What Wire Size for 17.33 Amps at 75 Feet?
10 AWG copper is a typical pick for 17.33A at 75 feet on 120V under a 3% drop target. It balances NEC branch-circuit ampacity and voltage drop over distance. Drop with 10 AWG at these inputs: 2.79V (2.33%). Real-world sizing also depends on insulation temperature rating, cable type, and install conditions.
No aluminum row: every aluminum size in our reference table sits past the 3% drop target at 75 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.
Use this citation when referencing this page.
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
The conductor needs to carry at least 17.33A 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), 10 AWG sits at a branch-circuit OCP of 30A because the NEC 240.4(D) small-conductor rule caps it below the 35A 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 (10 AWG NM-B = 30A), 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)
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 12 AWG (one size thinner) at these inputs gives a voltage drop of 4.46V (3.71% on 120V), and its branch-circuit OCP cap under typical conditions is 20A.
Limiting factor here: voltage drop, not ampacity. 12 AWG is still above the 17.33A load at its 20A branch-circuit OCP cap, so the conductor temperature margin is fine for this run. What pushes it off this page's pick is the 3.71% 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 8 AWG (one size thicker) would reduce voltage drop to 1.75V (1.46% on 120V). More expensive wire but better performance and more headroom for future load increases.
Wattage at This Amperage
17.33A at 120V delivers 2,079.6 watts (DC / resistive load). See conversion.