When sizing branch circuits or feeders, the direct answer for standard residential copper wire current capacity (at the 60°C column for NM-B cable) is: 14 AWG = 15A, 12 AWG = 20A, 10 AWG = 30A, 8 AWG = 40A, and 6 AWG = 55A. If you are pulling individual THHN/THWN-2 conductors in conduit and terminating on 75°C rated equipment, you can use the 75°C column: 14 AWG = 20A, 12 AWG = 25A, 10 AWG = 35A, 8 AWG = 50A, and 6 AWG = 65A.

Safety Warning: Any work involving mains voltage (>50V AC) requires de-energizing the panel, locking out the breaker, and verifying the circuit is dead with a tested multimeter or non-contact voltage tester before touching any conductors. Local codes may require a licensed electrician for panel and feeder work.

The Master AWG Wire Current Chart (NEC Table 310.16)

The following data is extracted from NFPA 70 (National Electrical Code) Table 310.16. This table assumes copper conductors, an ambient temperature of 30°C (86°F), and not more than three current-carrying conductors in a raceway or cable.

Table 310.16 Allowable Ampacities of Insulated Copper Conductors (Rated 0-2000V)
AWG / kcmil 60°C (140°F)
NM-B / Romex		 75°C (167°F)
THHN in Conduit		 90°C (194°F)
Derating Base
14 AWG 15A 20A 25A
12 AWG 20A 25A 30A
10 AWG 30A 35A 40A
8 AWG 40A 50A 55A
6 AWG 55A 65A 75A
4 AWG 70A 85A 95A
3 AWG 85A 100A 115A
2 AWG 95A 115A 130A
1 AWG 110A 130A 145A
1/0 AWG 125A 150A 170A
2/0 AWG 145A 175A 195A
3/0 AWG 165A 200A 225A
4/0 AWG 195A 230A 260A

How to Read This Table

The columns represent the temperature rating of the wire's insulation. 60°C applies primarily to NM-B (Romex) cable assemblies. 75°C applies to individual THHN/THWN-2 wires pulled in conduit and terminated on standard modern breakers and lugs. 90°C is almost never used for final ampacity; it exists solely as a mathematical baseline for calculating derating factors (discussed below). Bookmark the bolded rows (14, 12, and 10 AWG) as they cover 90% of residential branch circuits.

Which Temperature Column Applies to Your Install?

The most common mistake DIYers make is looking at a spool of THHN wire, seeing the 90°C rating printed on the jacket, and using the 90°C column to size their breaker. This violates NEC 110.14(C), which dictates that the allowable ampacity is limited by the lowest temperature rating of any connected device, conductor, or terminal in the entire circuit.

The Weakest Link Rule: If you run 90°C THHN wire in conduit, but terminate it on a standard 15A or 20A duplex receptacle rated for 60°C, the entire circuit's ampacity is capped at the 60°C column.
  • Use the 60°C Column When: You are using NM-B (Romex) cable, or terminating 15A/20A circuits on standard residential receptacles and switches that lack a 75°C marking.
  • Use the 75°C Column When: You are pulling individual THHN/THWN-2 conductors in conduit and terminating them on equipment explicitly marked 75°C (which includes almost all modern panelboard breakers, subpanel lugs, and 30A+ receptacles like dryer or range outlets).
  • Use the 90°C Column When: You are calculating derating adjustments for bundling or high ambient temperatures. You start your math here, then compare the final derated number to the 75°C or 60°C column to find your actual allowable limit.

Derating Modifiers: When Base Ampacity Drops

The base chart assumes a 30°C (86°F) ambient environment and a maximum of three current-carrying conductors in a single conduit. When reality deviates from this, you must apply derating multipliers from NEC Table 310.15(C)(1) and Table 310.15(B)(1).

Bundling Derating (More than 3 wires in a conduit)

Wires generate heat. When you bundle them tightly inside a PVC or EMT conduit, they cannot dissipate that heat, which degrades the insulation over time. If you pull 4 to 6 current-carrying conductors in one conduit, you must multiply the base ampacity by 80%. For 7 to 9 conductors, the multiplier drops to 70%.

