Low-voltage busbars are designed according to IEC 61439 standards, with key parameters including rated current, short-circuit withstand capacity, temperature rise limits, material type, insulation, and mounting conditions.

Key Technical Parameters

Rated Current (Ir): The continuous current a busbar can carry without exceeding permissible temperature rise. Copper busbars typically allow a temperature rise of 70°C above ambient, while aluminum busbars are limited to 55°C above ambient temperature . Short-Circuit Current (Isc): Maximum current the busbar can withstand during a fault for a specified duration (usually 1–3 seconds). This ensures the busbar can survive short-circuit events without mechanical or thermal damage . Material Type: Busbars are usually made of copper or aluminum. Copper offers higher conductivity and smaller cross-sectional area but is more expensive, whereas aluminum is lighter and cheaper but requires a larger cross-section to carry the same current . Temperature Rise and Thermal Limits: IEC 61439 sets the upper safe temperature limit at 140°C for busbars under maximum working load, assuming an ambient temperature of 35°C. Thermal performance is verified through testing or calculation to prevent insulation degradation and fire hazards . Insulation and Enclosure: Busbars may be installed in open-air or enclosed assemblies. Enclosure type affects cooling and heat dissipation. IEC 61439 specifies minimum clearances, creepage distances, and protection against electric shock . Mounting Orientation: Vertical or horizontal installation impacts airflow and cooling efficiency. Proper support and spacing are required to maintain thermal and mechanical performance . Environmental Conditions: Factors such as ambient temperature, altitude, and humidity influence busbar sizing. IEC 61439 requires derating for high-altitude installations, typically increasing clearances by 1% per 100 meters above 2000 meters . Diversity Factor: Busbars rarely operate at full load continuously. A diversity factor is applied to determine the main busbar current requirement based on total equipment load, improving efficiency and reducing oversizing . Forms of Internal Separation: IEC 61439 defines separation levels (Form 1 to Form 4b) to segregate busbars, functional units, and terminals, enhancing arc fault containment and personnel protection .

Practical Sizing Example

A 50 mm × 10 mm copper busbar in open air can typically carry about 1000 A at 35°C ambient temperature with a 70°C temperature rise limit. Aluminum would require a larger cross-section to achieve the same current rating .

Additional Considerations

• Corrosion resistance and electromagnetic compatibility are tested under IEC 61439.
• Short-circuit withstand strength can be verified by calculation, testing, or comparison with reference designs.
• Support systems and finger-safe covers are used to ensure mechanical stability and safety . By adhering to these parameters, low-voltage busbars can safely and efficiently distribute power in switchgear, control gear assemblies, and industrial distribution systems while complying with international standards .