Practical Guide by Shenghua Cable

Choosing the right cable cross-sectional area is critical for electrical safety, efficiency, and cost-effectiveness. While many engineers rely on experience or simplified formulas, a scientific approach ensures long-term reliability and optimal performance. Drawing on decades of experience, Shenghua Cable (Shanghai Shenghua Cable Technology Group Co., Ltd.) presents four practical methods to determine the correct cable cross-section for different applications.

Discover Shenghua Cable’s full product range here:https://www.shanpowercable.com/

The most straightforward method is to ensure that a cable does not exceed its long-term operating temperature under normal load.

• PVC-insulated cable: 70°C

• XLPE-insulated cable: 90°C

Example:

• Transformer capacity: 2500 kVA

• Supply voltage: 10 kV

• Cable type: XLPE, laid in cable bridge

Step 1: Calculate rated current

I=250010.5*1.732≈137AI = frac{2500}{10.5 times 1.732} approx 137AI=10.5*1.7322500​≈137A

Step 2: Check cable manual

• YJV-8.7/10KV-3X25 → 120A

• YJV-8.7/10KV-3X35 → 140A

Step 3: Select cable

• YJV-8.7/10KV-3X35 satisfies 137A

Note: This method does not account for voltage drop or short-circuit thermal stability.

This method balances material cost and power loss. Smaller cables reduce investment but increase losses; larger cables reduce losses but increase cost. The optimal size is determined using the economic current density (A/mm²) based on equipment operation hours.

Example:

• Equipment rated current: 150A

• Annual operating hours: 8000 hours

• Economic current density: 1.75 A/mm²

$S=economic\; densityI=1.75150\approx 85.7mm²$

Step 2: Select nearest standard size → 95 mm²

This method ensures both safety and cost-effectiveness.

For long cable runs, voltage drop becomes significant and may affect equipment operation. The allowable drop is often 7% for a 400V line.

Voltage drop formula:

S=I⋅ρ⋅LΔUS = frac{I cdot rho cdot L}{Delta U}S=ΔUI⋅ρ⋅L​

• III = rated current

• ρrhoρ = conductor resistivity

• LLL = cable length

• ΔUDelta UΔU = allowable voltage drop

Example:

• Device voltage: 380V

• Rated current: 150A

• Copper cable resistivity: 0.0175 Ω·mm²/m

• Cable length: 600 m

• Allowable voltage drop: 26.6V

S=150*0.0175*60026.6≈59.2 mm²S = frac{150 times 0.0175 times 600}{26.6} approx 59.2 text{ mm²}S=26.6150*0.0175*600​≈59.2 mm²

Step 2: Select nearest standard size → 70 mm²

This ensures voltage stability along long cable runs.

For medium- and high-voltage cables (≥6 kV), cross-section selection must account for short-circuit thermal stability.

Formula:

$Smin=CIdti$

• IdI_dId​ = short-circuit current

• tit_iti​ = breaker interruption time

• CCC = cable thermal coefficient (typically 80)

Example:

• Short-circuit current: 18 kA

• Thermal coefficient: 80

• Breaker time: 0.25 s

Smin=18000*0.2580≈112.5 mm²S_{text{min}} = frac{18000 times sqrt{0.25}}{80} approx 112.5 text{ mm²}Smin​=8018000*0.25​​≈112.5 mm²

Step 2: Select nearest standard size → 120 mm²

Even if the rated current is small, the cable must withstand short-circuit stress.

By combining scientific selection methods with quality manufacturing, Shenghua Cable ensures:

• Accurate cross-sectional sizing for safety and efficiency

• Reliable thermal and electrical performance

• Compliance with international standards and certifications

• Long-term durability in industrial and power distribution systems

Shenghua Cable offers full guidance and technical support for project-specific cable sizing.

Explore our product portfolio:https://www.shanpowercable.com/

Selecting the correct cable cross-sectional area is more than following experience. By considering long-term current capacity, economic density, voltage drop, and short-circuit thermal stability, engineers can ensure safe, reliable, and cost-effective installations.

Shenghua Cable combines technical expertise with premium-quality materials to provide solutions that stand the test of time.