(Iz) = current carryng capacity of the cable where it is installed. (It) = tabulated current for a single circuit at ambient temp of 30°
(Ib) = the actual current to be carried. (In) = is the Circuit Breaker rating in Amps.(I2) = the current at which the CB opens.
(Ca) = correction factor for Ambient temp. (Cg) = correction factor for grouping. (Ci) = correction factor for thermal insulation.
One method to determine the Potential short circuit current if you do not have a Loop Impedance Tester.
Find the volt drop of the system V1-V2 Divided by the Load gives Zs. Where V1 is the open circuit voltage,
V2 is the voltage under load and load is the amperage of the system.
IE: (V1)240 - (V2)238 = 2 divided by the Load 40Amps = 0.05 Ω.
Then PSC = System voltage (Uo) / (Zs) 240 ÷ 0.05 = 4800 Amp.
Enter different values in the boxes below and click on Send, you can use the Tab button to move between boxes.

V1  V2  Load in Amps  Calculate
Cable Selection, Copper Only, up to 25mm², above this Cable Reactance must be considered.
Enter your proposed cable size,type of insulation,Voltage,ambient temp (30 is norm) your cable length and circuit load in Amps.

 Cable size Insulation Voltage Abient Temp Cable length in Mtrs Design Amperage Circuit Breaker 1 mm² PVC 220V 25 6 Amp typ B 1.5 mm² Thermosetting 230V 30 10 Amp typ B 2.5 mm² M.I. Pvc covered 240V 35 16 Amp typ B 4 mm² M.I. Bare 380V 40 20 Amp typ B 6 mm² 400V 45 25 Amp typ B 10 mm² 415V 50 32 Amp typ B 16 mm² 55 40 Amp typ B 25 mm² 50 Amp typ B 63 Amp typ B