When sizing conductors for residential or commercial branch circuits, the definitive reference is the wire size for amps chart derived from NFPA 70 (National Electrical Code) Table 310.16. For the most common household queries: a 20-amp circuit requires a minimum of 12 AWG copper, a 30-amp circuit requires 10 AWG copper, and a 50-amp circuit requires 6 AWG copper. However, pulling the correct gauge requires understanding temperature columns, terminal ratings, and derating factors.
How to Read the Wire Size for Amps Chart
Table 310.16 is divided into temperature columns: 60°C, 75°C, and 90°C. These columns represent the maximum allowable ampacity based on the thermal rating of the wire insulation (e.g., TW is 60°C, THWN is 75°C, THHN is 90°C). Modern THHN/THWN-2 wire is rated for 90°C, but you rarely get to use the 90°C column for your final breaker sizing.
Which column applies to your installation? The NEC enforces a 'weakest link' rule. Your final ampacity is limited by the lowest temperature rating of any connected component, including the wire, the breaker terminals, and the receptacle lugs. Most standard residential breakers and receptacles are rated for 75°C. Therefore, you must use the 75°C column for wires 8 AWG and larger.
The 240.4(D) Exception: For small conductors, NEC 240.4(D) strictly caps overcurrent protection regardless of the insulation rating. Even if you pull 12 AWG THHN (rated 30A in the 90°C column), the code legally caps 12 AWG at 20 amps, 10 AWG at 30 amps, and 14 AWG at 15 amps. The 90°C column for these small wires is only used as a starting point for derating math, not for final breaker sizing.
The Complete Wire Size for Amps Chart (NEC Table 310.16)
The following data is sourced directly from NFPA 70 (NEC) Table 310.16, assuming an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a raceway. Use the quick-jump links below to find the most frequently queried residential sizes.
- Quick Jump: 12 AWG (20A circuits)
- Quick Jump: 10 AWG (30A circuits)
- Quick Jump: 6 AWG (50A circuits)
- Quick Jump: 4 AWG (60A EV chargers)
- Quick Jump: 3 AWG (100A subpanels)
| AWG / kcmil | Copper 60°C | Copper 75°C | Copper 90°C | Aluminum 75°C |
|---|---|---|---|---|
| 14 | 15A* | 20A* | 25A* | N/A |
| 12 | 20A* | 25A* | 30A* | N/A |
| 10 | 30A* | 35A* | 40A* | N/A |
| 8 | 40A | 50A | 55A | 40A |
| 6 | 55A | 65A | 75A | 50A |
| 4 | 70A | 85A | 95A | 65A |
| 3 | 85A | 100A | 110A | 75A |
| 2 | 95A | 115A | 130A | 90A |
| 1 | 110A | 130A | 150A | 100A |
| 1/0 | 125A | 150A | 170A | 120A |
| 2/0 | 145A | 175A | 195A | 135A |
| 3/0 | 165A | 200A | 225A | 155A |
| 4/0 | 195A | 230A | 260A | 180A |
*Per NEC 240.4(D), the overcurrent protection for 14, 12, and 10 AWG copper is strictly capped at 15A, 20A, and 30A respectively, regardless of the higher values shown in the 75°C and 90°C columns.
Derating and What the Table Cannot Tell You
The base ampacities in the chart above assume ideal conditions: an ambient temperature of 86°F (30°C) and no more than three current-carrying conductors bundled together. When real-world conditions deviate, you must apply derating factors.
How derating rows modify the base value: If you pull four to six current-carrying conductors through a single conduit, NEC Chapter 9, Table 314.16(B) requires you to multiply the base ampacity by 80%. For example, if you have four 10 AWG THHN wires in a conduit, you start with the 90°C column value (40A). Multiplying 40A by 0.80 yields a derated ampacity of 32A. Because 32A is still above the 240.4(D) cap of 30A, you can still protect that circuit with a 30-amp breaker. However, if you bundle nine conductors together, the derating factor drops to 70% (40A x 0.70 = 28A), forcing you to upsize to 8 AWG wire to maintain a 30-amp circuit. For comprehensive derating tables, refer to the Electrical Contractor Magazine (ECMAG) code guidelines.
What the table cannot tell you: Table 310.16 is purely a thermal limit chart. It cannot tell you if your wire is thick enough to prevent excessive voltage drop over long distances. A 10 AWG wire carrying 20 amps on a 150-foot run will result in a voltage drop of roughly 7.7 volts (over 6% on a 120V circuit), which exceeds the NEC's recommended 3% limit for branch circuits. For long feeder runs, always run a voltage drop calculation; you will frequently need to upsize the wire one or two gauges larger than the ampacity chart dictates.
Frequently Asked Questions
What wire size for 50 amps?
For a standard 50-amp circuit (like an electric range or heavy-duty shop tool), the wire size for amps chart dictates a minimum of 6 AWG copper at the 75°C column (rated 65A). If you are using aluminum, you must step up to 4 AWG aluminum (rated 65A at 75°C). If the run exceeds 75 feet, upsize to 4 AWG copper to mitigate voltage drop.
Can I use the 90°C column for my breaker ampacity?
No. While modern THHN wire is manufactured with 90°C insulation, almost all residential breakers, lugs, and receptacles are only rated for 75°C. The NEC requires you to use the lowest temperature rating in the circuit. The 90°C column is exclusively used as the mathematical baseline for applying derating factors (like conduit fill or high ambient temperatures) before checking the final result against the 75°C or 60°C limits.
What size wire for 100 amps?
To feed a 100-amp subpanel, the chart requires a minimum of 3 AWG copper (rated 100A at 75°C) or 1 AWG aluminum (rated 100A at 75°C). Because aluminum is significantly cheaper and lighter, 1 AWG or 1/0 AWG aluminum (often sold as 1-1-1-2 or 2-2-2-4 SER cable) is the standard choice for 100-amp feeder runs in modern construction.
Does a ground wire count in the ampacity chart?
No. Equipment grounding conductors (EGCs) do not carry current under normal operating conditions; they only carry fault current during a short circuit. Therefore, bare copper or green insulated ground wires do not count as current-carrying conductors when calculating conduit fill derating. Only the ungrounded (hot) and grounded (neutral) conductors count toward your bundling derating math.
