Cable • Cable Length • Voltage Drop

Calculate Maximum Cable Length

Calculate how long a cable should be at most for a given voltage drop.

Cable • Cable Length • Voltage Drop

Calculate how long a cable should be at most for a given voltage drop.

Calculation Values

Current in Amps

Conductor Cross-Section in mm²

Voltage in V

Permissible Voltage Drop in %

Power Factor cos φ

Conductivity κ

copper 58, aluminum 37

System type: 1 = single-phase, 3 = three-phase

Note: This calculator provides a technical estimate for guidance only. For electrical installations, standards, protective measures, installation method, ambient temperature, grouping, protective devices and manufacturer specifications must also be checked.

Formula Used

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

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

The calculated length is the one-way cable length in meters.

Frequently Asked Questions

What does one-way cable length mean?

The one-way cable length is the distance from the feed point to the load, not the combined outgoing and return path.

Can I use the calculated length directly?

It serves as a guideline. Current-carrying capacity, protective devices, installation method and applicable standards must also be checked.

Why is cos φ relevant?

The power factor affects the effective voltage drop calculation for single- and three-phase systems.

Practical guidance

Derive maximum cable length from voltage drop

The result is the one-way distance at which the selected conductor reaches the chosen voltage-drop target.

Input values explained

Current: Enter the expected operating current, not a fuse rating. Motors and electronic power supplies may draw much higher starting or peak currents.
Conductor cross-section: Enter the cross-section of one loaded conductor in mm², not the sum of all cores in a cable.
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.
Permitted voltage drop: This percentage limits the calculated voltage loss. It is a design assumption and must suit the circuit and applicable requirements.
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.
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.
Electrical system: Choose single-phase AC for a 230 V circuit and three-phase for a balanced three-phase system. This selection changes the formula factor.

Example: 2.5 mm² at 16 A

For 230 V single-phase, copper, cos φ 0.90 and 3%, calculate the one-way limit.

L = (6.9 V × 58 × 2.5) ÷ (2 × 16 × 0.90) ≈ 34.74 m

The one-way distance is about 34.7 m. The return conductor is already included by factor 2.

Length alone is not approval

A shorter cable can still fail ampacity or fault-disconnection checks; a larger conductor can extend the permitted run.

Calculation limits

Upstream voltage drop is not included.
Loop impedance, short-circuit protection and minimum sizes remain unverified.