The base ampacity of 2/0 AWG copper wire is 195 amps in the 90°C column (THHN/THWN-2) and 175 amps in the 75°C column (XHHW, THHW), per NEC Table 310.16. However, your actual usable ampacity is almost always limited by the 75°C terminal ratings of your breakers and lugs, capping standard installations at 175A. The only major exception is for whole-house dwelling services, where NEC 310.12 allows 2/0 copper to be used on a 200-amp residential service panel despite its lower base rating.
How to Read the NEC 310.16 Ampacity Table for 2/0 Copper
Before pulling wire or sizing a breaker, you must understand how the National Electrical Code (NEC) structures ampacity charts. The table below is an excerpt of the standard service and feeder sizes from NFPA 70 (NEC) Table 310.16, assuming an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway.
How to read the columns:
- 60°C Column (TW, UF-B): Used for older installations, specific underground feeder cables, and circuits rated 100A or less that do not have a marked temperature rating.
- 75°C Column (THHW, THWN, XHHW, USE): The standard baseline for almost all modern breakers, lugs, and busbars. If your equipment is rated 75°C, this is your maximum allowable continuous current.
- 90°C Column (THHN, THWN-2, XHHW-2): You cannot use this column to size your breaker. This higher rating is used exclusively as the starting point for calculating temperature and bundling derating.
| AWG / kcmil | 60°C (140°F) TW, UF |
75°C (167°F) THWN, XHHW |
90°C (194°F) THHN, THWN-2 |
|---|---|---|---|
| 1 AWG | 110A | 130A | 145A |
| 2/0 AWG (Target) | 145A | 175A | 195A |
| 3/0 AWG | 165A | 200A | 225A |
| 4/0 AWG | 195A | 230A | 260A |
| 250 kcmil | 215A | 255A | 290A |
Source: NFPA 70 National Electrical Code, Table 310.16. Copper conductors, 30°C ambient. Always verify with your local AHJ.
Temperature Derating and What the Table Cannot Tell You
The 195A and 175A figures assume ideal conditions: an ambient air temperature of 30°C (86°F) and a maximum of three current-carrying conductors bundled together. When real-world jobsite conditions deviate, you must apply adjustment factors from NEC Table 310.15(C)(1) and ambient temperature correction factors.
A Worked Derating Example
Suppose you are pulling four current-carrying conductors (e.g., two hots, a neutral carrying unbalanced load, and a grounded conductor) through a conduit in a standard 30°C environment using 2/0 THHN copper.
- Start at the 90°C column: The base ampacity for 2/0 THHN is 195A.
- Apply the bundling adjustment: For 4 to 6 current-carrying conductors, the NEC mandates an 80% adjustment factor.
- Calculate the derated value: 195A × 0.80 = 156A.
- Check the termination limit (NEC 110.14(C)): Your breaker lugs are rated for 75°C, which has a base limit of 175A.
- Final Verdict: You must use the lower of the derated 90°C value (156A) or the 75°C termination limit (175A). Your maximum allowable ampacity for this specific pull is 156 amps.
Pro-Tip for Conduit Fill: 2/0 AWG THHN is physically thick. When pulling three 2/0 conductors plus a ground through EMT or PVC, you will quickly approach the 40% conduit fill limit mandated by NEC Chapter 9, Table 1. Always calculate physical fill alongside electrical derating to avoid jamming the wire during the pull.
What the Ampacity Table Cannot Tell You
Ampacity charts only address thermal limits (preventing the insulation from melting). They completely ignore three critical jobsite realities:
- Voltage Drop: NEC Table 310.16 does not account for distance. According to Southwire's Chapter 9 data, uncoated 2/0 copper has a resistance of roughly 0.194 ohms per 1,000 feet at 75°C. On a 150-foot run carrying 150A at 240V, you will experience a ~4.3V drop (1.8%), which is acceptable. But on a 400-foot run to a detached workshop, that same wire will drop nearly 5%, potentially causing motor starting issues. You must upsize to 3/0 or 4/0 for long runs regardless of ampacity.
- Pulling Tension: The Copper Development Association notes that excessive pulling force can stretch the copper strands, altering the metallurgical properties and reducing the cross-sectional area. Use proper wire-pulling compound and a swivel pulling eye rated for the pound-force limit of 2/0 stranding.
- Short-Circuit Withstand: Ampacity assumes normal continuous loading. Under a massive fault condition, the thermal mass of 2/0 copper dictates how long it takes to melt before the breaker trips. This is calculated using fault-current formulas, not standard ampacity tables.
Frequently Asked Questions About 2/0 Copper Wire
What size breaker can I use with 2/0 copper wire?
For standard commercial or subpanel feeder applications, the maximum standard breaker size is 175 amps. This is dictated by the 75°C terminal rating of standard molded-case circuit breakers (NEC 110.14(C)). While the wire insulation (THHN) can handle 195A, the breaker lugs cannot. If your calculated continuous load is exactly 150A, a 150A breaker is appropriate. You cannot use the 'next size up' rule (NEC 240.4(B)) to put a 200A breaker on 2/0 copper for a standard feeder, because 200A exceeds the wire's 75°C termination limit of 175A.
Can I use 2/0 copper wire for a 200-amp residential service?
Yes. This is one of the most common points of confusion in residential wiring. Under NEC Article 310.12(A), for single-phase, 120/240-volt, 3-wire dwelling service-entrance conductors rated 100 through 400 amps, the conductor size can be selected from a specific dwelling-service table rather than the standard 310.16 ampacity table. For a 200-amp residential service, NEC 310.12 explicitly permits 2/0 AWG copper (or 4/0 AWG aluminum). This exception exists because residential loads are highly diversified; a 200A panel rarely sees a true continuous 200A draw across both legs simultaneously.
How does 2/0 copper ampacity compare to 2/0 aluminum?
In the 75°C column, 2/0 copper is rated for 175A, while 2/0 aluminum (XHHW/THWN) is rated for 135A (or 150A for specific AA-8000 series alloy building wire under certain conditions). Copper carries roughly 16% to 25% more current than aluminum in the exact same physical cross-section. However, aluminum is significantly lighter and cheaper. If you are running a 200A residential service and choose aluminum, you must step up to 4/0 AWG to meet the NEC 310.12 requirement. For a 150A feeder, 2/0 aluminum is insufficient; you would need 1/0 aluminum (rated 135A) or 1 AWG copper.
Does the 90°C column mean I can pull 195 amps continuously?
No. The 90°C rating of THHN/THWN-2 insulation is almost never used for final overcurrent protection sizing. NEC 110.14(C)(1) requires you to use the lowest temperature rating of any connected device, termination, or conductor in the circuit. Because nearly all modern breakers, panelboard lugs, and disconnect switches are tested and rated for a maximum of 75°C, your circuit is bottlenecked at the 75°C limit (175A for 2/0 copper). The 90°C column exists purely to give you a higher mathematical starting point when applying ambient temperature and conduit bundling derating factors.
Is 2/0 copper wire always stranded?
Yes. Solid copper wire is generally only manufactured up to 8 AWG (and sometimes 6 AWG for specific grounding applications). At 2/0 AWG (which has a cross-sectional area of 67,430 circular mils), the wire is far too rigid to be pulled through conduit or bent into tight panelboard radiuses as a solid core. 2/0 copper is always stranded, typically featuring 19 strands for standard Class B stranding, or finer stranding (Class I or M) for flexible welding cable or battery inverter applications. Always use a ratcheting wire cutter and a proper stripping tool to avoid nicking the outer strands, which creates hot spots under high current.
