For standard residential NM-B (Romex) cable, you must use the 60°C column of the NEC ampacity table: 14 AWG for 15A, 12 AWG for 20A, 10 AWG for 30A, 8 AWG for 40A, and 6 AWG for 55A. For single THHN/THWN wires pulled through conduit, you can utilize the higher 75°C or 90°C columns, provided your termination points (breakers and lugs) are rated for those temperatures. Sizing wire isn't just about matching a breaker; it requires navigating insulation ratings, terminal limits, and bundling derations.
The Direct Answer: Quick-Jump Wire Gauge Chart Amperage
Bookmark this section for the five most common residential branch circuit and feeder sizes. These values assume copper wire and standard residential termination limits (NEC 110.14(C)).
- 15A Circuit (Lighting/Bedrooms): 14 AWG Copper (NM-B) or 12 AWG Copper (THHN in conduit).
- 20A Circuit (Kitchen/Bath/Outlets): 12 AWG Copper (NM-B or THHN).
- 30A Circuit (Dryer/RV Outlet): 10 AWG Copper (NM-B or THHN).
- 40A Circuit (Range/EVSE): 8 AWG Copper (NM-B) or 8 AWG Copper (THHN).
- 100A Subpanel Feeder: 3 AWG Copper or 1/0 AWG Aluminum (THHN in conduit).
How to Read the NEC 310.16 Ampacity Table
The NFPA 70 (National Electrical Code) Table 310.16 is the master reference for conductor ampacity. However, reading it incorrectly is the most common cause of failed inspections and overheated terminals.
Which column applies to your installation?
- 60°C Column: Use this for NM-B (Romex) cable, UF-B cable, and any circuit 100A or less where the equipment is not explicitly marked with a higher temperature rating.
- 75°C Column: Use this for THHN/THWN in conduit for circuits 100A or less, provided the lugs are marked 'AL/CU' or '75°C'. Also use this for most standard residential subpanel feeders.
- 90°C Column: Use this only as a starting point for derating calculations (adjusting for heat or bundling). You almost never use the 90°C column for final breaker sizing in residential work.
Complete Wire Gauge Chart Amperage Data (NEC Table 310.16)
The following table reproduces the core residential and light-commercial values from NEC Table 310.16 (formerly 310.15(B)(16)). Values are for not more than three current-carrying conductors in a raceway or cable, at an ambient temperature of 30°C (86°F).
| AWG / kcmil | Copper 60°C (NM-B) | Copper 75°C (THHN) | Copper 90°C (THHN) | Aluminum 60°C | Aluminum 75°C (THHN) | Aluminum 90°C (THHN) |
|---|---|---|---|---|---|---|
| 14 | 15A | 20A | 25A | - | - | - |
| 12 | 20A | 25A | 30A | 15A | 20A | 25A |
| 10 | 30A | 35A | 40A | 25A | 30A | 40A |
| 8 | 40A | 50A | 55A | 30A | 40A | 45A |
| 6 | 55A | 65A | 75A | 40A | 50A | 60A |
| 4 | 70A | 85A | 95A | 55A | 65A | 75A |
| 3 | 85A | 100A | 115A | 65A | 75A | 85A |
| 2 | 95A | 115A | 130A | 75A | 90A | 100A |
| 1 | 110A | 130A | 145A | 85A | 100A | 120A |
| 1/0 | 125A | 150A | 170A | 100A | 120A | 135A |
| 2/0 | 145A | 175A | 195A | 115A | 135A | 150A |
| 3/0 | 165A | 200A | 225A | 130A | 155A | 175A |
| 4/0 | 195A | 230A | 260A | 150A | 180A | 205A |
Note: Aluminum 14 AWG is omitted as it is not permitted for general residential branch circuits under standard NEC applications.
Derating: When Base Values Drop
The ampacities listed above assume ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. When you deviate from this, you must apply derating factors, which is where the 90°C column becomes useful.
Worked Numeric Example: Bundled THHN in Conduit
You are pulling four current-carrying 12 AWG THHN (90°C rated) wires through a single conduit to feed two 240V circuits.
- Find Base 90°C Ampacity: Table 310.16 lists 12 AWG Copper at 90°C as 30A.
- Apply Bundling Derating: NEC Table 310.15(C)(1) states that 4 to 6 current-carrying conductors require an 80% adjustment factor.
- Calculate Derated Ampacity: 30A × 0.80 = 24A.
- Check Terminal Limits: Your breakers and receptacles are rated for 60°C. The 60°C column for 12 AWG is 20A.
- Final Pick: Compare 24A (derated wire capacity) to 20A (terminal limit). The lower value wins. Your maximum allowable ampacity is 20A, meaning you must use a 20A breaker.
Decision Tree: Picking Your Exact Wire and Breaker
Use this decision path to terminate your planning phase and pick a concrete material list.
| Installation Scenario | Wire Type & Gauge | Breaker Size |
|---|---|---|
| Standard 120V wall outlets & lighting inside drywall | 12 AWG NM-B (Romex) Copper | 20A Single-Pole |
| 30A RV receptacle or window AC unit (short run < 50ft) | 10 AWG NM-B or THHN Copper | 30A Single/Double-Pole |
| 100A Subpanel feeder in PVC conduit (run < 100ft) | 3 AWG THHN Copper OR 1/0 AWG THHN Aluminum | 100A Double-Pole |
| 200A Main Service Entrance (Meter to Panel) | 4/0 AWG Aluminum (XHHW-2 or SER Cable) | 200A Main Breaker |
| 50A EV Charger or Electric Range (in conduit) | 6 AWG THHN Copper | 50A Double-Pole |
What This Table Cannot Tell You
While NEC Table 310.16 dictates thermal limits, it does not account for three critical physical and electrical realities on the jobsite:
- Voltage Drop on Long Runs: If your run exceeds 100 feet, the wire might safely handle the heat, but the voltage at the load end will sag below acceptable limits (typically a 3% drop limit for branch circuits). For long runs, you must upsize the wire based on circular mils (NEC Chapter 9, Table 8) and the voltage drop formula, not just ampacity.
- Physical Lug Sizing: A 6 AWG wire is rated for 55A (60°C column), but it physically will not fit under the pressure plate of a standard 15A or 20A duplex receptacle. If you must upsize wire for voltage drop, you will need to use a pigtail or a terminal block to step down to a gauge that fits the device lugs.
- Grounding Conductor Sizing: Table 310.16 sizes your current-carrying conductors (hots and neutrals). Equipment grounding conductors (EGCs) are sized entirely differently using NEC Table 250.122, which bases the ground wire size on the rating of the overcurrent breaker, not the load.
Default Recommendation: For 95% of standard residential DIY branch circuits inside walls, buy 12 AWG NM-B copper cable and pair it with 20A AFCI/GFCI breakers. It provides a safe, code-compliant baseline that covers lighting and receptacles without requiring complex derating math, leaving 14 AWG strictly for dedicated, low-draw lighting circuits where local code permits.
