Ampacity by temperature rating
| Temperature rating | Ampacity | Typical insulation |
|---|---|---|
| 60°C | 65 A | — |
| 75°C | 75 A | THW |
| 90°C | 85 A | THHN / THWN-2, XHHW-2 |
Reference tables · Aluminum ampacity
2023 NEC · Table 310.16
3 AWG aluminum wire ampacity
At a 75°C termination rating, 3 AWG aluminum carries 75 A under the published table's basis conditions — 30°C ambient, no more than three current-carrying conductors.
What 3 AWG aluminum is used for
3 AWG aluminum carries 75 A at 75°C, putting it in feeder and subpanel territory — detached garages, workshops, and service upgrades. It pairs with a 70 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 75 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 | 83.3 A | 66.6 A | 58.3 A | 41.6 A | 37.5 A |
| 30°C | 75 A | 60 A | 52.5 A | 37.5 A | 33.8 A |
| 40°C | 66 A | 52.8 A | 46.2 A | 33 A | 29.7 A |
| 50°C | 56.3 A | 45 A | 39.4 A | 28.1 A | 25.3 A |
Properties
| Circular mils | 52,620 |
|---|---|
| DC resistance | 0.403 Ω per 1000 ft |
| Ampacity at 75°C | 75 A |
| Overcurrent ceiling | Set by ampacity |
| Largest standard breaker | 70 A |
| Area, THHN / THWN-2 | 0.0973 in² |
| Area, XHHW-2 | 0.0962 in² |
| Area, THW | 0.1134 in² |
Voltage drop over distance
Single-phase 240 V, carrying 75 A on 3 AWG aluminum.
| One-way distance | Drop | Within 3%? |
|---|---|---|
| 25 ft | 0.63% | Yes |
| 50 ft | 1.26% | Yes |
| 100 ft | 2.52% | Yes |
| 150 ft | 3.78% | No |
| 200 ft | 5.04% | No |
| 300 ft | 7.55% | 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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