AWG 2/0 Ampacity Chart: Sizing Breakers and Feeders for Heavy Loads

The base ampacity for 2/0 AWG copper wire is 175 amps in the 75°C column and 195 amps in the 90°C column, per NEC Table 310.16. For 2/0 AWG aluminum, the ratings are 135 amps (75°C) and 150 amps (90°C). However, the final allowable ampacity for your specific installation depends entirely on termination temperature limits, conduit fill derating, and whether you are wiring a main service entrance or a subpanel feeder.

AWG 2/0 Ampacity: The Quick Reference Table (NEC 310.16)

Before pulling wire, you need to know how to read the ampacity tables. The National Electrical Code (NEC) Table 310.16 organizes wire capacity by conductor material (Copper vs. Aluminum), insulation type (THHN, XHHW-2, etc.), and temperature rating (60°C, 75°C, 90°C). Bookmark this section for quick job-site reference. The values below assume an ambient air temperature of 30°C (86°F) and no more than three current-carrying conductors in a raceway.

Which Temperature Column Applies to Your Installation?

The most common mistake DIYers and junior electricians make is using the 90°C column to size their breaker. You almost never get to use the 90°C rating for your final overcurrent protection size due to the weakest link rule.

Standard breakers, panelboard busbars, and disconnect lugs are typically rated for 75°C. Even if you pull 90°C THHN wire, the termination point is only good for 75°C. Therefore, the 75°C column (175A for copper, 135A for aluminum) dictates your maximum breaker size.

So why buy 90°C THHN wire at all? The 90°C column is strictly used as the starting baseline for derating calculations (which we cover below). Once you apply your derating math to the 90°C value, you compare that result to the 75°C termination limit. The final allowable ampacity is the lower of the two numbers.

The 200-Amp Residential Service Exception (NEC 310.12)

If 2/0 copper is only rated for 175 amps in the 75°C column, why is it the standard wire used for 200-amp residential main panels?

This is due to the residential service exception found in NEC Article 310.12(A). For single-phase, 120/240V, 3-wire service entrance conductors supplying the entire dwelling, the code allows you to size the wire at 83% of the service rating.

• 200 Amps × 0.83 = 166 Amps.
• 2/0 AWG Copper (75°C rating) = 175 Amps.

Because 175A is greater than 166A, 2/0 copper is legally permitted for a 200A main service. Warning: This 83% rule applies only to the main service entrance conductors between the utility meter and the main disconnect. It does not apply to subpanel feeders. If you are feeding a 200A subpanel from a 200A main panel, you must use 3/0 AWG copper or 4/0 AWG aluminum, because standard feeder rules (NEC 310.14) require the wire ampacity to match or exceed the breaker size.

How Derating Factors Modify Your Base Ampacity

Ampacity tables assume ideal conditions: 86°F (30°C) ambient temperature and no more than three current-carrying conductors bundled together. When you deviate from this, you must apply adjustment factors from NEC Table 310.15(C)(1) and Table 310.15(B)(1).

Worked Example: Bundled Conductors in a Hot Attic
Imagine you are pulling four current-carrying conductors (two hots, a neutral carrying unbalanced load, and an equipment ground which doesn't count) through an attic where the ambient temperature reaches 110°F (43°C).

1. Conduit Fill Adjustment: 4 current-carrying conductors requires an 80% adjustment factor.
2. Temperature Correction: 110°F ambient requires a 0.87 correction factor for 90°C wire.
3. The Math: Start with the 90°C base for 2/0 Cu (195A).
   195A × 0.80 (bundling) × 0.87 (temp) = 135.7 Amps.
4. The Weakest Link Check: Compare 135.7A to the 75°C termination limit (175A). The lower number wins.

Your final derated ampacity for this 2/0 copper run is 135 amps. You must protect this wire with a breaker no larger than 125A (the next standard size down per NEC 240.4(B) if 135A isn't a standard breaker size, though 125A is standard).

Decision Path: Sizing Your Breaker and Wire

Use this decision tree to lock in your exact material and breaker size for common 2/0 AWG scenarios. This terminates the guesswork and gives you a concrete shopping list.

What the Ampacity Table Cannot Tell You

NEC Table 310.16 only protects the wire from melting under continuous load. It completely ignores voltage drop and short-circuit fault current.

Voltage Drop Limitations:
If you are feeding a detached garage subpanel 250 feet away from the main panel, 2/0 copper carrying a continuous 150A load will experience significant voltage drop. Using the standard single-phase voltage drop formula (VD = 2 × K × I × D / CM), a 250-foot run of 2/0 copper at 150A yields roughly a 5.3V drop on a 240V circuit (about 2.2%). While technically under the 3% NEC informational recommendation, if your load spikes to the full 175A capacity, the drop exceeds 2.5%, which can cause motor burnout on heavy equipment like air compressors or well pumps. For runs over 150 feet at high continuous loads, upsize to 3/0 or 4/0 copper to maintain power quality.

Fault Current (AIC Ratings):
Ampacity tables do not tell you if the wire can survive a dead short before the breaker trips. If your utility transformer can deliver 40,000 Amps of fault current, your panel and breakers must have an adequate Amps Interrupting Capacity (AIC) rating (e.g., 42k or 65k AIC). The 2/0 wire itself is generally sufficient for residential fault levels, but the breaker terminating it must be rated to handle the explosive magnetic forces of a short circuit without welding its contacts shut.

Always verify your local Authority Having Jurisdiction (AHJ) requirements, as some municipalities mandate voltage drop calculations for feeders exceeding 100 feet, overriding the baseline ampacity table allowances.