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Wire size calculator / 3/0 AWG ampacity

How many amps can 3/0 gauge wire carry?

NEC Table 310.16 listings for 3/0 AWG, the selected small-conductor note when this tool has one, and a Chapter 9 Table 8 voltage-drop example. Not a breaker schedule.

Three-aught has a copper cell that matches the 200 A load discussed in the subpanel guide. Open the copper cells and check which temperature column actually prints that load. The neighboring 60°C and 90°C cells have different values, so the label alone does not establish ampacity. A match still describes only the table’s assumptions.

Those assumptions are 30°C ambient and not more than three current-carrying conductors, at the temperature you picked. They are not a subpanel, a service, or a long feeder. The subpanel guide runs its stated examples through the calculator, and voltage drop can leave this row. Use this page for the 3/0 cells and the 3/0 resistance.

The example current of 180 A does not equal any copper temperature cell for 3/0 AWG. It is above the 60°C copper cell of 165 A, so a 60°C terminal cap does not cover this current before any other correction. The prefilled calculator uses 240 V, 150 ft one way, 75°C insulation, and 75°C terminals. Those are inputs, not a required circuit.

The selected NEC 240.4(D) column in this tool has no special ceiling for 3/0 AWG. A blank is not permission to omit overcurrent protection. Table ampacity, the terminal cap, and voltage drop still apply.

Aluminum 3/0 AWG is listed at 130 A (60°C), 155 A (75°C), and 175 A (90°C), against copper 165 A, 200 A, and 225 A. Stranded resistance at 75°C is 0.126 Ω/kft aluminum and 0.0766 Ω/kft copper. The same label is not the same conductor. Some equipment permits copper only.

This chart’s Table 8 row for 3/0 AWG publishes stranded resistance only (0.0766 Ω/kft copper, 0.126 Ω/kft aluminum). The calculator uses that stranded value.

Table 8 lists 19 strands and 167800 circular mils for 3/0 AWG. The rounded nominal area is 85.01 mm². Bare stranded diameter is 0.47 in, which excludes insulation and is not conduit fill.

3/0 AWG from NEC Table 310.16 (30°C ambient, not more than three current-carrying conductors) and Chapter 9 Table 8 at 75°C. A dash means no listing. Bare diameter excludes insulation.
ListingCopperAluminum
60°C ampacity (A)165130
75°C ampacity (A)200155
90°C ampacity (A)225175
Stranded Ω/kft0.07660.126
Solid Ω/kft——
Selected 240.4(D) ceiling (A)——
Circular mils167800
Rounded mm²85.01
Strands19
Bare diameter (in)0.47

For 3/0 AWG itself, not for whatever size the calculator recommends, Table 8 stranded copper resistance of 0.0766 Ω/kft at 75°C gives 4.14 V (1.72% of 240 V) using 2 × I × R × L / 1,000. Reactance is omitted. Displayed volts are rounded to two decimals. The same inputs with stranded aluminum resistance 0.126 Ω/kft give 6.80 V (2.83%). If that percentage is outside the prefilled drop limit, the calculator will name a different size. That is the voltage-drop check, not a second ampacity table.

From 2/0 AWG to 3/0 AWG, the 75°C copper listing goes from 175 A to 200 A. Stranded copper resistance at 75°C goes from 0.0967 Ω/kft to 0.0766 Ω/kft.

From 3/0 AWG to 4/0 AWG, the 75°C copper listing goes from 200 A to 230 A. Stranded copper resistance at 75°C goes from 0.0766 Ω/kft to 0.0608 Ω/kft.

The copper 75°C cell lists 200 A. That is the table cell under its own assumptions, not a feeder design.

Planning estimate only. Consult local code and a qualified electrician before buying wire or energizing a circuit. Presets are hypothetical loads; this tool does not design motor, PV, battery, appliance, or EV installations.

Sources for these cells: existing Table 310.16 numerical cells in NFPA’s public development record, pp. 142–143 (proposed changes are not treated as adopted code) and NFPA 70 (2017), Chapter 9 Table 8, printed p. 689, in a third-party-hosted copy. The same publication supplies 110.14 (terminals and aluminum), 210.19/215.2 (continuous loads), 240.4(D) (small conductors), 250.24/250.32 (grounding), and 625.41/625.42 (EV loads). Schneider Electric’s voltage-drop formulas support the arithmetic; Table 8 AC results here omit reactance and assume unity power factor. Resistance and geometry are construction- and temperature-specific. Adopted editions and local amendments can differ.

