New Standard for Low-Voltage Busbar Withstand Voltage

The IEC 61439 series establishes the new standard for low-voltage busbar withstand voltage, requiring verification of dielectric strength, short-circuit performance, and temperature rise for assemblies up to 1000 V AC or 1500 V DC.

Overview of IE

C 61439The IEC 61439 standard, introduced in 2009, replaces the older IEC 60439 series and governs the design, verification, and testing of low-voltage switchgear and controlgear assemblies, including busbars. It applies to assemblies with voltage ratings up to 1000 V AC and 1500 V DC and covers power distribution, photovoltaic systems, and general low-voltage applications. The standard eliminates the distinction between Type-Tested Assemblies (TTA) and Partially Type-Tested Assemblies (PTTA), requiring all assemblies to meet uniform safety and performance benchmarks.

Withstand Voltage Requirements

Dielectric withstand voltage is a critical aspect of IEC 61439 compliance. Busbars and assemblies must be tested to ensure they can withstand overvoltages without insulation breakdown. Verification can be performed through: Design calculations based on reference assembliesActual testing of the assembly under specified voltage conditionsComparison with previously tested assemblies meeting the same construction and material criteria The standard specifies that the average ambient temperature during testing should not exceed 35 °C, and the assembly must maintain insulation integrity under rated voltage conditions.

Short-

Circuit and Thermal VerificationIn addition to dielectric testing, IEC 61439 requires verification of: Short-circuit withstand strength, ensuring busbars can handle fault currents without mechanical or thermal failureTemperature rise limits, preventing insulation degradation and fire hazards under rated current conditions These tests ensure that busbars maintain safe operation under both normal and fault conditions. Key Changes from Previous StandardsCompared to IEC 60439, the new standard: Introduces uniform verification methods for all assembliesProvides detailed guidance on dielectric properties, short-circuit performance, and rated diversity factorAllows verification by calculation or testing, provided the assembly meets reference design criteria Emphasizes documentation of assembly drawings, technical specifications, and test reports for compliance Practical ImplicationsManufacturers and system designers must ensure that low-voltage busbars: Are designed and tested according to IEC 61439 dielectric and thermal requirementsCan safely withstand rated voltages and fault currentsInclude proper documentation for regulatory compliance and market access By adhering to IEC 61439, busbar assemblies achieve enhanced safety, reliability, and performance, meeting modern low-voltage electrical system requirements.