NEC Voltage Drop Calculator

Calculate voltage drop per NEC 210.19(A) and 215.2(A) recommendations. Free, no account required.

Circuit Details

Conductor Material

Wire Size

System Voltage (V)

Load Current (amps)

One-way Distance (feet)

Phase

Circuit Type

Branch circuit (3% max recommended)Feeder + branch (5% max recommended)

6.60% voltage drop

Exceeds NEC recommended 3% maximum. Consider upsizing the conductor.

Conductor resistance1.9800 Ω/1,000 ft (copper, 75°C)

Formula: Vd = 2 × L × R × I / 10002 × 100 × 1.9800 × 20

Voltage drop7.92 V

Percent drop6.60%

Voltage at load112.1 V

0%3% recommended max5%

NEC Voltage Drop Recommendations

NEC 210.19(A) Informational Note No. 4: Branch circuits should not exceed 3% voltage drop. The total voltage drop for feeder and branch circuit combined should not exceed 5%.

NEC 215.2(A) Informational Note No. 2: Feeders should be sized so that the voltage drop is not more than 3% at the farthest outlet of power, heating, and lighting loads.

Note: These are recommendations (informational notes), not mandatory code requirements. However, they are frequently tested on electrician licensing exams and considered best practice.

Common Voltage Drop Scenarios

Circuit	Wire	Max Distance (3%)
20A, 120V	12 AWG Cu	45 ft
20A, 240V	12 AWG Cu	90 ft
30A, 240V	10 AWG Cu	96 ft
40A, 240V	8 AWG Cu	115 ft
50A, 240V	6 AWG Cu	146 ft

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This calculator uses DC resistance values from NEC Chapter 9 Table 8 at 75°C. AC circuits may have slightly different effective impedance due to reactance. Always verify with your local AHJ and the current NEC edition adopted in your jurisdiction.