Wire Gauge for 15A at 75 ft on 120V — NEC Calculator

For 15A at 75 ft on 120V, use 10 AWG copper. Voltage drop: 2.33%. Per NEC 2023 Table 310.16.

Load current (amps)

One-way distance (ft)

System voltage

Conductor

Insulation temp

Max VD% (NEC rec 3%)

Phase

Advanced options — derating, breaker & conduit

Conductors in raceway

Ambient temperature

Continuous load (3+ hrs)Breaker ≥ 125% per NEC 210.19

10 AWGcopper

Ampacity OKVD 2.33%VD GOVERNS

Long run (75 ft) requires upsizing from 14 AWG to 10 AWG for voltage drop.

Ampacity30Aat 60°C

Voltage drop2.33%2.8V

At load117.2Vreceiving end

Circular mils10,3805.26 mm²

Min for ampacity

14 AWG

4,110 CM

Min for ≤3% VDgoverns

10 AWG

10,380 CM

Breaker size15ANEC 240.6(A)

Wire cost est.~$108150 ft THHN

Conduit size3/4" EMT3 conductors

Ground (EGC)14 AWG CuNEC 250.122

Power loss40.5W~$49.67/yr

Copper vs Aluminum (for 15A at 75 ft on 120V)

Copper

14 AWG

VD: 5.9% · 2.08 mm²

Aluminum

12 AWG

VD: 6.1% · 3.31 mm²

Verify this result

This answer is computed by WireGaugeEngine.sizeWire (v1.0.0), current for the NEC 2023 edition. The same inputs always produce the same figure and the same fingerprint below, so you can reproduce and cite it.

Standards

NEC 2023 — Table 310.16 (allowable ampacities)
ASTM B258-18 — AWG diameters and cross-sectional areas

Assumptions

Conductor materialcopper
Temperature rating60°C column
Phasesingle
Current-carrying conductors3
Ambient temperature30°C
Max voltage drop3%

Inputs & outputs

in · amps15
in · voltage120
in · distanceFt75
in · phasesingle
in · materialcopper
in · tempRating60
in · conductorCount3
in · ambientTempC30
in · maxVdropPct3
out · recommendedWire10 AWG
out · ampacity30
out · voltageDropPct2.33
out · breakerAmps15
out · groundWire14 AWG Cu
out · conduit3/4"
out · vdropDriventrue

Computation fingerprint (SHA-256)

9a89e88fba901ebf7f894aae615b8c50488adf4c52fa76a2b18d7b81a4c3d025

Wire Gauge for 15A at 75 ft on 120V — NEC Calculator

4(D)(3) capping 14 AWG at a 15 A breaker. At 75 ft, ampacity is not the governing constraint. 19(A) requires roughly 8,960 circular mils at this load and length, which pushes past 14 AWG (4,110 CM) and past 12 AWG (6,530 CM) to 10 AWG (10,380 CM). 7 %).

What wire gauge for 15A at 75 ft on 120V?

For a 15A circuit at 75 ft on 120V, use 10 AWG copper conductor.

At 75 ft, voltage drop is the governing constraint — 14 AWG meets ampacity alone, but the long run requires 10 AWG to stay within 3% voltage drop.

Recommended wire gauge

Voltage drop governs

10 AWG copper

30A ampacity | 2.33% VD | 117.2V at load

Minimum wire by constraint

Required CMs: 8,063 CM. Formula: CM = (2 × K × I × L) / (V × 3%)

Constraint	Min Wire	CM	Detail
Ampacity only	14 AWG	4,110	15A at 60°C
Voltage drop ≤ 3%	10 AWG	10,380	8,063 CM required
Recommended	10 AWG	10,380	VD governs

Wire size by run distance

Distance sensitivity for 15A on 120V at 3% voltage-drop target.

One-way distance	Recommended gauge	Voltage drop	Receiving voltage	Governing constraint
25 ft	14 AWG	1.96%	117.6V	Ampacity
50 ft	12 AWG	2.47%	117V	Voltage drop
75 ft	10 AWG	2.33%	117.2V	Voltage drop
100 ft	8 AWG	1.95%	117.7V	Voltage drop
150 ft	8 AWG	2.93%	116.5V	Voltage drop
200 ft	6 AWG	2.46%	117.1V	Voltage drop

Copper vs aluminum for this run

Material comparison uses the same amps, voltage, distance, temperature rating, and voltage-drop limit.

Material	Recommended gauge	Ampacity	Voltage drop	Resistance	Governing constraint
copper	10 AWG	30A	2.33%	1.24 ohm/kft	Voltage drop
aluminum	8 AWG	30A	2.41%	1.26 ohm/kft	Voltage drop

Protection, conduit, cost, and loss planning

These planning values are generated from the recommended conductor and are not a substitute for field code review.

Planning item	Computed value	Why it matters
Standard breaker	15A	NEC 240.6(A): use 15A breaker (next standard size ≥ 15A)
Copper EGC	14 AWG Cu	NEC Table 250.122: 15A OCPD → EGC ≥ 14 AWG Cu (or 12 AWG Al)
Aluminum EGC	12 AWG Al	Use only where aluminum grounding conductors are permitted and listed.
EMT conduit estimate	3/4"	3 modeled conductors.
Wire cost estimate	$108	Approx. 2024 retail THHN pricing. 150 ft total (75 ft × 2 conductors).
Power loss	40.5W	354.8 kWh/year at full-duty planning.

