The Direct Answer: 4/0 Copper Ampacity & Power Capacity
Per the National Electrical Code (NEC) Table 310.16, 4/0 AWG copper wire is good for 230 amps in the standard 75°C termination column, and 260 amps in the 90°C insulation column. For nearly all residential and commercial breaker terminations, the 75°C rating of 230A is the legal limit you must design around.
To convert this current capacity into real-world power delivery (Watts or kilowatts), we use the standard electrical power formulas. Here is the formula with values substituted for a standard 240V single-phase residential service assuming a purely resistive load (Power Factor = 1.0):
Single-Phase Power Formula:
P = V × I × PF
P = 240V × 230A × 1.0
P = 55,200 Watts (55.2 kW)
If you are pulling this wire for a commercial three-phase panel, the formula shifts to include the square root of 3 (1.732). For a 208V three-phase system: P = 1.732 × 208V × 230A × 1.0 = 82,928 Watts (82.9 kW).
Neighboring Wire Sizes & Ampacity Chart (±20% Range)
When sizing feeders or service entrance conductors, it is critical to see where 4/0 AWG sits relative to its immediate neighbors. 4/0 AWG has a cross-sectional area of 211,600 circular mils. The table below covers the ±20% range of physical wire mass, showing how ampacity scales across the 60°C, 75°C, and 90°C columns for copper conductors.
| Wire Size (Copper) | 60°C Column | 75°C Column (Standard) | 90°C Column (Derating) |
|---|---|---|---|
| 2/0 AWG | 145A | 175A | 195A |
| 3/0 AWG | 165A | 200A | 225A |
| 4/0 AWG (0000) | 195A | 230A | 260A |
| 250 kcmil | 215A | 255A | 290A |
| 300 kcmil | 240A | 285A | 320A |
Source: NFPA 70 (National Electrical Code) Table 310.16. Always verify against the specific edition adopted by your local Authority Having Jurisdiction (AHJ).
How Voltage, Phase, and Power Factor Shift the Load
A common point of confusion on the bench is assuming that a wire's ampacity changes when you switch from a 120V circuit to a 480V circuit. The ampacity (230A) is a thermal limit of the copper mass and insulation; it does not shift with voltage. What shifts drastically is the power capacity (Watts) that 230A can deliver.
Furthermore, if you are calculating power for inductive loads (like HVAC compressors or industrial motors), you must account for Power Factor (PF). Here is how the real power delivery shifts across common system configurations at the 230A limit:
| System Configuration | Voltage | Power at 1.0 PF (Resistive) | Power at 0.8 PF (Inductive) |
|---|---|---|---|
| Single-Phase | 120V | 27.6 kW | 22.0 kW |
| Single-Phase | 240V | 55.2 kW | 44.1 kW |
| Three-Phase | 208V | 82.9 kW | 66.3 kW |
| Three-Phase | 480V | 191.3 kW | 153.0 kW |
If you are trying to convert this 230A capacity into Watts for a motor load without knowing the Power Factor (PF), the calculation is practically meaningless. As shown above, a 230A load at 0.8 PF delivers 20% less real work (kW) than a 230A resistive load. Additionally, if you do not know the ambient temperature of the wire's routing path, the 230A baseline ampacity is meaningless, as heat inherently degrades current-carrying capacity.
Critical Assumptions That Fix (or Break) This Rating
The 230A rating is not an absolute law of physics; it is a conditional rating based on strict installation assumptions outlined by the National Electrical Code and industry testing standards. If your installation violates these assumptions, you must derate the wire.
- Termination Temperature (NEC 110.14(C)): Even if you use 90°C THHN wire (rated for 260A), if the breaker or lug it terminates in is only rated for 75°C, your legal maximum ampacity is capped at the 75°C column (230A). Most modern breakers up to 100A are 60°C rated, while larger frames are 75°C rated.
- Ambient Temperature: Table 310.16 assumes an ambient temperature of 30°C (86°F). If you route 4/0 copper through an attic that reaches 110°F (43°C), you must apply a temperature correction factor. At 43°C, the 90°C column must be multiplied by 0.82, dropping your baseline from 260A to 213A before you even look at terminations.
- Conductor Bundling: The baseline ampacity assumes a maximum of three current-carrying conductors in a raceway. If you pull four or more current-carrying conductors in the same conduit, you must apply NEC Table 310.15(C)(1) derating factors. Four to six conductors require an 80% derating multiplier.
Frequently Asked Questions
Can I use 4/0 copper wire for a 250-amp service?
No. A standard 4/0 AWG copper conductor maxes out at 230A (75°C) or 260A (90°C). However, NEC 110.14(C) termination rules and standard service entrance calculations typically require 250 kcmil copper (rated 255A at 75°C) or 350 kcmil aluminum for a 250-amp main service. While NEC 240.4(B) allows rounding up to the next standard breaker size (250A) if the calculated load does not exceed 230A, using 4/0 for a full 250A continuous service panel is a code violation in most jurisdictions.
Does 4/0 aluminum carry the same amps as 4/0 copper?
No. Aluminum has higher electrical resistance than copper. According to NEC Table 310.16, 4/0 AWG aluminum (or copper-clad aluminum) is rated for 180 amps in the 60°C column and 205 amps in the 75°C column. If a spec sheet calls for 4/0 copper and you substitute aluminum, you will severely under-size the feeder, creating a fire hazard at the terminations.
What size breaker do I use with 4/0 copper wire?
For standard residential and commercial applications, 4/0 copper is most commonly paired with a 200-amp main breaker. Because the wire is rated for 230A at 75°C, a 200A breaker provides a safe, code-compliant margin. Under NEC 240.4(B) (the "next size up" rule), you could technically protect a 230A load with a 250A breaker, provided the load is not continuous, but 200A or 225A breakers are the standard industry pairing for this wire gauge.
How much voltage drop will I see on a 200-foot run of 4/0 copper?
Voltage drop depends entirely on the actual current drawn, not the wire's maximum ampacity. If you pull a full 200 amps through a 200-foot single-phase 240V run of 4/0 copper, the voltage drop is approximately 3.1 volts (about 1.3%). This is well within the NEC recommended 3% maximum for branch circuits and feeders. If your actual load is only 100 amps, the drop halves to roughly 0.65%.
