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Cable sizing

Cable Size and Voltage Drop Calculator

Enter current, route length, voltage, and installation method to find a preliminary cable size that satisfies corrected ampacity and voltage-drop limits.Start calculating
A / mm²Current and protectionPDFStandalone reportSBC 401Method reference

Calculator

Enter your data and see the result immediately

Calculate copper or aluminium cable size from current, length, phase, installation method, temperature, grouping, and voltage drop using an IEC-based method.

Calculator

Cable size

Current, voltage drop, and derating
Calculation inputsResults update instantly
Supply system
Study resultTAYAR TK
Tayar TK
Preliminary engineering studyCable size
Date: 2026-07-23Report reference: KWH-CABLE-2026

Preliminary cable size

A preliminary selection satisfying corrected ampacity and the entered voltage-drop limit.

Suggested conductor10mm²
Corrected ampacity40.02A
Voltage drop1.81%
Voltage drop4.16V
Ambient factor0.87
Grouping factor1
Table method / loaded conductorsA1 / 2
Reference ampacity46 A
Calculation method

The first 70°C PVC size satisfying Ib ≤ Iz after temperature, grouping, soil, and voltage-drop checks is selected, using two loaded conductors for single phase and three for three phase.

Engineering notes
  • Typical voltage-drop limits are 3% for lighting and 5% for other uses from a public LV supply.
  • Method A1 is used conservatively for conduit, E for tray, and D for an underground duct. Direct burial, cable spacing, moisture, and harmonics require project-specific factors.
  • Verify insulation, manufacturer data, terminations, and short-circuit withstand; this table does not replace detailed IEC/SBC design.
Safety approval

Do not use this estimate for installation before checking nameplate data, site conditions, short-circuit protection, and earthing.

kwh.tirtk.com.satirtk.com.saC.R 1009172880

This is a planning and comparison estimate. Final protection and conductor selection requires review by a licensed engineer or electrician, site-condition checks, manufacturer instructions, and the applicable code.

Calculation guide

Why current alone cannot size a cable

A selected size must satisfy corrected current-carrying capacity and the chosen voltage-drop limit. A cable can pass the thermal check yet fail because the route is long.

The calculator separates copper and aluminium tables, two loaded conductors for single phase, three for three phase, installation reference methods, and starting correction factors. Final design still depends on the actual cable, insulation, protection, and site.

Cable sizing steps

  1. Determine the actual design current.
  2. Select phase, voltage, and power factor.
  3. Choose conductor material and installation.
  4. Enter temperature, grouped circuits, and route length.
  5. Review corrected ampacity and voltage drop together.

Inputs that must not be ignored

  • Air or ground temperature.
  • Circuit grouping and arrangement.
  • Route length and power factor.
  • Breaker coordination and short-circuit conditions.
Method references
SBC 401IEC 60364-5-52

Frequently asked questions

Cable sizing frequently asked questions

How do I size a cable by amps?

Start with design current, apply the installation ampacity table and correction factors, then check voltage drop for the route length.

Is aluminium equivalent to copper?

No. Resistance and ampacity differ, so the calculator uses separate tabulated data rather than one blanket multiplier.

When does length require a larger cable?

When voltage drop exceeds the selected limit even though thermal ampacity remains adequate.

Is the result ready for construction?

It is preliminary. Review the actual cable, fault current, protection, manufacturer data, and applicable local code.