The IEC 61439 series of standards sets out the regulations for power distribution boards as well as assemblies for power distribution in public networks, construction sites, and for prefabricated busbar trunking and cabling systems. This article explains the ABCN arrangement requirements based on electrical installation practices and Chinese national standards. Understanding ABCN: Functional Codes in Power Systems In a three-phase system, each busbar corresponds to a specific electrical function: A, B, C Phases (Live. IEC 61439 is a standard developed by the International Electrotechnical Commission (IEC) that covers design verification for low-voltage electrical products and assemblies. Instead, proper torque, contact pressure, and joint design govern contact resistance and long-term reliability inside an industrial electrical enclosure. They carry large currents and must be properly sized to ensure safety, performance, and compliance.