A 3/0 AWG copper conductor carries 200 amps in the 75°C column of NEC Table 310.16, with 165 amps at 60°C and 225 amps at 90°C.
No wire label starts more arguments than the one that just says 225 amps. A 3/0 AWG copper conductor does sit at 225 amps in the 90°C column of the code table, yet the circuit rating usually lands at 200 amps — and on older gear, at 165. Terminals, bundling, and ambient heat all get a vote. Sorting out 3/0 copper wire ampacity in the right order is what keeps a feeder correctly protected instead of merely close.
3/0 Copper Wire Ampacity: Which Temperature Column Applies
The governing column is set by the weakest temperature rating anywhere in the circuit. Modern 75°C panels, lugs, and THHN/THWN-2 copper put 3/0 at 200 amps, while the 90°C column’s 225 amps exists for adjustment and correction math — it does not, by itself, authorize a 225-amp circuit.
| Condition | 3/0 Copper Ampacity | When It Governs |
|---|---|---|
| 60°C column | 165 A | Equipment or terminations marked 60°C, older gear |
| 75°C column | 200 A | Typical 75°C terminals on modern panels and lugs |
| 90°C column | 225 A | Derating and correction math only, where equipment allows |
| Ambient above 30°C | Below table value | Rooftops, attics, hot mechanical rooms |
| 4–6 current-carrying conductors | Adjustment factors apply | Bundled feeders sharing one raceway |
| Continuous load, 3+ hours | Size at 125% | EV chargers, motors, steady data loads |
| Bare 3/0 copper | Separate data set | Overhead and grounding work, not insulated building wire |
The NEC Section 310.16 ampacity table is the source behind every figure above.
Product pages that advertise “225 A ampacity at maximum temperature” are quoting the 90°C column, not a universal circuit rating. If you are stocking up before a feeder pull, the tested picks in our 3/0 copper wire buying roundup show which spools carry the listing you need.
What Pulls A 3/0 Copper Circuit Below Its Table Number?
Five things do it: 60°C terminations, ambient heat above 30°C, more than three current-carrying conductors in a raceway, a continuous load, and plain old size confusion.
- Ambient temperature. Table 310.16 assumes 30°C (86°F). A rooftop run or attic pull hotter than that needs a correction factor, which drops usable amps fast.
- Conductor count. Four to six current-carrying conductors in one raceway require adjustment factors; the base table assumes three or fewer.
- Termination ratings. A 90°C conductor landed on 75°C lugs behaves as a 75°C conductor for ampacity purposes, and 60°C gear drags it down to 165 amps.
- Continuous load. Anything drawing for three hours or more gets sized at 125 percent, so a 160-amp continuous draw needs a 200-amp design.
- The 3 versus 3/0 mix-up. 3 AWG copper is a much smaller conductor with a much lower ampacity. The slash changes everything.
Sizing The Breaker And The Terminations Around The Wire
The breaker follows the load and the equipment listing, never the tallest number in the conductor’s column. Work the checks in this order and the rating falls out on its own.
- Read the conductor’s listing — THHN, THWN-2, or XHHW-2 — rather than assuming every 3/0 spool behaves alike.
- Check the markings on breakers, lugs, and the panel to fix the terminal column, then apply NEC 110.14(C).
- Count current-carrying conductors and apply adjustment factors for anything above three.
- Correct for the ambient temperature at the installation, not the temperature at the supply house.
- Multiply continuous loads by 125 percent before choosing a breaker frame.
- Confirm the breaker, disconnect, and connected equipment are listed for the voltage, current, and conditions — then check local amendments with the authority having jurisdiction.
When the numbers line up, the installed breaker is the smaller of the corrected conductor ampacity and the equipment rating, and a 200-amp feeder on 3/0 copper is the common result.
FAQs
Is 3/0 copper the same as 3-gauge wire?
No. 3/0 AWG, sometimes written 000, is a far larger conductor than 3 AWG and carries several times the current. Mixing the two up is one of the most common ordering errors on feeder projects, because the sizes look almost identical on a supply house shelf tag.
Can I size a 225-amp breaker from the 90°C column?
Only if every termination in the circuit — breaker, lugs, panel, splices, and connected equipment — is rated and listed for 90°C operation. Most building equipment tops out at 75°C, which caps the circuit at 200 amps no matter what insulation the conductor carries.
Does direct burial raise the ampacity?
No. NEC Table 310.16 covers conductors in raceway, cable, or buried directly in earth using the same 60°C, 75°C, and 90°C values, provided no more than three carry current. Soil conditions and burial depth are separate requirements, and terminations still control the usable column.
References & Sources
- International Code Council. “NEC Section 310.16 — Ampacities of Insulated Conductors.” Source of the 60°C, 75°C, and 90°C ampacity values for 3/0 copper.
- Southwire. “SIMpull THHN/THWN-2 Copper, Specification 10000.” Lists 3/0 copper at 200 A at 75°C and 225 A at 90°C, citing NEC Sections 310.15 and 110.14(C).