Cable cross-sectional area and MCB
What cable do I run and what MCB do I fit for this load?
Advanced conditions and parameters · Copper · B2 · 30 °C
Result
Minimum cross-sectional area1.5mm²
Recommended MCBC10A
Design current9.15A
Corrected current-carrying capacity16.5A
Correction factor applied1.000
Voltage drop1.35%
The cross-sectional area follows from the current-carrying capacity, so it is the thermal minimum. Annex 5.32 sets minimums per type of circuit that can be larger (2.5 mm² for socket outlets), and the voltage drop over the route length is checked separately. Minimum cross-sectional area by type of circuit →
Calculation assumptions
The result holds under the conditions below. If your situation differs, change the values in the advanced section.
- power factor cos φ = 0.95
- ambient temperature 30 °C
- run in conduit in an ordinary, not thermally insulating wall (installation method B2); current-carrying capacities from I7-2011 Annex 5.10
- 2 loaded conductors (phase and neutral, single-phase)
- a single circuit in the conduit, no grouping
- PVC insulation, 70 °C at the conductor
- copper conductor
- 25 % design reserve on the working current — the app’s own choice, not a code requirement
- the proposed cross-section has a corrected Iz strictly above the rated current of the breaker (In): at exact equality Iz = In (zero margin) it goes up one size — the code allows equality, but any deviation in temperature or grouping would make it non-compliant
- 230 V single-phase / 400 V between lines on three-phase
The results are indicative and do not replace a design checked by a registered electrician. Every tool states its assumptions.