Busbar Sizing Calculation: Methods and Standards

Busbar Sizing Fundamentals

Busbars are the backbone of any electrical panel, carrying current from the incomer to individual feeders.

Current Density Method

The simplest method uses current density values:

• Copper busbars: 1.6 - 2.0 A/mm²
• Aluminium busbars: 1.0 - 1.2 A/mm²

Formula

Cross Section (mm²) = Rated Current (A) / Current Density (A/mm²)

Example

For 2000A copper busbar:

• Area = 2000 / 1.8 = 1111 mm²
• Use 100mm × 12mm bars, 1 bar per phase = 1200 mm²

Short Circuit Withstand

Busbars must withstand short circuit forces:

• Thermal: I²t ≤ K²S² (where K=143 for copper)
• Mechanical: Electromagnetic forces between bars

Temperature Rise Limits

• Maximum temperature: 90°C for bolted connections
• Temperature rise: 50°C above 40°C ambient
• As per IS 8623 Part 1

Use Our Calculator

Try our free busbar sizing calculator in the Engineering Tools Hub for instant results.

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