For standard residential 120V/240V branch circuits using copper wire in a 30°C (86°F) ambient environment, you must use the 60°C column for circuits up to 100A, and the 75°C column for circuits over 100A. The baseline amperages are: 14 AWG = 15A, 12 AWG = 20A, 10 AWG = 30A, 8 AWG = 40A, and 6 AWG = 55A. While the insulation on modern THHN wire is rated for 90°C, the National Electrical Code (NEC) restricts your final ampacity to the lowest temperature rating of any connected device, terminal, or cable type in the circuit.

The Master Electrical Wiring Amperage Chart (NEC Table 310.16)

This electrical wiring amperage chart is derived directly from NEC Table 310.16 (formerly 310.15(B)(16) in older code cycles). It applies specifically to copper conductors with up to three current-carrying conductors in a raceway, cable, or earth, at an ambient temperature of 30°C (86°F).

How to read this table: Locate your wire gauge (AWG or kcmil) in the left column. Read across to the temperature column that matches your installation's "weakest link" (explained below). The number at the intersection is your maximum allowable ampacity before applying any derating factors.
Table 310.16 Allowable Ampacities of Insulated Copper Conductors (30°C Ambient)
Wire Size (AWG/kcmil) 60°C (140°F) Column 75°C (167°F) Column 90°C (194°F) Column
14 AWG15A20A25A
12 AWG20A25A30A
10 AWG30A35A40A
8 AWG40A50A55A
6 AWG55A65A75A
4 AWG70A85A95A
3 AWG85A100A115A
2 AWG95A115A130A
1 AWG110A130A145A
1/0 AWG125A150A170A
2/0 AWG145A175A195A
3/0 AWG165A200A225A
4/0 AWG195A230A260A

Quick-Jump: Most Queried Residential Wire Sizes

For 80% of residential DIY and professional rough-in work, you will be pulling from this shortlist. These assume standard 60°C terminations and 30°C ambient temperatures.

  • 15A Lighting Circuits: 14 AWG copper (14/2 NM-B). Breaker: 15A.
  • 20A Receptacle/Appliance Circuits: 12 AWG copper (12/2 NM-B). Breaker: 20A.
  • 30A Dryer/Water Heater (120V control): 10 AWG copper (10/2 or 10/3 NM-B). Breaker: 30A.
  • 40A Range/Cooktop: 8 AWG copper (8/3 NM-B or THHN in conduit). Breaker: 40A.
  • 50A Range/EV Charger: 6 AWG copper (6/3 NM-B or THHN in conduit). Breaker: 50A.
  • 60A Subpanel Feeder: 4 AWG copper (THHN in conduit) or 6 AWG copper (if 75°C rated terminals and cable). Breaker: 60A.

Which Temperature Column Applies to Your Installation?

The most common code violation made by hobbyists and junior apprentices is sizing wire using the 90°C column because they bought THHN wire. This is incorrect. Per NEC 110.14(C), your allowable ampacity is dictated by the lowest temperature rating of any component in the circuit. This is known as the "weakest link" rule.

Here is how to determine your column:

  1. Check the cable type: If you are using NM-B (Romex), NEC 334.80 strictly limits you to the 60°C column, regardless of the fact that the individual THHN wires inside the sheath are rated for 90°C.
  2. Check the devices: Standard 15A and 20A duplex receptacles, light switches, and smart home modules are almost universally rated for 60°C. If your circuit terminates at one of these, you must use the 60°C column.
  3. Check the breaker: Most modern standard breakers (like Square D Homeline or Siemens QP) have terminals rated for 75°C. However, if the breaker is 75°C but the receptacle is 60°C, the 60°C column wins.
  4. The 100A Threshold: NEC 110.14(C)(1) allows you to use the 75°C column for circuits rated over 100A, provided the equipment is marked for 75°C (which nearly all modern subpanel lugs and large breakers are).

Derating Factors: When Base Ampacity Drops

The chart above assumes ideal conditions: exactly three current-carrying conductors in a raceway and an ambient temperature of 30°C (86°F). Real-world jobsites rarely stay ideal. When conditions change, you must apply derating factors to the 90°C column base value (this is the one time you use the 90°C column) to find your adjusted ampacity.

1. Bundling (More than 3 current-carrying conductors):
If you pull four to six current-carrying conductors through a single conduit, you must multiply the 90°C base ampacity by 80%. (Note: Grounding wires and neutral wires that only carry unbalanced load do not count as current-carrying for this calculation, but a neutral on a multi-wire branch circuit or a non-linear load circuit does).

Worked Example: You are pulling four current-carrying 10 AWG THHN wires through a single EMT conduit for two 240V circuits.
* Base 90°C ampacity for 10 AWG = 40A.
* Derating factor for 4-6 conductors = 80% (0.80).
* Adjusted ampacity = 40A × 0.80 = 32A.
* Because 32A is greater than the 30A breaker protecting the circuit, 10 AWG is still code-compliant. If you added a third circuit (6 current-carrying wires), the derating drops to 70% (40A × 0.70 = 28A). At 28A, you could no longer use a 30A breaker and would be forced to upsize to 8 AWG wire.

2. Ambient Temperature:
If your conduit runs through an attic that reaches 110°F (43°C), you must apply a temperature correction factor. For THHN (90°C insulation) at 41-45°C ambient, the correction factor is 0.82. Always consult NEC Table 310.15(B)(1) for exact multipliers.

Decision Path: Sizing Your Next Branch Circuit

Use this if-then decision tree to terminate your wire sizing process with a concrete, code-compliant pick. Do not guess; follow the math.

Step Condition / Action Result
1. Calculate Load Is the load continuous (on for 3+ hours)? If YES: Multiply load by 1.25. If NO: Use exact load.
2. Size Breaker Select standard breaker size ≥ calculated load. e.g., 16A continuous × 1.25 = 20A. Pick 20A breaker.
3. Base Wire Size Look up breaker size in the 60°C column (for <100A). 20A breaker requires wire rated ≥ 20A. Pick 12 AWG.
4. Check Derating Are there >3 wires in conduit or high ambient heat? If YES: Apply derating to 90°C column. If result < breaker size, upsize wire.
5. Final Pick Confirm termination ratings and voltage drop. Terminate with concrete selection.
Default Pick for Standard Kitchen/Bath: For a standard 20A small-appliance branch circuit, use 12 AWG copper (12/2 NM-B for concealed framing, or 12 AWG THHN in 1/2" EMT for exposed masonry), protected by a 20A AFCI/GFCI dual-function breaker.

What This Chart Cannot Tell You (And When to Call a Pro)

An electrical wiring amperage chart dictates thermal limits (preventing the wire from melting), but it does not account for voltage drop or fault currents.

  • Voltage Drop: If you are running a 50A EV charger 150 feet from the panel, 6 AWG copper will keep the wire from catching fire, but the voltage drop will exceed the recommended 3% threshold, causing your charger to fault or operate inefficiently. For long runs, you must upsize the wire (e.g., to 4 AWG or 3 AWG) purely for voltage drop mitigation, even if the ampacity chart says 6 AWG is thermally sufficient.
  • Short Circuit Let-Through Current: This chart does not tell you if your wire can withstand the magnetic and thermal forces of a dead short. That is determined by the breaker's Ampere Interrupting Capacity (AIC) and the wire's short-circuit withstand rating.
  • Service Entrance Work: Sizing the main service conductors from the utility transformer to your meter/main panel involves utility-specific rules, fault current calculations, and local AHJ (Authority Having Jurisdiction) mandates. Never use a standard branch-circuit chart for service entrance upgrades; defer this to a licensed electrician and your local utility provider.