What Wire Size for 8.63 Amps at 100 Feet?

For 8.63 amps at 100 feet on a 120V circuit, 12 AWG copper is a common starting point under a 3% voltage-drop target. On a 240V circuit the same current often allows 14 AWG, because the 3% allowable drop is a larger number of volts at higher source voltage. Actual install sizing still depends on conductor material, insulation/termination temperature, cable type, ambient and bundling conditions, and local code.

8.63A at 100ft · 120V three-phase L-L · 3% drop target
12 AWG copper
On a 240V circuit (copper)14 AWG
Voltage drop (120V, copper)2.96V (2.47%)

No aluminum row: every aluminum size in our reference table sits past the 3% drop target at 100 feet on 120V, or the amperage is below the 30A residential threshold where aluminum is not a typical pick. On a higher source voltage, a shorter run, or a looser drop target, aluminum is still the standard feeder material at higher amperages.

check_circle Within the 3% branch and 5% feeder+branch total drop targets
12 AWG Cu

Assumes a 120V source on a three-phase L-L circuit and a 3% voltage-drop target. Each material is picked independently against the same target, so the copper and aluminum results are two separate recommendations, not an ampacity equivalence. Switch to single-phase / DC →

How Wire Size Is Determined

Step 1: NEC Branch-Circuit Ampacity

12 AWG branch-circuit OCP (20A under NEC 240.4(D)) ≥ 8.63A ✓

The conductor needs to carry at least 8.63A without going past its temperature rating, and the OCP protecting it needs to respect the NEC branch-circuit cap. Under the typical assumptions used in this table (copper, 75°C termination, no bundling or ambient derates), 12 AWG sits at a branch-circuit OCP of 20A because the NEC 240.4(D) small-conductor rule caps it below the 25A 75°C ampacity table value. That is not a universal number: NM-B cable (Romex) follows the 60°C column in residential use per NEC 334.80 (12 AWG NM-B = 20A), bundling more than three current-carrying conductors requires a 310.15(C)(1) adjustment, ambient temperatures above 30°C require a 310.15(B) correction, and 60°C terminations on typical residential equipment can pull the usable value lower still. Use the nameplate and local code for the actual install value.

Step 2: Voltage Drop Check

%VD = (√3 × L × I × R) ÷ (1000 × V) × 100 (three-phase L-L; √3 factor)

(√3 × 100 × 8.63 × 1.98) ÷ (1000 × 120) × 100 = 2.47%

NEC 210.19(A) Informational Note 4 recommends ≤ 3% for branch circuits and ≤ 5% for feeder + branch total as performance targets, not hard code requirements. This run sits within the 3% target used for this calculation.

Practical Information

What If You Go One Size Smaller?

Using 14 AWG (one size thinner) at these inputs gives a voltage drop of 4.69V (3.91% on 120V), and its branch-circuit OCP cap under typical conditions is 15A.

Limiting factor here: voltage drop, not ampacity. 14 AWG is still above the 8.63A load at its 15A branch-circuit OCP cap, so the conductor temperature margin is fine for this run. What pushes it off this page's pick is the 3.91% drop sitting past the 3% target, which is a performance recommendation (NEC 210.19(A) Informational Note 4), not a code requirement. On shorter runs or at higher source voltage the same gauge would often clear the drop target too.

What If You Go One Size Larger?

Using 10 AWG (one size thicker) would reduce voltage drop to 1.85V (1.54% on 120V). More expensive wire but better performance and more headroom for future load increases.

Wattage at This Amperage

8.63A at 120V delivers 1,035.6 watts (DC / resistive load). See conversion.

Related Calculations

trending_down V-drop: 12 AWG, 8.63A, 100ft electric_bolt 8.63A to watts at 120V functions Wire sizing formula

Frequently Asked Questions

8.63A at 100ft on 120V is commonly served by 12 AWG copper to land under the 3% voltage-drop target, under the typical 75°C-termination assumptions used in this table. Actual install sizing also depends on conductor material, insulation and termination temperature rating, cable type, ambient and bundling conditions, and local code.
Copper and aluminum are picked independently against the same drop target on this site; neither pick implies ampacity equivalence with the other. At 8.63A residential branch-circuit territory, copper is the default. Aluminum in 14/12/10 AWG is not typical for residential branches, both for code reasons (the NEC 240.4(D) small-conductor rule caps aluminum branch OCP tighter than copper) and because termination and anti-oxidation requirements add cost at that scale.
Yes, but you may need thicker wire. At 200ft on 120V, check the wire size calculator. You may need to go up one or two gauges.
Voltage drop scales linearly with distance: doubling the one-way run length doubles the drop in volts. At 8.63A on 120V, a 100ft run is often served by 12 AWG to land under the 3% drop target, a run half that length can sometimes use one gauge thinner, and a run double that length usually needs one or two gauges thicker. Ampacity is set by the conductor itself (Table 310.16 at the applicable termination temperature), so the binding constraint is ampacity on short runs and voltage drop on long runs.
NEC 210.19(A) Informational Note 4 recommends ≤3% for branch circuits and ≤5% total (feeder + branch). These are performance recommendations, not hard code requirements.
This calculator provides estimates for reference purposes only. Always consult a licensed electrician and verify compliance with the National Electrical Code (NEC) and local electrical codes before performing any electrical work.
person Written by Sean Day verified Reviewed by WireResult update Last updated Apr 11, 2026