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What Size Wire for 100 Amps?

For 100 amps with the displayed 75 C termination defaults, start with 3 AWG copper or 1 AWG aluminum. This page sits at the common subpanel and small-service planning boundary.
Load
100 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
Copper3 AWG100 A100 ATermination rated 75 CPasses defaults
Aluminum1 AWG100 A100 ATermination rated 75 CPasses defaults
What Size Wire for 100 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 100 A ChangesAt 100 A, the conductor answer depends heavily on the equipment and load calculation. The page result is a 75 C default, but equipment rated 100 A or less is often treated as 60 C unless marked otherwise, and the feeder or service load calculation must justify the 100 A rating before wire is selected.

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
90 A3 AWG90 A2 AWG90 A
100 A (this page)3 AWG100 A1 AWG100 A
110 A2 AWG110 A1/0 AWG110 A
Copper and aluminum starting sizes for 100 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.

100 A Is the Common Feeder Boundary

Feeder / subpanel context for a 100 A circuit.

A 100 A wire-size search is often a garage subpanel, shop feeder, ADU feeder, service-equipment conversation, or a panel-capacity question after adding EVSE or electric appliances.

Under the displayed 75 C termination defaults, copper stays 3 AWG from 90 A to 100 A, while aluminum moves from 2 AWG to 1 AWG. The next 110 A page moves both materials larger, so 100 A is a real decision point rather than just another row.

What Changes This Answer

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

  • Check 60 C equipment before ordering

    The direct answer assumes 75 C terminations. If 100 A equipment must be treated at 60 C, the displayed 3 AWG copper and 1 AWG aluminum answer can move larger.

  • Load calculation owns the rating

    A 100 A conductor answer assumes 100 A is the correct feeder or service rating. Run the dwelling, feeder, or equipment load calculation first.

  • Do not miss the aluminum jump

    Under these defaults, 90 A aluminum is 2 AWG, while 100 A aluminum moves to 1 AWG.

  • Compare 110 A before upsizing

    The adjacent 110 A page moves copper to 2 AWG and aluminum to 1/0 AWG. Do not change the planned rating without load and equipment support.

100 Amp Wire Size FAQs

What size wire for 100 amps?
Under the 75 C termination defaults on this page, start with 3 AWG copper or 1 AWG aluminum. Equipment limited to 60 C can force a larger conductor.
Is 100 A a feeder or service answer?
It can be either. This page gives the conductor starting point, but service and feeder work still needs the load calculation, service-entrance conductor product requirements, utility or AHJ requirements, grounding, bonding, and lug checks.
Why does aluminum change from 90 A to 100 A?
Under the displayed defaults, aluminum moves from 2 AWG at 90 A to 1 AWG at 100 A, while copper stays 3 AWG.
Can I use the 100 A answer for a 110 A feeder?
No. The 110 A page moves to 2 AWG copper and 1/0 AWG aluminum under the same defaults.