current drawn by motor

Discussion in 'General Electronics Chat' started by shahnawaz, Jul 3, 2012.

  1. shahnawaz

    Thread Starter Active Member

    Dec 30, 2008
    Hi all,

    i am trying to make an Auto Transfer switching(ATS) pannel for 03 input supply with one output supply.
    my load is 8 x 10HP 3/p motors. please tell me how much current an AC 10HP 3/Phase motor can drawn. my friend said its as per below farmula
    to convert the HP into Watt -10 x 746
    to get the amp frm the watt -7460/400
    total current taken by the motor -18.65amp

    so please tell me is it the right farmula. if not then how i can calculate to get the exact ampere of a 10hp 3/p motor.

    thanks in advance
  2. BillB3857

    AAC Fanatic!

    Feb 28, 2009
    That formula does not consider starting current which can be as high as 3X running current.
    The best way to know the motor current requirement is to read the nameplate on the motor.
  3. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    3phase motor formula

    HP x 746 =Amps
    1.73 x E x Eff x PF

    rule of thumb says 1.25Amps per HP

    E= Voltage
    Eff= Efficiency
    PF= power factor correction
    HP= Horse Power
  4. crutschow


    Mar 14, 2008
    That would be only for one particular mains voltage. The current per HP varies with the voltage.
  5. GetDeviceInfo

    AAC Fanatic!

    Jun 7, 2009
    not sure what your local codes are, but in North America, the code states that nameplate data is your first source. Calculations are allowed, but if you don't know amps, how would you know pf/efficiencies?