How to Read the NEC Table 310.16 Ampacity Chart
When sizing conductors for residential or commercial branch circuits and feeders, the master reference in the United States is the electric cable ampacity chart published in NFPA 70, specifically National Electrical Code (NEC) Table 310.16. This table defines the maximum continuous current a specific wire gauge can safely carry before its insulation begins to degrade or fail.
Before you pick a wire size, you must understand how to read the temperature columns. The table is divided into three temperature ratings for copper: 60°C (140°F), 75°C (167°F), and 90°C (194°F). The column you are legally required to use depends entirely on your termination points (breakers, lugs, and receptacles), not just the wire insulation. Under NEC 110.14(C)(1)(a), if your circuit is rated 100 amps or less, or uses wire sizes 14 AWG through 1 AWG, you must use the 60°C column to determine your final ampacity, even if you pull 90°C THHN wire. For circuits over 100A or wire sizes larger than 1 AWG, you default to the 75°C column. The 90°C column is almost exclusively used as the starting baseline for calculating derating factors, not for final breaker sizing.
Master Copper Electric Cable Ampacity Chart
Below is the complete electric cable ampacity chart for standard copper conductors, sourced directly from NEC Table 310.16 (2020/2023 editions). We have included the standard maximum overcurrent protection (breaker) sizes permitted by NEC 240.4. Bookmark-friendly quick-jump IDs are embedded in the most queried residential rows.
| AWG / kcmil | 60°C (140°F) THW, THWN, UF |
75°C (167°F) THHN, XHHW |
90°C (194°F) THHN-2, XHHW-2 |
Standard Max Breaker (NEC 240.4) |
|---|---|---|---|---|
| 14 AWG | 15A | 20A | 25A | 15A |
| 12 AWG | 20A | 25A | 30A | 20A |
| 10 AWG | 30A | 35A | 40A | 30A |
| 8 AWG | 40A | 50A | 55A | 40A / 50A* |
| 6 AWG | 55A | 65A | 75A | 60A |
| 4 AWG | 70A | 85A | 95A | 80A |
| 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: 8 AWG is limited to 40A when terminated in standard 60°C residential receptacles, but can be protected at 50A for dedicated hardwired appliances (like ranges) where 75°C terminations are verified. Always verify manufacturer terminal ratings.
Derating Factors and What the Table Cannot Tell You
The base numbers in the electric cable ampacity chart assume you are running no more than three current-carrying conductors in a raceway, in an ambient temperature of 30°C (86°F). Real-world jobsites rarely match these perfect laboratory conditions.
How Derating Modifies the Base Value
When you bundle multiple circuits together, the heat generated by adjacent wires traps thermal energy, reducing the wire's ability to shed heat. According to NEC Table 315.15(C)(1), if you pull 4 to 6 current-carrying conductors in a single conduit, you must multiply the 90°C column ampacity by 80%. For 7 to 9 conductors, you multiply by 70%.
For example, if you pull four 12 AWG THHN (90°C) circuits in one EMT conduit, your starting ampacity is 30A (from the 90°C column). Multiply 30A by 0.80, and your derated ampacity drops to 24A. Because 24A still exceeds the 20A breaker requirement, you are legally clear to use a 20A breaker. If you added a fifth circuit (requiring a 70% derate), 30A x 0.70 = 21A, which still passes. But if you hit 10 conductors (50% derate), 30A x 0.50 = 15A, forcing you to upsize to 10 AWG wire to maintain a 20A circuit.
What the Ampacity Table Cannot Tell You
Relying solely on Table 310.16 will lead to failed inspections or underperforming circuits if you ignore these three physical realities:
- Voltage Drop: The NEC ampacity chart only prevents the wire from melting. It does not guarantee your tools will run. Chapter 9, Note 4 recommends a maximum 3% voltage drop for branch circuits. A 12 AWG wire on a 100-foot run to a 15A load will suffer nearly a 6% voltage drop. You must upsize to 8 AWG to maintain efficiency, even though 12 AWG is technically rated for the amperage.
- Physical Terminal Fit: A 4/0 AWG wire has an ampacity well over 200A, but it physically will not fit under the lug of a standard 200A residential main breaker. You must consult the breaker manufacturer's datasheet for maximum wire bending radius and lug torque specifications.
- Available Fault Current: Ampacity measures continuous thermal load. It does not measure a wire's ability to withstand the explosive magnetic forces of a 10,000-amp short circuit for the milliseconds before the breaker trips. Ensure your equipment AIC (Ampere Interrupting Capacity) ratings match your utility's transformer output.
Electric Cable Ampacity Chart FAQs
Can I use the 90°C column to size my breaker for a standard home outlet?
No. Standard residential duplex receptacles (like the Leviton 5262) and typical 15A/20A circuit breakers are only tested and rated for 60°C terminations. Even if you pull 12 AWG THHN-2 wire (which has a 90°C rating of 30A), NEC 110.14(C) forces you to use the 60°C column (20A) to size your breaker. The 90°C column is strictly a mathematical baseline for conduit derating calculations.
How does bundling wires in a conduit change my ampacity?
When you place more than three current-carrying conductors in a single raceway, you must apply a derating factor to the 90°C column value. For 4-6 wires, multiply by 80%; for 7-9 wires, multiply by 70%. Note that equipment grounding conductors (bare copper or green) do not count as current-carrying, but grounded neutrals on multi-wire branch circuits (MWBC) or standard single-phase 120V circuits do count. For exact bundling math, refer to Cerro Wire's official ampacity and derating tables.
Does this electric cable ampacity chart apply to aluminum wire?
No, the chart above is strictly for copper. Aluminum has higher electrical resistance and requires a larger cross-sectional area to carry the same current. For aluminum, you must consult the right side of NEC Table 310.16. As a general rule of thumb, aluminum wire needs to be sized two AWG steps larger than copper for the same amperage (e.g., use 2/0 Aluminum where you would use 1/0 Copper for a 150A feeder), and you must use anti-oxidant paste (like Noalox) on all aluminum terminations to prevent thermal runaway.
Why is my 8 AWG wire rated for 40A on the chart but I have to use a 30A breaker?
If you are wiring a standard 120V/240V branch circuit and terminating on standard receptacles or a subpanel lug rated for 60°C, 8 AWG copper is clamped to 40A. However, NEC 240.4(D) places strict limits on small conductors to protect the wire from transient spikes. More importantly, if you are wiring a specific appliance (like a water heater or dryer), the manufacturer's installation manual dictates the breaker size. If the manual specifies a 30A maximum overcurrent protection device (OCPD), you must install a 30A breaker, regardless of the fact that the 8 AWG wire could safely handle more. The manufacturer's listing overrides the general ampacity table.
