6 AWG ampacity by temperature column
| Conductor | 60°C | 75°C | 90°C | 240.4(D) |
|---|---|---|---|---|
| Copper | 55 A60 A breaker | 65 A70 A breaker | 75 A80 A breaker | no cap |
| Aluminum | 40 A40 A breaker | 50 A50 A breaker | 55 A60 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 6 gauge wire
- 6 AWG copper: 60 A on a 60°C column and 70 A on a 75°C column.
- 6 AWG aluminum: 40 A on a 60°C column and 50 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: 60 A on the 60°C column and 70 A on the 75°C column. Where an ampacity falls between standard ratings, 240.4(B) permits the next size up, so 60 A protects the 55 A 60°C ampacity and 70 A protects the 65 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 40 A at 60°C and 50 A at 75°C. 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 6 gauge wire is used for
- 50 A to 70 A feeders and subpanels
- Ground rods and other grounding electrode connections
- Equipment grounding conductor on 200 A circuits
Six gauge is where the ampacity table stops matching breaker sizes. At 60°C it carries 55 A and at 75°C 65 A, neither of which is a standard rating, so 240.4(B) allows the next size up: a 60 A device on the 60°C value and a 70 A device on the 75°C value. That is why 6 AWG copper on a 60 A breaker is legal at 55 A of ampacity, and why the same conductor needs a 75°C column to justify 70 A.
It is the largest grounding electrode conductor 250.66(A) ever requires for a rod, pipe, or plate electrode, whatever the service size. A 200 A service with 2/0 copper service conductors reads 4 AWG from Table 250.66, and that electrode connection still stops at 6 AWG. Table 250.122 makes 6 AWG copper the equipment grounding conductor for a 200 A circuit, and 250.122(B) raises it in proportion if the phase conductors are increased for voltage drop.
Aluminum at 6 AWG is a 50 A conductor on a 75°C column where copper at the same size needs 75°C to reach 70 A, so the material choice moves the breaker by a full standard step. Box fill is 5.00 cubic inches per counted conductor, the largest step in Table 314.16(B), which is why 6 AWG splices belong in a junction box or a panel rather than in a device box.
Grounding with 6 AWG
As an equipment grounding conductor, 6 AWG is sized from the overcurrent device rather than from the phase conductors. Table 250.122 names 6 AWG copper on the 200 A row and 6 AWG aluminum on the 100 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, 6 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 1 or 1/0 AWG, and aluminum where the service runs 1/0 AWG or smaller. It is also the largest grounding electrode conductor 250.66(A) ever requires for a rod, pipe, or plate electrode, whatever the service size.
Voltage drop and run limits
Chapter 9 Table 8 lists 6 AWG copper at 0.491 ohms per 1000 ft at 75°C and aluminum at 0.808 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 |
|---|---|---|---|
| 6 AWG copper at 55 A | 65 ft | 130 ft | 150 ft |
| 6 AWG aluminum at 40 A | 55 ft | 110 ft | 125 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.
Box fill with 6 AWG
Table 314.16(B) allows 5.00 cubic inches per counted conductor at this size. Every conductor that originates outside a box and terminates or is spliced inside it counts once, each device yoke counts as two of the largest conductor in the box, and all the equipment grounding conductors together count as one. The total is compared against the box volume from Table 314.16(A). Table 314.16(B) stops at 6 AWG, so a larger conductor is sized by the pull and bend rules in 314.28 instead.
Where 6 AWG sits
| Conductor | 60°C | 75°C | 90°C |
|---|---|---|---|
| 8 AWG copper | 40 A | 50 A | 55 A |
| 6 AWG copper | 55 A | 65 A | 75 A |
| 4 AWG copper | 70 A | 85 A | 95 A |
6 AWG questions
- How many amps can 6 gauge wire handle?
- 6 AWG copper handles 55 A at 60°C, 65 A at 75°C, and 75 A at 90°C. No 240.4(D) cap applies at this size, so the breaker follows the column: 60 A at 60°C and 70 A at 75°C. Aluminum at the same size handles 40 A, 50 A, and 55 A.
- What size breaker for 6 gauge wire?
- 60 A on the 60°C column and 70 A on the 75°C column. Where an ampacity falls between standard ratings, 240.4(B) permits the next size up, so 60 A protects the 55 A 60°C ampacity and 70 A protects the 65 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 40 A at 60°C and 50 A at 75°C.
- What is 6 gauge wire used for?
- 50 A to 70 A feeders and subpanels; ground rods and other grounding electrode connections; equipment grounding conductor on 200 A circuits. Six gauge is where the ampacity table stops matching breaker sizes. At 60°C it carries 55 A and at 75°C 65 A, neither of which is a standard rating, so 240.4(B) allows the next size up: a 60 A device on the 60°C value and a 70 A device on the 75°C value. That is why 6 AWG copper on a 60 A breaker is legal at 55 A of ampacity, and why the same conductor needs a 75°C column to justify 70 A.
- What size ground wire with 6 gauge conductors?
- 6 AWG copper is the equipment grounding conductor for 200 A circuits in Table 250.122, and 6 AWG aluminum is the ground for 100 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 6 gauge a grounding electrode conductor?
- Yes, in one place. 6 AWG copper is the grounding electrode conductor where the service conductors are 1 or 1/0 AWG, and 6 AWG aluminum is the grounding electrode conductor where the service conductors are 1/0 AWG or smaller. It is also the largest grounding electrode conductor 250.66(A) ever requires for a rod, pipe, or plate electrode, whatever the service size.
- Is 6 AWG aluminum as good as copper?
- It carries less. In Table 310.16, 6 AWG aluminum is 40 A, 50 A, and 55 A against 55 A, 65 A, and 75 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.