Cable • Power • Limit

Calculate Maximum Power Over a Cable

Roughly calculate how much power can be transmitted over a cable for a given voltage drop.

Cable • Power • Limit

Roughly calculate how much power can be transmitted over a cable for a given voltage drop.

Calculation Values

Conductor Cross-Section in mm²

Cable Length in m

Voltage in V

Permissible Voltage Drop in %

Power Factor cos φ

Conductivity κ

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

Imax = (ΔU × κ × A) / (factor × L × cos φ)

Single-phase: P = U × I × cos φ

Three-phase: P = √3 × U × I × cos φ

The factor is 2 for single-phase and √3 for three-phase.

Frequently Asked Questions

Is this the absolute maximum power?

No. The calculator looks at the voltage drop. Thermal current-carrying capacity and protective devices must be checked separately.

Why can three-phase transmit more power?

At the same voltage and current, balanced three-phase systems transmit power over three line conductors.

What happens with a smaller cos φ?

With a smaller power factor, the transmittable real power decreases.

Practical guidance

Limit transferable power by voltage drop

This reverse calculation finds the current and active power that exactly use the selected voltage-drop allowance.

Input values explained

Conductor cross-section: Enter the cross-section of one loaded conductor in mm², not the sum of all cores in a cable.
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.
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 over 25 m

For 230 V single-phase copper, cos φ 0.90 and 3%, calculate the voltage-drop-limited power.

I ≈ 22.23 A; P = 230 V × 22.23 A × 0.90 ≈ 4.60 kW

4.60 kW is not a thermal continuous-power rating. Ampacity may impose a lower limit.

Maximum means voltage drop only

The output must not be read as a cable or breaker recommendation.

Calculation limits

Ampacity, protection and fault-disconnection checks are absent.
Continuous duty, inrush and ambient conditions can be more restrictive.