The base ampacity for 1 AWG copper wire is 130 amps (in the 75°C column) and 145 amps (in the 90°C column). For 1 AWG aluminum or copper-clad aluminum, the base ampacity is 100 amps (75°C) and 115 amps (90°C). These baseline values assume an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled in a single raceway or cable.
Whether you are pulling a 100-amp subpanel feeder, wiring a heavy-duty EV charger, or sizing conductors for a large workshop welder, 1 AWG is a critical threshold in residential and light commercial electrical work. Below is the complete reference data, derating mathematics, and installation rules you need to size this conductor correctly and pass inspection.
How to Read the 1 AWG Ampacity Table (NEC 310.16)
Before pulling wire, you must understand how to read the ampacity tables published in NFPA 70, the National Electrical Code (NEC). The table is divided into three primary temperature columns: 60°C (140°F), 75°C (167°F), and 90°C (194°F).
Per NEC 110.14(C), the allowable ampacity of a conductor is limited by the lowest temperature rating of any connected device, terminal, or splice in the circuit. Because nearly all modern circuit breakers, panelboard lugs, and disconnect switches are rated for 75°C terminations, the 75°C column is your default limit for final overcurrent protection sizing. The 90°C column is almost exclusively used as the starting point for derating calculations (adjusting for heat and bundling), but your final calculated ampacity cannot exceed the 75°C termination limit.
If you are working with older equipment (pre-1980s) or specific lighting fixtures that lack a marked temperature rating, you are legally required to default to the more conservative 60°C column, which drops 1 AWG copper to just 110 amps.
The Complete #1 Wire Ampacity Reference Chart
The following table provides the exact ampacities for 1 AWG wire, flanked by adjacent sizes (2 AWG and 1/0 AWG) for context. This data is sourced directly from NEC Table 310.16 for standard insulation types like THHN, THWN-2, XHHW, and THW.
| AWG Size | Material | 60°C (140°F) | 75°C (167°F) | 90°C (194°F) |
|---|---|---|---|---|
| 2 AWG | Copper | 95A | 115A | 130A |
| 1 AWG | Copper | 110A | 130A | 145A |
| 1/0 AWG | Copper | 125A | 150A | 170A |
| 2 AWG | Aluminum | 75A | 90A | 100A |
| 1 AWG | Aluminum | 85A | 100A | 115A |
| 1/0 AWG | Aluminum | 100A | 120A | 135A |
Derating and Real-World Installation Factors
The baseline numbers above assume perfect conditions. In the real world, heat builds up in conduit, and ambient temperatures in attics or rooftops routinely exceed 30°C. Here is how derating rows modify the base value, and what the table cannot tell you.
How Derating Modifies the Base Value
When you have four to six current-carrying conductors in a single conduit, NEC Table 310.15(C)(1) requires you to multiply the base ampacity by 80%. Crucially, you always start your derating math from the 90°C column.
- Example: You are pulling four 1 AWG copper THHN wires (two hots, one neutral, one ground; the ground does not count as current-carrying, leaving 3 current-carrying conductors. Wait, if it's a multi-wire branch circuit or a 3-phase feeder, you might have 4 current-carrying). Let's assume 4 current-carrying 1 AWG copper conductors in a raceway.
- Step 1: Start at the 90°C column for 1 AWG Copper = 145A.
- Step 2: Apply the 80% bundling adjustment: 145A × 0.80 = 116A.
- Step 3: Compare to the termination limit (75°C column = 130A).
- Result: The final allowable ampacity is the lower of the two numbers: 116A. You can no longer protect this wire with a 125A or 130A breaker; you must drop to a 110A breaker (or the next standard size down if specific continuous load rules apply).
What the Table Cannot Tell You: Voltage Drop
NEC Table 310.16 only addresses thermal limits (preventing the insulation from melting). It completely ignores voltage drop. According to data from the Copper Development Association, 1 AWG copper wire has a resistance of roughly 0.156 ohms per 1,000 feet.
If you are running a 100-amp, 240V subpanel feeder using 1 AWG copper:
- At 100 feet, the voltage drop is roughly 3.1V (1.3%). This is well within the NEC's recommended 3% maximum for feeders.
- At 250 feet, the drop increases to 7.8V (3.25%). You have exceeded the 3% recommendation, and sensitive electronics at the subpanel may experience brownouts under heavy load. You would need to upsize to 1/0 AWG or 2/0 AWG to compensate for the distance, even though 1 AWG is thermally sufficient.
Frequently Asked Questions About 1 AWG Wire Sizing
Can I use 1 AWG aluminum wire for a 100-amp subpanel?
Yes. Looking at the 75°C column in the chart above, 1 AWG aluminum is rated for exactly 100 amps. Because standard subpanel main breakers or feeder lugs are rated for 75°C, this is a perfectly code-compliant match for a 100A feeder. However, aluminum is highly susceptible to voltage drop over distance. If your subpanel is more than 100 feet from the main panel, you should upsize to 1/0 AWG aluminum to maintain voltage stability. Always use an antioxidant compound (like Noalox) on aluminum terminations to prevent oxidation and subsequent high-resistance heating.
What size conduit is required for three 1 AWG THHN wires?
For a standard 120/240V single-phase subpanel feeder, you need two hot conductors, one neutral, and one equipment grounding conductor (EGC). If you are pulling three 1 AWG THHN conductors (two hots, one neutral) plus a smaller 1 AWG or 3 AWG ground, you must calculate conduit fill per NEC Chapter 9, Table 1. Three 1 AWG THHN wires plus one 3 AWG ground will comfortably fit inside a 1-inch Schedule 40 PVC conduit (which allows 40% fill for over 2 wires). If you are using four 1 AWG wires (using the neutral as a current-carrying conductor in specific configurations), you must step up to 1.25-inch conduit to prevent jamming and insulation damage during the pull.
Why does my 1 AWG wire have a 90°C rating if the breaker is only rated for 75°C?
This is one of the most common points of confusion for apprentices and DIYers. Modern THHN/THWN-2 wire is manufactured with 90°C insulation because it provides a thinner, more heat-resistant dielectric layer, making the wire easier to pull and more resilient to short-term overloads. The 90°C rating is not wasted; it acts as a thermal buffer. As demonstrated in the derating example above, you use the 90°C column to absorb the mathematical penalties of conduit bundling and high ambient temperatures. As long as your final derated number doesn't exceed the 75°C termination limit of your breaker, the 90°C insulation keeps the wire safe under the hood.
