01 — Tools
Calculate cable cross-section
The cross-section of a cable is determined by two conditions: it has to carry the current thermally, and the voltage drop over the length has to stay within the permitted range. On longer runs the voltage drop is almost always the governing factor – and that is what this tool calculates.
Result
- Next standard cross-sectionSeries to IEC 60228
- —mm²
- Calculated requirement
- —mm²
- Permissible voltage drop
- —V
- Actual voltage drop at standard cross-section
- —%
Please fill all fields with valid numbers.
A guide, not a design to standard. The applicable standards and case-by-case verification govern.
Worked example
The default case the calculator starts with, worked through once. Change the values above and it recalculates immediately.
Inputs
- System
- Three-phase (3~)
- Operating current
- 32 A
- One-way cable length
- 45 m
- Nominal voltage
- 400 V
- Permissible voltage drop
- 3 %
- Power factor cos φ
- 0.9
- Conductor material
- Copper (κ = 56 m/Ω·mm²)
Result
- Next standard cross-section
- 4 mm²
- Calculated requirement
- 3.34 mm²
- Permissible voltage drop
- 12 V
- Actual voltage drop at standard cross-section
- 2.51 %
Formula
- Three-phase: A = (√3 · L · I · cos φ) / (κ · Δu)
- Single-phase: A = (2 · L · I · cos φ) / (κ · Δu)
- DC: A = (2 · L · I) / (κ · Δu)
- Δu = U · Δu% / 100
Assumptions and standards
- κ = 56 m/(Ω·mm²) for copper, 35 m/(Ω·mm²) for aluminium at 20 °C.
- Calculated with resistive component only; inductive reactance is not included. For large cross-sections from about 95 mm² and long runs the result is therefore slightly optimistic.
- Thermal current-carrying capacity by installation method (IEC 60364-5-52) has to be checked separately – this calculator does not check it.
- Standard cross-sections to IEC 60228.
Frequently asked
What voltage drop is permissible?
In Germany, 3 % for lighting and 5 % for other loads is customary for consumer installations, measured from the point of supply. Industrial plants often apply stricter internal limits – the operator’s specification always governs.
Why is the one-way length used?
The return path is already in the factor: 2 for single-phase and DC, √3 for three-phase. So enter the one-way distance from supply to load.
Does this replace design to standard?
No. The calculator gives the cross-section from voltage drop. A complete design also covers current-carrying capacity by installation method, grouping, ambient temperature, short-circuit withstand and protection against indirect contact.
Calculating is the easy part.
A formula gives you a number. Designing a plant also demands installation method, grouping, discrimination, the standards in force and a look at the installed base. That is what we take on.
Contact
Tell us what it is about.
A phone call or three lines is enough. From the very start you talk to the people who will later work on your project – not to a distribution list.
Direct
- Phone+49 (0) 5247 4070-66
- Emailinfo@fisekon.com
- AvailabilityMon – Fri, 8:00 – 17:00 CET
Locations
33428 Marienfeld (Harsewinkel)Gütersloh officeWagenfeldstr. 2
33332 Gütersloh
Or write to us
We usually reply within one working day.