1. What is a NEC Voltage Drop Calculator?

Definition: This calculator estimates the voltage drop in an electrical circuit based on conductor properties and current flow, following NEC guidelines.

Purpose: It helps electricians and engineers ensure proper voltage levels at load points by accounting for conductor resistance.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( VD \) — Voltage drop (volts)
• \( \rho \) — Resistivity of conductor material (Ω·m)
• \( L \) — Length of conductor (meters, one-way)
• \( I \) — Current flow (amps)
• \( A \) — Cross-sectional area of conductor (m²)

Explanation: The formula accounts for the round-trip path of current (hence the 2) through the conductor's resistance.

3. Importance of Voltage Drop Calculation

Details: Proper voltage drop calculation ensures electrical equipment receives adequate voltage for proper operation and prevents energy waste.

4. Using the Calculator

Tips: Enter the conductor resistivity (default 1.72×10⁻⁸ Ω·m for copper), length, current, and cross-sectional area. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why is the resistivity value multiplied by 2?
A: The factor of 2 accounts for the round-trip path of current (both the "hot" and "neutral" conductors in AC systems).

Q2: What's a typical resistivity value for copper?
A: Copper has a resistivity of about 1.72×10⁻⁸ Ω·m at 20°C. For aluminum, use 2.65×10⁻⁸ Ω·m.

Q3: How does conductor length affect voltage drop?
A: Voltage drop increases linearly with conductor length - double the length means double the voltage drop.

Q4: What's the maximum acceptable voltage drop?
A: NEC recommends no more than 3% voltage drop for branch circuits and 5% for feeder and branch circuits combined.

Q5: How can I reduce voltage drop?
A: Use larger conductors, shorter runs, higher voltage systems, or reduce the current load.