Calculation of Electrical Cable size

the determination of cable size in done on cost basis. The most economical area of conductors that for which the total annual cost of transmission line is minimum. This ia also known as Kelvin's Law.

First we calculate the amp rating of the equipment.for cu we take 2.5A & for alu we take 1.5 to 1.7A for 1sqmm cable.

It depends on a lot of factors like current density for mm^2 temperature is the cable on cable trays or buried or inclosed in PVC is that a 3 phase cable multicore or what and also depends on the voltage but in general making a current density 2 A/mm^2 for copper for simple applications is good.