For a standard 100-amp circuit, you need 3 AWG copper or 1 AWG aluminum wire. This baseline assumes a 75°C termination rating, up to three current-carrying conductors in a raceway, and an ambient temperature of 30°C (86°F). If your run exceeds 100 feet, or if you are bundling multiple circuits in a single conduit, you will need to upsize to compensate for voltage drop and thermal derating.

The 100 Amp Wire Size Chart (NEC Table 310.16)

The following data is extracted from NEC Table 310.16 (formerly 310.15(B)(16)), the definitive standard for conductor ampacity in the United States. This table covers the most common AWG sizes used in residential and light commercial branch circuits and subpanel feeders.

How to Read This Table: The columns are divided by conductor material (Copper vs. Aluminum/Copper-Clad) and then by the temperature rating of the wire's insulation (60°C, 75°C, and 90°C). The numbers represent the maximum allowable ampacity (current in amps) before the insulation begins to degrade. Note: Small conductor rules (NEC 240.4(D)) cap 14 AWG at 15A, 12 AWG at 20A, and 10 AWG at 30A for overcurrent protection, regardless of the 75°C/90°C column values.

Quick-Jump to Most Queried Sizes: 4 AWG | 3 AWG (100A Cu) | 2 AWG | 1 AWG (100A Al) | 1/0 AWG

Source: NFPA 70 National Electrical Code (NEC) Table 310.16. Ambient temperature 30°C.
AWG / kcmil Cu 60°C Cu 75°C Cu 90°C Al 60°C Al 75°C Al 90°C
141520*25*------
122025*30*1520*25*
103035*40*2530*35*
8405055304045
6556575405055
4708595556575
385100110657585
2951151307590100
111013014585100115
1/0125150170100120135
2/0145175195115135150
3/0165200225130155170
4/0195230260150180205

Which Temperature Column Applies to Your Installation?

The most common mistake DIYers and junior apprentices make is looking at the 90°C column because they bought THHN wire (which has a 90°C insulation rating). You cannot use the 90°C column for base sizing.

According to NEC 110.14(C), the ampacity of a conductor is limited by the lowest temperature rating of any connected device, lug, or terminal in the circuit. Nearly all modern circuit breakers rated 100A and below are tested and listed for 75°C terminations. Therefore, you must use the 75°C column to select your wire size, even if the wire insulation itself is rated for 90°C.

The 90°C Column Exception: The 90°C column is strictly reserved for derating calculations (adjusting for ambient heat or conductor bundling) and for equipment specifically listed and marked for 90°C terminations, which is exceptionally rare in residential and light commercial panels.

Derating and What the Chart Cannot Tell You

How Derating Modifies the Base Value

Table 310.16 assumes you have no more than three current-carrying conductors in a raceway and an ambient temperature of 30°C (86°F). If you pull two 240V circuits (four hot wires) through a single conduit, the wires heat each other up. NEC Table 310.15(C)(1) requires an 80% derating factor for 4-6 current-carrying conductors.

Worked Example: You are pulling two 100A circuits (4 hots) in one PVC conduit using 3 AWG THHN copper.
1. Base 90°C ampacity for 3 AWG Cu = 110A.
2. Apply 80% derating: 110A × 0.80 = 88A.
3. Because 88A is less than your 100A breaker, 3 AWG fails. You must upsize to 2 AWG THHN (130A × 0.80 = 104A). Since 104A is greater than the 75°C termination limit of 115A, your final allowable ampacity is 104A, which safely clears the 100A breaker requirement.

What the Chart Cannot Tell You: Voltage Drop

Table 310.16 only tells you the size required to keep the wire from melting. It does not account for distance. If you are feeding a 100A subpanel in a detached garage 150 feet away, 3 AWG copper will yield a voltage drop of roughly 4.5% at full load. While the National Fire Protection Association (NFPA) recommends keeping feeder voltage drop under 3% for reasonable efficiency, local codes may enforce this strictly.

For a 150-foot, 100A run at 240V, you should upsize to 1 AWG copper or 2/0 AWG aluminum to keep voltage drop under 3%. Always verify long runs using a dedicated voltage drop calculator before purchasing wire.

100 Amp Wire Sizing FAQ

Can I use 2 AWG copper for a 100 amp breaker?

Yes. 2 AWG copper is rated for 115A in the 75°C column, which exceeds the 100A requirement. Upsizing is always electrically safe. The only physical limitation is whether the 2 AWG wire will physically fit into the breaker's lug. Most modern 100A breakers (like Square D QO or Homeline) easily accept up to 1/0 or 2/0 AWG, but always check the manufacturer's wiring diagram printed on the breaker label to confirm the maximum lug capacity.

What size ground wire do I need for a 100 amp feeder?

Wire sizing charts for current-carrying conductors do not apply to equipment grounding conductors (EGC). According to NEC Table 250.122, a 100-amp overcurrent device requires a minimum 8 AWG copper or 6 AWG aluminum ground wire. If you upsized your current-carrying conductors for voltage drop (e.g., using 1 AWG copper instead of 3 AWG), NEC 250.122(B) requires you to increase the ground wire proportionally.

Is it safe to parallel two 8 AWG wires for 100 amps?

No. NEC 310.10(G) strictly prohibits paralleling conductors smaller than 1/0 AWG. Paralleling requires identical lengths, identical materials, and identical routing to ensure current splits evenly. If one 8 AWG wire develops a slightly higher resistance due to a loose termination, it will push the excess current onto the second wire, overloading it and creating a fire hazard before the 100A breaker trips. Always use a single, properly sized 3 AWG copper or 1 AWG aluminum conductor.

How does a 100 amp wire size chart change for 240V vs 120V?

It does not change at all. Ampacity is a measure of thermal limits (current generating heat), which is entirely independent of system voltage. Whether you are pushing 100 amps at 12V DC, 120V AC, or 240V AC, the wire must be sized to handle 100 amps of current. Voltage only dictates the required insulation thickness (e.g., 600V rated THHN) and affects your voltage drop calculations over distance.