Anyone installing a new socket, cooker, or EV wallbox must choose the correct cable cross-section — too small means overheating and fire risk, too large means unnecessary material cost. The cable sizing calculator automatically determines the minimum cross-section and maximum permissible cable length for a given voltage drop using the VDE formula. This lets you meet the requirements of DIN VDE 0100 without having to work through the formulas yourself.
Step by Step: How to Use the Cable Sizing Calculator
- Enter the supply voltage: Choose 230 V (single-phase AC) or 400 V (three-phase). A household cooker or wallbox typically runs on 400 V; standard socket circuits use 230 V.
- Enter the rated current: Enter the current rating of the intended circuit breaker — typically 16 A for sockets, 25 A for air conditioners, 32 A for 11 kW wallboxes.
- Enter the cable length: Measure the one-way distance from the distribution board to the outlet. The calculator automatically accounts for both the live and return conductor (factor of 2 in the formula).
- Set the maximum voltage drop: DIN VDE 0100-520 allows 3% for final circuits (= 6.9 V at 230 V). In commercial installations, 5% is sometimes permitted for sub-mains.
- Read the result: The calculator shows the calculated minimum cross-section. Always select the next larger standard size (1.5 / 2.5 / 4 / 6 / 10 / 16 mm²) — never round down.
Practical Examples
Example 1 – Cooker circuit: 400 V three-phase, 16 A breaker, 12 m cable run, 3% voltage drop limit. Calculation: A = (2 × 12 × 16 × 0.0178) / (0.03 × 400) = 0.57 mm². The standard size would be 1.5 mm², but VDE requires a minimum of 2.5 mm² for cooker circuits — the calculator flags this.
Example 2 – EV wallbox: 230 V, 32 A, 18 m from the distribution board. A = (2 × 18 × 32 × 0.0178) / (0.03 × 230) = 2.98 mm² → select standard size 4 mm².
Example 3 – Air conditioner: 230 V, 25 A, 9 m cable run. A = (2 × 9 × 25 × 0.0178) / 6.9 = 1.16 mm² → calculated value is 1.5 mm², but the current-carrying capacity table requires at least 2.5 mm² for 25 A.
Cable Sizing per DIN VDE 0100
Minimum cross-section: A = (2 × L × I × ρ) / (ΔU_max × U). Reference values: 16 A cooker → 2.5 mm²; 25 A air conditioner → 4 mm²; 32 A EV charger → 6 mm². Copper resistivity ρ = 0.0178 Ω·mm²/m.
Frequently Asked Questions (FAQ)
Why is the calculated minimum cross-section sometimes not enough?
The voltage drop formula is only one of two criteria. The cable must also be able to carry the continuous current thermally — which depends on installation method (conduit, embedded in plaster, buried), grouping, and ambient temperature. The calculator always shows the larger of the two required values.
Does the 3% rule apply to all wiring in a building?
No. The total voltage drop from the metering point to the last load must not exceed 5%. If the incoming supply cable is long, less budget remains for the final circuits.
What is the difference between the calculated cross-section and the nominal cross-section?
The calculated value is the mathematical minimum. Only standardized cross-sections are available commercially (e.g. NYM-J, NYY cable). Always round up to the next larger standard size — never down.
