Cable Tray Designing and Selection

Cable Tray Design in Electrical Systems – Example & Calculation

Cable trays are one of the most widely used methods for laying power cables in electrical systems. They are preferred over underground trenching where:

• Digging is not feasible or digging cost is very high.

• Space constraints exist in industrial or commercial setups.

• Aesthetic and maintenance-friendly cabling is required.

Cable trays (especially perforated type) ensure easy installation, heat dissipation, and organized routing of cables.

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General Recommendations for Cable Tray Design

1. Spare Capacity: Always design with 10–20% spare capacity for future expansion.

2. Cable Spacing: Maintain 5–10 mm clearance between adjacent cables for ventilation and safety.

3. Weight Capacity: Ensure tray weight carrying capacity > total cable weight per meter.

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Example: Designing a Cable Tray for Aluminum Cables

We will design a tray for the following cables:

• 10 Nos. 2.5 mm² × 4 Core cables

• 10 Nos. 25 mm² × 4 Core cables

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Step 1: Total Outer Diameter of Cables

• Diameter of 2.5 mm² cable = 16 mm
  → Total = 10 × 16 = 160 mm

• Diameter of 25 mm² cable = 25 mm
  → Total = 10 × 25 = 250 mm

• Total Diameter = 160 + 250 = 410 mm

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Step 2: Total Weight of Cables

• Weight of 2.5 mm² cable = 0.56 kg/m
  → Total = 10 × 0.56 = 5.6 kg/m

• Weight of 25 mm² cable = 1.11 kg/m
  → Total = 10 × 1.11 = 11.1 kg/m

• Total Weight = 5.6 + 11.1 = 16.7 kg/m

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Step 3: Width Requirement

Formula:
Total Width = (Number of cables × Min. spacing) + Total cable diameter

= (20 × 5 mm) + 410 mm
= 510 mm

Now add 10% spare:
= 1.1 × 510 = 561 mm

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Step 4: Area Requirement

Formula:
Total Area = Width × Maximum cable height

= 561 × 25 = 14,025 mm²
Now add 10% spare:
= 1.1 × 14,025 = 15,428 mm²

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Step 5: Selecting Suitable Cable Tray

From calculations:

• Option 1: One 600 mm × 50 mm tray (area = 30,000 mm², load capacity = 50 kg/m)

• Option 2: Two 300 mm × 50 mm trays (combined area = 30,000 mm²)

• Option 3: One 300 mm × 50 mm tray with cables layered one above another (less preferred, difficult for maintenance).

✅ Final Choice: 600 mm × 50 mm perforated cable tray is most practical and maintenance-friendly.

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Key Takeaways

• Always consider spare capacity for future expansion.

• Verify both width and weight capacity of tray before selection.

• Perforated trays are preferred in most electrical systems due to better cooling and neat appearance.