Calculate the size of cable
Find the cable size for given load
1) Find consumed load
Consumed load = Total load * Demand Factor (Kilo Watts)
And Define Voltage drop.
2) Find load in KVA (Kilo voltage ampere)
Consumed Load (KVA) = KW * Power factor
3) Calculate full load curren (F.C.L.) from KVA
Current (F.L.C.)= (KVA * 1000) / (1.732 * Voltage)
Where 1.732 = sqrt(3) (For three phase) And if there is one phase system then 1.732 replaces by 1.
4) Now Find different Correction Factor (For this factor refers IS code)
K1 = Temperature Correction factor in AIR
K2 = Temperature Correction factor in Ground
K3 = Thermal resistance factor (When Thermal resistance of soil is known)
K4 = Soil correction factor (When Thermal resistance factor is not known)
K5 = Cable Depth factor
K6 = Cable Correction factor ( Distance between two parallel Cable)
K7 = Cable grouping Factor ( OR No. of tray factor)
Now, Cable De rating factor K = K1*K2*K3*K4*K5*K6*K7
5) Select the cable And Find out it's Current Capacity , Voltage drop and Short circuit capacity.
If this cable should satisfy all condition that select that cable..
1) De rating Ampere = K * Ampere ( Ampere of selected cable)
De rating ampere > Full load current ( if this condition is satisfied than ok.)
2) Voltage drop = (1.732 * (F.L.C.) * (R*Cos$+ J*sin$) * L * 100) / (Voltage * No. of run * 1000)
Where F.L.C. = Full load current
R = Resistance
J = Reactance
$ = Angle ( $ = Power factor )
Voltage drop < Permissible voltage drop ( o.k.)
3) Short circuit capacity
Short circuit capacity of cable > System short circuit capacity at that point ( o. k .)