Answer / er. ankush miglani 0971815107

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

Answer / tharik

good

3phase cable size calculation formula

Answer / bala

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

Answer / robert nithin

mv= (VD*1000)/L*I

VD= VOLTAGE DROP(AS PER COUNTRY STANDARDS)
L = LENGTH OF CABLE
I = CURRENT RATING
I = P/(1.73*V*PF)
PF= POWER FACTOR
MV= MILLI VOLTAGE DROP/AMP/METER

SELECT THE CABLE DEPENDING UPON THE MV RATING IN PRODUCT CATALOGS

Answer / anupam mathur

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.

Answer / bala

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

Answer / tauqeer hussain

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)

Answer / mohammed motawe

i will give you the basic eqaution,

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

Answer / premgin

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

Software like E Tap can also be utilised

Answer / tushar jana

I dont understand why people are complicating the issue....
the answer is very simple.

Consider Cable selection for the 3ph motor of 1kW

Formula>> P= root(3) x V x I x Cos(Phi) x Eff
p= power... Say 1kW
V= voltage (415Volt)
I= Unknown
Cos(phi)= 0.85.. say
Eff= Efficiency..= 0.85... say

Now,calculating this, we get>> I= 1.9Amp.. say approx 2A

Now derate this current (bcoz, cable will be laid in duct
or undergroung,etc) consider derating factor as 0.7 (say)
Then current is 2A/0.7=2.85A... say 3A..

now see the cable catlogue of any company.. say polycab..
See which size of cable can carry 3A current and use it...
thats it..

Approx.. for 1kW motor, 3Cx 2.5 Sq.mm cable is sufficient
upto 275m length.

NOTE: This is rough method of calculation. If cable length
is more or motor size is more... then voltage drop
calculation is also to be done.

Contact- 9665065050

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