Most DIYers and apprentices searching for ampacity AWG values just need the quick residential baselines: 14 AWG is 15 amps, 12 AWG is 20 amps, and 10 AWG is 30 amps. But if you are pulling THHN in conduit, sizing a subpanel feeder, or working in a hot attic, relying on those basic numbers can lead to a failed inspection, a tripped breaker, or a melted termination lug. The allowable ampacity of a wire depends entirely on its insulation temperature rating, the termination limits of the devices it connects to, and the physical environment of the run.
How to Read the NEC Ampacity AWG Table
Before looking at the numbers, you must understand how to read the table and, more importantly, which column applies to your specific installation. The National Electrical Code (NEC) Table 310.16 provides ampacities for copper and aluminum conductors across three primary temperature columns: 60°C (140°F), 75°C (167°F), and 90°C (194°F).
You can only use the ampacity column that matches the lowest temperature rating of any connected device, terminal, or splice. Most modern residential breakers and receptacles are rated for 75°C. However, standard NM-B (Romex) cable is legally limited to the 60°C column for ampacity sizing, even though the individual wires inside it have 90°C insulation. You only get to use the 90°C column as a starting point for derating calculations, not for final breaker sizing.
Complete AWG Ampacity Reference Chart
The following table covers the most queried copper wire sizes for residential and light commercial use. These values are sourced directly from NFPA 70 (NEC) Table 310.16, assuming an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway.
| AWG / kcmil | 60°C (140°F) NM-B / TW |
75°C (167°F) THWN / XHHW |
90°C (194°F) THHN / THWN-2 |
Max Standard Breaker |
|---|---|---|---|---|
| 14 AWG | 15A | 20A | 25A | 15A (NEC 240.4(D)) |
| 12 AWG | 20A | 25A | 30A | 20A (NEC 240.4(D)) |
| 10 AWG | 30A | 35A | 40A | 30A (NEC 240.4(D)) |
| 8 AWG | 40A | 50A | 55A | 40A / 50A |
| 6 AWG | 55A | 65A | 75A | 60A / 70A |
| 4 AWG | 70A | 85A | 95A | 80A / 90A |
| 3 AWG | 85A | 100A | 110A | 100A |
| 2 AWG | 95A | 115A | 130A | 110A / 125A |
| 1 AWG | 110A | 130A | 145A | 125A |
| 1/0 AWG | 125A | 150A | 170A | 150A |
| 2/0 AWG | 145A | 175A | 195A | 175A |
| 3/0 AWG | 165A | 200A | 225A | 200A |
| 4/0 AWG | 195A | 230A | 260A | 225A / 250A |
Note: The 'Max Standard Breaker' column assumes standard overcurrent protection rules under NEC 240.4(B) and the specific small-conductor restrictions of 240.4(D). Always verify local AHJ amendments.
Derating Factors: Modifying the Base Value
The numbers in the table above are ideal-scenario baselines. In the real world, how derating rows modify the base value is where most mistakes happen. Derating is required when you exceed 30°C (86°F) ambient temperature or when you bundle more than three current-carrying conductors in a single conduit.
Here is how you apply the math using the 90°C column as your starting baseline (per EC&M NEC code basics):
- Bundling (NEC 310.15(C)(1)): If you pull four 12 AWG THHN wires through a conduit (two hots, one neutral, one ground), you have three current-carrying conductors (the ground does not count). No derating needed. But if you pull two 120V circuits (four hots, two neutrals), you have four current-carrying conductors. You must apply an 80% adjustment factor.
- Ambient Temperature (NEC 310.15(B)(1)): If that same conduit runs through an attic that hits 110°F (43°C), you must apply a 0.87 temperature correction factor to the 90°C column.
You are pulling four 12 AWG THHN wires (two multi-wire branch circuits) in a conduit in a 110°F attic.
1. Base 90°C ampacity for 12 AWG = 30A.
2. Bundling (4 conductors) = 30A × 0.80 = 24A.
3. Ambient temp (110°F) = 24A × 0.87 = 20.88A.
Result: The final derated ampacity is 20.88A. Because this is greater than the 20A breaker protecting the circuit, the installation is code-compliant. If the attic hit 122°F (0.82 factor), the final ampacity would drop to 19.7A, forcing you to upsize to 10 AWG wire.
What This Table Cannot Tell You
While NEC Table 310.16 is the bible for thermal limits, it has blind spots. Relying on it exclusively will cause failures in three specific scenarios:
- Voltage Drop: The table tells you what the wire can handle thermally, not electrically over distance. A 12 AWG wire can safely carry 20A, but if you run it 150 feet to a shed, you will experience a voltage drop exceeding the recommended 3% limit. Your tools will bog down and lights will dim. You must upsize to 10 AWG or 8 AWG for distance, even if the breaker is only 20A.
- Physical Termination Fit: You might calculate that 2/0 AWG is perfect for a 150A subpanel feeder. But if the lugs on your specific brand of load center are only rated to physically accept up to 1/0 AWG, you cannot land the wire. Always check the manufacturer's spec sheet for lug capacity.
- Short-Circuit Withstand: Ampacity is about continuous heat dissipation. It does not tell you if the wire can survive the massive magnetic and thermal forces of a 10,000-amp short circuit before the breaker trips. For high-fault-current service entrances, engineers must calculate short-circuit withstand ratings separately.
AWG Ampacity FAQ
What is the ampacity of 8 AWG wire for a 50-amp breaker?
If you are using 8 AWG NM-B (Romex), the ampacity is 40A (60°C column), and it cannot be used on a 50-amp breaker. If you are pulling individual 8 AWG THHN/THWN-2 wires in conduit and terminating on 75°C rated lugs, the ampacity is 50A, and it is perfectly legal for a 50-amp breaker. Always verify the insulation type and termination ratings before sizing.
Does the ground wire count towards AWG ampacity derating?
No. Under NEC 310.15(C)(1), equipment grounding conductors (bare copper or green) are not considered 'current-carrying conductors' for the purpose of bundling derating. They only carry current during a fault condition. However, if you are using a grounded conductor (a neutral/grounded leg) that carries unbalanced current, it does count. Note: On a standard 120V circuit, the neutral carries the same current as the hot, so it counts. On a balanced 240V-only circuit (like a water heater), the neutral carries zero unbalanced current and does not count.
Can I use the 90°C column for sizing my main panel feeder?
You can use the 90°C column to start your derating calculations (for ambient temperature or bundling), but your final ampacity cannot exceed the 75°C column value. This is because virtually all residential and commercial panelboard lugs and breakers are only tested and rated for 75°C terminations (NEC 110.14(C)). If the 90°C derated value is higher than the 75°C base value, you must cap it at the 75°C number.
Why is 14 AWG limited to 15 amps when the table says 20A or 25A?
NEC 240.4(D) places a hard, specific restriction on small conductors to prevent fires in older homes and to account for the physical fragility of small wires under fault conditions. Regardless of the insulation rating or the 75°C/90°C columns, 14 AWG copper is strictly limited to 15A overcurrent protection, 12 AWG to 20A, and 10 AWG to 30A. There are very few exceptions to this rule (such as specific motor circuits or HVAC equipment), but for general branch circuits, these limits are absolute.
