What Wire Size for 0.42 Amps at 150 Feet?

For 0.42 amps at 150 feet on a 120V circuit, 14 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.

0.42A at 150ft · 120V single-phase / DC · 3% drop target

14 AWG copper

On a 240V circuit (copper)14 AWG

Voltage drop (120V, copper)0.3956V (0.3297%)

No aluminum row: every aluminum size in our reference table sits past the 3% drop target at 150 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

Amps

Feet

Gauge (Cu / Al)

14 AWG Cu

Assumes a 120V source on a single-phase / DC 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 three-phase L-L →

How Wire Size Is Determined

Step 1: NEC Branch-Circuit Ampacity

14 AWG branch-circuit OCP (15A under NEC 240.4(D)) ≥ 0.42A ✓

The conductor needs to carry at least 0.42A 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), 14 AWG sits at a branch-circuit OCP of 15A because the NEC 240.4(D) small-conductor rule caps it below the 20A 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 (14 AWG NM-B = 15A), 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 = (2 × L × I × R) ÷ (1000 × V) × 100 (single-phase / DC; round-trip factor of 2)

(2 × 150 × 0.42 × 3.14) ÷ (1000 × 120) × 100 = 0.3297%

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?

The recommended gauge is already the smallest suitable option in our table.

What If You Go One Size Larger?

Using 12 AWG (one size thicker) would reduce voltage drop to 0.2495V (0.2079% on 120V). More expensive wire but better performance and more headroom for future load increases.

Wattage at This Amperage

0.42A at 120V delivers 50.4 watts (DC / resistive load). See conversion.

Related Calculations

trending_down V-drop: 14 AWG, 0.42A, 150ft electric_bolt 0.42A to watts at 120V functions Wire sizing formula

Frequently Asked Questions

What wire size for 0.42 amps at 150 feet on 120V?expand_more

0.42A at 150ft on 120V is commonly served by 14 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.

Do I need to upsize wire for continuous loads?expand_more

NEC 210.19(A) (branch circuits) and 215.3 (feeders) size the conductor and overcurrent device at not less than 125% of the continuous load plus 100% of any non-continuous load. For a 0.42A continuous load that points the sizing math at the 0.525A figure, but the actual conductor and breaker pick still depends on termination temperature rating, cable type, bundling and ambient conditions, and any 240.4(D) or 240.4(B) provisions. Treat this as the input to a sizing decision, not the output.

How much does 14 AWG wire cost?expand_more

Copper wire pricing tracks the LME copper spot price and varies with insulation type, cable assembly (THHN, NM-B, MC, SE, USE), and quantity. Check current pricing with a local electrical supply house or distributor catalog; commodity-driven numbers inlined on a calculator page age quickly.

Why does distance affect wire size?expand_more

Voltage drop scales linearly with distance: doubling the one-way run length doubles the drop in volts. At 0.42A on 120V, a 150ft run is often served by 14 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.

Can I run 0.42A on a longer distance?expand_more

Yes, but you may need thicker wire. At 300ft on 120V, check the wire size calculator. You may need to go up one or two gauges.

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.