Voltage Drop Calculator - calculatorsee.com


Voltage Drop Calculator

Calculate voltage drop, percentage loss, and end-of-run voltage across copper and aluminum conductors according to the National Electrical Code (NEC).

Calculator Inputs

Nominal voltage.
Wire metal.
American Wire Gauge.
ft
Distance from panel to load.
A
Operating current.

Calculated Results

Calculated Voltage Drop
4.58 Volts (3.82%)
Voltage at End of Run 115.42 Volts
NEC Recommended Limit 3.00% Max (Fail: Upsize to 10 AWG)
Total Conductor Resistance 0.305 Ohms (Ω)
Values calculate live as you adjust inputs.

About Voltage Drop Calculator

Calculates resistive electrical potential loss across long wire runs to prevent motor overheating and ensure National Electrical Code (NEC 3% branch circuit) compliance.

What is Voltage Drop Calculator?

Calculates resistive electrical potential loss across long wire runs to prevent motor overheating and ensure National Electrical Code (NEC 3% branch circuit) compliance.

How to Use This Calculator

  1. Select nominal voltage.
  2. Choose copper or aluminum conductor.
  3. Select wire gauge (AWG).
  4. Enter distance in feet and current in amps.
  5. Review voltage drop and NEC compliance.

The Mathematical Formula & Variables

Voltage Drop = 2 * K * Current * Distance / Circular Mils (where K=12.9 for copper)

Step-by-Step Worked Example

Scenario: 120V single-phase circuit running 15A over 100 ft of 12 AWG copper wire (6,530 CMil).

  1. V_drop = (2 * 12.9 * 15 * 100) / 6,530 = 38,700 / 6,530 = 5.93 Volts.
  2. Percentage drop = 5.93 / 120 = 4.94% (exceeds recommended 3% max; upsize to 10 AWG).

Result: Voltage Drop: 4.58V to 5.93V

Frequently Asked Questions

What is the NEC maximum recommended voltage drop?

The National Electrical Code recommends a maximum voltage drop of 3% for branch circuits, and 5% total combining branch circuits and feeders.