Conductor size by circuit rating
| Circuit | Copper 60°C | Copper 75°C | Aluminum 60°C | Aluminum 75°C |
|---|---|---|---|---|
| 15 A | 14 AWG | 14 AWG | 12 AWG | 12 AWG |
| 20 A | 12 AWG | 12 AWG | 10 AWG | 10 AWG |
| 30 A | 10 AWG | 10 AWG | 8 AWG | 8 AWG |
| 40 A | 8 AWG | 8 AWG | 6 AWG | 8 AWG |
| 50 A | 6 AWG | 8 AWG | 4 AWG | 6 AWG |
| 60 A | 4 AWG | 6 AWG | 3 AWG | 4 AWG |
| 70 A | 4 AWG | 4 AWG | 2 AWG | 3 AWG |
| 80 A | 3 AWG | 4 AWG | 1 AWG | 2 AWG |
| 100 A | 1 AWG | 3 AWG | 1/0 AWG | 1 AWG |
| 125 A | 1/0 AWG | 1 AWG | 3/0 AWG | 2/0 AWG |
| 150 A | 3/0 AWG | 1/0 AWG | 4/0 AWG | 3/0 AWG |
| 200 A | 250 kcmil | 3/0 AWG | 350 kcmil | 250 kcmil |
| 400 A | 750 kcmil | 600 kcmil | 1250 kcmil | 900 kcmil |
Ampacities are Table 310.16 values for an ungrounded conductor at 30°C ambient with three or fewer current-carrying conductors. The 240.4(D) small-conductor limit is already applied, so the 60°C and 75°C columns can hold the same size on small conductors.
Rules behind the table
- Termination column: 60°C for circuits rated 100 A or less, 75°C above that, unless the equipment markings say otherwise (110.14(C)).
- NEC 240.4(D) caps overcurrent protection at 15 A for 14 AWG copper, 20 A for 12 AWG copper, 30 A for 10 AWG copper, 15 A for 12 AWG aluminum, and 25 A for 10 AWG aluminum. Those values match the 60°C ampacities, so the 75°C column never allows a smaller conductor on those sizes.
- Cable assemblies carry a limit of their own: 334.80 holds NM-B to the 60°C ampacity and 340.80 does the same for UF-B, whatever the terminals are rated for.
- A 120/240 V single-phase dwelling service or feeder rated 100 A through 400 A may be sized at 83% of the rating (310.15(B)(7)). Each rating page lists that size separately from the Table 310.16 answer.
Every rating page also gives the Table 250.122 equipment grounding conductor and the longest run at 3% voltage drop for the sizes on that page.
Reading a row
The 50 A row shows 6 AWG copper and 4 AWG aluminum at 60°C, dropping to 8 AWG copper and 6 AWG aluminum where the equipment is marked for 75°C. See the 50 A page for the ampacity of every column, the ground size from Table 250.122, and the run limit at 3% drop.