Cable Sizing Calculation for Electrical Loads
I. Three-Phase Load Calculation
Step 1: Determine the Load Current
The load current can be calculated using the formula:
I = P / (√3 × V × Power Factor)
Where:
P = 15,000 W (15 kW)
V = 400 V (three-phase)
Power Factor = 0.9
Calculation:
I = 15,000 / (√3 × 400 × 0.9)
≈ 24.0 A
Step 2: Select the Type of Cable
For PVC-insulated cables:
2.5 mm² PVC cable handles around 20 A
4 mm² PVC cable handles around 30 A
Selected: 4 mm² PVC cable (provides a safety margin above 24.0 A).
Step 3: Check Voltage Drop
The voltage drop can be calculated using the formula:
Voltage Drop = (√3 × I × L × R) / 1000
Where:
I = 24.0 A
L = 100 m
R = 5.09 Ω/km for 4 mm² cable
Calculation:
Voltage Drop = (√3 × 24.0 × 100 × 5.09) / 1000
≈ 21.3 V
Step 4: Percentage Voltage Drop
Percentage Voltage Drop = (21.3 V / 400 V) × 100
≈ 5.33%
II. Single-Phase Load Calculation
Step 1: Determine the Load Current
The load current can be calculated using the formula:
I = P / (V × Power Factor)
Where:
P = 15,000 W (15 kW)
V = 230 V (single-phase)
Power Factor = 0.9
Calculation:
I = 15,000 / (230 × 0.9)
≈ 72.5 A
Step 2: Select the Type of Cable
For PVC-insulated cables:
10 mm² PVC cable handles around 70 A
16 mm² PVC cable handles around 90 A
Selected: 16 mm² PVC cable (provides a safety margin above 72.5A).
Step 3: Check Voltage Drop
The voltage drop can be calculated using the formula:
Voltage Drop = (2 × I × L × R) / 1000
Where:
I = 72.5 A
L = 100 m
R = 1.21 Ω/km for 16 mm² cable
Calculation:
Voltage Drop = (2 × 72.5 × 100 × 1.21) / 1000
≈ 17.5 V
Step 4: Percentage Voltage Drop
Percentage Voltage Drop = (17.5 V / 230 V) × 100
≈ 7.6%