1. Introduction

Designing and sizing a busbar correctly is one of the most important aspects of electrical system engineering.
A well-designed busbar ensures safe current distribution, thermal stability, and long-term reliability.
Incorrect sizing can result in overheating, energy loss, and catastrophic equipment failure.
This article provides a detailed guide to busbar design principles, current carrying capacity, sizing calculations, and engineering best practices for copper and aluminum busbars.

2. Key Principles of Busbar Design

A successful busbar design is based on balancing electrical, mechanical, and thermal considerations. The main design principles are:

• Electrical Capacity: Ensure the busbar can handle maximum load current without excessive temperature rise.
• Thermal Management: Consider ambient temperature, enclosure ventilation, and heat dissipation.
• Mechanical Strength: Ensure rigidity against short-circuit forces and vibrations.
• Safety Clearance: Maintain adequate spacing to prevent arcing and dielectric breakdown.
• Material Selection: Choose copper or aluminum based on conductivity, cost, and application.

3. Factors Affecting Busbar Sizing

Busbar sizing depends on multiple factors:

• Current Rating: The maximum continuous current the busbar must carry.
• Short-Circuit Withstand: The ability to handle fault currents without deformation.
• Voltage Rating: Determines insulation thickness and clearance requirements.
• Temperature Rise: Limited typically to 30–50°C above ambient, depending on standards.
• Environment: Humidity, corrosive atmosphere, or outdoor exposure affects coating and material choice.

4. Material Considerations: Copper vs. Aluminum

The choice between copper and aluminum busbars has major implications:

• Copper Busbars: Higher conductivity (~56 MS/m), smaller cross-sectional area required, excellent durability, but more expensive and heavier.
• Aluminum Busbars: Lower conductivity (~35 MS/m), requires larger cross-sectional area, lightweight and cheaper, but prone to oxidation.
• Plated Busbars: Tin or silver-plated copper improves contact resistance and prevents oxidation.

5. Busbar Current Carrying Capacity (Ampacity)

The ampacity of a busbar depends on its cross-sectional area, shape, and cooling conditions.
General thumb rules for copper busbars (in open air) are:

• 10 × 2 mm copper busbar ≈ 250 A
• 20 × 5 mm copper busbar ≈ 630 A
• 40 × 10 mm copper busbar ≈ 1600 A

Aluminum busbars of equivalent capacity require about 1.6 times the cross-sectional area of copper.

6. Busbar Sizing Calculation Method

The simplified formula for determining busbar cross-section area is:

A = I / J
      

Where:

• A: Cross-sectional area (mm²)
• I: Current rating (A)
• J: Current density (A/mm²), typically:
  • Copper: 1.2–1.6 A/mm²
  • Aluminum: 0.8–1.2 A/mm²

For example, for a 2000 A system using copper:

A = 2000 / 1.5 ≈ 1333 mm²
      

This can be achieved with a 100 mm × 13 mm copper bar.

7. Short-Circuit Withstand Capacity

Busbars must withstand the mechanical forces of short-circuit currents. The force between conductors is proportional to:

F = (μ₀ × I² × L) / (2πd)
      

Where:

• μ₀: Permeability of free space
• I: Short-circuit current (A)
• L: Length of conductor (m)
• d: Distance between conductors (m)

This calculation helps determine support spacing and busbar thickness for mechanical stability.

8. Busbar Layout and Spacing Rules

Proper layout ensures safety and performance:

• Phase Separation: Maintain adequate clearance between phases to avoid arcing.
• Ventilation: Allow airflow between busbars for cooling.
• Parallel Bars: Use multiple parallel bars for high currents instead of a single thick bar.
• Insulation: Apply heat-shrink, epoxy coating, or PVC insulation if installed in compact panels.

9. Standards for Busbar Design

International standards provide design guidelines:

• IEC 61439: Defines temperature rise and safety requirements for busbar systems.
• IEC 62271: Covers high-voltage busbar design.
• UL 857: Standards for busways and busbar enclosures.
• NEC (NFPA 70): U.S. electrical code for busbar sizing and clearances.

10. Best Practices for Busbar Design

• Use copper for critical and high-current applications; aluminum for cost-sensitive large systems.
• Design for 125–150% of expected load current for future expansion.
• Use multiple smaller parallel busbars instead of one oversized bar for better cooling.
• Always consider ambient temperature and derating factors.
• Coat exposed surfaces to prevent oxidation and corrosion.

11. Conclusion

Proper busbar design and sizing is essential for safe, reliable, and cost-effective electrical distribution.
By following engineering principles, applying correct calculations, and adhering to international standards,
engineers can design busbar systems that provide long-term stability and efficiency.
Whether using copper or aluminum, careful consideration of electrical, thermal, and mechanical factors is the key to success.