4/0 copper wire, also written 0000 AWG, is a heavy 211,600-circular-mil conductor that can carry up to 260 amps at 90°C in NEC tables.
One wrong ampacity guess is all it takes to undersize a feeder, and knowing what 4/0 copper wire is starts with the three temperature ratings that govern it. 4/0 — pronounced “four-aught” — is the largest of the aught sizes in the American Wire Gauge system, sitting one step above 3/0 and just below 250 kcmil. It’s the size electricians reach for when a service entrance or industrial feeder has to move serious current without the voltage drop of a smaller conductor.
What 4/0 Copper Wire Is: Gauge, Size, And Construction
4/0 copper wire is a heavy copper conductor — roughly half an inch across — built to carry high current over short and medium distances. The “4/0” name is a gauge designation, not a spec sheet: stranded products come in different builds, with one Southwire 4/0 conductor using 7 strands and another using 19, so the exact outside diameter shifts by a few hundredths of an inch depending on the product and temper.
What stays consistent across products is the cross-section. That area in circular mils is what determines how much current the conductor can carry, and its DC resistance tells you how much voltage you’ll lose over a long run. The figures for typical 4/0 products sit in the table below.
| Spec | 4/0 AWG Figure | Notes For Buyers |
|---|---|---|
| Gauge size | 4/0 = 0000 AWG | Largest “aught” size; pronounced four-aught |
| Conductor area | 211,600 cmils (136.52 mm²) | Southwire catalog value |
| Outside diameter | 0.509–0.522 in (1.29–1.33 cm) | Varies with stranding and temper |
| Strand count | 7 or 19 strands | Depends on the specific product |
| DC resistance | 0.050–0.052 ohms/1,000 ft | Measured at 20–25°C, varies by temper |
| Voltage rating (insulated) | 600 V | Typical XHHW-2 building wire, rated 90°C |
| Insulation options | Bare, XHHW-2, other types | Bare copper has no insulation rating |
4/0 Copper Wire Ampacity: The Temperature Ratings That Decide It
The usable ampacity of 4/0 copper wire is 195, 230, or 260 amps, and which number applies depends on the temperature rating of the whole installation — not on the wire alone. NEC-style tables list 4/0 copper at 195 A in the 60°C column, 230 A in the 75°C column, and 260 A in the 90°C column. Cerrowire’s chart carries the same 230 A and 260 A figures, and Lapp Tannehill’s table lists all three.
The trap is mixing columns. The 260 A figure only holds when everything in the path — the insulation, the lugs, the breaker terminations — is rated for 90°C. Most panel and breaker lugs are rated 75°C, and the lowest-rated component governs the whole circuit. Ampacity tables also shift with bundling, ambient temperature, and installation method, which is why the same wire can show different numbers in different references. Cerrowire’s ampacity chart is a solid place to confirm the standard figures for each temperature column.
Where Is 4/0 Copper Wire Used?
4/0 copper wire shows up wherever a circuit has to move serious current: service-entrance conductors, high-current feeders between panels, power distribution runs, and heavy grounding or bonding conductors. Insulated 4/0 products handle the wiring jobs — a typical XHHW-2 4/0 is rated 600 V and 90°C — while bare 4/0 copper, sold on large reels, is mainly a utility and industrial product for grounding and bonding, where the exposed conductor is bonded to ground and isn’t a shock hazard.
For shop builds, feeder runs, and off-grid systems, 4/0 is often the sweet spot between ampacity and cost. If you’re ready to buy, our roundup of the best 4/0 copper wire compares insulated and bare builds side by side.
Before you buy, run through this short list:
- Confirm the load ampacity and pick the wire size from the correct temperature column — don’t shop on the 90°C number if your terminations are 75°C.
- Check the insulation type and temperature rating on the exact product; bare copper has no insulation rating at all.
- Verify the voltage rating and intended application on the product page or datasheet before purchase.
- Match the conductor to the termination rating and installation method; the highest table value only counts where the whole system supports it.
FAQs
How many amps can 4/0 copper wire carry?
NEC-based ampacity tables list 4/0 copper at 195 amps in the 60°C column, 230 amps in the 75°C column, and 260 amps in the 90°C column. The rating that applies to your circuit is the lowest one in the path — a 90°C-rated wire connected to a 75°C breaker lug is limited to 230 amps.
Is 4/0 the same as 0000 AWG?
Yes. 4/0 AWG and 0000 AWG are two ways of writing the same American Wire Gauge size, pronounced “four-aught.” The gauge number only describes the conductor size — strand count, insulation, and voltage rating are separate product attributes that vary by manufacturer and application.
Can you use bare 4/0 copper wire for regular circuit wiring?
No. Bare 4/0 copper has no insulation, so it’s not suitable where shock protection or code compliance requires an insulated conductor. It belongs in grounding and bonding roles, like utility and industrial installations, while insulated products such as XHHW-2 handle feeders and service conductors.
References & Sources
- Cerrowire. “Ampacity Charts.” NEC-based ampacity reference listing 4/0 copper at 230 A (75°C) and 260 A (90°C).
- Lapp Tannehill. “Ampacity Chart.” Lists 4/0 AWG copper at 195/230/260 A across the 60/75/90°C columns.
- Southwire. “Bare Copper Solid or Compressed.” Product listing documenting 211,600 cmils, 136.52 mm², and 0.521 in diameter for 4/0 copper.