When sizing conductors for residential or commercial electrical systems, the definitive wire amp chart is governed by NEC Table 310.16 (formerly 310.15(B)(16)). For a standard 20A residential branch circuit, you need 12 AWG copper. For a 60A subpanel feeder, you need 4 AWG copper or 2 AWG aluminum. However, simply reading the base numbers off the chart without applying termination temperature limits and derating factors is the most common cause of failed electrical inspections and overheated lugs.

How to Read the NEC Wire Amp Chart (The Columns Explained)

The wire amp chart is divided into temperature columns: 60°C (140°F), 75°C (167°F), and 90°C (194°F). These columns represent the maximum allowable ampacity based on the thermal rating of the wire's insulation (e.g., THHN is 90°C, THWN is 75°C, TW is 60°C). However, the insulation rating is only half the equation. According to NFPA 70 (NEC) Section 110.14(C), the allowable ampacity is ultimately bottlenecked by the temperature rating of the terminations (the breaker lugs, receptacles, or splices) the wire connects to.

The Golden Rule of Termination Columns:
For circuits rated 100A or less, you must use the 60°C column to determine the wire's base ampacity for overcurrent protection sizing, unless the equipment is explicitly marked for 75°C. Most modern breakers are 75°C rated, but standard 15A and 20A duplex receptacles are typically only rated for 60°C terminations. You can always use the 90°C column for derating calculations, but the final adjusted ampacity cannot exceed the 60°C or 75°C termination limit.

The Complete Copper & Aluminum Wire Amp Chart (NEC 310.16)

The following table reproduces the core values from the 2023 NEC Table 310.16 for ambient temperatures of 30°C (86°F). This data applies to not more than three current-carrying conductors in a raceway, cable, or earth.

NEC Table 310.16 Allowable Ampacities (30°C Ambient, Up to 3 Conductors)
AWG / kcmil Copper 60°C Copper 75°C Copper 90°C Aluminum 60°C Aluminum 75°C Aluminum 90°C
1415-25---
1220-3015--
1030-4025--
8405055304045
6556575405060
4708595556575
385100115657585
2951151307590100
111013014585100115
1/0125150170100120135
2/0145175195115135150
3/0165200225130155175
4/0195230260150180205

Quick-Jump: Most Queried Branch Circuit & Feeder Sizes

Bookmark this section for the most common residential and light-commercial sizing scenarios. These assume standard 75°C breaker terminations and 60°C receptacle terminations where applicable.

  • 15A Branch Circuit (Lighting/Receptacles): 14 AWG Copper (NM-B or THHN).
  • 20A Branch Circuit (Kitchen/Bath/Laundry): 12 AWG Copper.
  • 30A Dryer/HVAC Circuit: 10 AWG Copper.
  • 40A Range/EV Charger Circuit: 8 AWG Copper.
  • 50A Hot Tub/Welder Circuit: 6 AWG Copper.
  • 60A Subpanel Feeder: 4 AWG Copper or 2 AWG Aluminum (using 75°C column).
  • 100A Subpanel Feeder: 3 AWG Copper or 1 AWG Aluminum. Note: For 100A residential dwelling services (not feeders), NEC 310.12 allows 4 AWG Copper or 2 AWG Aluminum due to the 83% dwelling service rule.
  • 200A Main Service: 2/0 AWG Copper or 4/0 AWG Aluminum (per NEC 310.12 dwelling service rules).

Derating: When the Chart Lies to You (Temperature & Bundling)

The base values in the wire amp chart assume an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. When these conditions change, the wire's ability to dissipate heat drops, and you must apply derating factors. According to OSHA electrical safety guidelines and NEC Article 310, ignoring derating is a primary cause of insulation meltdown in commercial conduit runs.

Ambient Temperature Correction: If your conduit runs through a hot attic or an outdoor environment where temperatures exceed 30°C, you must multiply the base ampacity by a correction factor. For example, if the ambient temperature is 46-50°C (115-122°F), the correction factor for 90°C THHN wire is 0.82. A 10 AWG THHN wire (base 40A at 90°C) derates to 32.8A. If this circuit terminates on a 60°C rated device, the final allowable ampacity is capped at the 60°C column value (30A).

Bundling (Conduit Fill) Adjustment: When you pull more than three current-carrying conductors in a single raceway, the mutual heating effect requires an adjustment factor. If you pull 4 to 6 conductors, multiply the 90°C base ampacity by 80%. If you pull 7 to 9 conductors, multiply by 70%. Neutral conductors that carry only the unbalanced load from other conductors in the same raceway do not count as current-carrying for this calculation, but a neutral on a 3-phase, 4-wire wye circuit with non-linear loads (like LED drivers or computers) does count due to harmonic triplen currents.

Decision Path: Pick Your Exact Wire Size in 4 Steps

Use this decision tree to finalize your wire selection without second-guessing the code. This framework terminates in a concrete pick, eliminating open-ended 'it depends' guesswork.

Step Condition / Question Action / Result
1. Base Load What is the maximum continuous load + non-continuous load? Calculate total amperage. If continuous (3+ hours), multiply load by 1.25.
2. Termination Limit What is the temperature rating of the breaker/lug? Find the AWG in the 60°C or 75°C column that meets or exceeds your Step 1 amperage. This is your minimum termination size.
3. Derating Check Are there >3 conductors in the pipe or ambient temp >30°C? If NO, your Step 2 AWG is your final pick. If YES, take your Step 2 AWG, look at its 90°C column value, and apply the derating multipliers.
4. Final Verification Does the derated 90°C value exceed the Step 1 amperage? If YES, keep the Step 2 AWG. If NO, step up one AWG size and repeat Step 3 until the derated 90°C value is high enough, while ensuring the physical wire still fits the termination lug.
Concrete Example: You need to run a 40A continuous load (50A total after 1.25x multiplier) in a conduit with 6 current-carrying conductors at 30°C ambient. The breaker is 75°C rated.
Step 2: 75°C column for 50A requires 8 AWG Copper (rated 50A).
Step 3: 6 conductors requires an 80% derating factor. 8 AWG at 90°C is 55A. 55A x 0.80 = 44A. This is less than our 50A requirement.
Step 4: Step up to 6 AWG. 6 AWG at 90°C is 75A. 75A x 0.80 = 60A. 60A > 50A. Final Pick: 6 AWG Copper THHN.

What the Wire Amp Chart Cannot Tell You

While NEC Table 310.16 dictates thermal limits, it completely ignores voltage drop. If you are running a 60A feeder 200 feet to a detached garage, 4 AWG copper will keep the wire from melting, but you will experience a voltage drop exceeding the recommended 3% threshold under full load. For long runs, you must calculate voltage drop using Chapter 9, Table 8 resistance values and upsized the wire accordingly (e.g., jumping from 4 AWG to 2 AWG). Furthermore, the chart does not account for physical lug capacity; always verify that the breaker or panel lug is physically rated to accept the larger wire size you selected for voltage drop compensation, or use a mechanical lug reducer.