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Question
How to calculate the current carrying capacity of 
electrical cables
 Question Submitted By :: Rakhi Kawatra
I also faced this Question!!     Rank Answer Posted By  
 
  Re: How to calculate the current carrying capacity of electrical cables
Answer
# 11
Well, First try to calculate the total load of the system.
For example total load is 1000KW. The current can be
calculated as P=1.732VICOS(PHI). Hence total current will
be 1732A by considering V=415volt, power factor=0.8.

Step2: To calculate the cable size

Vd = mV/L/A

where Vd= Allowable voltage drop which is normally 2.5
percentage to 4 percent.
L = Lenght of the cable from the source to feeder
A = Ampere rating

Let us consider L = 1000Meters
A = 1732A
Vd = 2.5 percentage of 415V as in U.A.E.
= 2.5*415/100 = 10.375

Use these value in the above formula

mV= Vd/L*A
= 10.375/1000*1732
= 0.005 volt

Refer to the cable catalogue in your region and find out
the current carrying capacity of the cable which will be
totally depend upon the atmospheric condition, in cold
place a smaller diameter of cable can carry larger current
and in hot areas the same size will carry lesser current.

In U.A.E. we are normally using 11x1c 630sqmm cable with
2500A incomer breaker. But cross check the voltage drop as
calculated above is within the limit of voltage drop of
these cables else you have to go to higher size of cable
untill the voltage drop met the design milli volt drop of
the cable.
 
Is This Answer Correct ?    6 Yes 5 No
Abdul Haseeb Khattal
 
  Re: How to calculate the current carrying capacity of electrical cables
Answer
# 12
BY SIMPLE
CURRENT DENSITY = LOAD CURRENT/AREA

FOR COPPER OR ALUMINIUM CURRENT DENSITY CAN BE VARIED ACCORDING TO OUR DESIGN.FOR GOOD DESIGN CURRENT DENSITY SHOULD BE REDUCED WHICH HELPS IN EASY TEMPERATURE DISSIPATION.

CONSIDER CURRENT DENSITY OF 0.6A/SQ.MM FOR cu OR AL
LOAD CURRENT-100A
THEN
0.6=100/AREA
AREA=166 SQ.MM

MEAN THAT 166 SQ.MM REQUIRED TO CONDUCT 100A.
 
Is This Answer Correct ?    2 Yes 5 No
Manojkumar
 
  Re: How to calculate the current carrying capacity of electrical cables
Answer
# 13
hi frnd.. what will u say for the given ques. if interviewer asked, How a manufacturer determines the current carrying capacity of electrical cables?? 
Is This Answer Correct ?    1 Yes 0 No
Himanshu
 
  Re: How to calculate the current carrying capacity of electrical cables
Answer
# 14
for 50KW motor
p=50
I = 50x 1.2 (thumb rule)
=60 A

Size of cable : 60x0.2(thumb rule)
: 12

so min size of cable req. 12 sqmm.
 
Is This Answer Correct ?    4 Yes 5 No
At
 

 
 
 
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