4/0 AWG ampacity by temperature column
| Conductor | 60°C | 75°C | 90°C | 240.4(D) |
|---|---|---|---|---|
| Copper | 195 A200 A breaker | 230 A250 A breaker | 260 A300 A breaker | no cap |
| Aluminum | 150 A150 A breaker | 180 A200 A breaker | 205 A225 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 4/0 wire
- 4/0 AWG copper: 200 A on a 60°C column and 250 A on a 75°C column.
- 4/0 AWG aluminum: 150 A on a 60°C column and 200 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: 200 A on the 60°C column and 250 A on the 75°C column. Where an ampacity falls between standard ratings, 240.4(B) permits the next size up, so 200 A protects the 195 A 60°C ampacity and 250 A protects the 230 A 75°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 150 A at 60°C and 200 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 4/0 wire is used for
- 225 A feeders and large residential services
- 200 A services in aluminum service-entrance cable
- Service conductors on multi-unit buildings
4/0 copper carries 195 A at 60°C, 230 A at 75°C, and 260 A at 90°C. At 75°C it is the conductor for a 225 A feeder, because 230 A clears the 225 A standard rating, and it is the size a 200 A service is upsized to when the run is long or when parallel sets are not worth the trouble.
4/0 aluminum is the most common residential service conductor for a different reason. It carries 150 A at 60°C and 180 A at 75°C, both below a 200 A service, but 310.15(B)(7) asks for only 83% of the rating on a dwelling service, which is 166 A on 200 A, so 4/0 aluminum meets the allowance on its 75°C ampacity alone rather than leaning on the next-size-up rule.
This is the last size in the AWG range; above it Table 310.16 switches to kcmil. Table 250.66 makes 4/0 aluminum the grounding electrode conductor for service conductors over 900 through 1750 kcmil, and Table 250.122 makes 4/0 copper the equipment grounding conductor for a 1600 A circuit.
Grounding with 4/0 AWG
As an equipment grounding conductor, 4/0 AWG is sized from the overcurrent device rather than from the phase conductors. Table 250.122 names 4/0 AWG copper on the 1600 A row and 4/0 AWG aluminum on the 1000 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, 4/0 AWG appears in Table 250.66, which is sized from the largest ungrounded service conductor rather than from the service rating: aluminum where the service runs over 900 through 1750 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 4/0 AWG copper at 0.0608 ohms per 1000 ft at 75°C and aluminum at 0.1 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 |
|---|---|---|---|
| 4/0 AWG copper at 195 A | 150 ft | 300 ft | 350 ft |
| 4/0 AWG aluminum at 150 A | 115 ft | 235 ft | 275 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 4/0 AWG sits
| Conductor | 60°C | 75°C | 90°C |
|---|---|---|---|
| 3/0 AWG copper | 165 A | 200 A | 225 A |
| 4/0 AWG copper | 195 A | 230 A | 260 A |
4/0 AWG questions
- How many amps can 4/0 wire handle?
- 4/0 AWG copper handles 195 A at 60°C, 230 A at 75°C, and 260 A at 90°C. No 240.4(D) cap applies at this size, so the breaker follows the column: 200 A at 60°C and 250 A at 75°C. Aluminum at the same size handles 150 A, 180 A, and 205 A.
- What size breaker for 4/0 wire?
- 200 A on the 60°C column and 250 A on the 75°C column. Where an ampacity falls between standard ratings, 240.4(B) permits the next size up, so 200 A protects the 195 A 60°C ampacity and 250 A protects the 230 A 75°C ampacity. It relaxes the device rather than the conductor, so a load at the full rating still needs the larger size. Aluminum takes 150 A at 60°C and 200 A at 75°C.
- What is 4/0 wire used for?
- 225 A feeders and large residential services; 200 A services in aluminum service-entrance cable; service conductors on multi-unit buildings. 4/0 copper carries 195 A at 60°C, 230 A at 75°C, and 260 A at 90°C. At 75°C it is the conductor for a 225 A feeder, because 230 A clears the 225 A standard rating, and it is the size a 200 A service is upsized to when the run is long or when parallel sets are not worth the trouble.
- What size ground wire with 4/0 conductors?
- 4/0 AWG copper is the equipment grounding conductor for 1600 A circuits in Table 250.122, and 4/0 AWG aluminum is the ground for 1000 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 4/0 a grounding electrode conductor?
- Yes, in one place. 4/0 AWG aluminum is the grounding electrode conductor where the service conductors are over 900 through 1750 kcmil.
- Is 4/0 AWG aluminum as good as copper?
- It carries less. In Table 310.16, 4/0 AWG aluminum is 150 A, 180 A, and 205 A against 195 A, 230 A, and 260 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.