Standard Requirements for Secondary Distribution Boxes in Factories

Secondary distribution boxes in factory buildings should comply with IEC 61439 standards, support 400V LV distribution, and be designed for safety, efficiency, and modular installation.Voltage Levels and Transformer RequirementsSecondary distribution boxes typically step down medium voltage (11kV or 6.6kV) to low voltage (up to 1kV) for factory use . Transformers should meet minimum capacity requirements, often 500 kVA or higher, depending on load, and LV distributor cables should be sized at 185 mm² Aluminium or larger, with HV cables at 150 mm² Aluminium or larger . Oil-cooled transformers are generally not recommended indoors due to fire risk .Design and Installation GuidelinesIndoor vs. Outdoor: Indoor substations are preferred in factories to protect equipment from dust, moisture, extreme temperatures, and theft, ensuring lower maintenance and higher reliability .Enclosures: Distribution boxes should have robust housings, often sheet steel, to protect sensitive electronics in harsh industrial environments .Decentralized Installation: Placing distribution boxes close to the load improves energy efficiency, reduces cable lengths, and allows flexible retrofits .Pluggable Components: Use modular, pluggable systems for fast installation, easy maintenance, and future expansion .Safety and ProtectionCircuit Breakers: Each area, machinery, or equipment should have dedicated circuit breakers (MCCB or ACB depending on current rating) to prevent overloads and short circuits .Lightning Protection: Install lightning protection systems to safeguard the building and electrical equipment .Compliance: All equipment must be new and comply with relevant standards, including IEC 61439 for switchgear and IEC 61535 for connectors .Cabling and DistributionMedium-Voltage Distribution: MV electricity is stepped down via main transformer substations (MBA) to supply medium-voltage switchboards (MSB) in the factory .Low-Voltage Distribution: MSBs feed LV distribution boxes, which supply machinery, lighting, HVAC, and other electrical loads .Cabling: Underground cabling is preferred over overhead lines to reduce exposure to environmental hazards and improve reliability .Additional ConsiderationsEnergy Efficiency: Decentralized distribution and smart distribution boxes support building automation and energy management, contributing to climate targets and operational cost savings .Redundancy: Critical loads may require UPS or DG backup, with proper isolation transformers to maintain power quality .Space Optimization: Modular and decentralized distribution reduces the need for large equipment rooms, freeing usable factory space . By following these standards and guidelines, factory buildings can ensure safe, reliable, and efficient secondary power distribution, while maintaining compliance with international electrical standards and supporting future scalability.