Low-voltage switchgear busbar specifications and models

Busbar configuration in low-voltage switchgear balances current capacity, thermal performance, mechanical strength, and compliance with IEC 61439 standards.

Busbar Types and Materials

Busbars are typically made of copper or aluminum, with copper preferred for high conductivity and smaller cross-sections . Common busbar types include:

• Rigid busbars: Solid metal bars, strong and stable, suitable for main current paths .
• Flexible busbars: Thin copper layers or braided conductors, used for connections to breakers where vibration or movement occurs .
• Flat busbars: Easy to install, good heat dissipation, widely used in compact designs .
• Tubular busbars: Hollow, lighter, and improve cooling in high-current systems .
• Laminated busbars: Thin conductors with insulation between layers, saving space in high-performance assemblies .
• Insulated or enclosed busbars: Reduce short-circuit risk and allow tighter layouts .

Configuration Principles

Busbar configuration involves horizontal and vertical arrangements to distribute power efficiently across the switchgear . Key considerations include:

• Current-carrying capacity: Busbars must handle continuous full-load current without exceeding temperature limits .
• Thermal management: Proper spacing, plating (tin or silver), and ventilation prevent overheating and insulation degradation .
• Short-circuit withstand: Busbars must survive high fault currents for 1–3 seconds, accounting for thermal and electromechanical stresses .
• Electromechanical forces: Magnetic forces during faults can deform busbars; supports and bracing must resist these forces .
• Creepage and clearance: Maintain safe distances to prevent flashovers or insulation breakdown .

Layout Strategies

• Standardized busbar families: Instead of unique sizes for each rating, designs often use a limited set of widths and adjust thickness, layering, or quantity as current increases .
• Horizontal busbars: Serve as the main current path, connecting incoming power to functional units .
• Vertical distribution busbars: Distribute power to outgoing circuits efficiently while maintaining space for functional units .
• Phase identification: Clear labeling and separation improve safety and maintenance .

Compliance with IEC 61439

IEC 61439 sets design verification, temperature rise limits, short-circuit withstand, dielectric properties, and protection against electric shock for low-voltage switchgear . Key points include:

• Maximum working voltage: 1000 V AC or 1500 V DC .
• Thermal limit: Busbar temperature should not exceed 140°C under rated load with 35°C ambient .
• Diversity factor: Determines main busbar current based on total equipment load, e.g., 2700 A total load with 0.6 diversity factor results in 1620 A main bus requirement .
• Verification: All assemblies must meet uniform safety and performance benchmarks, eliminating distinctions between type-tested and partially tested assemblies .

Summary

A well-designed low-voltage switchgear busbar system ensures reliable power distribution, safety, and long-term performance. Proper material selection, busbar type, spacing, and layout, combined with compliance to IEC 61439, are critical for handling continuous and fault currents, managing heat, and maintaining mechanical integrity while optimizing space for functional units .