IEC 61439-1 permits a maximum temperature rise of 70 K for uninsulated copper or aluminum conductors (busbars) when measured at a 35 °C reference ambient. For terminals connecting external conductors, the allowable thermal rise is tighter — 55 K — to protect cable insulation at. Quick Answer: Busbar sizing must satisfy both continuous thermal performance and short-circuit mechanical withstand. This guide is written for engineers, EPC teams, and procurement managers who need clear equipment decisions, RFQ details, and commissioning checks. switchgear busbar sizing decisions. " LV Switchgear Bus bar temperature rise shall not exceed 45°C under rated current". Not many local vendors can achieve this? #4. Statistical analysis from electrical utilities worldwide reveals that thermal-related failures account for 30-40% of all high voltage switchgear breakdowns, with average repair costs. Undersized busbars are one of the leading causes of switchgear failures: they overheat, degrade insulation, and can trigger cascading short circuits.