Why does low voltage (12V DC) drop so much faster than 120V AC?

Voltage drop is absolute: losing 2 Volts on a 120V circuit is only a 1.6% drop (harmless). But losing 2 Volts on a 12V circuit is a massive 16.7% drop, which will cause electronics to shut down. Low voltage requires much thicker wire.

What is the NEC rule on allowable voltage drop?

The National Electrical Code (NEC Article 210.19(A)) recommends that voltage drop on branch circuits should not exceed 3% for reasonable efficiency, and total drop (feeder + branch) should not exceed 5%.

What happens when voltage drops too much?

Excessive voltage drop causes electric motors to overheat and burn out, LED lights to flicker or dim, computer power supplies to reboot, and wires to generate dangerous resistive heat inside walls.

Why is one-way distance doubled in the calculation?

Electricity flows in a complete closed loop: out along the hot conductor and back along the neutral (or negative) return wire. The total current path length is twice the one-way physical distance.

Should I use Copper or Aluminum wire?

Copper has lower electrical resistance and is required for residential branch wiring (15A/20A). Aluminum is cheaper and lighter, making it popular for heavy service entrance cables (100A–200A), but requires one size thicker gauge.

DIY & Trades100% Client-Side Local Execution•Updated 2026

Wire Gauge (AWG) & Voltage Drop Calculator (Ohm's Law)

Name: Wire Gauge (AWG) & Voltage Drop Calculator (Ohm's Law)
Author: AnshuTechy

Calculate circuit resistance, terminal voltage drop percentage, and verify National Electrical Code (NEC) 3% safety compliance across AC and DC runs.Documentation & FAQs ↓

Wire Gauge (AWG) & Voltage Drop Calculator (Ohm's Law) — Interactive Console

Runs locally in your browser • Instant output

Circuit Voltage (V)

Current Load (Amperes)

One-Way Distance (Feet)

Wire Gauge (AWG)

Conductor Material

Total Circuit Resistance0.307 Ω

Voltage Drop Percentage3.84%⚠ Exceeds NEC 3.0% limit! Upgrade wire gauge.

Voltage at Load End115.4 VDrop: 4.60 Volts lost

Cable Heat Power Loss69.1 WWasted power over 2× run

Step-by-Step Instructions

4 Steps to Completion

1Phase 1

Select your circuit voltage (12V DC, 24V DC, 120V AC, or 240V AC).

2Phase 2

Enter the circuit current load in Amperes (Amps).

3Phase 3

Enter the one-way wire distance from electrical panel to load (in feet or meters).

4Phase 4

Select wire gauge (AWG) and conductor material (Copper vs Aluminum) to see drop percentage.

Practical Use Cases & Real-World Scenarios

Solar & RV Battery Wiring

Size low-voltage 12V and 24V DC inverter cables to prevent excessive power loss over distance.

Long Outdoor Extension Runs

Check if running a 100-foot extension cord will starve power tools or air compressors of voltage.

EV Charger & Subpanel Sizing

Ensure 240V 50A electric vehicle charging circuits stay well below the 3% voltage drop threshold.

Wire Gauge (AWG) & Voltage Drop Calculator (Ohm's Law)

Step-by-Step Instructions

Practical Use Cases & Real-World Scenarios

AC and DC Circuit Flexibility

Standard AWG Conductor Table

NEC 3% Safety Compliance Badge

Energy Loss & Heat Dissipation

Frequently Asked Questions

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