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What Size Wire for 100 Amps at 400 Feet?

At 400 ft, a 100 A feeder is deep into voltage-drop sizing under these defaults: 3/0 AWG copper or 250 kcmil aluminum, with layout and load assumptions worth revisiting before purchase.
Load
100 A
Distance
400 ft
Band
100 A feeder
Defaults
Non-continuous, 75 C lugs, 86 F, 240 V single-phase

Computed Starting Point

Ampacity and voltage drop under common defaults for this amp and distance.

MaterialComputed sizeOCPDUsable ampacityGoverning constraintDefault check
Copper3/0 AWG100 A200 AVoltage dropPasses defaults
Aluminum250 kcmil100 A205 AVoltage dropPasses defaults
What Size Wire for 100 Amps at 400 Feet? under common non-continuous defaults: THHN or XHHW-2 insulation, 75 C terminations, 86 F ambient, 240 V single-phase and no more than three current-carrying conductors.

What 400 ft ChangesAt 400 ft, voltage drop dominates the page result and pushes the default answer to 3/0 copper or 250 kcmil aluminum. The next best engineering move may be a different equipment location, a different load assumption, or a project-specific design review rather than blindly accepting a very large conductor.

Run the wire size calculatorCheck voltage drop alone

Zero-Length vs This Distance

If the distance-adjusted size is larger, voltage drop governed under these defaults.

CaseCopper sizeCopper constraintAluminum sizeAluminum constraint
Ampacity only (0 ft)3 AWGTermination rated 75 C1 AWGTermination rated 75 C
400 ft (this page)3/0 AWGVoltage drop250 kcmilVoltage drop
Copper and aluminum sizes for 100 A with no distance entered versus 400 ft one-way.

Adjacent Distances at This Amp

Neighboring published lengths for 100 A under the same defaults.

DistanceCopper sizeAluminum sizeCopper constraint
300 ft2/0 AWG4/0 AWGVoltage drop
400 ft (this page)3/0 AWG250 kcmilVoltage drop
100 A copper and aluminum starting sizes across neighboring distance pages.

400 ft Is an Extreme 100 A Feeder Run

100 A feeder context for 100 A at 400 ft.

A 400 ft 100 A run is usually a remote shop, barn, pump location, gate equipment, detached structure or long site feeder. At this distance, the conductor answer is tied to civil layout and equipment placement, not just an electrical table lookup.

The default result has moved far from the zero-length 100 A conductor. This page should make the user pause before buying: confirm the real load, route, voltage and whether carrying 100 A the whole way is still the right design.

What Changes This Long-Run Answer

Checks that matter for distance-governed sizing in this amp band.

  • Reconfirm the full 100 A load

    If the actual design load is well below 100 A, the voltage-drop result can change substantially. Do not size from the feeder rating if the sustained load is lower.

  • Review the route before ordering

    At 400 ft, trench changes, extra sweeps and verticals are expensive. Lock the measured one-way path before committing to conductor.

  • Check raceway, bends and lugs as a package

    3/0 copper and 250 kcmil aluminum need equipment that accepts the size and a raceway path that can be pulled and terminated cleanly.

  • Escalate unusual site conditions

    Remote buildings, utility coordination, generators, pumps and large motors can add rules outside this default 100 A feeder planning answer.

100 A at 400 ft FAQs

What size wire for 100 amps at 400 feet?
Under the defaults on this page, start with 3/0 AWG copper or 250 kcmil aluminum. Voltage drop is the governing constraint.
Should I still use 100 A at 400 ft?
Maybe, but this is the distance where the load calculation, equipment location and actual operating current deserve another pass before ordering very large conductors.
Does the 400 ft answer guarantee code approval?
No. It is a calculator-derived planning result under stated defaults. The adopted edition, AHJ, utility requirements, equipment instructions and verified project conditions still control.