Quick table (copper, 2.5% drop)
1.5 mm² — up to 16 A (lighting); 2.5 mm² — up to 25 A (sockets); 4 mm² — up to 32 A (stove, AC); 6 mm² — up to 40 A (3-phase input); 10 mm² — up to 50 A; 16 mm² — up to 63 A.
Breaker rule
The breaker protects the cable: In ≤ Iz × 0.9-1.0. For 2.5 mm² with Iz=25 A, the breaker is C16-C20, not C25 — otherwise the cable works at the limit.
Voltage drop check
Up to 25 m — the table works. From 30 m, check ΔU: for lighting no more than 3%, for the rest 5%. Otherwise increase the section.
Examples
Electric oven 7 kW 1-phase: I=30 A → cable 6 mm², breaker C32. AC 3.5 kW: I=16 A → 2.5 mm², C20. Washing machine 2.2 kW: I=10 A → 2.5 mm², C16 (reserve for heater).
Three-phase
For 3-phase: I = P / (√3·380·cosφ). A cottage input of 15 kW at 380 V: I≈27 A → 5×6 mm², input breaker C32.
GorkyCAD does it for you
Selects the section by tables PUE 1.3.4-1.3.7 and IEC 60364-5-52, checks the breaker and drop — 41 checks cover the whole project.