Cable Ampacity Calculator

Estimate the current-carrying capacity (ampacity) of a copper conductor based on cross-section area and installation method.

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mm²
A/mm²

3-5 for enclosed, 5-8 for open air

For temperature, grouping, etc.

V

Derated Ampacity

24.0 A

Base Ampacity30.0 A
Max Power at This Ampacity5,520 W
Max Power5.52 kW

Derated Ampacity vs Conductor Cross Section

View formula & how it works →

Cable Ampacity Estimation

Ampacity is the maximum continuous current a conductor can carry without exceeding its temperature rating.

Formula

Ampacity = Cross Section x Current Density x Derating Factor

Current Density Guidelines

  • Open air: 5-8 A/mm^2
  • In conduit: 3-5 A/mm^2
  • Underground: 2-4 A/mm^2

    • Derating Factors

  • Ambient temperature above 30 C: 0.7-0.9
  • Multiple cables in conduit: 0.5-0.8
  • Direct burial: 0.7-0.85

    • Always verify with NEC/IEC tables for your specific installation.

    Example Calculation

    6 mm^2 copper cable, 5 A/mm^2, derating 0.8, at 230 V.

    1. 01Base ampacity: 6 x 5 = 30 A
    2. 02Derated: 30 x 0.8 = 24 A
    3. 03Max power: 24 x 230 = 5,520 W = 5.52 kW

    Frequently Asked Questions

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