Ampacity by temperature rating
| Temperature rating | Ampacity | Typical insulation |
|---|---|---|
| 60°C | 15 A | — |
| 75°C | 20 A | THW |
| 90°C | 25 A | THHN / THWN-2, XHHW-2 |
Reference tables · Copper ampacity
2023 NEC · Table 310.16
14 AWG copper wire ampacity
At a 75°C termination rating, 14 AWG copper carries 20 A under the published table's basis conditions — 30°C ambient, no more than three current-carrying conductors. Overcurrent protection is separately capped at 15 A by the small-conductor rule.
What 14 AWG copper is used for
14 AWG copper is the smallest conductor in general branch-circuit use, and it is a 15 A conductor in practice. It is what most residential lighting circuits are wired in, and the reason a 15 A breaker is the smallest standard rating.
Note the gap between the table and the ceiling. The 90°C column reads 25 A, but a 14 AWG copper conductor cannot be protected above 15 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 20 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 | 15 A | 15 A | 15 A | 11.1 A | 10 A |
| 30°C | 15 A | 15 A | 14 A | 10 A | 9 A |
| 40°C | 15 A | 14.1 A | 12.3 A | 8.8 A | 7.9 A |
| 50°C | 15 A | 12 A | 10.5 A | 7.5 A | 6.8 A |
Properties
| Circular mils | 4,110 |
|---|---|
| DC resistance | 3.14 Ω per 1000 ft |
| Ampacity at 75°C | 20 A |
| Overcurrent ceiling | 15 A (small-conductor rule) |
| Largest standard breaker | 15 A |
| Area, THHN / THWN-2 | 0.0097 in² |
| Area, XHHW-2 | 0.0139 in² |
| Area, THW | 0.0209 in² |
Voltage drop over distance
Single-phase 240 V, carrying 15 A on 14 AWG copper.
| One-way distance | Drop | Within 3%? |
|---|---|---|
| 25 ft | 0.98% | Yes |
| 50 ft | 1.96% | Yes |
| 100 ft | 3.92% | No |
| 150 ft | 5.89% | No |
| 200 ft | 7.85% | No |
| 300 ft | 11.77% | 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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