Wire size for a 125 and 150 amp feeder
| Breaker | Copper, 75°C | Aluminum, 75°C | Ground wire (Cu / Al) |
|---|---|---|---|
| 125 A | 1 AWG | 2/0 AWG | 6 AWG / 4 AWG |
| 150 A | 1/0 AWG | 3/0 AWG | 6 AWG / 4 AWG |
Above 100 A you use the 75°C column of NEC Table 310.16. That is why the copper size is 1 AWG for 125 A (130 A in the table) and 1/0 AWG for 150 A (150 A in the table). The ground comes from NEC Table 250.122, which gives 6 AWG copper or 4 AWG aluminum for any breaker from 101 to 200 A.
Not the same as a service
If you are feeding a whole house from the utility, NEC 310.12 lets a single-family dwelling use smaller conductors, and the 200 amp service page has that table. That shortcut is for the service or main feeder that carries the whole load of a home. A sub panel in a detached garage or barn uses the sizes above.
How far can it run?
These are the longest one-way runs within 3% voltage drop at the full rated current on 240 V.
| Wire | At 125 A | At 150 A |
|---|---|---|
| 1 AWG copper | 187 ft | 156 ft |
| 1/0 AWG copper | 236 ft | 196 ft |
| 2/0 AWG copper | 297 ft | 248 ft |
| 1/0 AWG aluminum | 143 ft | 120 ft |
| 2/0 AWG aluminum | 181 ft | 151 ft |
| 3/0 AWG aluminum | 228 ft | 190 ft |
Most feeders do not run at their full rating all day, so the real drop is lower. Put your own distance into the voltage drop calculator if you're close to the limit.
For other breaker sizes, see the breaker to wire size chart.
Frequently asked questions
What size wire for a 150 amp breaker?
1/0 AWG copper or 3/0 AWG aluminum at 75°C.
What size wire for a 125 amp breaker?
1 AWG copper or 2/0 AWG aluminum at 75°C.
What size ground wire for a 150 amp sub panel?
6 AWG copper or 4 AWG aluminum, from NEC Table 250.122.
Can I use 2 AWG for a 125 amp breaker?
Not as a regular feeder. 2 AWG copper is rated 115 A at 75°C, which is under 125 A.