2/0 AWG ampacity by temperature column
| Conductor | 60°C | 75°C | 90°C | 240.4(D) |
|---|---|---|---|---|
| Copper | 145 A150 A breaker | 175 A175 A breaker | 195 A200 A breaker | no cap |
| Aluminum | 115 A125 A breaker | 135 A150 A breaker | 150 A150 A breaker | no cap |
Ampacities are NEC Table 310.16 values for a conductor at 30°C ambient in a raceway, cable, or direct burial with three or fewer current-carrying conductors. Ambient correction and conductor adjustment are applied to these numbers before the 240.4(D) cap is checked, never after it.
What size breaker for 2/0 wire
- 2/0 AWG copper: 150 A on a 60°C column and 175 A on a 75°C column.
- 2/0 AWG aluminum: 125 A on a 60°C column and 150 A on a 75°C column.
No small-conductor cap applies at this size, so the device follows the column the equipment is listed for: 150 A on the 60°C column and 175 A on the 75°C column. Where an ampacity falls between standard ratings, 240.4(B) permits the next size up, so 150 A protects the 145 A 60°C ampacity. It relaxes the device rather than the conductor: 210.19(A)(1) still requires an ampacity at least equal to the calculated load. The allowance does not reach a multioutlet branch circuit supplying receptacles for cord-and-plug-connected portable loads, and it stops at an 800 A device. Aluminum at this size takes 125 A at 60°C and 150 A at 75°C, since 240.4(B) carries the device to the next standard rating where the ampacity falls between two. 334.80 and 340.80 hold NM-B and UF-B cable to the 60°C column whatever the terminals are marked, so a cable assembly is read from the left-hand column while conductors in raceway are read from the column the equipment is listed for.
What 2/0 wire is used for
- 200 A dwelling services under 310.15(B)(7)
- Service conductors to detached buildings
- Equipment grounding conductor on 1000 A circuits
2/0 copper carries 145 A at 60°C, 175 A at 75°C, and 195 A at 90°C. It is the smallest copper conductor that meets the 310.15(B)(7) allowance for a 200 A dwelling service, because 83% of 200 A is 166 A and 2/0 reaches 175 A at 75°C. That is why a 200 A house is often wired in 2/0 copper rather than in 3/0.
The 90°C value would allow a 200 A device under 240.4(B), but only where every termination is listed for 90°C conductors, which service equipment rarely is. In practice the 75°C column decides, and 2/0 is a 175 A conductor at the panel.
Table 250.66 makes 2/0 copper the grounding electrode conductor where the service conductors are over 600 through 1100 kcmil, and Table 250.122 makes it the equipment grounding conductor for a 1000 A circuit. Aluminum 2/0 is a 150 A conductor on a 75°C column, since that value is a standard rating with no room above it.
Grounding with 2/0 AWG
As an equipment grounding conductor, 2/0 AWG is sized from the overcurrent device rather than from the phase conductors. Table 250.122 names 2/0 AWG copper on the 1000 A row and 2/0 AWG aluminum on the 600 A row. 250.122(B) raises the ground in the same proportion as the phase conductors when they are increased for voltage drop, and 250.122(A) caps it at the size of the conductors it runs with.
As a grounding electrode conductor, 2/0 AWG appears in Table 250.66, which is sized from the largest ungrounded service conductor rather than from the service rating: copper where the service runs over 600 through 1100 kcmil. The table value is what the service conductor calls for; the caps in 250.66(A) through (C) apply to the electrode connection itself.
Voltage drop and run limits
Chapter 9 Table 8 lists 2/0 AWG copper at 0.0967 ohms per 1000 ft at 75°C and aluminum at 0.159 ohms per 1000 ft. Resistance is what a voltage-drop calculation multiplies by current and length, so a conductor twice as long drops twice the volts.
| Conductor | 120 V single phase | 240 V single phase | 240 V three phase |
|---|---|---|---|
| 2/0 AWG copper at 145 A | 125 ft | 255 ft | 295 ft |
| 2/0 AWG aluminum at 115 A | 95 ft | 195 ft | 225 ft |
NEC 210.19(A)(1) Informational Note 4 recommends keeping branch-circuit drop at or below 3%. The lengths above are floored to the nearest 5 ft so a listed length never exceeds the computed limit, and they leave reactance out, which makes a large conductor in steel raceway fall short. Halving the current doubles the distance.
Where 2/0 AWG sits
| Conductor | 60°C | 75°C | 90°C |
|---|---|---|---|
| 1/0 AWG copper | 125 A | 150 A | 170 A |
| 2/0 AWG copper | 145 A | 175 A | 195 A |
| 3/0 AWG copper | 165 A | 200 A | 225 A |
2/0 AWG questions
- How many amps can 2/0 wire handle?
- 2/0 AWG copper handles 145 A at 60°C, 175 A at 75°C, and 195 A at 90°C. No 240.4(D) cap applies at this size, so the breaker follows the column: 150 A at 60°C and 175 A at 75°C. Aluminum at the same size handles 115 A, 135 A, and 150 A.
- What size breaker for 2/0 wire?
- 150 A on the 60°C column and 175 A on the 75°C column. Where an ampacity falls between standard ratings, 240.4(B) permits the next size up, so 150 A protects the 145 A 60°C ampacity. It relaxes the device rather than the conductor, so a load at the full rating still needs the larger size. Aluminum takes 125 A at 60°C and 150 A at 75°C.
- What is 2/0 wire used for?
- 200 A dwelling services under 310.15(B)(7); service conductors to detached buildings; equipment grounding conductor on 1000 A circuits. 2/0 copper carries 145 A at 60°C, 175 A at 75°C, and 195 A at 90°C. It is the smallest copper conductor that meets the 310.15(B)(7) allowance for a 200 A dwelling service, because 83% of 200 A is 166 A and 2/0 reaches 175 A at 75°C. That is why a 200 A house is often wired in 2/0 copper rather than in 3/0.
- What size ground wire with 2/0 conductors?
- 2/0 AWG copper is the equipment grounding conductor for 1000 A circuits in Table 250.122, and 2/0 AWG aluminum is the ground for 600 A circuits. The ground is sized from the overcurrent device rather than from the phase conductors, and 250.122(B) raises it in the same proportion if the phase conductors are increased for voltage drop. It never has to be larger than the conductors it runs with.
- Is 2/0 a grounding electrode conductor?
- Yes, in one place. 2/0 AWG copper is the grounding electrode conductor where the service conductors are over 600 through 1100 kcmil.
- Is 2/0 AWG aluminum as good as copper?
- It carries less. In Table 310.16, 2/0 AWG aluminum is 115 A, 135 A, and 150 A against 145 A, 175 A, and 195 A for copper, so a load that copper serves at this size usually needs one size larger in aluminum. The lugs and devices it lands on have to be listed for aluminum conductors.