When sizing a cable, calculating the voltage drop alone is not enough — the cable must also be able to carry the flowing current thermally on a continuous basis without heating to a dangerous level. DIN VDE 0298-4 defines how installation method, grouping, and ambient temperature affect the current carrying capacity. The cable cross-section calculator combines both criteria and specifies the safe minimum cross-section.
Step by Step: How to Use the Cable Cross-Section Calculator
- Enter the operating current: The expected continuous current in amperes — either the protective device rating (e.g. 16 A) or the actual appliance current from the rating plate (power ÷ voltage).
- Select the installation method: Open air / wall surface: best heat dissipation; embedded in plaster / in conduit: reduced capacity; buried in ground: often higher capacity than embedded. VDE tables distinguish methods A1, A2, B1, B2, C, D, E, F, G.
- Apply the grouping factor: Multiple cables close together (grouping) heat each other up. With 5 cables bundled in a conduit, carrying capacity drops by approximately 30%.
- Enter the ambient temperature: Standard is 30 °C. In cable trays inside industrial halls (40–50 °C), the carrying capacity must be multiplied by a temperature correction factor below 1.
- Check the result: The calculator shows the larger required cross-section of the two criteria (thermal and voltage drop). Always select the next standard cross-section upward.
Practical Examples
Example 1 – Socket circuit: 16 A protective device, installation method B2 (embedded in conduit in plaster), single cable. Carrying capacity from VDE table: 1.5 mm² → 15.5 A (insufficient), 2.5 mm² → 21 A → minimum 2.5 mm².
Example 2 – Industrial installation with grouping: 25 A motor current, 6 cables bundled in a cable tray, 40 °C ambient. Grouping factor 0.7, temperature factor 0.91: effective current for selection = 25 / (0.7 × 0.91) = 39.2 A → cross-section must carry 39.2 A: 10 mm² (42 A per table).
Example 3 – Wallbox buried underground: 32 A, buried installation (method D1), directly in ground at 20 cm depth, single cable. Underground installation allows higher carrying capacity: 6 mm² → 44 A → 6 mm² is sufficient (in free air, 10 mm² would have been required).
Cable Cross-Section Calculation per DIN VDE
Cross-section: A = (2 × L × I × ρ) / ΔU. Installation method affects capacity: underground +30%; grouping −30%. Reference values: 1.5 mm² up to 16 A; 2.5 mm² up to 20 A; 4 mm² up to 25 A; 6 mm² up to 32 A (depending on installation).
Frequently Asked Questions (FAQ)
What is the difference between the cable cross-section calculator and the cable sizing calculator?
Both calculate the required conductor cross-section, but with a different focus: the cable cross-section calculator emphasises thermal carrying capacity per DIN VDE 0298-4 with installation correction factors; the cable sizing calculator concentrates on voltage drop per DIN VDE 0100-520. For a complete design, both should be checked.
What exactly does cable grouping mean?
Grouping describes the simultaneous installation of several loaded conductors in close proximity. Mutual heating reduces the individual carrying capacity. In cable trays: 4 cables side by side → factor 0.8; 9 cables → factor 0.7; 16 cables → factor 0.61.
Does DIN VDE 0298-4 also apply to DC installations (e.g. PV systems)?
Yes, thermal carrying capacity applies equally to direct and alternating current. For voltage drop in DC, however, the factor of 2 for the forward and return conductor does not apply — instead, the actual conductor length is used, since the positive and negative conductors are physically separate.
