Test Method: The test is performed by injecting the calculated fault current into the busbar system. The incomer SCPD is disabled to prevent tripping, and the test checks the ability of the busbars to withstand mechanical forces without physical deformation or. IEC 61439 requires busbar systems in LV assemblies to be verified for short-circuit withstand strength, not just current-carrying capacity. Busbar support spacing is a critical design variable: wider spacing reduces short-circuit withstand rating. Verification under IEC 61439 can be done by testing. 7 cycles of 24 h each to salt mist test according to IEC 60068-2-11; (Test Ka: Salt mist), at a temperature of (35 ± 2) °C. The test shall be carried out according to IEC 60068-2-2 Test Bb, at a temperature of 70 °C, with natural air circulation, for a duration of 168 h (7 days) and with a recovery. 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 IEC 61439. Figure 1: High-performance VIOX industrial low voltage switchgear assembly, demonstrating modern compartment design, reliable circuit protection, and clear busbar phase identification for superior substation safety. What Does IEC 61439 Require for Low Voltage Switchgear Design? IEC 61439. Insulation tester leads must be connected between the one-phase busbar and the earth. The test voltage shall be selected based on combination & voltage class.