How to Calculate Voltage Drop for Cable Runs
When this applies
Use this guide for preliminary electrical checks where transparent resistance assumptions are required before detailed code-based design.
Tool to use
Ohm’s-law voltage drop from total resistance or uniform conductor geometry (DC-equivalent).
Open Voltage Drop Calculator →Steps
- 1Decide whether you already know loop resistance or need to build it from geometry.
- 2If geometric, set material, length, area, temperature, and series-conductor count.
- 3Compute loop resistance consistently, then apply V = I*R.
- 4Compare drop against your project voltage budget criteria.
- 5Escalate to full impedance and code checks for final design.
Examples
- Checking a DC feeder run against a low-voltage instrumentation budget.
- Comparing copper vs aluminum options for the same cable route length.
What to avoid
- Forgetting return path resistance in loop estimates.
- Mixing cross-section units (mm^2 vs m^2).
- Presenting resistive-only drop as a full AC power-quality study.
Related tools
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FAQ
Is this an ampacity or code-compliance tool?
No. It is a transparent voltage-drop estimator, not a regulatory sizing engine.
Can I apply this directly to long AC feeders with high reactance?
Only as a first pass; use full impedance methods for final AC studies.