What is a safe voltage drop?

Most electrical codes recommend keeping the drop below 3% for branch circuits to ensure equipment safety.

Voltage Drop – Electrical Wire Sizing Service | CalcTools

Calculate voltage loss over long wire distances. Essential service for safe electrical installs.

Electricity isn't perfectly efficient; as current travels through a wire, it meets resistance, causing power to be lost as heat. This 'Voltage Drop' can cause motors to overheat and lights to flicker, especially over long distances. Our Voltage Drop service helps you determine if your chosen wire gauge is sufficient for your load and distance, ensuring your installation is safe, efficient, and code-compliant.

Supply Voltage (V)

Current (A) (A)

Distance (ft) (ft)

Wire Gauge (AWG) (AWG)

Calculated Drop

4.76 V

Voltage drop: 4.76V (3.97%)

Supply Voltage120 V

Current (A)15 A

Distance (ft)100 ft

Wire Gauge (AWG)12 AWG

Warning: Drop exceeds 3% threshold.

How it Works

The tool uses the standard resistance per thousand feet for copper AWG conductors. It calculates the total circuit resistance (round trip) and applies Ohm's Law to find the specific voltage lost between the source and the load.

Calculation Formula

V_drop = I × R_total

Calculation Examples

1. **Long Run**: 120V, 15A, 100ft on 14 AWG = **~7.5V loss (6.3%)**.

Why use this tool in your daily life?

Professional-grade electrical safety. This service is a vital check for anyone powering detached buildings or outdoor equipment, helping you choose the right materials to prevent fire hazards and equipment damage.