Wire AWG Current Rating Chart: NEC 310.16 Ampacity & Sizing Guide

How to Read the NEC 310.16 Ampacity Table

The allowable wire AWG current rating (ampacity) is not a single fixed number; it is determined by the conductor material, the insulation temperature rating, and the terminal temperature rating of the connected equipment. The definitive source for these values in the United States is NEC Table 310.16 (formerly 310.15(B)(16)), published by the National Fire Protection Association (NFPA).

When reading the master chart below, you will see three distinct temperature columns: 60°C (140°F), 75°C (167°F), and 90°C (194°F). These columns correspond to the thermal limits of the wire's insulation and the equipment terminals. A common and dangerous mistake is looking at a wire's insulation rating (e.g., THHN is 90°C) and using the 90°C column to size the breaker. In reality, the breaker or receptacle terminals dictate your baseline ampacity, while the 90°C column is reserved strictly for calculating derating adjustments before capping the final value at the terminal limit.

Copper Wire AWG Current Rating Master Chart

The following data is extracted directly from NEC Table 310.16 for copper conductors. This table represents the baseline ampacity before any ambient temperature or bundling corrections are applied.

Decision Path: Which Column Applies to Your Install?

Choosing the wrong column is the most frequent cause of failed electrical inspections and overheated terminals. Use this decision tree to lock in your baseline ampacity column, as mandated by NEC Article 110.14(C).

How Derating Modifies Your Base AWG Rating

The ampacities in the master table assume ideal conditions: 30°C ambient air and no more than three current-carrying conductors (CCCs) in a raceway. When you bundle wires or run them through hot attics, the insulation cannot dissipate heat, and the wire's effective current rating drops. This is where the 90°C column saves you from having to upsize your wire unnecessarily.

Worked Numeric Example:
You are pulling four 12 AWG THHN current-carrying conductors through a conduit in a standard basement (30°C ambient). You need to protect them with a 20A breaker.

1. Base Value: Look at the 90°C column for 12 AWG THHN. The base ampacity is 30A.
2. Bundling Factor: NEC Table 310.15(C)(1) states that 4 to 6 CCCs require an 80% adjustment factor.
3. Derated Ampacity: 30A × 0.80 = 24A.
4. Terminal Cap: Your breaker terminals are rated for 60°C (or 75°C). The 60°C limit for 12 AWG is 20A; the 75°C limit is 25A. Because your derated value (24A) is higher than the 60°C terminal limit (20A), the wire is legally permitted to carry 20A. You can use 12 AWG on a 20A breaker.

If you had five CCCs in that conduit (requiring a 70% derating factor: 30A × 0.70 = 21A), you would still be fine for a 20A breaker. But if you had seven CCCs (50% factor: 30A × 0.50 = 15A), the derated ampacity falls below the breaker size, forcing you to step up to 10 AWG wire.

What This Table Cannot Tell You (The Edge Cases)

While NEC Table 310.16 is the bible for preventing wires from melting, it is blind to several critical installation realities. Always cross-reference these factors before pulling wire:

• Voltage Drop: Ampacity only addresses thermal limits. If you are running a 50A circuit 150 feet to a detached garage, 6 AWG copper will not overheat, but you will experience severe voltage drop. For runs over 100 feet, calculate voltage drop and typically upsize by one or two AWG sizes to maintain a 3% maximum drop.
• Conduit Fill Capacity: Chapter 9 of the NEC limits how much physical space wires can take up inside a conduit (usually 40% for three or more wires). You might have the correct AWG for the current, but if you are pulling four 4/0 AWG feeders, they physically will not fit inside a 1-inch PVC conduit.
• Aluminum Conductors: The table above is strictly for copper. If you are using aluminum (common for service entrance feeders like 2-2-2-4 AL), aluminum has higher resistance. You must use the aluminum-specific columns in NEC 310.16, which generally require sizing up two AWG sizes compared to copper for the same ampacity.

Quick-Jump: Most Queried Residential Wire Sizes

Bookmark this section for fast lookups on the most common home wiring scenarios. These recommendations assume standard copper THHN/THWN-2 or NM-B (Romex) cable, standard residential breakers (which default to the 60°C column for circuits ≤100A), and standard ambient temperatures.

• 15-Amp Lighting/Receptacle Circuit: Use 14 AWG (Rated 15A at 60°C). Note: 12 AWG is also acceptable and often preferred by pros to minimize voltage drop and allow future upgrades.
• 20-Amp Kitchen/Bath/Garage Circuit: Use 12 AWG (Rated 20A at 60°C).
• 30-Amp Dryer/Water Heater Circuit: Use 10 AWG (Rated 30A at 60°C).
• 50-Amp Range/Hot Tub Circuit: Use 6 AWG (Rated 55A at 60°C).
  Critical Warning: Many DIYers mistakenly use 8 AWG for 50A circuits because the 75°C column lists 8 AWG at 50A. However, unless your 50A breaker is explicitly stamped 75°C, NEC 110.14(C) forces you to the 60°C column, where 8 AWG is only rated for 40A. Using 8 AWG on a 50A breaker in a standard residential panel is a code violation and a fire hazard. Always use 6 AWG copper for 50A.
• 100-Amp Subpanel Feeder: Use 3 AWG copper (Rated 85A at 60°C, but 100A at 75°C. Subpanel lugs are typically rated 75°C, allowing the 75°C column to be used for feeders over 100A, but for exactly 100A, verify lug markings. If unmarked, step up to 2 AWG to satisfy the 60°C 95A limit, or use 1/0 Aluminum).

For comprehensive technical data on specific insulation types like XHHW-2 or THHN, refer to the Southwire wire and cable technical resources or the manufacturer's official specification sheets. Always verify your final wire and breaker sizing with your local Authority Having Jurisdiction (AHJ), as local amendments to the NEC can override general guidance.