How to calculate maximum short circuit current rating?

First we have to understand what is maximum short circuit current rating?

“The maximum short circuit current a component, assembly, or equipment can safely withstand when protected by a specific overcurrent protective device, or for a specified time interval"

Let's have and example of Cable Size 6.35/11 kV –1C x 300 Sq.mm.(Unarmoured )

Requirements :- 300 Amps for 2 Seconds.

Calculation for fault current of Insulation screen i.e. copper tape

The Formula used for Calculation of Short Ckt./ Fault Current :-

I^2 = K^2*S^2*Loge((Q1+B)/(Q0+B))/T

I(t) = Ish/sqrt(T)

Where I = Fault current in Amps

T = Duration of short circuit (fault current)in seconds

K = Constant (226 for copper)

S = Area of copper tape = 50 x 0.07 = 3.5 sq.mm

Q1 = Final temperature of copper tape = 200 OC

Q0 = Initial temperature of copper tape = 80 OC

B = Reciprocal of the temperature co-efficient of resistance of the copper tape per OC at O 0C = 234.5 = Constant

I ^2 = 226 2 X (3.5) 2 loge (200 + 234.5)/( 2 80+234.5 )/I = 317 Amps for 2 seconds for each core.