For standard residential and commercial branch circuits using copper wire, match your breaker size to the 60°C column of NEC Table 310.16: use 14 AWG for 15A, 12 AWG for 20A, 10 AWG for 30A, 8 AWG for 40A, and 6 AWG for 50A. This assumes standard NM-B (Romex) cable in an ambient temperature not exceeding 86°F (30°C). If you are pulling individual THHN conductors in conduit to 75°C-rated terminations, you can utilize the higher 75°C column ampacities, provided your breaker and device lugs are explicitly rated for 75°C.
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- 14 AWG (15 Amp Circuits)
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- 10 AWG (30 Amp Circuits)
- 8 AWG (40 Amp Circuits)
- 6 AWG (50 Amp Circuits)
The Master Copper Amperage Chart (NEC Table 310.16)
The following data is extracted directly from NFPA 70 (National Electrical Code) Table 310.16. It applies strictly to copper conductors with an ambient temperature of 86°F (30°C) and not more than three current-carrying conductors in a raceway or cable.
| AWG Size | 60°C Column (NM-B / TW / UF) | 75°C Column (THWN / THHN in Conduit) | 90°C Column (THHN 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 | 110A |
| 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 |
Source: NFPA 70 (NEC) Table 310.16. For aluminum conductors, consult the separate aluminum columns in the standard.
How to Read This Chart and Pick Your Column
The most common mistake DIYers and junior electricians make is looking at the 90°C column because it offers the highest ampacity, then sizing their breaker to that number. This is a code violation and a fire hazard. Here is exactly how to select your column based on your installation method:
- The 60°C Column: Use this column if you are installing NM-B (Romex), UF-B (underground feeder), or TW cable. You must also use this column if your circuit breaker, receptacle, or device lugs are only rated for 60°C (common on older equipment and virtually all standard 15A/20A residential receptacles). Per NEC 110.14(C), the lowest temperature rating of any component in the circuit dictates the column you must use for final termination ampacity.
- The 75°C Column: Use this column when pulling individual THHN/THWN-2 conductors in conduit, assuming your breakers and termination lugs are explicitly marked 75°C. Most modern commercial breakers and heavy-duty residential breakers (30A and above) carry a 75°C rating.
- The 90°C Column: Never use this column for final breaker sizing. The 90°C ampacity is used exclusively as the starting baseline for calculating temperature and bundling derating adjustments. Once you apply your derating math, you must compare the result to the 60°C or 75°C column (depending on your terminations) and use the lower of the two values.
Notice that 14 AWG copper has a 90°C rating of 25A and a 75°C rating of 20A. However, NEC 240.4(D) strictly limits the overcurrent protection for 14 AWG copper to 15A, regardless of the insulation temperature rating or derating calculations. You cannot put a 20A breaker on 14 AWG wire, even if your math says the insulation can handle it.
The Derating Decision Path: When Base Ampacity Drops
Base ampacity assumes an ambient temperature of 86°F (30°C) and a maximum of three current-carrying conductors in a raceway. If your installation deviates from this, you must apply adjustment factors. Use the decision tree below to determine your final allowable ampacity, referencing the Cerrowire Ampacity Adjustment Tables or NEC Tables 310.15(B)(1) and 310.15(C)(1).
| Installation Condition | Decision / Action Required | Multiplier to Apply to 90°C Base |
|---|---|---|
| Ambient temp is 86°F (30°C) or lower | No temperature correction needed. | 100% |
| Ambient temp is 104°F (40°C) in an attic | Apply temperature correction factor. | 91% |
| Ambient temp is 122°F (50°C) near a roof deck | Apply temperature correction factor. | 82% |
| 4 to 6 current-carrying conductors in one conduit | Apply bundling adjustment factor (neutral counts if carrying unbalanced non-linear load; ground never counts). | 80% |
| 7 to 9 current-carrying conductors in one conduit | Apply bundling adjustment factor. | 70% |
Worked Derating Example: You are pulling four current-carrying 12 AWG THHN conductors through a conduit routed through an attic that reaches 113°F (45°C). You want to terminate on a 20A breaker with 75°C lugs.
