Ampacity by temperature rating
| Temperature rating | Ampacity | Typical insulation |
|---|---|---|
| 60°C | 20 A | — |
| 75°C | 25 A | THW |
| 90°C | 30 A | THHN / THWN-2, XHHW-2 |
Reference tables · Copper ampacity
2023 NEC · Table 310.16
12 AWG copper wire ampacity
At a 75°C termination rating, 12 AWG copper carries 25 A under the published table's basis conditions — 30°C ambient, no more than three current-carrying conductors. Overcurrent protection is separately capped at 20 A by the small-conductor rule.
What 12 AWG copper is used for
12 AWG copper is the workhorse of 20 A branch circuits — receptacles, kitchen small-appliance circuits, and general-purpose power. It pairs with a 20 A breaker and is the smallest conductor most jurisdictions accept for receptacle circuits in a kitchen or garage.
Note the gap between the table and the ceiling. The 90°C column reads 30 A, but a 12 AWG copper conductor cannot be protected above 20 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 25 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 | 20 A | 20 A | 19.4 A | 13.9 A | 12.5 A |
| 30°C | 20 A | 20 A | 17.5 A | 12.5 A | 11.3 A |
| 40°C | 20 A | 17.6 A | 15.4 A | 11 A | 9.9 A |
| 50°C | 18.8 A | 15 A | 13.1 A | 9.4 A | 8.4 A |
Properties
| Circular mils | 6,530 |
|---|---|
| DC resistance | 1.98 Ω per 1000 ft |
| Ampacity at 75°C | 25 A |
| Overcurrent ceiling | 20 A (small-conductor rule) |
| Largest standard breaker | 20 A |
| Area, THHN / THWN-2 | 0.0133 in² |
| Area, XHHW-2 | 0.0181 in² |
| Area, THW | 0.026 in² |
Voltage drop over distance
Single-phase 240 V, carrying 20 A on 12 AWG copper.
| One-way distance | Drop | Within 3%? |
|---|---|---|
| 25 ft | 0.82% | Yes |
| 50 ft | 1.65% | Yes |
| 100 ft | 3.29% | No |
| 150 ft | 4.94% | No |
| 200 ft | 6.58% | No |
| 300 ft | 9.88% | 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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