Ampacity by temperature rating
| Temperature rating | Ampacity | Typical insulation |
|---|---|---|
| 60°C | 210 A | — |
| 75°C | 250 A | THW |
| 90°C | 280 A | THHN / THWN-2, XHHW-2 |
Reference tables · Aluminum ampacity
2023 NEC · Table 310.16
350 kcmil aluminum wire ampacity
At a 75°C termination rating, 350 kcmil aluminum carries 250 A under the published table's basis conditions — 30°C ambient, no more than three current-carrying conductors.
What 350 kcmil aluminum is used for
350 kcmil aluminum carries 250 A at 75°C. Conductors in the kcmil range are service, feeder, and distribution conductors, frequently run as paralleled sets under rules this reference does not model. It pairs with a 250 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 250 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 | 277.5 A | 222 A | 194.3 A | 138.8 A | 124.9 A |
| 30°C | 250 A | 200 A | 175 A | 125 A | 112.5 A |
| 40°C | 220 A | 176 A | 154 A | 110 A | 99 A |
| 50°C | 187.5 A | 150 A | 131.3 A | 93.8 A | 84.4 A |
Properties
| Circular mils | 350,000 |
|---|---|
| DC resistance | 0.0605 Ω per 1000 ft |
| Ampacity at 75°C | 250 A |
| Overcurrent ceiling | Set by ampacity |
| Largest standard breaker | 250 A |
| Area, THHN / THWN-2 | 0.5242 in² |
| Area, XHHW-2 | 0.5166 in² |
| Area, THW | 0.5958 in² |
Voltage drop over distance
Single-phase 240 V, carrying 250 A on 350 kcmil aluminum.
| One-way distance | Drop | Within 3%? |
|---|---|---|
| 25 ft | 0.32% | Yes |
| 50 ft | 0.63% | Yes |
| 100 ft | 1.26% | Yes |
| 150 ft | 1.89% | Yes |
| 200 ft | 2.52% | Yes |
| 300 ft | 3.79% | 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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