Answer / shantanu dash

The cable size of a motor mainly depends on the following
factors.

(i) Rated Current of Motor
(ii) Starting current and starting time of the Motor on
load.
(iii) Type of starters used for starting the Motor

Answer / govind

Thae cable size of the motor is decided from the rated load
(in Amps)of motor.

Answer / bhupatsinh

its depends on motor max. current, votage, and lenght of
cable.and volatage drop.

Answer / arvind

The cable size of motor depend on rated current of motor,
but as the motor draw more current at starting which will
be around 2-3times the rated current, so cable size will
going to be increased i.e, wherever we will calculate we
take 20% extra for selection of your cable

Answer / sanjeev pal

motor cable is decided according to motor rated current
given in specification plate. WHEN MOTOR is initially
running condition then motor draw current 1.5 times more its
rated current. so this factor decided cable size of motor

example 10 HP MOTOR rated current is 14.7 or 15 ampere
when initial running condition draw 1.5 times more
14.7 * 1.5 = 22.05 ampere then current caring capacity
of cable is 22 Ampere must be necessary.

correct answer hai

Answer / imran khan

Cable size of motor is decided on the following factors:
1. Full load current of motor(Since P=VICoso/Sqrt3VICoso)
2. Length of Cable.
3. Method of cable laying.(Air(Tray)/Underground(duct)).
4. Voltage drop of cable.

Calculation will be as:
1. If cable is laid on Tray/underground take its
corrosponding derating factors.
2. Multiply all derating factors & this derating factor is
multiplied by current carrying capacity of the cable which
you are going to sellect(from catalogue).
3. Above current should not be less than full load current
of motor.
4. Then check voltage drop (Vd=(IxLxmV/A/m)/(Rx1000))
where Vd=Voltage drop, I=Current(full load),L=length of
Cable(site requirement),mV/A/m=millivolt/Ampere/meter(from
catalogue),R=No. of Runs of cable.
5. Above voltage drop should not be more than 4%/2.5%(As
per requirement).

Answer / mithilesh

in Most of above answer every one stating about staring
current, current rating of motor but only one guy stated
about voltage drop of cable.

i think guy who stated about voltage drop,current rating,
power rating of motor( because starting current varies
with Hp rating of motor lower the hp higher the staring
current) his answer is more regionable than others.

from my experince i would say only full load current rating
of motor & voltage drop of motor will be enough to
calculate the cable size because staring current is only
for less time. and all cable has been designed for 2-3
times of rated current for 1 min. this answer will be
perfect for higher rated motor( more than 50hp)

less than 50 hp motor we have take consideration of
sttarting current( because starting current 3-4 times of
full load current).
is

Answer / md gufran yaqub

cable size for motor is decided based on
-rated load
-starting method and current withdrawn generally conductor
size is selected 2-3 times that of rated load
-length of cable and duty type decides the cable insulation
-obviously the cable rating should not be less than
protecting device

Answer / praful nandankar

To limit the starting current there are various protection
devices. Manufacturers always design the motor cable taken
into consideration the after effects of starting current.It
depends on the motor rated current and the voltage drop
which is already mentioned in some answers.

Answer / dilanka

motor drowse starting current which will be around 2-3 times
the rated current. so cable size going to be increase.How
ever it is suitable to select 125% or 130% current rate for
cable because the cable can withstand without any damage for
few second. you must check the cable manufacturing data to
find this specific time and it should be more than the
starting time period of the motor.

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