Cable cross-section and MCB calculator

From the power or the current we calculate the operating current and select the MCB and a copper cable of sufficient cross-section, taking the installation method, the temperature and the grouping into account.

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How does the calculator choose?

First we calculate the operating current from the power (P / (230 · cos φ) for single-phase, P / (√3 · 400 · cos φ) for three-phase), or use the current you entered directly. Then:

1. MCB: the smallest standard rating (6, 10, 13, 16, 20, 25, 32, 40, 50, 63 A) that can carry the operating current.
2. Cross-section: the smallest copper cross-section whose corrected current-carrying capacity reaches the rated current of the MCB. The capacity depends on the installation method (B2: in conduit or embedded in the wall, C: fixed on the wall), the ambient temperature and the number of circuits running together.
3. Voltage drop: if you enter the cable length, the calculator chooses a cross-section for which the drop stays within the selected limit (3 % or 5 %).

What does corrected current-carrying capacity mean?

The base value in the table applies to a 30 °C environment and a single circuit. In a warmer place, or when several circuits run together, the cable can carry less: the temperature and grouping factors take this into account, and both are shown under the result.

Limits of the calculation

It calculates for copper conductors and PVC insulation, on two-core (single-phase) or three-core (three-phase) loaded cables, for installation methods B2 and C. Above 63 A, for aluminium conductors and for other installation methods it gives no suggestion. The result is informative: the selected cable and protection must be approved by the electrical designer.

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