The 2/0 AWG amp rating is the maximum continuous current—typically 175 amps for copper and 135 amps for aluminum at 75°C—that a 2/0 gauge conductor can safely carry without exceeding its insulation temperature limits. If you are sizing a feeder for a 150A subpanel, wiring a high-output solar inverter, or building a 48V off-grid battery bank, 2/0 (pronounced "two-aught") is the exact threshold where you transition from standard branch circuit wiring into heavy-duty feeder territory. Getting this right dictates your breaker size, conduit fill capacity, voltage drop over distance, and the physical torque required at your termination lugs.
The Core Numbers: Ampacity by Material and Temperature
To determine the exact ampacity of 2/0 wire, you must look at the National Electrical Code (NEC) Table 310.16. However, the most common mistake DIYers and junior electricians make is reading the wrong temperature column. Most modern wire insulation (like THHN or XHHW-2) is rated for 90°C, but NEC 110.14(C) strictly limits your termination ampacity to the lowest temperature rating of any connected component, which is almost always 75°C for breakers and lugs rated 100A and above.
| Material | 60°C Column (Older Equipment) | 75°C Column (Standard Terminations) | 90°C Column (Derating/Adjustments Only) |
|---|---|---|---|
| Copper (THHN/XHHW) | 145 Amps | 175 Amps | 195 Amps |
| Aluminum (XHHW-2) | 115 Amps | 135 Amps | 150 Amps |
Common Confusions: 2 AWG vs 2/0 AWG and the 90°C Trap
There are two major pitfalls when ordering and installing 2/0 wire that lead to failed inspections or overheated panels.
1. Confusing 2 AWG with 2/0 AWG: In the American Wire Gauge system, the "/0" denotes "aught" (zero). As you add zeros, the wire gets thicker. 2 AWG is a much smaller wire with a diameter of roughly 0.257 inches and a 75°C ampacity of 115A (copper). 2/0 AWG has a diameter of 0.364 inches and an ampacity of 175A. Ordering "2 gauge" when you need "two-aught" will leave you with a wire that is dangerously undersized for a 150A load and physically loose inside lugs designed for the thicker 2/0 conductor.
2. The 90°C Ampacity Trap: Because THHN wire is printed with a 90°C rating on the jacket, many builders assume they can push 195 amps through 2/0 copper. This is a severe code violation. The 90°C column is legally permitted only for ampacity derating calculations (such as when you have more than three current-carrying conductors in a single conduit or high ambient temperatures). The final derated ampacity must still be compared against the 75°C termination limit, and the lower of the two numbers governs your breaker size.
Worked Numeric Example: Sizing a 150A Subpanel Feeder
Let’s look at a real-world scenario. You need to run a feeder from a 200A main panel to a new 150A subpanel in a detached workshop. The one-way distance is 120 feet. You plan to use copper THHN in PVC conduit.
Step 1: Check Base Ampacity
A 150A non-continuous load requires a wire rated for at least 150A. Looking at the 75°C column, 2/0 copper is rated for 175A. This passes the baseline NEC requirement.
Step 2: Calculate Voltage Drop
While the NEC recommends keeping voltage drop under 3% for feeders, it doesn't strictly enforce it unless specific equipment requires it. Still, good practice demands we check the math using the standard single-phase voltage drop formula:
VD = (2 × K × I × D) / CM
- K (Copper resistivity) = 12.9 ohms-cmil/ft
- I (Current) = 150 Amps
- D (Distance) = 120 feet
- CM (Circular Mils for 2/0 AWG) = 133,100
VD = (2 × 12.9 × 150 × 120) / 133,100
VD = 464,400 / 133,100 = 3.49 Volts
On a 240V system, a 3.49V drop is exactly 1.45%. Because this is well under the 3% recommendation, 2/0 copper THHN is the perfect, code-compliant choice for this run. If the distance had been 250 feet, the drop would exceed 3%, and you would need to step up to 3/0 or 4/0 AWG to compensate, even though the 75°C ampacity requirement was already met.
Where You Meet 2/0 Wire in Practice
You won't find 2/0 wire running to standard wall outlets or lighting circuits. This gauge is reserved for high-current infrastructure:
- Subpanel Feeders: The most common residential use is feeding a 150A subpanel from a 200A main service, either in a 4-wire configuration (two hots, neutral, ground) inside conduit or as part of a pre-assembled SER (Service Entrance Rated) cable.
- Heavy-Duty EV Chargers: While most home EV chargers run on 60A or 100A circuits, commercial installations or multi-stall Tesla Wall Connectors utilizing load-sharing often require 2/0 feeders to supply the distribution panel.
- Large Solar Inverters: Commercial string inverters (like large SMA or SolarEdge three-phase units) often output between 120A and 160A, necessitating 2/0 copper for the AC output runs to the combiner panel.
- 48V Off-Grid Battery Banks: In low-voltage, high-current DC systems, a 10,000W 48V inverter pulls over 200A from the batteries. While 2/0 is sometimes used for short jumper runs between batteries, 4/0 is usually preferred for the main inverter bus to minimize DC voltage drop.
Frequently Asked Questions
What size breaker can I use with 2/0 copper wire?
Under standard NEC rules, you can protect 2/0 copper wire (rated 175A at 75°C) with a maximum 175A breaker. Because 175A is a standard breaker size listed in NEC 240.6, you cannot use the "next size up" rule to jump to a 200A breaker. If your calculated load requires a 200A breaker, you must step up to 3/0 AWG copper or 4/0 AWG aluminum.
Can I use 2/0 aluminum wire for a 150-amp residential service?
Yes, but only because of a specific exception. Standard Table 310.16 lists 2/0 aluminum at just 135A (75°C column), which is insufficient for 150A. However, NEC 310.12(A) provides a special allowance for dwelling units: it explicitly permits 2/0 AWG aluminum for 150A residential services and feeders. This exception exists because residential loads are highly diversified and rarely draw a continuous 150A. Note that this exception applies only to residential dwellings; a 150A commercial subpanel would still require 3/0 or 4/0 aluminum.
How much does 2/0 copper wire cost per foot?
As of early 2026, bare 2/0 AWG copper THHN wire typically costs between $4.50 and $6.50 per foot, depending on market copper fluctuations and whether you are buying by the spool or cut-to-length. If you are buying pre-assembled 4-4-4-6 Aluminum SER cable (a common alternative for subpanels), the price drops significantly to roughly $1.50 to $2.50 per foot. Always check local electrical supply houses like Graybar or CED, as they often beat big-box store pricing on heavy feeder wire.
What is the torque specification for 2/0 AWG lugs?
NEC 110.14(D) mandates that you must torque terminations to the manufacturer's specified values. For 2/0 AWG wire in heavy-duty 150A-200A main breaker lugs (such as Square D Homeline or Eaton BR panels), the required torque is typically between 150 in-lbs and 250 in-lbs (roughly 12 to 20 ft-lbs). Do not guess this value. Use a calibrated digital torque wrench or torque screwdriver. Under-torquing causes high-resistance connections that melt lugs under load; over-torquing can snap the lug setscrew or crush the conductor strands, creating a localized hot spot.
