Formula Used
The calculator multiplies the reference cable ampacity by every enabled correction factor. Parallel cables increase the starting ampacity before factors apply. The result is the estimated allowable operating current.
Derated ampacity: Iderated = Ibase × Kinstallation × Ktemperature × Kgrouping × Ksoil × Kdepth × Kinsulation × Kharmonics × Kother.
Required base ampacity: Irequired base = Idesign ÷ combined correction factor. The recommended cable is the first reference size meeting that value. Always confirm the result using approved project data.
How to Use This Calculator
- Select the calculation mode and reference profile.
- Enter current directly or calculate it from power.
- Choose the conductor material, size, insulation, and parallel count.
- Select the installation method and environmental conditions.
- Enter cable grouping, burial, insulation, and harmonic details.
- Add voltage-drop and protective-device information.
- Review every applied factor before accepting the result.
Use manufacturer ampacity data whenever it is available. Replace reference factors with approved project values. A qualified designer should verify the final selection.
Example Data
| Example | Load | Cable | Installation | Key factors |
|---|---|---|---|---|
| Commercial feeder | 80 A, 400 V, three-phase | 35 mm² copper XLPE | Cable tray | 40°C, three grouped circuits |
| Underground pump | 55 kW, 415 V, three-phase | 70 mm² aluminum XLPE | Direct burial | 0.8 m depth, 3.0 K·m/W soil |
| Rooftop solar feeder | 120 A DC | 50 mm² copper XLPE | Rooftop tray | 55°C ambient, 0.85 solar factor |
Frequently Asked Questions
What is cable derating?
Cable derating reduces a conductor’s tabulated ampacity for actual installation conditions. Heat, grouping, insulation, and harmonics can reduce safe current capacity.
Is the built-in ampacity table an official code table?
No. It is a general engineering reference table for estimation. Replace it with approved manufacturer or locally adopted code data.
Why do grouped cables need derating?
Grouped cables heat each other and lose cooling surface. The grouping factor reduces allowable current to reflect that thermal interaction.
How does ambient temperature affect ampacity?
Higher ambient temperature leaves less thermal headroom. The temperature factor decreases as ambient temperature approaches the cable’s maximum conductor temperature.
Can I enter manufacturer factors?
Yes. Use custom base ampacity and manufacturer limitation factor fields. These values can replace generic assumptions with project-specific data.
Does the calculator check voltage drop?
Yes. It estimates voltage drop using conductor resistance, reactance, length, current, power factor, temperature, and parallel conductors.
How are parallel cables handled?
The calculator multiplies base ampacity by the parallel cable count. It also divides voltage-drop impedance across the parallel conductors.
Why are harmonics included?
Nonlinear loads can increase conductor and neutral heating. Harmonic derating helps flag installations needing detailed measurements and neutral review.
What does the limiting condition show?
It identifies the smallest applied factor. That condition has the greatest single influence on the calculated cable capacity.
Should breaker rating equal derated ampacity?
Not always. Protection coordination depends on load type, cable capacity, fault protection, starting current, and locally adopted requirements.
Can this result replace an electrical design review?
No. Final selection must follow local regulations, manufacturer data, fault calculations, installation drawings, and qualified professional approval.