12 AWG ampacity by temperature column
| Conductor | 60°C | 75°C | 90°C | 240.4(D) |
|---|---|---|---|---|
| Copper | 20 A20 A breaker | 25 A20 A breaker | 30 A20 A breaker | 20 A |
| Aluminum | 15 A15 A breaker | 20 A15 A breaker | 25 A15 A breaker | 15 A |
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 12 gauge wire
- 12 AWG copper: 20 A, held there by 240.4(D)(5).
- 12 AWG aluminum: 15 A, held there by 240.4(D)(4).
240.4(D)(5) caps overcurrent protection on 12 AWG copper at 20 A, so the device is 20 A whatever the terminations are marked and whatever the 20 A in the 90°C column becomes after correction. The higher columns are derating arithmetic: they describe how much current the insulation survives at 30°C ambient with three current-carrying conductors, not how large a breaker the conductor will protect. Aluminum at this size is held at 15 A by 240.4(D)(4), whatever the 20 A in its 75°C column would otherwise take. 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 12 gauge wire is used for
- 20 A kitchen small-appliance, laundry, and bathroom circuits
- Dishwasher, disposal, and other 120 V appliance circuits
- Garage, outdoor, and unfinished-basement receptacles
Twelve gauge is the branch-circuit size for anything that is not lighting. At 60°C it carries exactly 20 A, which is also its 240.4(D)(5) cap, so 12 AWG copper and a 20 A breaker line up without any next-size-up arithmetic. 334.80 holds 12/2 NM-B to the 60°C column whatever the terminals are marked, and this is the minimum size for the kitchen, laundry, and bathroom circuits named in 210.11(C).
The higher columns are what derating works from, not what the breaker is set to. A 12 AWG THHN conductor can lose a quarter of its 90°C ampacity to ambient correction and conduit fill and still sit on a 20 A breaker, because the cap is a ceiling on the device rather than a statement about the insulation. The same cap is what makes 12 AWG aluminum a 15 A conductor in every column.
Box fill rises to 2.25 cubic inches per counted conductor under Table 314.16(B) from 2.00 at 14 AWG, which matters when a 20 A circuit is extended into a box that was set up for 14 AWG. Distance is the other limit: a kitchen circuit on the far side of a house is where the 3% figure pulls an installer up to 10 AWG, since drop grows with length and the table for this size stops well short of a long run.
Grounding with 12 AWG
As an equipment grounding conductor, 12 AWG is sized from the overcurrent device rather than from the phase conductors. Table 250.122 names 12 AWG copper on the 20 A row and 12 AWG aluminum on the 15 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.
Table 250.66 never lists 12 AWG as a grounding electrode conductor, so it is used for phase conductors, neutrals, and equipment grounds rather than for the connection to earth.
Voltage drop and run limits
Chapter 9 Table 8 lists 12 AWG copper at 1.98 ohms per 1000 ft at 75°C and aluminum at 3.25 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 |
|---|---|---|---|
| 12 AWG copper at 20 A | 45 ft | 90 ft | 100 ft |
| 12 AWG aluminum at 15 A | 35 ft | 70 ft | 85 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 12 AWG
Table 314.16(B) allows 2.25 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 12 AWG sits
| Conductor | 60°C | 75°C | 90°C |
|---|---|---|---|
| 14 AWG copper | 15 A | 20 A | 25 A |
| 12 AWG copper | 20 A | 25 A | 30 A |
| 10 AWG copper | 30 A | 35 A | 40 A |
12 AWG questions
- How many amps can 12 gauge wire handle?
- 12 AWG copper handles 20 A at 60°C, 25 A at 75°C, and 30 A at 90°C. The 60°C value is also the protection limit, because 240.4(D)(5) caps the device at 20 A after any correction and adjustment, so the higher columns are for derating rather than for a bigger breaker. Aluminum at the same size handles 15 A, 20 A, and 25 A.
- What size breaker for 12 gauge wire?
- 20 A. 240.4(D)(5) caps overcurrent protection at 20 A, and the cap applies after ambient correction and conductor adjustment. Aluminum takes 15 A at this size.
- What is 12 gauge wire used for?
- 20 A kitchen small-appliance, laundry, and bathroom circuits; dishwasher, disposal, and other 120 V appliance circuits; garage, outdoor, and unfinished-basement receptacles. Twelve gauge is the branch-circuit size for anything that is not lighting. At 60°C it carries exactly 20 A, which is also its 240.4(D)(5) cap, so 12 AWG copper and a 20 A breaker line up without any next-size-up arithmetic. 334.80 holds 12/2 NM-B to the 60°C column whatever the terminals are marked, and this is the minimum size for the kitchen, laundry, and bathroom circuits named in 210.11(C).
- What size ground wire with 12 gauge conductors?
- 12 AWG copper is the equipment grounding conductor for 20 A circuits in Table 250.122, and 12 AWG aluminum is the ground for 15 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 12 AWG aluminum as good as copper?
- It carries less. In Table 310.16, 12 AWG aluminum is 15 A, 20 A, and 25 A against 20 A, 25 A, and 30 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.