Ampacity by temperature rating
| Temperature rating | Ampacity | Typical insulation |
|---|---|---|
| 60°C | 85 A | — |
| 75°C | 100 A | THW |
| 90°C | 115 A | THHN / THWN-2, XHHW-2 |
Reference tables · Copper ampacity
2023 NEC · Table 310.16
3 AWG copper wire ampacity
At a 75°C termination rating, 3 AWG copper carries 100 A under the published table's basis conditions — 30°C ambient, no more than three current-carrying conductors.
What 3 AWG copper is used for
3 AWG copper carries 100 A at 75°C, putting it in feeder and subpanel territory — detached garages, workshops, and service upgrades. It pairs with a 100 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 100 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 | 111 A | 88.8 A | 77.7 A | 55.5 A | 50 A |
| 30°C | 100 A | 80 A | 70 A | 50 A | 45 A |
| 40°C | 88 A | 70.4 A | 61.6 A | 44 A | 39.6 A |
| 50°C | 75 A | 60 A | 52.5 A | 37.5 A | 33.8 A |
Properties
| Circular mils | 52,620 |
|---|---|
| DC resistance | 0.245 Ω per 1000 ft |
| Ampacity at 75°C | 100 A |
| Overcurrent ceiling | Set by ampacity |
| Largest standard breaker | 100 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 100 A on 3 AWG copper.
| One-way distance | Drop | Within 3%? |
|---|---|---|
| 25 ft | 0.51% | Yes |
| 50 ft | 1.02% | Yes |
| 100 ft | 2.04% | Yes |
| 150 ft | 3.06% | No |
| 200 ft | 4.09% | No |
| 300 ft | 6.13% | 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
Related