Motor Starting Current and Transformer Size


I have 2 motors of 35KW and 2HP.  There is another electrical linear load of 400KW. Kindly guide me what current will draw when the motor starts and cable size as distance is 40m. 

Kindly also guide me what size of transformer is required? 

Please explain with calculation.

Kind Regards,


asked 2/10/2014
  • 1. Starting current will depend on the type of start (DOL,S/D.soft starter) employed.
    2. Will both the motors and Linear load be started at the same time?
    3. To know the transformer size what is the voltage level of motors and linear load and what is your incoming supply to Xmer? - ram31 3/26/2014

3 Answers

cable sizing doesn't depend on starting current but fuse/cb only
answered 4/23/2014 naban 6
  • cable size will depend
    1 .Load current(current required by device which it is connected)
    2. type of installation(air,underground,duct)
    3. Ambient temperature
    4.Grouping factors
    5. voltage drops as per local regulations
    6 .Short circuit current capacity Adiabatic equation) - ram31 4/27/2014

Dear friend

U have a total connected load of 437 KW, first u have to decided what type of starter do u have for the motor load because a) DOL starter for lesser than 13HP the starting current is 7XFLC with good torque (b) Star Delta Starter 13HP to 48 HP starting current is 3XFLC with poor torque (c) Auto TC greater than 48HP is 4XFLC with average torque and (d) VSD starting current is 0.5 to 1.5XFLC with excellent torque, so keeping in view of above facts it seems to install 750KVA transformer
Cable sizing should be 3 times of FLC
Fuse should be 125% of the FLC
answered 4/2/2014 Sathya Narayana JE E/M 46
Sathya Narayana JE E/M
Provide the following details to provide answer-
. Type of start employed for motors 2. Will both the motors and linear load start at same time? 3. What is the voltage level,frequency of motors and linear load? 4. What is the incoming supply to Xmer?
answered 3/26/2014 ram31 66

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