For standard residential copper wire, the baseline AWG ampacity limits are: 14 AWG = 15A, 12 AWG = 20A, 10 AWG = 30A, 8 AWG = 40A, 6 AWG = 55A, 4 AWG = 70A, and 2 AWG = 95A. These values assume copper conductors, a maximum of three current-carrying wires in a raceway, and an ambient temperature of 30°C (86°F). However, picking the right wire requires more than just matching the breaker size to the base chart. You must account for termination temperature ratings, bundling derations, and specific National Electrical Code (NEC) exceptions.

How to Read the NEC AWG Ampacity Table

The master reference for wire sizing in the United States is NEC Table 310.16. When you look at this table, you will see three distinct temperature columns: 60°C (140°F), 75°C (167°F), and 90°C (194°F). Knowing which column applies to your installation is the most common point of failure for DIYers and junior apprentices.

The Weakest Link Rule (NEC 110.14(C)): Your allowable ampacity is limited by the lowest temperature rating of any component in the circuit. If you pull 90°C THHN wire through conduit, but your breaker and receptacles are only rated for 75°C, you must use the 75°C column to determine your maximum ampacity. The 90°C column is generally only used as a starting point for calculating derating factors.

There is one massive exception to the weakest link rule that trips up many builders: NEC 240.4(D). This section explicitly caps the overcurrent protection for small conductors. Regardless of whether your 12 AWG wire has 90°C insulation and your breaker is rated 75°C, NEC 240.4(D) hard-limits 14 AWG to 15A, 12 AWG to 20A, and 10 AWG to 30A. You cannot put a 25A breaker on 12 AWG wire just because the 75°C column allows 25A.

The Master AWG Ampacity Reference Chart

The following table provides the allowable ampacities for insulated conductors rated up to 2000 volts.

Source: NFPA 70 (National Electrical Code), Table 310.16. Assumes 30°C ambient temperature and not more than three current-carrying conductors in a raceway.

NEC Table 310.16 Allowable Ampacities (Copper & Aluminum)
AWG / kcmil Copper 60°C Copper 75°C Copper 90°C Aluminum 60°C Aluminum 75°C Aluminum 90°C
14152025---
12202530152025
10303540253035
8405055304045
6556575405060
4708595556575
385100110657585
2951151307590100
111013014585100115
1/0125150170100120135
2/0145175195115135150
3/0165200225130155175
4/0195230260150180205

Quick-Jump: Most Queried Wire Sizes

For residential branch circuits and standard feeders using NM-B (Romex) or THHN in conduit, these are the baseline limits you will reference 90% of the time. Bookmark this section for quick jobsite lookups.

  • 14 AWG Copper: 15 Amps (Lighting, standard bedroom/living room receptacles)
  • 12 AWG Copper: 20 Amps (Kitchen/bathroom small appliance circuits, garage outlets)
  • 10 AWG Copper: 30 Amps (Standard electric dryers, RV hookups, window AC units)
  • 8 AWG Copper: 40 Amps (Electric cooktops, larger HVAC condenser units)
  • 6 AWG Copper: 55 Amps (Electric ranges, subpanel feeders up to 50A/60A depending on specific appliance allowances)
  • 4 AWG Copper: 70 Amps (Heavy-duty subpanels, EV chargers requiring 60A+ continuous)
  • 2 AWG Copper / 1/0 Aluminum: 95A / 120A (Standard 100A residential subpanel feeders)

Derating and Adjustment Factors

The base ampacity table assumes you have no more than three current-carrying conductors in a conduit and an ambient temperature of 30°C. When you bundle wires together, they cannot dissipate heat as effectively. NEC Table 310.15(C)(1) mandates that you apply a derating multiplier to the 90°C column of the ampacity chart when you have 4 or more current-carrying conductors.

Worked Example: You are pulling two 20A circuits (4 current-carrying wires: two hots, two neutrals) through a single conduit using 12 AWG THHN.
1. Base 90°C ampacity for 12 AWG is 30A.
2. For 4-6 conductors, the derating factor is 80%.
3. 30A × 0.80 = 24A.
4. Because 24A is still greater than your 20A breaker size, 12 AWG THHN is perfectly legal and safe. If you added a third circuit (6 wires), the derating would still be 80%, but if you added a fourth (8 wires), the derating drops to 70% (30A × 0.70 = 21A), which still passes, but you are approaching the limit.

Sizing Decision Path: Which Wire and Breaker to Pick

Use this decision tree to lock in your exact wire gauge and breaker size for common residential and light commercial applications. This path assumes standard copper conductors and 75°C rated terminations.

Application / Load Max Continuous Load Required Wire (Copper) Required Breaker
General Lighting / Bedroom Outlets 12 Amps 14 AWG NM-B 15A Single-Pole
Kitchen / Bathroom GFCI Outlets 16 Amps 12 AWG NM-B 20A Single-Pole
Standard Electric Dryer (30A Receptacle) 24 Amps 10 AWG (3-conductor + ground) 30A Double-Pole
Level 2 EV Charger (Hardwired 40A) 32 Amps (Continuous) 8 AWG THHN 40A Double-Pole
Electric Range / Oven (50A Receptacle) 40 Amps 6 AWG NM-B or THHN 50A Double-Pole
100-Amp Subpanel Feeder (Short Run) 100 Amps 3 AWG THHN or 2 AWG NM-B 100A Main Breaker

What the Ampacity Table Cannot Tell You

Relying solely on NEC Table 310.16 will leave you blind to three critical field variables that can cause a system to fail inspection or overheat:

  1. Voltage Drop: The ampacity table only prevents the wire insulation from melting; it does not guarantee usable voltage at the load. For any run exceeding 75 to 100 feet, you must calculate voltage drop. A 3% drop is the standard target for branch circuits. If you are running a 50A EV charger 120 feet from the panel, 6 AWG copper will carry the current safely, but the voltage drop will exceed 4%. You must step up to 4 AWG.
  2. Physical Lug Fitment: Ampacity charts do not account for the physical dimensions of the wire versus the terminal lugs on your equipment. A 50A breaker is often designed to accept a maximum of 6 AWG or 4 AWG wire. If you upsize to 2 AWG to mitigate voltage drop on a long run, you may find the wire physically will not fit into the breaker lug. In this case, you must use a step-down pigtail or a larger breaker frame.
  3. Short-Circuit Interrupting Capacity: The table tells you what the wire can handle continuously, but not what it can survive during a fault. Ensure your breaker's AIC (Ampere Interrupting Capacity) rating matches your utility's available fault current, typically 10kA for residential panels.
Default Recommendation: If your calculated continuous load falls exactly on a boundary (e.g., exactly 30A), or if your conduit run exceeds 75 feet, always step up one AWG size. The marginal cost difference between 10 AWG and 8 AWG copper is negligible compared to the cost of ripping out drywall to replace an undersized feeder five years from now.