Copper cable short circuit current withstand

[J2019L]

A 70 sqmm copper cable can withstand a short circuit current of 8.05kA for 1 second. If the protection relay operates in 0.2 second, then what is the maximum fault current that the cable can tolerate?

The solve method seems to apply: 8.05kA * sqrt(1/0.2) = 18.0 KA
Is there someone can find the source document to proof this concept?

[Wanderer20001us]

A 70 sqmm copper cable can withstand a short circuit current of 8.05kA for 1 second. If the protection relay operates in 0.2 second, then what is the maximum fault current that the cable can tolerate?

The solve method seems to apply: 8.05kA * sqrt(1/0.2) = 18.0 KA
Is there someone can find the source document to proof this concept?

I²T = I²T. Damage energy remains constant.