Small busbars in low-voltage switchgear are compact conductive bars designed to safely distribute current while optimizing space, thermal performance, and compliance with IEC 61439 standards.
Definition and Purpose
A busbar is an electrically conductive strip or bar used to distribute power to multiple circuits in parallel or as a common tapping point for neutral or ground connections. In small or compact switchgear, busbars must balance current-carrying capacity, thermal management, and space efficiency.
Design Considerations
Current Carrying Capacity: The busbar must handle the continuous full-load current without exceeding permissible temperature rise limits. This depends on the cross-sectional area, material (copper or aluminum), ambient temperature, and ventilation. Copper is preferred for small cross-sections due to its higher conductivity and current density.
Thermal Management: Excessive heating can degrade insulation and reduce service life. Proper spacing, plating (tin or silver), and ventilation improve heat dissipation.
IE
C 61439 sets the maximum safe temperature rise at 140°C above ambient for low-voltage assemblies.
Short-
Circuit Withstand: Busbars must withstand high fault currents for short durations (typically 1–3 seconds). Compact designs, such as sandwich or laminated busbars, improve short-circuit strength and reduce electromagnetic forces. Electromechanical Forces: Fault currents generate magnetic forces between conductors.
Busbar supports and bracing must resist these forces to prevent deformation. The force increases with the square of the current and inversely with spacing. Space Optimization: Small busbars allow compact switchgear layouts, enabling more outgoing units and modular expansion.
Pre-engineered modular busbar systems can be adapted to standard IEC device widths, improving panel layout efficiency.
Material Options
Copper: High conductivity, best for minimal cross-section and high current density. Aluminum: Lighter, suitable when weight reduction is critical. CoppAl®: Aluminum core with copper cladding, combining conductivity and reduced weight.
Flexible Busbars: Flat copper mesh (e.g., Ultraflexx®) absorbs vibrations and switching shocks, ideal for tight spaces.
Standards and Compliance
Small busbars in low-voltage switchgear must comply with IEC 61439, which defines design verification, thermal performance, and test requirements for assemblies up to 1000 V AC or 1500 V DC. The standard also introduces diversity factors to calculate main busbar current based on total equipment load, ensuring safe operation without oversizing.
Practical Implementation
Use pre-engineered modular busbar systems for compact switchgear to simplify installation and ensure compatibility with standard devices. Optimize cross-section and spacing based on thermal rating, short-circuit level, and electromechanical forces. Select copper for highest current density in small busbars, or aluminum for weight-sensitive applications.
Consider flexible busbars for vibration-prone or modular systems to improve reliability and reduce installation complexity. In summary, small busbars in voltage switchgear are engineered to maximize current capacity, minimize space, and maintain thermal and mechanical safety, while adhering to IEC standards and material best practices. Proper design ensures reliable, scalable, and efficient low-voltage switchgear assemblies.
