Voltage Drop Calculator

Next Steps

• Run your actual one-way conductor length and load current to establish baseline drop.
• Compare alternate conductor sizes/materials when drop exceeds your target threshold.
• Confirm final design with applicable code requirements and project constraints.

Worked Example

Example: A long feeder run may pass ampacity but fail voltage-drop goals. This calculator helps you catch that early so you can resize conductors or adjust routing before install.

Detailed Explanation

Voltage drop is influenced by current, conductor resistance, and circuit length. This estimator helps identify risk during planning and retrofit scoping, but final conductor selection still requires full code compliance checks, installation method constraints, and equipment tolerance review.

• Uses a built-in approximate conductor resistance table in ohms per 1000 feet for copper and aluminum.
• Converts resistance to ohms per foot, then applies one-way length and phase-specific voltage-drop equations.
• Calculates drop percent from system voltage and compares against the selected allowed threshold.

Common Mistakes

• Using total round-trip distance when the calculator expects one-way length (or vice versa).
• Checking ampacity only and ignoring voltage-drop performance at end-use equipment.
• Assuming all loads have the same voltage-drop tolerance.

When to Call a Professional

Use a licensed electrician or engineer when voltage-drop results affect critical equipment, safety compliance, or final permit submissions.

Conclusion

Voltage-drop checks improve reliability and equipment performance. Pair this estimate with full code review for final circuit decisions.

About This Calculator

About this calculator: Electricians, estimators, and inspectors.

Educational planning tool. Verify final electrical design with licensed professionals and applicable code requirements.

Written by BuildCalcTools Team - Practical electrical planning support.