sorry i dont have the xat formula for that but
for ALUMINIUM CABLE: 1sq.mm = 1.2 A of current
CU: 1sq.mm = 5.0 A of current
and the relation b/w A & KW IS
1KW= 1000*A*240*COS#
A- CURRENT
240= VOLTAGE
COS# = POWER FACTOR (.8 TO .99)
NOW IF U KNOW THE EXACT CURRENT LOAD OR LOAD IN THE FORM OF
KW U CAN EASILY FIND THE AMPERE RATING.
AFTER FINDING THE AMPERE RATING U CAN CALCULATE THE THE
SIZE OF THE CABLE. ANKUSH MIGLANI
9718151073
ankushmiglani2000@gmail.com

Hai
First u will convert the KW OR kvA loads to AMph
After u can select the suitable cable from cable manufuture
catalouge . that u will consider derating factor = 0.72
For Example
50 A
16 SQ XLPE Al cable may be suitable
The 16 sqmm cable suitable for 70A ( DATA TAKEN FROM
HAVEELS CATALOUGE)
70 * 0.72 = 50.4 A
So the cable suitable for the above load.
after u will cross check voltage drop for the cable

Cable size depends on 1)Voltage Drop, 2)Distance, and 3)Load
So u have to calculate first the permissible voltage drop.
For lighting circuit permissible voltage drop:
2% of the rated voltage + 1 volt
2 X 230 /100 +1 = 460/100 + 1 volt = 5.6V

For motoring load
5% of the rated voltage

5 X 415/100 = 20.75 V

Now the formula for calculating voltage drop:

Voltage Drop = I X D (r X 0.85 + Xc X 0.53)/No. of runs X 1000
I : Current
D : Distance
r : Resistance
Xc : Capacitive reactance

If the voltage drop comes within the limits then ur cable
selection is ok.

Hai
The formula is delda v =
rt3 x I X Z X L/ 1000 x no OF runs
% OF VOLTAGE DROPS = Deta v
------ X 100
APPLIED VOLTAGE
The % of voltage voltage drops should be below 3 %
I = Requird current
Z = Cable impedance
L = cABLE LENGTH

First how many Amp you required
Example - 80
then you go to cable catalouge find out suitable cable
size
then calculate original current carring capacity of that
cable and multifly with 0.72 ( derating factor )
example in catalouge may be 35 sq mm cable and current
carring capacity may be 125 A
125 X 0.72 = 90
The carring carring capacity point of view this cable will
be ok
next you will check voltage drop with help of above said
fomula

PL = V*I*Pf=S*Pf ; i need to calculate the load current ,

I= PL/(V*Pf); as per ADDC(abu dhabi electricity), Pf=0.9
V=230 volt,

From the load CURRENT i can choose the rated current of
cable, take into account the voltage drop, so refer to
cataloge of any cables and wires company like oman cables

regarding with three phase just put cu(3) in the equations
best regards

We can use fromula for Voltage Drop Calculation
VD = mVxIxL/1000
VD = Voltage Drop
mV = Milli Volt(Given Rating Cable Manufacture)
Example 16sqmm mV =2.5 mv/a/m
I = Load Current
L = Lenght of Cable
Exapmle #
Voltage = 415vAC, Ampere = 25, Length of Cable = 100Meter

VD = 2.5x25x100/1000
= 6250/1000
= 6.25 (in volt)
= 1.50% (in percent)

See dear the basic soultion to cable size calculatiion in
sismple form can be done like this

Vd= ( mv* I * lenghth)*100/(400*1000)

I u can calualte from the Kw value for the particular pf
simple P/554

L required length

mV is the volatage drop/amp/km that can be obtained for the
particluar size of cable from supplier

eg. for 4cx16 its around 2.5 for most suppliers

100/400 is just amultiplication factor for converting it in
to 3 phase

Now do calulation and check if voltage drop limit is below
2.5 or 4 as per your standards

Simple.

But be cutious this is the simplest method and suitabel
method,many factors like grouping factor,derating
factor,spacing factor,type of laying,etc has to be taken
for apt analysis

Voltage drop works on Ohms Law.Multiply the route length in
metres by the the number of ampers of current that the
appliance draws,and then multiply by the number of milivolts
per ampere metre (mV/A.m)
Formula: Vd = L x I x Vc /1000
Where: Vd is the voltage drop measured in volts
L is the length of the cable in metre
I is the circuit current in Ampere
Vc is the millivolts per amper per metre droped
along the cable
1000 is a correction factor applied because Vc is in
millivolts and Vd is in volts.