Worked Example: You are pulling four 12 AWG THHN wires (two hots, one neutral, one ground) through a single 1/2-inch EMT conduit to feed a multi-wire branch circuit.
1. Base 90°C ampacity for 12 AWG = 30A.
2. 4 current-carrying conductors (the ground does not count) = 80% multiplier.
3. 30A × 0.80 = 24A final derated ampacity.
4. Because 24A is greater than your 20A breaker, this installation is perfectly legal and safe.

Ambient Temperature Derating

If your conduit runs through an attic in a southern climate where temperatures hit 40°C (104°F), the wire's ability to shed heat is compromised. You must apply an ambient temperature correction factor. For 90°C THHN at 40°C ambient, the multiplier is 0.91. Always apply both bundling and ambient multipliers sequentially if both conditions exist.

Decision Tree: Pick Your Wire for Common Loads

Stop guessing. Use this decision matrix to select the exact wire gauge and type for standard residential loads. This assumes standard 120V/240V residential splits, copper conductors, and runs under 75 feet.

Application / Load Breaker Size Wire Type Required AWG Why This Pick?
Standard 120V Lighting / Receptacles 15A or 20A NM-B (Romex) 14 AWG (15A) or 12 AWG (20A) 60°C terminal limits on standard devices cap NM-B at these values.
Kitchen / Bath Small Appliance 20A NM-B (Romex) 12 AWG NEC requires 20A minimum for kitchen small-appliance branches.
Electric Dryer (30A / 240V) 30A NM-B or THHN 10 AWG 10 AWG NM-B is rated 30A at 60°C; matches standard NEMA 10-30 / 14-30 terminals.
EV Level 2 Charger (48A continuous) 60A THHN in Conduit 4 AWG Continuous loads require 125% sizing (48A × 1.25 = 60A). 4 AWG THHN at 75°C = 85A, providing safe headroom.
100A Subpanel Feeder 100A THHN in Conduit 3 AWG 3 AWG copper at 75°C is exactly 100A. (If using NM-B, you must upsize to 2 AWG for 95A, or use 1/0 AL SER cable).

What the Ampacity Table Cannot Tell You

NEC Table 310.16 only tells you the maximum current a wire can carry before its insulation begins to thermally degrade. It completely ignores voltage drop. If you push 30A through 10 AWG copper wire over a distance of 100 feet, the wire won't melt, but your equipment will starve.

The Voltage Drop Reality Check

The NEC recommends (in Informational Note to 210.19) a maximum 3% voltage drop on branch circuits and 5% total for feeder + branch combined. Let's run the math on a 30A, 120V workshop outlet located 100 feet from the panel using 10 AWG copper:

  • Resistance: 10 AWG uncoated copper is ~1.24 ohms per 1,000 feet.
  • Total Loop: 100 feet out + 100 feet back = 200 feet.
  • Loop Resistance: 1.24 × (200 / 1000) = 0.248 ohms.
  • Voltage Drop: 30A × 0.248 ohms = 7.44 Volts.
  • Percentage Drop: (7.44 / 120) × 100 = 6.2%.
Actionable Fix: A 6.2% drop on a 120V branch circuit will cause motors to overheat and electronics to brownout. To fix this, you must ignore the ampacity chart's baseline and upsize to 6 AWG copper (0.491 ohms/kft), which drops the loss to 2.94V (2.45%), safely under the 3% threshold. Always calculate voltage drop for any 120V run exceeding 50 feet or any 240V run exceeding 100 feet.

Finally, the table assumes standard installation methods. It cannot account for physical constraints like pulling 4 AWG wire through tight conduit bends (where you should consider aluminum SER cable for feeders due to stiffness) or the specific thermal insulation covering wires buried in attic blown-in cellulose, which may require further local AHJ adjustments. When in doubt, upsizing one gauge costs marginally more in copper but buys massive thermal and voltage-drop headroom.