Requirements for main busbars of low-voltage switchgear

Low-voltage switchgear busbars must comply with IEC 61439 standards, ensuring proper current-carrying capacity, thermal performance, mechanical strength, short-circuit withstand, and safety protections.Key Design and Compliance RequirementsVoltage Rating and Application: Busbars in low-voltage switchgear are designed for up to 1000 V AC or 1500 V DC, suitable for power distribution, control gear assemblies, and photovoltaic systems (IEC 61439) . Current Carrying Capacity: The busbar must handle the continuous rated current of the system. Designers often use a diversity factor to calculate the main busbar current, accounting for non-simultaneous loads. For example, a total equipment requirement of 2700 A with a diversity factor of 0.6 results in a main busbar rating of 1620 A . Thermal Performance: IEC 61439 sets a maximum temperature rise limit of 140°C (105 K above ambient 35°C) to prevent insulation degradation and fire hazards. Busbar geometry should support heat dissipation, avoiding trapped heat inside the enclosure . Short-Circuit Withstand: Busbars must withstand short-circuit stresses without permanent deformation. Verification can be done through testing, calculation, or comparison with reference assemblies . Mechanical Strength: Busbars must maintain structural integrity under mechanical loads, including vibration, impact, and operational cycles. IEC 61439 requires 200 operating cycles for functional units and tests for corrosion resistance, damp heat, and salt mist exposure . Insulation and Safety: Busbars must meet dielectric strength requirements and provide protection against electric shock. Barriers and enclosures must comply with IP ratings (e.g., IPXXD for accessible parts) and IK ratings for impact resistance . Material and Cross-Section: Copper is commonly used for its conductivity and thermal performance. Designers often standardize busbar widths and adjust thickness, layering, or quantity to meet current ratings efficiently while optimizing space . Electromagnetic Compatibility (EMC): Busbars and assemblies must comply with EMC requirements to prevent interference with other equipment . Verification Methods: IEC 61439 eliminates the distinction between Type-Tested Assemblies (TTA) and Partially Type-Tested Assemblies (PTTA), requiring all assemblies to meet uniform safety and performance benchmarks through calculation, testing, or reference comparison .SummaryTo comply with IEC 61439, low-voltage switchgear busbars must be designed with careful consideration of current capacity, thermal limits, mechanical strength, short-circuit withstand, insulation, corrosion resistance, and EMC compliance. Proper sizing, material selection, and verification ensure safe, reliable, and efficient operation in industrial and commercial electrical systems.