This guide covers busbar design standards, installation engineering practices, and IEC 61439 requirements, while comparing copper and aluminum options for sizing and selection. These busbars are not merely simple current conductors; they serve as the strategic backbone, interconnecting various components within the. IEC 61439 is a standard developed by the International Electrotechnical Commission (IEC) that covers design verification for low-voltage electrical products and assemblies. The IEC 61439. When designing electrical power systems, one of the most critical aspects is selecting the right size for busbars. UL-listed or UL-recognized busbars are commonly specified in North American electrical projects.