- Start with 90°C base: 12 AWG at 90°C = 30A.
- Apply bundling (4 conductors): 30A × 0.80 = 24A.
- Apply temperature (113°F / 45°C): The correction factor for 90°C wire at 45°C is 87%. 24A × 0.87 = 20.88A.
- Check termination limit: The 75°C column for 12 AWG is 25A.
- Final Verdict: Compare the derated value (20.88A) to the termination limit (25A). The lowest value wins. 20.88A is greater than your 20A breaker, so 12 AWG THHN is legally permitted here. If the attic reached 122°F, the math would drop below 20A, forcing an upgrade to 10 AWG.
What This Chart Cannot Tell You
An amperage chart is a thermal limit reference, not a complete design tool. Relying on it blindly will cause you to fail inspections or experience equipment failure in three specific scenarios:
- Voltage Drop Over Distance: NEC Table 310.16 does not account for voltage drop. If you run a 12 AWG copper wire 150 feet to a 120V receptacle drawing 15A, the wire will not overheat (it is within the 20A thermal limit), but the voltage at the receptacle will drop to roughly 111V. This violates the NEC informational note recommending a maximum 3% voltage drop for branch circuits. For runs over 50 feet, always run a voltage drop calculation; you will frequently need to upsize wire by one or two AWG steps purely to maintain voltage, even if the amperage chart says the smaller wire is thermally safe.
- Continuous vs. Non-Continuous Loads: The ampacities in the chart assume non-continuous loads. If your load will run for 3 hours or more continuously (like a commercial HVAC unit, a hardwired EV charger, or commercial lighting), NEC 210.20(A) requires you to size the overcurrent device at 125% of the continuous load. A 16A continuous load requires a 20A breaker (16 × 1.25 = 20), which then dictates 12 AWG wire, not 14 AWG.
- Local AHJ Amendments: Some municipalities outright ban 14 AWG wire for any branch circuit, mandating 12 AWG as the minimum baseline for all 15A and 20A receptacle circuits to reduce voltage drop and provide a safety margin. Your local Authority Having Jurisdiction (AHJ) always supersedes the baseline NEC text.
Definitive Wire Picks for Standard Circuits
If you are wiring standard residential circuits and want to bypass the complex derating math because you are running standard NM-B cable in conditioned spaces (under 86°F) with no more than three current-carrying conductors bundled together, use this definitive pick list. Buy exactly this wire for these breakers:
- 15A Lighting & Receptacle Circuits: 14 AWG NM-B (Copper). Upgrade to 12 AWG if the run from the panel exceeds 50 feet to mitigate voltage drop.
- 20A Kitchen, Bath, & Garage Receptacles: 12 AWG NM-B (Copper). Mandatory for small-appliance branch circuits.
- 30A Electric Dryers & RV Outlets: 10 AWG NM-B or 10 AWG THHN in conduit (2-pole 30A breaker).
- 40A Electric Cooktops & HVAC Condensers: 8 AWG NM-B or 8 AWG THHN in conduit. Note: Many modern 40A breakers require the wire to be stripped to a specific length and torqued to 45 in-lbs; check the breaker label.
- 50A Electric Ranges, Hot Tubs, & EVSE Chargers: 6 AWG NM-B. If pulling THHN in conduit to a 75°C rated EV charger disconnect, 8 AWG THHN is thermally permitted (rated 50A at 75°C), but 6 AWG is heavily recommended to prevent voltage drop during the 4+ hour continuous charge cycle.
- 100A Subpanel Feeders: Do not use copper NM-B. Pull 3 AWG or 2 AWG copper THHN/THWN-2 in conduit, or use 1/0 AWG aluminum SER cable if the lugs are rated 75°C (which saves significant material cost while remaining fully code-compliant).
