The direct answer for 3/0 AWG ampacity depends on your conductor material and termination temperatures. 3/0 AWG copper wire has an ampacity of 200 amps at 75°C and 225 amps at 90°C. For 3/0 AWG aluminum (or copper-clad aluminum), the ampacity is 155 amps at 75°C and 180 amps at 90°C. In standard residential and commercial installations, the 75°C column dictates your maximum breaker size due to terminal temperature limits.
The 3/0 AWG Ampacity Reference Table (NEC 310.16)
To use this table correctly, you must understand the columns and rows. The rows define the wire material (Copper vs. Aluminum) and the insulation type (THHN/THWN-2 or XHHW-2). The columns represent the temperature rating of the insulation. How to read this table: Find your wire material in the first column, then move right to the temperature column that matches your equipment's termination rating (usually 75°C for modern breakers). The values below are sourced directly from National Fire Protection Association (NFPA) NEC Table 310.16.
Quick-jump to the most queried values:
| Wire Size (AWG) | Material | Insulation Type | 60°C (140°F) | 75°C (167°F) | 90°C (194°F) |
|---|---|---|---|---|---|
| 2/0 AWG | Copper | THHN / THWN-2 | 145A | 175A | 195A |
| 3/0 AWG | Copper | THHN / THWN-2 | 165A | 200A | 225A |
| 4/0 AWG | Copper | THHN / THWN-2 | 195A | 230A | 260A |
| 2/0 AWG | Aluminum | XHHW-2 / THWN-2 | 115A | 135A | 150A |
| 3/0 AWG | Aluminum | XHHW-2 / THWN-2 | 130A | 155A | 180A |
| 4/0 AWG | Aluminum | XHHW-2 / THWN-2 | 150A | 180A | 205A |
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 90°C THHN wire, and assuming they can push 225 amps through a 3/0 copper conductor. This violates NEC 110.14(C) regarding temperature limitations of equipment terminations.
So, when do you use the 90°C column? You use it exclusively as your starting point for derating calculations (covered below) and for equipment specifically listed and marked for 90°C terminations, which is rare in standard commercial and residential gear. The 60°C column is generally reserved for older equipment, specific appliance wiring, or when the equipment's temperature rating is entirely unmarked (common in older NM-B cable installations).
Derating 3/0 AWG: When Base Ampacity Drops
The ampacity table above assumes two conditions: an ambient air temperature of 30°C (86°F), and no more than three current-carrying conductors bundled together in a raceway or cable. When you deviate from these conditions, you must apply correction and adjustment factors.
1. Bundling (More than 3 Current-Carrying Conductors)
If you pull four to six current-carrying conductors through a single conduit, NEC 310.15(C)(1) requires you to multiply the base ampacity by 80%. Crucial rule: You always apply the derating factor to the 90°C column, not the 75°C column.
- Base 90°C Ampacity (3/0 Cu): 225A
- Derating Factor (4-6 conductors): 0.80
- Derated Ampacity: 225A × 0.80 = 180A
After derating, you must compare this result (180A) to the 75°C termination limit (200A). Because 180A is lower, your new maximum circuit ampacity is 180A. You must protect this circuit with a breaker sized at 175A or lower (the next standard size down, as 180A is not a standard breaker size per NEC 240.6).
2. Ambient Temperature Corrections
If your conduit runs across a hot rooftop or through a boiler room where the ambient temperature exceeds 30°C (86°F), you must apply temperature correction factors from NEC Table 310.15(B)(1). Like bundling, this factor is applied to the 90°C column. If a 3/0 copper wire runs through an environment with an ambient temperature of 40°C (104°F), the correction factor for 90°C insulation is 0.91. The adjusted ampacity becomes 225A × 0.91 = 204.75A. Since 204.75A is still higher than the 75°C termination limit of 200A, the termination limit remains the governing factor.
What the Ampacity Table Cannot Tell You
While the NEC ampacity tables dictate thermal limits to prevent insulation meltdown and fire, they do not account for power quality, physical installation constraints, or fault currents. Relying solely on the ampacity chart for 3/0 AWG wire can lead to poorly performing or physically impossible installations.
Voltage Drop Constraints
Ampacity tables assume a perfect zero-resistance wire, which does not exist. 3/0 AWG copper has a cross-sectional area of 167,800 circular mils (CM). If you are running a 200-amp, 240-volt feeder to a detached workshop 200 feet away, you must calculate voltage drop. Using the standard single-phase formula VD = (2 × K × I × L) / CM (where K=12.9 for copper):
- VD = (2 × 12.9 × 200A × 200ft) / 167,800 CM
- VD = 1,032,000 / 167,800 = 6.15 Volts
A 6.15V drop on a 240V system is a 2.56% drop, which is well within the NEC Informational Note recommendation of 3% for feeders. However, if that run was 300 feet, the drop would hit 3.84%, exceeding the 3% guideline and potentially causing motor starting issues or dimming lights. In that scenario, you would need to upsize to 4/0 AWG or 250 kcmil, even though 3/0 AWG is thermally rated for the 200A load. Use tools like the Southwire Voltage Drop Calculator to verify long runs.
Conduit Fill and Bending Radius
3/0 AWG wire is exceptionally thick and stiff. Three strands of 3/0 THHN copper have a combined cross-sectional area that dictates strict conduit fill limits. Per NEC Chapter 9, you cannot cram three 3/0 THHN conductors into a 1-inch EMT or PVC pipe; the maximum fill for three conductors is 40%. You will need a minimum of 1.5-inch EMT or 2-inch Schedule 40 PVC to legally and physically pull three 3/0 AWG THHN wires. Furthermore, the bending radius for 3/0 wire requires wide sweeps. Attempting to bend this wire into tight junction boxes will result in damaged insulation, crushed conductors, and a failed inspection.
Short Circuit Withstand Rating
Ampacity measures continuous thermal loading. It does not tell you how the wire behaves during a 10,000-amp short circuit event. The wire's ability to withstand the magnetic and thermal forces of a fault before the breaker trips depends on the specific insulation thickness, the bracing of the conductors in the panel, and the let-through current of the upstream overcurrent protective device. Always ensure your panel bus bars and breaker AIC (Ampere Interrupting Capacity) ratings match the available fault current at your service entrance.