Related guides

Open the wire size calculator · Ampacity chart · Voltage drop calculator · Printable chart

Check an example against 3/0 AWG

The form starts from this page’s example. The address stays on this guide until you edit a field. After an edit, a shared link includes those settings in the URL, and opening that link sends the URL to the host.

Circuit

Headline metal

Both metals are compared. Verify equipment compatibility; some equipment permits copper only.

System

General NEC notes suggest 3% on a branch or feeder and 5% combined. Special equipment and local codes may require other limits; upstream drop is not included.

Estimated size

Enter the load current and the one-way distance. The size appears here, with the limit that set it.

Temperature and bundling

These conditions affect the table ampacity used for the comparison.

Conductor insulation

Use the rating marked for wet or dry conditions. THHN is 90°C dry; XHHW is 90°C dry or 75°C wet. For NM-B use 90°C insulation and a 60°C cap below.

Terminal / cable ampacity cap

Use the lowest applicable rating at either end, including cable limits. The general unmarked default is 60°C for equipment rated ≤100 A or marked for 14–1 AWG. Confirm equipment markings before selecting 75°C; NM-B remains capped at 60°C.

Equipment grounding conductors are excluded. Verify neutrals, harmonic loads, and all other current-carrying conductors in the raceway or cable; the automatic count does not check these.

AC impedance (Chapter 9 Table 9)

At power factor 1, the reactance term is zero, but Table 9 AC resistance still applies. Unlisted sizes have no Table 9 result.

Planning estimate only. Consult local code and a qualified electrician before buying wire or energizing a circuit. Presets are hypothetical loads; this tool does not design motor, PV, battery, appliance, or EV installations.

Questions

How many amps can 3/0 gauge wire carry?

3/0 AWG copper in NEC Table 310.16 is listed at 165 A at 60°C, 200 A at 75°C, and 225 A at 90°C. Aluminum 3/0 AWG is listed at 130 A (60°C), 155 A (75°C), and 175 A (90°C), against copper 165 A, 200 A, and 225 A. Stranded resistance at 75°C is 0.126 Ω/kft aluminum and 0.0766 Ω/kft copper. The same label is not the same conductor. Some equipment permits copper only. Those cells assume not more than three current-carrying conductors and 30°C ambient. They are not a breaker size by themselves. The selected NEC 240.4(D) column in this tool has no special ceiling for 3/0 AWG. A blank is not permission to omit overcurrent protection. Table ampacity, the terminal cap, and voltage drop still apply. Planning estimate only. Consult local code and a qualified electrician.

Does a hotter temperature column raise the breaker for 3/0 AWG?

This tool’s selected NEC 240.4(D) column has no special ceiling for 3/0 AWG. The blank is not permission to omit overcurrent protection, and it does not turn the 90°C cell into a breaker rating. Terminal and cable limits still cap the usable ampacity. Exceptions in the code are not checked. Planning estimate only. Consult local code and a qualified electrician.

What voltage drop does 3/0 AWG have on the example?

For 3/0 AWG itself, not for whatever size the calculator recommends, Table 8 stranded copper resistance of 0.0766 Ω/kft at 75°C gives 4.14 V (1.72% of 240 V) using 2 × I × R × L / 1,000. Reactance is omitted. Displayed volts are rounded to two decimals. The same inputs with stranded aluminum resistance 0.126 Ω/kft give 6.80 V (2.83%). If that percentage is outside the prefilled drop limit, the calculator will name a different size. That is the voltage-drop check, not a second ampacity table.

Does a 200 A cell on this row size a 200 A subpanel?

No. A Table 310.16 cell equal to 200 A, if one is printed below, is the listing under that column’s assumptions. A subpanel also needs a load calculation, a terminal rating, a length, a metal the equipment allows, and the adopted code’s feeder rules. This calculator does not perform that design. The subpanel guide shows estimates only under the assumptions in each row.