For standard 120V and 240V residential branch circuits, the direct answer for wire sizing relies on the 60°C column for circuits rated 100A and under, and the 75°C column for circuits over 100A, per NEC 110.14(C). While modern wire insulation like THHN is rated for 90°C, the termination points (breakers, lugs, and receptacles) are typically only rated for 60°C or 75°C. You must size the wire based on the weakest link in the chain.
How to Read the NEC AC Wire Size Chart
Before pulling wire, you need to understand the three temperature columns in the National Electrical Code (NEC) Table 310.16. The ampacity (current-carrying capacity) of a copper conductor changes based on its insulation type and the temperature rating of the terminals it connects to.
Per NEC 110.14(C)(1)(a), circuits rated 100A or less, or marked for 14 AWG through 1 AWG conductors, must be sized using the 60°C column. Circuits over 100A, or marked for conductors larger than 1 AWG, use the 75°C column. The 90°C column is almost never used for final ampacity sizing; it is strictly used as the starting baseline for calculating derating factors (like conduit fill or ambient heat) before applying the termination temperature limit.
The Master AC Wire Size Chart (NEC Table 310.16)
The following table details the allowable ampacities for insulated copper conductors rated up to 2000 volts. This data is sourced directly from the NFPA 70 (NEC 2023) Table 310.16, assuming an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway.
| AWG / kcmil | 60°C (140°F) TW, UF |
75°C (167°F) THW, THWN, XHHW |
90°C (194°F) THHN, THWN-2, XHHW-2 |
|---|---|---|---|
| 14 | 15A | 20A | 25A |
| 12 | 20A | 25A | 30A |
| 10 | 30A | 35A | 40A |
| 8 | 40A | 50A | 55A |
| 6 | 55A | 65A | 75A |
| 4 | 70A | 85A | 95A |
| 3 | 85A | 100A | 115A |
| 2 | 95A | 115A | 130A |
| 1 | 110A | 130A | 145A |
| 1/0 | 125A | 150A | 170A |
Source: NFPA 70 (National Electrical Code), 2023 Edition, Table 310.16. Values apply to copper conductors. For aluminum, refer to the right side of the official NEC table.
Quick-Jump: Most Queried Residential Wire Sizes
Bookmark this section for the most common branch circuit and feeder applications. These picks assume standard NM-B (Romex) cable for indoor dry locations, or individual THHN/THWN-2 conductors in conduit, terminating on standard residential breakers.
- 15 Amp Circuit (Lighting/Receptacles): 14 AWG Copper. (Max breaker: 15A. NEC 240.4(D) strictly limits 14 AWG to 15A, even though the 75°C column says 20A).
- 20 Amp Circuit (Kitchen/Bath/Laundry): 12 AWG Copper. (Max breaker: 20A).
- 30 Amp Circuit (Dryer/Water Heater): 10 AWG Copper. (Max breaker: 30A).
- 40 Amp Circuit (Range/Cooktop): 8 AWG Copper. (Max breaker: 40A).
- 50 Amp Circuit (EV Charger/Subpanel): 6 AWG Copper. (Note: 6 AWG in the 60°C column is 55A, which allows the use of the next standard breaker size up, 60A, per NEC 240.4(B), but it is universally protected at 50A for continuous EV loads).
- 100 Amp Subpanel Feeder: 3 AWG Copper (if using THHN in conduit) or 2 AWG Copper (if using NM-B cable, since NM-B is restricted to the 60°C column).
Derating Factors: When the Base Chart Lies
The ampacities in the master chart assume two things: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors (CCCs) in a single conduit. If you violate either condition, you must apply derating factors from NEC Table 310.15(B)(1)(1) and Table 310.15(B)(1)(2).
Here is how the math works on the jobsite:
Imagine you are pulling four 12 AWG THHN wires (two hots, one neutral, one ground) through an EMT conduit in an attic where the ambient temperature reaches 40°C (104°F). The ground wire does not count as a CCC. You have 3 CCCs, but the temperature is elevated.
- Start at the 90°C column: 12 AWG THHN at 90°C is rated for 30A.
- Apply Temperature Correction (40°C ambient): The correction factor for 90°C wire at 40°C is 0.91. (30A × 0.91 = 27.3A).
- Apply Bundling Derating: If you had 4 to 6 CCCs, you would multiply by 80%. Since we only have 3 CCCs, bundling derating is 100%.
- Check Termination Limits: Your calculated derated ampacity is 27.3A. However, your breaker terminals are rated for 60°C. The 60°C limit for 12 AWG is 20A. Therefore, your final maximum continuous load is capped at 20A. The wire is still safe to use on a 20A breaker.
In a multi-wire branch circuit (MWBC) sharing a neutral, the neutral carries only the unbalanced load and does not count as a CCC. However, in a 3-phase, 4-wire wye circuit where the major load is nonlinear (like LED drivers or computers), the neutral carries harmonic currents and must be counted as a CCC, triggering derating.
Decision Tree: Picking Your Exact Wire and Breaker
Use this decision matrix to terminate your planning phase and pick a concrete part number. This assumes standard residential copper wiring, 75°C rated breakers, and runs under 50 feet.
| Application / Load | Max Continuous Amps | Required AWG (NM-B / THHN) | Breaker Size | Concrete Pick (Buy This) |
|---|---|---|---|---|
| Standard Bedroom Receptacles | 12A | 14 AWG NM-B | 15A AFCI | Southwire 14/2 Romex SIMpull |
| Kitchen Small Appliance | 16A | 12 AWG NM-B | 20A GFCI/AFCI | Southwire 12/2 Romex SIMpull |
| Electric Dryer (240V) | 24A | 10 AWG NM-B | 30A Standard | Southwire 10/3 Romex with Ground |
| Level 2 EV Charger (240V) | 40A (Continuous) | 6 AWG THHN | 50A Standard | Cerrowire 6 AWG THHN (x2 Hots, x1 Ground) |
| 100A Subpanel Feeder | 80A (Continuous) | 3 AWG THHN / 2 AWG NM-B | 100A Main | 3 AWG THHN in 1.25" EMT Conduit |
Note on Continuous Loads: NEC 210.20(A) requires branch circuit overcurrent devices to be rated at 125% of the continuous load (operating for 3 hours or more). A 40A EV charger requires a 50A breaker (40 × 1.25 = 50).
What This Chart Cannot Tell You
An ampacity chart guarantees the wire will not melt or start a fire under specific thermal conditions. It does not guarantee the equipment at the end of the wire will function correctly. Here is what you must calculate separately:
- Voltage Drop: The NEC recommends (but does not strictly mandate for all branch circuits) a maximum voltage drop of 3% for branch circuits and 5% overall from the service entrance. If you are running a 50A EV charger 150 feet from the panel, 6 AWG copper will experience a voltage drop exceeding 3%. You must step up to 4 AWG copper to maintain voltage stability, even though 6 AWG is thermally rated for the 50A breaker. Use the Southwire Voltage Drop Calculator to verify long runs.
- Aluminum vs. Copper: The chart above is strictly for copper. If you are using aluminum (common for service entrance feeders like 2-2-2-4 MHF), the ampacity is significantly lower. For example, 2 AWG aluminum is only rated for 90A at 75°C, not 115A like copper.
- Local AHJ Overrides: Your local Authority Having Jurisdiction (inspector) may have amendments to the NEC. Some municipalities require 12 AWG minimum for all 15A and 20A receptacle circuits, effectively banning 14 AWG from residential construction entirely. Always verify with your local building department before pulling permits.
