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Cable cross-section calculator by power and current (PUE)

Conductor cross-section is chosen so the cable doesn't overheat under working current. Enter the current directly, or the load power — the calculator picks the smallest cross-section from PUE's continuous current tables.

The ladder of standard cross-sections: the calculated current and the first size that can carry it — — — — — — — — — — Calculated current —
Steps are standard cross-sections, mm²; below each is its continuous current rating. The first step above the line is the right one.

Input data

Result

Recommended cross-section, S — мм²
Calculated current, I — А
Apparent power, SApparent power S (kVA) — the load including its reactive part. Used to size a generator, UPS, or transformer; active power (kW) is always lower. — кВА
Allowed current for the cross-sectionContinuous current rating — the current a conductor can carry indefinitely without overheating. Must be no less than the calculated load current. — А
Recommended breaker — А

A base selection without derating factors for ambient temperature, cable grouping, or insulation type. The breaker rating is chosen to protect the cable (In ≤ Iallowed) and to carry the load (In ≥ Icalc); refine the result by selectivity and curve (B/C/D). For a real project, apply the coefficients from PUE and GOST R 50571.5.52.

How it's calculated

  1. Calculate the load's working current: for three-phase, I = P / (√3 · U · cos φ); for single-phase, I = P / (U · cos φ). If the current is already known, enter it directly and skip power.
  2. In the continuous current table, find the smallest standard cross-section whose allowed current is no less than the calculated one — accounting for conductor material and installation method.
  3. Pick the breaker: its rating must be no higher than the cable's allowed current, so the breaker protects the cable, and no lower than the working current, so it doesn't trip under load.

Example: 10 kW, three-phase 380 V, cos φ 0.95 → 16 A. Copper, open in air: the nearest cross-section is 1.5 mm² with an allowed current of 23 A. A standard breaker size — 20 A: bigger than the working 16 A, smaller than the allowed 23 A.

Continuous current rating, A — PUE-7, Ch. 1.3 (tables 1.3.4 / 1.3.6 for copper, 1.3.7 / 1.3.8 for aluminum)
Conductor cross-section, S, мм² Copper Aluminum
Open, in air In conduit or duct Open, in air In conduit or duct
1.5 23 19 — —
2.5 30 27 24 20
4 41 38 32 28
6 50 46 39 36
10 80 70 60 50
16 100 85 75 60
25 140 115 105 85
35 170 135 130 100
50 215 185 165 140
70 270 225 210 175
95 330 275 255 215
120 385 315 295 245

PUE-7, Ch. 1.3: tables 1.3.4 / 1.3.6 (copper) and 1.3.7 / 1.3.8 (aluminum) — continuous current ratings for wires and cables.

This is an estimate

Verify final values against current standards, the project design, and equipment nameplates.

Explained in the article Выбор сечения кабеля и номинала автомата по таблицам ПУЭ

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