The baseline 2/0 AWG current rating (ampacity) for copper wire is 195 amps at 75°C and 175 amps at 60°C. For aluminum 2/0 wire, the rating is 150 amps at 75°C and 135 amps at 60°C. These values assume a standard 30°C (86°F) ambient temperature and no more than three current-carrying conductors bundled together in a raceway or cable, per NEC Table 310.16.
However, pulling a single number from a chart without understanding the installation environment is how feeder cables overheat and melt terminal lugs. The actual allowable ampacity on your jobsite depends entirely on your termination equipment ratings, ambient heat, and conduit fill. Below is the definitive reference for sizing 2/0 AWG feeders, service entrances, and heavy branch circuits.
The Master 2/0 AWG Ampacity Reference (NEC Table 310.16)
How to read this table: This data is extracted from the 2023/2026 National Electrical Code Table 310.16 (formerly 310.15(B)(16)). The columns represent the temperature rating of the wire insulation and the connected equipment terminations. Most modern residential and commercial breakers and lugs are rated for 75°C, while older equipment or specific NM-B (Romex) cables are limited to the 60°C column. The 90°C column is generally reserved strictly for derating calculations, not final termination limits. For a complete breakdown of insulation types, refer to the Cerrowire NEC Ampacity Charts.
| Conductor Material | 60°C Column (140°F) | 75°C Column (167°F) | 90°C Column (194°F) | Common Insulation Types |
|---|---|---|---|---|
| Copper (Cu) | 175 Amps | 195 Amps | 225 Amps | THHN, THWN-2, XHHW-2, THW |
| Aluminum (Al) | 135 Amps | 150 Amps | 170 Amps | XHHW-2, THWN-2, USE-2 |
Bookmark Quick-Jump: Most Queried 2/0 Values
- 200-Amp Residential Service Entrance (Copper): Use the 75°C column (195A). Because 195A is less than the 200A main breaker, 2/0 Cu is not legally sufficient for a full 200A service unless specific residential whole-house derating allowances apply (NEC 310.12). You typically need 4/0 Al or 2/0 Cu specifically listed for 200A service.
- 150-Amp Subpanel Feeder (Aluminum): Use the 75°C column (150A). 2/0 Aluminum is the exact match for a 150A breaker.
- NM-B (Romex) Cable Limitation: If you are somehow using a 2/0 NM-B cable assembly, NEC 334.80 forces you to use the 60°C column, capping copper at 175A and aluminum at 135A.
Which Temperature Column Applies to Your Installation?
The most common mistake DIYers and junior apprentices make is looking at the 90°C rating of THHN wire (225A for copper) and assuming they can put it on a 225A breaker. This violates NEC 110.14(C), which dictates that the ampacity of a circuit is limited by the lowest temperature rating of any connected component.
Here is the decision framework for selecting your column:
- Check the Breaker and Lug Ratings: Look at the schematic sticker inside your panelboard or the stamp on the breaker lug. Almost all modern equipment rated 100A and above is marked 75°C. Equipment rated below 100A is often marked 60°C unless specified otherwise.
- Apply the Weakest Link Rule: If your 2/0 THHN wire is rated 90°C, but it terminates on a 75°C breaker lug, your baseline ampacity is capped at the 75°C value (195A for copper).
- When to use the 90°C column: You only use the 90°C column as your starting point for ambient temperature corrections and bundling derating. Once you apply those mathematical penalties, you compare the result to the 75°C termination limit. Your final allowable ampacity is whichever number is lower.
Derating Factors: How Bundling and Heat Modify the Base Value
Ampacity tables assume ideal conditions: 30°C ambient air and a maximum of three current-carrying conductors in a raceway. When you stuff more wires into a conduit or run it across a hot roof, the wire cannot dissipate heat. The NEC requires you to penalize (derate) the ampacity.
Worked Numeric Example: 2/0 Cu THHN on a Hot Roof
The Scenario: You are pulling four current-carrying 2/0 AWG copper THHN wires through an EMT conduit on a roof where the ambient temperature reaches 40°C (104°F). The wires terminate on a standard 75°C rated 200A subpanel lug.
Step 1: Start with the 90°C column for derating.
Base 90°C ampacity for 2/0 Cu = 225A.
Step 2: Apply the Bundling Derating Factor.
NEC Table 310.15(C)(1) states that 4 to 6 current-carrying conductors require an 80% adjustment factor.
225A × 0.80 = 180A.
Step 3: Apply the Ambient Temperature Correction.
NEC Table 310.15(B)(1) for 40°C ambient using the 90°C insulation column gives a correction factor of 0.91.
180A × 0.91 = 163.8A.
Step 4: Compare to the Termination Limit (NEC 110.14(C)).
The 75°C termination limit for 2/0 Cu is 195A.
Compare the derated value (163.8A) to the termination limit (195A). The lower number wins.
Final Result: The true allowable ampacity for this specific 2/0 AWG installation is 163 amps. You cannot protect this feeder with a 175A or 200A breaker; you must step down to a 150A breaker or upsize the wire to 3/0 or 4/0 AWG.
What the Ampacity Table Cannot Tell You
While NEC Table 310.16 prevents wires from melting under continuous load, it completely ignores three critical real-world engineering constraints that will ruin a 2/0 AWG installation if overlooked.
1. Voltage Drop Over Distance
Ampacity is about heat; voltage drop is about performance. If you are running a 2/0 aluminum feeder 250 feet to a detached garage subpanel, the wire will safely carry 150A without catching fire, but the voltage at the far end will sag below 110V under heavy load. This causes motorized tools to overheat and smart home electronics to brownout. For long runs, always calculate voltage drop (aiming for <3% on feeders) and be prepared to upsize to 4/0 or 250 kcmil regardless of the breaker size.
2. Physical Bending Radius and Conduit Fill
2/0 AWG wire is incredibly stiff. NEC Chapter 9, Table 1 limits conduit fill to 40% for three or more wires. If you try to jam four 2/0 THHN wires into a 1-inch PVC conduit, you will physically damage the insulation during the pull and create excessive heat buildup. Furthermore, NEC 300.34 requires you to maintain specific bending radii to prevent the conductor from kinking or stressing the termination lugs. Always use a conduit fill calculator and oversized sweeping elbows for this gauge.
3. Fault Current and Let-Through Energy
Ampacity tables assume normal operating conditions. They do not tell you what happens during a dead short. If your utility transformer can deliver 22,000 Amps of fault current, your 2/0 wire and the breaker must have an adequate Amps Interrupting Capacity (AIC) and withstand rating. If the breaker clears the fault too slowly, the magnetic forces can physically rip the 2/0 conductors out of their lugs before the thermal trip element ever reacts.
