The electrical wire capacity chart (officially NEC Table 310.16) dictates that standard 14 AWG copper handles 15 amps, 12 AWG handles 20 amps, and 10 AWG handles 30 amps when using the 60°C column for typical residential branch circuits. While the wire insulation itself may be rated for much higher temperatures, the physical terminals on your breakers and receptacles dictate the legal ampacity limit for the circuit.
The Core Electrical Wire Capacity Chart (NEC Table 310.16)
Before sizing a breaker or pulling wire, you must understand how to read the ampacity table. The National Electrical Code (NEC) publishes this data based on three primary temperature columns: 60°C, 75°C, and 90°C.
Most modern residential wire, such as NM-B (Romex) and THHN, features 90°C insulation. However, NEC Article 110.14(C) requires that for circuits rated 100A or less, you must size the wire based on the 60°C column because standard residential breakers, switches, and receptacles are only tested and rated for 60°C terminations. You may use the 90°C column for derating calculations (discussed below), but your final circuit ampacity cannot exceed the 60°C value for standard home wiring. For larger feeder circuits over 100A with appropriately rated terminals, the 75°C column applies.
Below is the definitive electrical wire capacity chart for copper conductors, sourced directly from the NFPA National Electrical Code (Table 310.16). This assumes an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a raceway or cable.
| AWG Size | 60°C Column (NM-B / Standard Terminals) | 75°C Column (Feeders / THWN-2) | 90°C Column (THHN / Derating Base) |
|---|---|---|---|
| 14 AWG | 15 Amps | 20 Amps | 25 Amps |
| 12 AWG | 20 Amps | 25 Amps | 30 Amps |
| 10 AWG | 30 Amps | 35 Amps | 40 Amps |
| 8 AWG | 40 Amps | 50 Amps | 55 Amps |
| 6 AWG | 55 Amps | 65 Amps | 75 Amps |
| 4 AWG | 70 Amps | 85 Amps | 95 Amps |
| 2 AWG | 95 Amps | 115 Amps | 130 Amps |
| 1/0 AWG | 125 Amps | 150 Amps | 170 Amps |
Derating and the 80% Rule: What the Chart Cannot Tell You
The electrical wire capacity chart provides baseline ampacities under ideal conditions. However, real-world installations rarely match ideal laboratory parameters. If you blindly follow the baseline numbers without accounting for installation environment and load duration, you risk overheated insulation, nuisance tripping, and fire hazards.
Ambient Temperature and Conduit Fill Derating
The baseline chart assumes an ambient temperature of 30°C (86°F) and a maximum of three current-carrying conductors in a single raceway. When you bundle wires together in conduit, they cannot dissipate heat effectively.
If you pull four to six current-carrying conductors through a single conduit, NEC Table 310.15(C)(1) requires you to apply an 80% adjustment factor. Here is how derating modifies the base value: you apply the percentage multiplier to the 90°C column, not the 60°C column.
- Example: You are pulling five 12 AWG THHN wires through a single EMT conduit. The 90°C column lists 30 amps. Multiply 30A by 0.80 (the derating factor for 4-6 wires) to get a derated ampacity of 24 amps.
- The Catch: Because your standard 20A breaker terminals are only rated for 60°C, your final legal circuit limit remains 20 amps. Derating allows the wire to survive the heat of the conduit, but terminal limitations still cap the breaker size.
The Continuous Load 80% Rule
The chart lists absolute maximum ampacities. It does not account for load duration. According to NEC Article 210.20(A), if a load is expected to run for three hours or more (a 'continuous load'), the branch circuit rating must be at least 125% of the continuous load. Conversely, this means you can only load a circuit to 80% of its rated capacity continuously.
- A 15A circuit (14 AWG) can only carry 12 amps continuously.
- A 20A circuit (12 AWG) can only carry 16 amps continuously.
- A 30A circuit (10 AWG) can only carry 24 amps continuously.
This is why a 48-amp Level 2 EV charger requires a 60A breaker and 6 AWG copper wire, rather than a 50A breaker. The 48A draw is continuous, requiring a circuit rated for 60A (48 x 1.25 = 60).
Voltage Drop: The Invisible Limitation
The most critical limitation of any ampacity chart is that it completely ignores voltage drop over distance. A 12 AWG copper wire is legally permitted to carry 20 amps whether it is 5 feet long or 150 feet long. However, pushing 20 amps through 150 feet of 12 AWG wire will result in a voltage drop of roughly 10 volts (over 8% on a 120V circuit).
While the NEC recommends keeping voltage drop under 3% for branch circuits and 5% overall, it is generally treated as an information note rather than a strict enforceable code in all jurisdictions. As a best practice, if your one-way wire run exceeds 50 feet on a 20A circuit, or 75 feet on a 15A circuit, you should increase your wire size by one AWG step to compensate for the resistance of the longer run.
Quick-Jump Reference: Most Queried Residential Wire Sizes
For fast reference on the jobsite or at the supply house, here are the standard pairings for the most common residential circuits. Bookmark this section for quick lookups when planning subpanels, appliance circuits, and general lighting.
- 14 AWG / 15A Breaker: Standard lighting circuits and general-purpose receptacles in bedrooms and living rooms. (Note: Many electricians exclusively use 12 AWG for all receptacles to prevent future overloading, reserving 14 AWG strictly for lighting).
- 12 AWG / 20A Breaker: Kitchen small-appliance circuits, bathroom GFCI receptacles, dining rooms, and dedicated appliance circuits (like a microwave or garbage disposal). Required by code for all 20A receptacles (NEMA 5-20R).
- 10 AWG / 30A Breaker: Standard electric clothes dryers (when using 10/3 NM-B with ground), electric water heaters, and dedicated window AC units requiring 30A service.
- 8 AWG / 40A Breaker: Older electric ranges or specific 40A HVAC condensing units. Frequently used for 40A EV chargers.
- 6 AWG / 50A Breaker: Modern electric ranges/ovens (50A NEMA 14-50R), hot tubs, and short-run subpanel feeders. Also the standard for hardwired 48A Level 2 EV charging stations.
- 4 AWG / 60A Breaker: Subpanel feeders for detached garages or workshops, and heavy-duty continuous-duty HVAC equipment.
- 2 AWG / 90A Breaker (or 100A at 75°C): The standard feeder size for a 100-amp residential subpanel when using copper wire in the 75°C column. (Note: For 100A service, 2 AWG aluminum SER cable is frequently used as a cost-saving alternative, which requires 1/0 AWG aluminum).