Sizing assumptions

Sizing uses copper conductor data, 60C ampacity, single-phase voltage drop, 3% maximum voltage drop, not more than 3 current-carrying conductors, and 30C ambient.

The recommended wire is the larger of the ampacity minimum and the voltage-drop minimum. Long runs can require upsizing even when ampacity alone passes.

Breaker sizing, equipment grounding conductor sizing, conduit estimate, power loss, and cost are computed from the recommended conductor for planning context.

Wire sizing FAQ

Why did the calculator recommend 10 AWG?
10 AWG is needed because voltage drop governs this 75 ft run even though 14 AWG meets ampacity alone.

Does voltage or amperage matter more?
Both matter. Amperage drives ampacity and heat, while voltage and distance drive the voltage-drop percentage seen at the load.

Can aluminum be used instead of copper?
Aluminum may be valid only with AL-rated equipment and code-approved terminations. The material comparison table shows how the recommendation changes when material changes.

What should be checked before installation?
Confirm breaker size, terminal temperature, insulation type, conductor count, raceway fill, ambient conditions, and local code before treating the planning result as final.

Common mistakes with wire size for 15 A at 120 V over 75 ft

Sizing by ampacity alone and pulling 14 AWG. It is code-legal — the 3 % figure is advisory — but at full load the far end of this run sits near 113 V. Motors, compressors, and anything with a heating element noticeably underperform at that voltage, and the symptom (dimming when a load kicks on) is routinely misdiagnosed as a panel problem.

Measuring the run on the floor plan. 75 ft here means one-way cable-path length.

wire size for 15 A at 120 V over 75 ft — frequently asked questions

Is 14 AWG illegal at 75 ft?
No. Ampacity-wise, 14 AWG copper handles 15 A at any residential length, and no NEC article sets a hard distance limit for branch circuits. The 3 % voltage-drop figure is an Informational Note — advisory. This page recommends 10 AWG because at 15 A and 75 ft that is what keeps delivered voltage near nominal, not because smaller wire violates code.

Why does the answer jump from 14 AWG to 10 AWG, skipping 12?
The required conductor size for 3 % drop at 15 A over 75 ft works out to about 8,960 circular mils. 12 AWG has 6,530 CM and would land at roughly 3.7 % — closer, but still over the target — so the calculation moves to the next standard size, 10 AWG at 10,380 CM, which brings the drop down to about 2.3 %.

Does the 125 % continuous-load rule change this circuit?
If the load runs 3 hours or more continuously, NEC 210.19(A) sizes conductor and breaker at 125 % of it: 15 A continuous would demand an 18.75 A rating — beyond both 14 AWG (capped at 15 A by 240.4(D)(3)) and a 15 A breaker. In that case this stops being a 15 A circuit design; the load belongs on a 20 A circuit with 12 AWG minimum, and at 75 ft the drop target still points to 10 AWG.

Sources & Standards

National Fire Protection Association. "NFPA 70: National Electrical Code," Table 310.16, 2023 Edition.Allowable ampacities of insulated copper and aluminum conductors (60°C / 75°C / 90°C columns) used in wire sizing
ASTM International. "Standard Specification for Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires Used as Electrical Conductors." ASTM B258-18, 2018.AWG conductor diameters and cross-sectional areas used in gauge conversions

Constraint

Min Wire

Detail

Ampacity only

14 AWG

4,110

15A at 60°C

Voltage drop ≤ 3%

10 AWG

10,380

8,063 CM required

Recommended

10 AWG

10,380

VD governs

One-way distance

Recommended gauge

Voltage drop

Receiving voltage

Governing constraint

25 ft

14 AWG

1.96%

117.6V

Ampacity

50 ft

12 AWG

2.47%

117V

Voltage drop

75 ft

10 AWG

2.33%

117.2V

Voltage drop

100 ft

8 AWG

1.95%

117.7V

Voltage drop

150 ft

8 AWG

2.93%

116.5V

Voltage drop

200 ft

6 AWG

2.46%

117.1V

Voltage drop

Material

Recommended gauge

Ampacity

Voltage drop

Resistance

Governing constraint

copper

10 AWG

30A

2.33%

1.24 ohm/kft

Voltage drop

aluminum

8 AWG

30A

2.41%

1.26 ohm/kft

Voltage drop

Planning item

Computed value

Why it matters

Standard breaker

15A

NEC 240.6(A): use 15A breaker (next standard size ≥ 15A)

Copper EGC

14 AWG Cu

NEC Table 250.122: 15A OCPD → EGC ≥ 14 AWG Cu (or 12 AWG Al)

Aluminum EGC

12 AWG Al

Use only where aluminum grounding conductors are permitted and listed.

EMT conduit estimate

3/4"

3 modeled conductors.

Wire cost estimate

$108

Approx. 2024 retail THHN pricing. 150 ft total (75 ft × 2 conductors).

Power loss

40.5W

354.8 kWh/year at full-duty planning.

Wire sizing FAQ

Why did the calculator recommend 10 AWG?
10 AWG is needed because voltage drop governs this 75 ft run even though 14 AWG meets ampacity alone.

Does voltage or amperage matter more?
Both matter. Amperage drives ampacity and heat, while voltage and distance drive the voltage-drop percentage seen at the load.

wire size for 15 A at 120 V over 75 ft — frequently asked questions