DIN 43 671 specifies the continuous currents for busbars at an ambient temperature of 35°C and an average busbar temperature of 65°C. With the aid of a correction factor (k2), the continuous currents specified in the follow-ing table may be adjusted to alternative oper-ating. IEC 61439 is a standard developed by the International Electrotechnical Commission (IEC) that covers design verification for low-voltage electrical products and assemblies. This standard defines the design verification, test requirements, and thermal performance of the assemblies. The current rating is calculated from the conductor cross-sectional area, material (copper or aluminium), and maximum. Undersized busbars are one of the leading causes of switchgear failures: they overheat, degrade insulation, and can trigger cascading short circuits.