Cable Selection
Cable Selection includes 8 Step Procedure
Step 1: Load Current
Step 2: Derating Factors
Step 3: Cable Capacity Chart
Step 4: 125% Rule
Step 5: Voltage Drop Check
Step 6: Short Circuit Rating
Step 7: Copper vs Aluminum
Step 8: Standard Cable Sizes (Cu / Al)
Step 1: Load Current
Single Phase: I = P / (V × PF)
Three Phase: I = P / (√3 × V × PF)
Step 2: Derating Factors
Ambient temperature, grouping, installation, soil resistivity, copper/aluminum, voltage level
Step 3: Cable Capacity Chart
IEC 60364 , NEC, VDE, BS 7671
Step 4: 125% Rule
Cable current ≥ Load × 1.25
Step 5: Voltage Drop Check
Lighting ≤3%, Power ≤5%
Step 6: Short Circuit Rating
Isc = k × A × √t
Step 7: Copper vs Aluminum
- Copper: high conductivity, small size, expensive, heavy
- Aluminum: medium conductivity, bigger, cheaper, light
Step 8: Standard Cable Sizes (Cu / Al)
Refer charts in guide
Example
40 kW, 400 V, 3Φ, PF 0.85 → Load current = 68 A → 125% margin = 85 A → select 25 mm² Cu