What is the maximum allowed voltage drop?

Standard electrical codes (like NEC) recommend a maximum voltage drop of 3% for branch circuits (from breaker panel to outlets) and 5% for the entire system (from service entrance to outlets).

How can I reduce voltage drop in a long run?

You can reduce voltage drop by using a larger wire size (higher cross-sectional area), reducing the load current, shortening the cable run, or using copper instead of aluminum.

How does three-phase voltage drop calculation differ?

Three-phase circuits share current across three conductors, reducing the line current return resistance. The three-phase voltage drop formula is multiplied by the square root of 3 (√3 ≈ 1.732) instead of 2 (for single-phase loop).

Voltage Drop Calculator

Calculate voltage drop and percentage drop for single-phase and three-phase electrical circuits. Input the supply voltage, material, conductor size, load current, and run distance.

Electrical Specifications

Source Voltage (V)

System Phase

Conductor Material

Current Load (Amps)

Conductor Size (AWG / Metric)

One-Way Distance

Voltage Drop Results

Voltage Drop (V)

--%

Load Voltage

voltage at device

Conductor Area: -- mm²

Conductor Resistance: -- Ω/km

Voltage Drop Calculations & NEC Guidelines

Voltage drop is computed using standard electrical cable resistivity (at 75°C):

Single Phase (1φ): V_drop = [2 × I × L × ρ] ÷ A

Three Phase (3φ): V_drop = [√3 × I × L × ρ] ÷ A

• I: Current load in Amperes.

• L: Conductor length in meters.

• A: Conductor cross-sectional area in square meters (m²).

• ρ (Resistivity constant): Copper = 2.12 × 10⁻⁸ Ω·m, Aluminum = 3.46 × 10⁻⁸ Ω·m (accounting for standard operating temperatures).

• NEC recommendation: The US National Electrical Code (NEC) recommends maintaining a voltage drop of **3% or less** on branch circuits, and **5% or less** total drop across both feeder and branch circuits for optimal equipment lifetime and efficiency.

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How to use Voltage Drop Calculator

Select the circuit phase (Single Phase 120V/240V or Three Phase 208V/480V) and conductor material (Copper or Aluminum).
Enter the cable size (AWG or Metric mm²), load current (Amps), and the distance (feet or meters).
Click Calculate to see the voltage drop in volts, percentage drop, and final voltage at the load.

What is Voltage Drop Calculator?

Voltage drop is the decrease in electrical potential along the path of a current flowing in an electrical circuit. This is caused by the electrical resistance of the cable conductors. If the voltage drop is too high, equipment may fail to operate, run inefficiently, or overheat.

The National Electrical Code (NEC) recommends keeping voltage drop under 3% for branch circuits and 5% overall. This calculator helps electrical engineers and electricians size cables appropriately to meet these limits.

FAQ

What is the maximum allowed voltage drop?: Standard electrical codes (like NEC) recommend a maximum voltage drop of 3% for branch circuits (from breaker panel to outlets) and 5% for the entire system (from service entrance to outlets).
How can I reduce voltage drop in a long run?: You can reduce voltage drop by using a larger wire size (higher cross-sectional area), reducing the load current, shortening the cable run, or using copper instead of aluminum.
How does three-phase voltage drop calculation differ?: Three-phase circuits share current across three conductors, reducing the line current return resistance. The three-phase voltage drop formula is multiplied by the square root of 3 (√3 ≈ 1.732) instead of 2 (for single-phase loop).

Voltage Drop Calculator

Electrical Specifications

Voltage Drop Results

Voltage Drop Calculations & NEC Guidelines

How to use Voltage Drop Calculator

What is Voltage Drop Calculator?

FAQ

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