AALASOS-ENGR
FreeAvailable now — free

Voltage Drop

Estimate circuit voltage drop.

Electrical Design SuiteStep 4 of 6

Project & Input Data

Phase
no.
no.

Your project criterion: enter the value from your governing code, specification or approved supplier data. No standard value is assumed.

no.

Your project criterion: enter the value from your governing code, specification or approved supplier data. No standard value is assumed.

%

Your project criterion: enter the value from your governing code, specification or approved supplier data. No standard value is assumed.

Engineering Assumptions

Direct calculation — Voltage-drop equation

  • Conductor resistance is taken from the manufacturer or code data used by the project.
  • All percentages and inputs are user-defined; the calculation is purely arithmetic and assumes no particular code or specification.

Formula Summary

  • ΔV(V) = k × I × L × R ÷ 1000, k=2 single-phase, k=√3 three-phase
  • ΔV% = ΔV ÷ V_system × 100

Results

Enter your data and press Calculate to see the results.

Engineering Insight

A negative remaining allowance means the limit is exceeded and calls for a larger cable section or a shorter route.

Recommended Action

Compare the calculated drop against your project's allowed limit before finalising the chosen section.

Next step

This calculator is fully usable as it is. Professional adds saved projects, calculation history and PDF/Excel reports; Premium adds the integrated workflows and the BOQ generator.

Workflow: Electrical Design SuiteAll tools in this disciplineCompare levels and pricing

Voltage drop decides whether a cable run is acceptable long before ampacity does on long circuits. Enter the design current, the one-way run length and the cable resistance per kilometre from your manufacturer data, and compare the result with the percentage limit you have adopted for the installation.

Method and assumptions

Voltage-drop equation

  • ΔV(V) = k × I × L × R ÷ 1000, k=2 single-phase, k=√3 three-phase
  • ΔV% = ΔV ÷ V_system × 100
  • Conductor resistance is taken from the manufacturer or code data used by the project.
  • All percentages and inputs are user-defined; the calculation is purely arithmetic and assumes no particular code or specification.

Worked example

A 63 A three-phase feeder, 55 m long, on a cable of 0.727 Ω/km, checked against a 3% limit on 400 V.

Worked example results
ResultValue
Voltage drop4.36 V
Voltage drop percent1.09 %
Remaining allowance1.91 %

These figures are produced by the same calculator engine used on this page.

Frequently asked questions

Where do I get resistance per km?
From the cable manufacturer's data for the conductor material, size and operating temperature. The tool has no cable table and assumes no value.
Is reactance considered?
No. The equation is resistive only (ΔV = k·I·L·R ÷ 1000). For large cables where reactance matters, use an impedance-based method.
Which percentage limit applies?
The allowable percentage is a project/regulatory criterion you enter. ALASOS does not claim compliance with any electrical code.

Related calculators

Next step

Free calculators are open to everyone. Project saving and PDF/Excel reports come with Professional, and integrated workflows with Premium.