Voltage drop scenario

Wire size for 30 amps at 150 feet

At 240 V single-phase, copper 8 AWG keeps a 30 amps load at about 2.87% drop over 150 feet — within the 3% design target used here. Adjust material, voltage, or phase below.

Phase

Voltage drop

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Enter a run to estimate voltage drop.

Estimated results
Voltage drop —
Percent drop —
Voltage at load —
Resistance used —
NEC 3% branch NEC 5% total
Estimate only — not a substitute for a licensed electrician. Based on NEC Ch.9 Table 8 DC resistance. Does not model ampacity, temperature derating, power factor, or continuous-load factors. Verify against the current NEC and your local code / AHJ.

30 amps at 150 feet: the short answer

At 240 V single-phase over 150 feet, a 30 amps load needs copper 8 AWG to stay near 2.87% — inside the 3% design target used for this comparison. For comparison, copper 12 AWG would drop about 17.37 V (7.24%) on the same run.

Before you pull wire

This is a voltage-drop estimate only. The conductor must also meet ampacity, temperature derating, and overcurrent rules — use the larger of the voltage-drop size and the ampacity size. Aluminum of the same size drops more, so it usually needs to go up one or two sizes. Always confirm with a licensed electrician and your local code (AHJ).

Sized for voltage drop using NEC Ch.9 Table 8 DC resistance. The 3% figure is a common design target from informational guidance, not a substitute for a code review.

Where this 30 amps, 150 feet scenario fits

A 30 A run at 150 feet resembles long rural and outbuilding projects: an RV connection, water-heating equipment, a compressor, or another dedicated 240 V load well away from the main panel. The long route makes voltage drop a design decision rather than a rounding error.

For a project like this, price more than one conductor size before trenching. The cost difference between gauges may be small compared with excavation and conduit, while changing the conductors later can be disruptive. Also confirm whether the actual equipment can tolerate the calculated load-end voltage.

Distance changes the conductor decision

Copper recommendations for a 30 amps load at 240 V single-phase, using the same 3% target
One-way distance Suggested copper size Calculated drop
50 ft 12 AWG 2.41%
100 ft 8 AWG 1.91%
150 ft 8 AWG 2.87%
200 ft 6 AWG 2.46%

Checks specific to this project

  • Use the equipment's maximum or nameplate current when it differs from the nominal circuit label.
  • Include vertical rises, sweeps, panel routing, and service loops in the one-way length.
  • Check starting current for motors or compressors; this steady-state calculation does not model startup sag.
  • Ask the AHJ whether the project is a branch circuit or feeder because other sizing rules differ.

FAQ

What wire size do I need for 30 amps at 150 feet?

For voltage drop at 240 V single-phase, copper 8 AWG keeps a 30 amps load near 2.87% over 150 feet, meeting the 3% design target used on this page. Ampacity, derating, equipment instructions, and local code may require a different size — confirm with a licensed electrician.

How much voltage drop does 30 amps over 150 feet have?

On a baseline copper 12 AWG at 240 V single-phase, 30 amps over 150 feet drops about 17.37 V (7.24%). Larger conductors drop less; the calculator shows the exact figure for any size.

Is this voltage-drop sizing the same as ampacity sizing?

No. This page sizes for voltage drop only, using NEC Chapter 9 Table 8 DC resistance. The conductor must also satisfy ampacity, temperature derating, and overcurrent-protection rules. Use the larger of the voltage-drop size and the ampacity size, and verify with your local code (AHJ).

Sources & verification

Source links and page assumptions reviewed .

Wire size for 20 amps at 100 feetWire size for 50 amps at 100 feetWire size for 50 amps at 200 feetWire size for 60 amps at 100 feetWire size for 100 amps at 100 feet All voltage drop scenarios How to calculate voltage drop

Estimate only, based on NEC Chapter 9 Table 8 DC resistance. Not a substitute for a licensed electrician or your local code (AHJ). Voltage-drop sizing does not replace ampacity, temperature derating, power factor, or continuous-load checks. Verify against the current NEC and local code before wiring. Based on NEC Ch.9 Table 8.