Wire Cross-Section • Current in Amps

Calculate Wire Cross-Section with Current in Amps

Choose system type and material, enter current, voltage, cos φ and cable length.

Wire Cross-Section • Current in Amps

Choose system type and material, enter current, voltage, cos φ and cable length.

Calculation Values

Note: This calculation is a technically sound simplification typical of online calculators. For practical sizing, standards, installation method, temperature, grouping, protective devices, cable type and manufacturer specifications must also be checked.

Formula Used

Depending on your selection, the calculator uses the correct single-phase or three-phase voltage drop formula with cos φ.

Three-phase: A = (√3 × L × I × cos φ) / (κ × ΔU)

Single-phase: A = (2 × L × I × cos φ) / (κ × ΔU)

FAQ

Frequently Asked Questions about Calculate Wire Cross-Section with Current in Amps

Briefly explained: formula, use case and key limits of the calculation.

When do I use the amp input? +

The amp input is suitable when the current is already known, for example from a nameplate or a technical specification.

What is the difference between single-phase and three-phase? +

Single-phase accounts for the outgoing and return conductor. Three-phase uses the factor √3.

Why is the voltage drop needed? +

The voltage drop limits the permissible voltage loss on the cable and directly affects the required cross-section.

Why is the result rounded up to standard cross-sections? +

In practice, standardized conductor cross-sections are used. A calculated intermediate value is therefore rounded up to the next common cross-section.

Practical guidance

Estimate cable size from a known operating current

Use this version when the load current is already known. It finds a cross-section from voltage drop only.

Input values explained

Current type: The current type determines whether the calculation uses factor 2 for outgoing and return conductors or √3 for balanced three-phase power.
Conductor material: Copper and aluminium have different conductivity. Aluminium generally requires a larger cross-section under otherwise equal conditions.
Current: Enter the expected operating current, not a fuse rating. Motors and electronic power supplies may draw much higher starting or peak currents.
Cable length: Enter the one-way distance from supply point to load. The required return path is already represented by the selected formula.
Voltage: Match the voltage to the selected electrical system. Single-phase calculations use line-to-neutral voltage, while three-phase calculations use voltage between two line conductors.
Power factor cos φ: cos φ is the ratio of active to apparent power. It is close to 1 for resistive heating loads; use the data-sheet value for motors and transformers.
Permitted voltage drop: This percentage limits the calculated voltage loss. It is a design assumption and must suit the circuit and applicable requirements.
Conductivity κ: κ is the calculation value for the conductor material. Common approximations are 58 for copper and 37 for aluminium; heating increases actual resistance.

Example: 16 A over 25 metres

Assume balanced 400 V three-phase, copper, 16 A, 25 m, cos φ 0.90 and a 3% voltage-drop limit.

A = (√3 × 25 m × 16 A × 0.90) ÷ (58 × 12 V) ≈ 0.90 mm²

Voltage drop alone points to the next standard size, 1.5 mm². This does not prove that 1.5 mm² can carry 16 A in the intended installation.

Not a complete cable design

Treat the result as a voltage-drop minimum. The final size must satisfy ampacity, fault protection and disconnection requirements as well.

Calculation limits

Installation method, ambient temperature, grouping and loaded-core count are missing.
Cable type, minimum sizes and protective-device requirements must be checked separately.