You will need
  • Calculator.
The load for the apartment is calculated as follows. Calculates the total capacity of the appliances that will be included in one branch of wiring, ie in those sockets that are connected to one common wire coming from the panel. Take a reference on the electrics and on the table to determine the size wire needed..
If it is not at hand, then can be calculated using the following formula. Current consumption of electrical appliances is calculated as;
I = P / U
Where I is the load current; P - power; U - voltage.

You can use a simplified calculation

I = 4 × P

Only in this formula, the capacity is calculated in kW, not watts as in the previous one.
Next is calculated the necessary diameter of wire:
d = k×I + 0,005
d - wire diameter in mm;

k - constant coefficient, for copper it is equal to 0,034.
But as in the trading network of the wire measured in the cross sectional area, then:
S = 0?785 * d2
where S is the cross - sectional area of the wire.
For example, at the same time included in the network appliances with a total capacity of 2.8 kW.

Load current: I = P / U = 2800 / 220 =12,7 And
d = k ×I + 0,005 = 0,034 ×12,7 + 0,005 = 0,5 mm

S = 0,785 × d2 = 0,785×0,52 = 0.2 mm2
To calculate the input cable, you need to calculate the total load power, and

on the same principle of calculation, as indicated above.
So you can roughly calculate the required cross-section of electrical wire, as they say in the eye. Based on the fact that copper wire is chosen based on S = 1 mm2 I = 10 A. Aluminum wire) S= 1 mm2, for a current = 8 A.
But in most cases, the installation of electrics based on the fact that the outlet wire is 2.5 mm2, and lighting - 1.5 mm2.