4/0 AWG (commonly read as "four-aught") is the standard heavy-duty feeder size for 200-amp residential services, large workshop subpanels, and high-draw EV charging stations. The exact 4/0 cable ampacity depends entirely on the conductor material and the temperature rating of your termination points. For 4/0 AWG Copper, the ampacity is 195A (60°C column), 230A (75°C column), and 260A (90°C column). For 4/0 AWG Aluminum, it is 150A (60°C), 180A (75°C), and 205A (90°C).

While these base numbers are pulled directly from the National Electrical Code (NEC), simply picking a number from the 90°C column and calling it a day will result in a failed inspection or a melted breaker lug. Below is the complete reference data, followed by the specific rules for applying it to your installation.

The Master 4/0 AWG Ampacity Reference (NEC Table 310.16)

The following data is extracted from NEC Table 310.16 (formerly 310.15(B)(16)). This table assumes an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway. We have included 2/0, 3/0, and 250 kcmil to provide context for the next size up and down, which is critical when voltage drop calculations force you to upsize.

Table 1: Allowable Ampacities of Insulated Conductors (NEC 310.16)
Wire Size (AWG/kcmil) Copper 60°C Copper 75°C Copper 90°C Aluminum 60°C Aluminum 75°C Aluminum 90°C
2/0 AWG 145A 175A 195A 115A 135A 150A
3/0 AWG 165A 200A 225A 130A 155A 175A
4/0 AWG (Target) 195A 230A 260A 150A 180A 205A
250 kcmil 215A 255A 290A 170A 205A 235A
Bookmark Quick-Jump: If you are wiring a standard 200A residential service entrance, jump to the Aluminum 75°C row for 4/0 (180A base) and read the note on NEC 310.12 below. If you are wiring a 200A subpanel feeder, you must use Copper 4/0 (230A at 75°C) or upsize to 250 kcmil Aluminum.

How to Read This Table

The columns represent the temperature rating of the weakest link in your circuit, which is almost always the breaker or busbar lug, not the wire insulation itself. Most modern THHN/THWN-2 wire is rated for 90°C, but you are rarely allowed to use the 90°C column to determine your final allowable ampacity. The 90°C column is primarily used as a mathematical starting point before applying derating factors.

Which Temperature Column Applies to Your Installation?

To select the correct column, you must follow the termination temperature rules outlined in NEC 110.14(C). The rule is simple: your circuit ampacity is limited by the lowest temperature rating of any connected component.

  • The 60°C Column: Use this if your equipment is older, unmarked, or explicitly rated for 60°C. This is common in older residential panels and smaller breakers (under 100A).
  • The 75°C Column: This is the default for almost all modern residential and commercial breakers rated 100A or higher. If you buy a new 200A main breaker from Square D, Eaton, or Siemens, the lugs are rated 75°C. Therefore, 4/0 Copper is good for 230A, and 4/0 Aluminum is good for 180A.
  • The 90°C Column: You can only use this column for your final ampacity if every single termination point (lugs, busbars, breakers) is explicitly marked and rated for 90°C. In standard panel work, this is exceptionally rare. Use the 90°C column only for derating calculations.
The 200A Residential Service Exception (NEC 310.12): You might notice that 4/0 Aluminum at 75°C is only rated for 180A, which is less than a 200A main breaker. However, NEC 310.12(A) provides a specific exception for single-phase, 120/240V, 3-wire service-entrance conductors supplying a dwelling. Under this specific article, 4/0 Aluminum is legally permitted on a 200A service. This exception does not apply to feeders running to a detached garage subpanel; for a 200A subpanel feeder, 4/0 Aluminum (180A) is undersized, and you must use 250 kcmil Aluminum or 4/0 Copper.

How Derating Rows Modify the Base 4/0 Value

The ampacities in Table 310.16 assume perfect conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. When real-world conditions deviate, you must apply adjustment factors from NEC Table 310.15(C)(1) and ambient temperature correction tables.

Here is how derating works in practice:
Imagine you are pulling four current-carrying conductors (e.g., two hots, a neutral carrying unbalanced load, and a ground—though grounds don't count, let's say you have two separate 240V circuits sharing a conduit, meaning 4 current-carrying hots) through a hot attic where the ambient temperature reaches 40°C (104°F). You are using 4/0 AWG THHN Copper.

  1. Start with the 90°C column: 4/0 THHN Copper at 90°C is 260A.
  2. Apply Ambient Temperature Correction: At 40°C ambient, the correction factor for 90°C insulation is 0.91. (260A × 0.91 = 236.6A).
  3. Apply Bundling Adjustment: For 4 to 6 current-carrying conductors in a raceway, the adjustment factor is 80%. (236.6A × 0.80 = 189.28A).
  4. Compare to Termination Rating: Your final derated ampacity is 189A. If your breaker lugs are rated 75°C (which allows 230A for 4/0 Cu), your circuit is now legally limited to 189A due to the heat in the attic and the wire bundling. You cannot put this on a 200A breaker.

For comprehensive ambient temperature correction charts and bundling multipliers, refer to the Cerrowire official ampacity and derating reference guides, which provide excellent visual matrices for these NEC tables.

What the Ampacity Table Cannot Tell You

Knowing the thermal limits of 4/0 wire is only half the battle. The NEC ampacity tables assume a short, perfectly installed run. They completely ignore three critical physical and electrical realities that dictate whether your 4/0 feeder will actually perform safely on the jobsite.

1. Voltage Drop Over Distance

Ampacity measures heat dissipation, not voltage retention. If you run 4/0 Copper 150 feet from your main panel to a detached workshop subpanel drawing a continuous 180A load, the wire won't melt, but your voltage will sag. Using the standard single-phase voltage drop formula (VD = 2 × K × I × D / Circular Mils), where K=12.9 for copper and 4/0 has 211,600 circular mils:

VD = (2 × 12.9 × 180 × 150) / 211,600 = 3.30 Volts.
On a 240V system, a 3.3V drop is roughly 1.37%, which is well within the NEC recommended 3% maximum for feeders. However, if that run was 350 feet, the drop would exceed 3%, and you would need to upsize to 250 kcmil or 300 kcmil purely for voltage drop, even though the 4/0 wire has enough ampacity to handle the heat.

2. Physical Bending Radius and Conduit Fill

4/0 cable is incredibly stiff. The NEC mandates specific bending radii for large conductors to prevent damaging the insulation or stressing the terminal lugs. Furthermore, pulling three 4/0 THHN conductors plus a 4 AWG ground requires a minimum of 1.5-inch to 2-inch PVC or EMT conduit depending on the exact insulation thickness and conduit type. Attempting to force 4/0 wire through undersized conduit sweeps will result in torn insulation and a failed pull.

3. Terminal Torque Specifications

A 4/0 wire carrying 200A will generate significant heat at the termination point if the mechanical connection is loose. Since the 2017 NEC cycle, inspectors strictly enforce NEC 110.14(D), which requires terminations to be tightened to the manufacturer's specified torque. You cannot simply "crank it down until it feels tight." You must use a calibrated inch-pound torque screwdriver or torque wrench. For a typical 200A main breaker lug accepting 4/0 wire, the required torque is often between 300 and 450 in-lbs (check the specific breaker datasheet). Undertorquing causes arcing and fires; overtorquing strips the aluminum lug threads or snaps the set screw.