Why correct cross-section matters
Cable cross-section is a critical parameter. Too small — cable overheats, insulation melts, fire risk. Too large — wasted money on copper, difficult installation. The engineer must find the exact value.
Calculation follows two criteria. The larger of the two is selected.
Criterion 1: Heating (continuous current rating)
Cables heat up when current flows. IEC 60364 / IS 732 specify maximum currents for each cross-section.
Example
Given: Icalc = 25 A, copper cable, 3 cores, in conduit.
Per IEC table: copper 2.5 mm² → 27 A (sufficient).
Check: Icalc (25 A) ≤ Imax (27 A) → 2.5 mm² passes heating criterion.
Criterion 2: Voltage drop
Per IEC, voltage drop from main panel to end consumer — max 5%.
Formula: ΔU% = (2 × L × Icalc × cos φ) / (γ × S × Unom) × 100%
Where:
- L — cable length (m)
- Icalc — calculated current (A)
- γ — conductivity (copper ≈ 57 m/(Ω·mm²))
- S — cross-section (mm²)
- Unom — nominal voltage (230 V single-phase)
Example
L = 30 m, Icalc = 25 A, cos φ = 0.92, copper.
At S = 2.5 mm²: ΔU% = 4.2% < 5% → passes.
At S = 1.5 mm²: ΔU% = 7.0% > 5% → fails.
Result: choose 2.5 mm² (passes both criteria).
GorkyCAD Algorithm
GorkyCAD performs this calculation automatically for every circuit segment:
1. Determines Icalc from group total load
You just need to review and approve.