Cable Voltage Drop Calculator
Calculate voltage drop along a cable and check it against the permitted limit.
About Cable Voltage Drop Calculator
Voltage drop is proportional to current, length and resistance per metre. Single-phase circuits incur twice the drop of the one-way calculation because both conductors carry current, while three-phase uses the √3 factor instead. Long circuits are usually sized by voltage drop rather than current-carrying capacity, which is why the maximum-length figure is the practical design output.
Formula
Cable Voltage Drop
Single phase: ΔV = 2 I R L; three phase: ΔV = √3 I R L
- factor 2
- Single-phase current flows out and back through two conductors
- √3
- Three-phase balanced systems use the line-to-line relationship
Worked example
With the default values below, Cable Voltage Drop Calculator returns Voltage Drop of 9.930. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Design currentminimum 0 A
- 32 A
- Cable route lengthminimum 0 m
- 45 m
- Conductor cross-sectional areaminimum 0.01 mm2
- 6 mm2
- Nominal voltageminimum 1 V
- 230 V
- Phasesone of Single phase, Three phase
- Single phase
- Permitted voltage dropaccepts 0–100 %
- 5 %
Results
- Voltage Drop
- 9.930 V
- Voltage Drop
- 4.318%
- Permitted Drop
- 11.500 V
- Maximum Length Within the Limit
- 52.11 m
- Verdict
- Within the permitted voltage drop
Step by step
- 1Values used
- 2Cable Voltage Drop
- 3Voltage Drop= 9.930 V
- 4Voltage Drop= 4.318
- 5Permitted Drop= 11.500 V
- 6Maximum Length Within the Limit= 52.11 m
- 7Verdict= Within the permitted voltage drop
Assumptions and limits
- The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Cable Voltage Drop calculated?
Single phase: ΔV = 2 I R L; three phase: ΔV = √3 I R L Voltage drop is proportional to current, length and resistance per metre. Single-phase circuits incur twice the drop of the one-way calculation because both conductors carry current, while three-phase uses the √3 factor instead.
Why does Cable Voltage Drop matter?
Long circuits are usually sized by voltage drop rather than current-carrying capacity, which is why the maximum-length figure is the practical design output.
What values do I need to enter?
This calculator takes 6 inputs: Design current, Cable route length, Conductor cross-sectional area, Nominal voltage, Phases, Permitted voltage drop. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.