Cable Size by Power
Single-phase 230 V circuit, PVC-insulated copper cable
How it is calculated
Circuit current Ib = P / (U · cos φ). The cable's current-carrying capacity Iz is the table value for two loaded PVC-insulated copper conductors (70 °C) and the chosen installation method, multiplied by the factors for air temperature and the number of cables in a group. A cross-section is suitable if Ib ≤ In ≤ Iz, where In is the breaker rating, and the voltage drop does not exceed the limit.
Voltage drop of a single-phase line ΔU = 2 · Ib · (R cos φ + X sin φ) · L / U, where R = 23.7 / S Ω/km is a conservative resistivity of copper for PVC at 70 °C, X = 0.08 Ω/km, and L is the line length in kilometres. The drop up to the apartment's board is not included.
Sources: tables B.52.2, B.52.4, B.52.14 and B.52.17 (row 1) of GOST R 50571.5.52-2011 (IEC 60364-5-52, in Russian); cable sizing and voltage drop — Electrical Installation Guide, Schneider Electric. Data checked on 13 October 2026.
FAQ
Why does the result differ from other tables?
The calculator takes the current-carrying capacities from the tables of IEC 60364-5-52 (in Russia, GOST R 50571.5.52-2011) for a PVC-insulated copper cable and reduces them by the factors for air temperature and the number of cables in a group. National wiring rules may be built for other conditions, so the numbers may not match.
What voltage drop limit should I choose?
The designer chooses it, taking into account the drop from the supply to the apartment's distribution board. The 4% in the field is the calculator's starting value, not a standard. The longer the line, the more often it is the voltage drop rather than heating that determines the cross-section.
Can I wire my home based on this calculation?
No. This is a preliminary estimate of one circuit. Checking that the breaker trips on a short circuit, the RCD, the bathroom requirements and the apartment's electrical design remain the electrician's job.