My question is whether bellow formula is correct to find bus size for 46kA for 0.5 second & what is RT in bellow formula.

formula to calculate the size of busbar to withstand the thermal stresses due to currents with duration of 0.2 sec to 5 sec.




Sp = RT( I x I x t) / K




Where Sp – is the cross sectional area of bus bar in millimeters.
I -    is the value of AC fault current.
t -    is the operating time of disconnecting device in seconds.
K –  is the factor depending on the material of the conductor, insulation and initial and final temperature.
Value of ‘k’ for copper is 143.


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