Ampacity by temperature rating
| Temperature rating | Ampacity | Typical insulation |
|---|---|---|
| 60°C | 30 A | — |
| 75°C | 35 A | THW |
| 90°C | 40 A | THHN / THWN-2, XHHW-2 |
Reference tables · Copper ampacity
2023 NEC · Table 310.16
10 AWG copper wire ampacity
At a 75°C termination rating, 10 AWG copper carries 35 A under the published table's basis conditions — 30°C ambient, no more than three current-carrying conductors. Overcurrent protection is separately capped at 30 A by the small-conductor rule.
What 10 AWG copper is used for
10 AWG copper is the standard conductor for 30 A circuits — electric water heaters, small subpanels, dryers on older installations, and window air conditioners. It carries 30 A and pairs with a 30 A overcurrent device.
Note the gap between the table and the ceiling. The 90°C column reads 40 A, but a 10 AWG copper conductor cannot be protected above 30 A regardless — the small-conductor rule sets that ceiling independently of ampacity. The higher table value exists so the conductor has headroom to be derated from, not so it can be put on a larger breaker.
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 35 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 | 30 A | 30 A | 27.2 A | 19.4 A | 17.5 A |
| 30°C | 30 A | 28 A | 24.5 A | 17.5 A | 15.8 A |
| 40°C | 30 A | 24.6 A | 21.6 A | 15.4 A | 13.9 A |
| 50°C | 26.3 A | 21 A | 18.4 A | 13.1 A | 11.8 A |
Properties
| Circular mils | 10,380 |
|---|---|
| DC resistance | 1.24 Ω per 1000 ft |
| Ampacity at 75°C | 35 A |
| Overcurrent ceiling | 30 A (small-conductor rule) |
| Largest standard breaker | 30 A |
| Area, THHN / THWN-2 | 0.0211 in² |
| Area, XHHW-2 | 0.0243 in² |
| Area, THW | 0.0333 in² |
Voltage drop over distance
Single-phase 240 V, carrying 30 A on 10 AWG copper.
| One-way distance | Drop | Within 3%? |
|---|---|---|
| 25 ft | 0.78% | Yes |
| 50 ft | 1.55% | Yes |
| 100 ft | 3.11% | No |
| 150 ft | 4.66% | No |
| 200 ft | 6.21% | No |
| 300 ft | 9.32% | 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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