81% | Yes |
| 50 ft | 1.63% | Yes |
| 100 ft | 3.26% | No |
| 150 ft | 4.88% | No |
| 200 ft | 6.51% | No |
| 300 ft | 9.77% | No |
Source: NFPA 70, National Electrical Code, Table 310.16; NFPA 70, National Electrical Code, Table 310.15(B)(1)(1); NFPA 70, National Electrical Code, Table 310.15(C)(1); NFPA 70, National Electrical Code, Chapter 9, Table 8. Published by NFPA.NEC 2023
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