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What Size Wire for 125 Amps?

For 125 amps with the displayed 75 C termination defaults, start with 1 AWG copper or 2/0 AWG aluminum. This page is mainly a subpanel bus-rating and full-feeder check.
Load
125 A
Distance
0 ft entered
Band
Feeder / subpanel
Defaults
Non-continuous, 75 C lugs, 86 F, 240 V single-phase
Conductor count
3 current-carrying

Computed Starting Point

The table uses common defaults. Change the calculator inputs for the actual installation.

MaterialComputed sizeOCPDUsable ampacityGoverning constraintDefault check
Copper1 AWG125 A130 ATermination rated 75 CPasses defaults
Aluminum2/0 AWG125 A135 ATermination rated 75 CPasses defaults
What Size Wire for 125 Amps? under common non-continuous defaults: THHN or XHHW-2 insulation, 75 C terminations, 86 F ambient, 240 V single-phase, no more than three current-carrying conductors, and 0 ft route length entered.

What 125 A ChangesAt 125 A, the conductor answer assumes a full 125 A feeder, not merely a panel that happens to have a 125 A bus. A 125 A subpanel can be fed at a smaller breaker when the calculated load and installation allow it, but this page shows the full 125 A conductor starting point.

Run the wire size calculator

Adjacent Amp Ratings

See whether stepping one standard size up or down forces a conductor jump under the same defaults.

LoadCopper sizeCopper OCPDAluminum sizeAluminum OCPD
110 A2 AWG110 A1/0 AWG110 A
125 A (this page)1 AWG125 A2/0 AWG125 A
150 A1/0 AWG150 A3/0 AWG150 A
Copper and aluminum starting sizes for 125 A and the neighboring published amp pages, under the same defaults as the result above.

A plateau means neighboring amp ratings share a conductor size under these defaults. A jump means a standard breaker change often needs a larger wire; confirm with your real ambient, length and terminations.

125 A Is the Subpanel Bus-Rating Check

Feeder / subpanel context for a 125 A circuit.

A 125 A wire-size search often comes from a subpanel label, garage panel, shop feeder, ADU feeder, or panel bus rating. The key question is whether the feeder is actually protected and loaded at 125 A, or whether a smaller feeder breaker is serving a panel with a larger bus rating.

Under the displayed 75 C termination defaults, copper moves from 2 AWG at 110 A to 1 AWG here, and aluminum moves from 1/0 AWG to 2/0 AWG. The next 150 A page moves both materials again and changes into the service / large-feeder band.

What Changes This Answer

Checks that can change the starting conductor under the displayed defaults.

  • Separate bus rating from feeder rating

    A panel bus label is a maximum equipment rating, not proof that the feeder must be 125 A. Size the conductors to the feeder overcurrent device and calculated load.

  • Do not reuse 110 A conductors

    Under these defaults, 110 A uses 2 AWG copper and 1/0 AWG aluminum. This 125 A page moves to 1 AWG copper and 2/0 AWG aluminum.

  • Load calculation before full capacity

    A full 125 A feeder should be justified by the dwelling, feeder, or equipment load calculation before the conductor is selected.

  • Check 60 C equipment limits

    The direct answer assumes 75 C terminations. For a full 125 A feeder, equipment limited to 60 C will force larger conductors than the displayed defaults.

  • Use distance for detached feeders

    Garage, shop, and ADU feeders can become voltage-drop governed on long runs. Enter the actual one-way route length before ordering wire.

125 Amp Wire Size FAQs

What size wire for a 125 amp subpanel?
Under the 75 C termination defaults on this page, start with 1 AWG copper or 2/0 AWG aluminum for a full 125 A feeder. Confirm the feeder breaker, calculated load, terminal rating, and route length.
Can I feed a 125 A panel with a smaller breaker?
Yes when the calculated load, equipment instructions, and installation allow it. In that case, size the feeder conductors to the smaller overcurrent device, not merely to the panel bus label.
Why does 125 A need larger wire than 110 A?
The adjacent 110 A page shows 2 AWG copper and 1/0 AWG aluminum under the same defaults. At 125 A, both materials move larger.
Is aluminum common for a 125 A feeder?
Yes, aluminum is common at this feeder size when all lugs and conductors are listed for aluminum. Confirm torque instructions, conductor bending space, and voltage drop.