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Voltage Drop Calculator

Calculate target wire sizing according to the National Electrical Code (NEC) 3% voltage drop guidelines.

Calculator Inputs

20 Amps
5A100A200A300A
Real-Time Results

Recommended Conductor Sizing

Calculation ReadyBased on your inputs, here is the recommended wire size to stay within a 3% voltage drop.

8 AWG Copper

NEC Table Ampacity:50A @ 75°C
Voltage Drop %:2.60%
Voltage at Load:116.9V
Disclaimer: The NEC 3% / 5% voltage drop figures are informational recommendations, not binding code text. However, local AHJs frequently adopt them as mandatory amendments. Always verify local code requirements and termination compatibility before installation.

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Frequently Asked Questions

What is the NEC voltage drop guideline?

The NEC recommends a maximum voltage drop of 3% for the farthest outlet of power, heating, or lighting, and a maximum of 5% for the combined feeder and branch circuit to ensure reasonable efficiency of operation.

Why does conductor material affect voltage drop?

Different materials have different resistance levels. Aluminum has higher resistance than copper, meaning it will experience a greater voltage drop over the same distance and load, requiring a larger wire size to compensate.