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Dear ;

I think that you posted another topic for Cables' Section Calculation where I explained the procedure to define the suitable sections of Cables to electrify the 70 AC, the cables are :

– For each Phase : **” 4** x** Single Core Cable of 300mm² “**

– For Neutral : **” 2** x** Single Core Cable of 300mm² “**

**About the Circuit Breaker size :**

we do as follow to define the specifications of the CB

– The Nominal Current for CB :

**I**n = 1250A

– The Thermal Protection :

**I**r = 1200A ( as the cables can carry ” 1246A ” with the installation conditions )

– The Magnetic Protection :

**I**m : we should calculate : the minimum Short Circuit Current at the end of cable ” Isc1min “, and the Earth Fault at the end of cable, then the value of ” Im ” will be smaller by ” 20% ” than the smallest one.

– The Breaking Capacity :

**BC**: we should calculate the maximum Short Circuit Current at the beginning of cable ” Isc3max “, then the value of ” BC ” will be equal or bigger than the calculated value.

But as I don't know : the Power of Transformer, the Earting system, and the Length of cable, I can't calculate the 2 last specifications.

Regards.