The base ampacity of 4/0 AWG (often written 0000) copper wire is 230 Amps in the 75°C column and 260 Amps in the 90°C column, per NEC Table 310.16. However, your actual usable ampacity in the field is almost always limited to the 75°C column (230A) because standard breakers, lugs, and disconnects are rated for 75°C terminations. 4/0 copper is the standard choice for 200A to 225A commercial feeders, heavy EV charging infrastructure, and large workshop subpanels where the residential service allowance does not apply.

Bench & Jobsite Note: Never size your breaker based solely on the 90°C column. The 90°C rating is a thermal limit for the wire insulation itself, not the equipment it connects to. Always terminate based on the lowest rated component in the circuit—usually the breaker lug.

NEC Table 310.16 Ampacity Chart for 4/0 AWG and Nearby Sizes

To use this table correctly, you must understand the three temperature columns. The 60°C column applies to older equipment, NM-B (Romex) cable, and specific NEC 240.4(D) small conductor rules. The 75°C column is your default for modern THHN/XHHW wire terminating on standard breakers and lugs. The 90°C column is used exclusively as the starting point for calculating ambient temperature and bundling derating factors, per NEC 310.15. The values below assume an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway.

Source: NFPA 70 (NEC 2023) Table 310.16 - Copper Conductors, Insulated
AWG Size 60°C (140°F) 75°C (167°F) 90°C (194°F) Common Insulation Types
1 AWG 110A 130A 145A THHN, XHHW-2, THWN-2
1/0 AWG 125A 150A 170A THHN, XHHW-2, THWN-2
2/0 AWG 145A 175A 195A THHN, XHHW-2, THWN-2
3/0 AWG 165A 200A 225A THHN, XHHW-2, THWN-2
4/0 AWG 195A 230A 260A THHN, XHHW-2, THWN-2

Bookmark this row: For standard 4/0 copper THHN in a typical subpanel feeder, your base allowable ampacity before derating is 230A (75°C column).

Which Temperature Column Applies to Your Installation?

The most common mistake DIYers and junior electricians make is reading the 90°C column (260A) and assuming they can protect a 4/0 copper wire with a 250A breaker. NEC 110.14(C) strictly governs termination temperatures. Unless your breaker, lug, and equipment are explicitly marked and tested for 90°C terminations—which is exceptionally rare in equipment under 600V—you are legally and physically bound to the 75°C column.

How Derating Rows Modify the Base Value

Derating is where the 90°C column earns its keep. When you pull more than three current-carrying conductors in a single conduit, or when your ambient temperature exceeds 86°F (30°C), the wire cannot dissipate heat as efficiently. NEC 310.15(C)(1) requires you to apply adjustment factors to the 90°C ampacity, then compare that result to the 75°C termination limit. You must use the lower of the two final numbers.

Worked Numeric Example:
Imagine you are pulling four current-carrying 4/0 AWG THHN copper conductors through a conduit to a 200A subpanel. Because you have four current-carrying conductors, Table 310.15(C)(1) mandates an 80% adjustment factor.

  1. Start with the 90°C column: 260A.
  2. Apply the derating factor: 260A × 0.80 = 208A.
  3. Check against the 75°C termination limit: The 75°C column is 230A.
  4. Final Verdict: 208A is less than 230A. Your derated ampacity is 208A. This is still sufficient for a 200A continuous or non-continuous load, but you cannot use this exact conduit run for a 225A panel.
Neutral & Ground Derating: Remember that a standard equipment grounding conductor (EGC) does not count as a current-carrying conductor. However, if you are running a multi-wire branch circuit or a feeder with significant non-linear harmonic loads (like a commercial LED lighting panel or VFD array), the neutral does count as current-carrying and triggers the derating math above. See NFPA 70 (NEC) Article 310.15 for exact harmonic definitions.

What the Ampacity Table Cannot Tell You (Edge Cases & Code Limits)

Table 310.16 is a thermal limit chart; it is not a complete engineering guide. Relying on it blindly will lead to failed inspections, excessive voltage drop, or physical installation nightmares. Here is what the table leaves out.

1. Voltage Drop Over Distance

Ampacity tells you the wire won't melt; it doesn't tell you the voltage will be usable at the other end. NEC Chapter 8 Informational Notes recommend a maximum 3% voltage drop for feeders. If you are running 4/0 copper 300 feet from a main panel to a detached barn subpanel on a 240V system, a 200A load will result in roughly a 3.8% voltage drop. While not a strict code violation in most jurisdictions, it will cause motors to run hot and lights to dim. For runs over 150 feet at 200A, you must calculate voltage drop using the specific resistance of copper (0.0608 ohms per 1000 ft for 4/0 uncoated copper) and consider upsizing to 250 kcmil or running parallel sets.

2. Conduit Fill and Physical Bending Radius

4/0 AWG THHN copper is massively thick and stiff. The cross-sectional area of a single 4/0 THHN wire is approximately 0.1158 square inches. If you are pulling four of them (two hots, one neutral, one ground) into PVC Schedule 80 conduit, you are dealing with nearly 0.47 square inches of wire. Per NEC Chapter 9, Table 1, you cannot exceed 40% conduit fill for three or more wires. This means you must use a minimum of 1.5-inch PVC conduit, and realistically, a 2-inch conduit to make the physical pull possible without destroying the insulation or requiring a massive winch. Furthermore, the bending radius for 4/0 wire requires deep junction boxes and sweeping conduit bends; standard 4x4 pull boxes will not work.

3. Residential Service vs. Feeder Rules (NEC 310.12)

If you are wiring a standard 200A residential service entrance (the main feed from the utility meter to the main breaker panel), you do not need 4/0 copper. NEC 310.12 provides a specific allowance for single-family dwellings, permitting 2/0 AWG copper (or 4/0 AWG aluminum) for a 200A residential service. The 4/0 copper requirement kicks in when you are wiring a feeder to a subpanel, a commercial building, or a multi-family dwelling where the 310.12 residential exception does not apply. Always verify if your local AHJ (Authority Having Jurisdiction) has adopted the latest 310.12 revisions, as some municipalities amend this table.

4. Termination Torque Requirements

A 4/0 copper wire requires significant mechanical force to terminate properly. NEC 110.14(D) mandates that connections be tightened to the manufacturer's specified torque. For a standard 200A-250A breaker lug accepting 4/0 wire, the required torque is typically between 300 and 400 inch-pounds (roughly 25 to 33 foot-pounds). Hand-tightening with a standard screwdriver will result in a high-resistance connection that will thermally fail under load. You must use a calibrated torque screwdriver or torque wrench to secure these lugs. Consult the Southwire Ampacity Chart and your specific breaker manufacturer's datasheet for exact torque values before energizing the panel.

Safety Warning: Working inside a panel with 4/0 AWG feeders means you are dealing with 200A to 250A of available fault current. De-energize the upstream source, lock out/tag out the breaker, and verify the bus is dead with a tested CAT III or CAT IV multimeter before touching any conductors. If you are unsure about service entrance work, defer to a licensed electrician and your local utility.