How calculate ampere for electric motor?

Generally for electric motor size,it rated by horsepower (hp) or kilowatts (kW) unit.We can recognize the electric motor size when refer to their kilowatts or horsepower.So from power (kW/hp), how we can know the full load ampere for electric motor?

This time i want share about how to calculated the full load ampere (FLA) of electric motor from their power rated.It not difficult if we know the right formula to get the answer.From this calculation we only can estimate the value of full load ampere.

We cannot get the actual full load ampere because it depend on efficiency of motor.If electric motors have a higher efficiency rating,it will draw fewer amps, for example a 10 HP motor with a 60% efficiency rating will draw about 65 amps at 230 VAC compared to about 45 amps for a motor with a 80% rating.

 

How to calculate from power ( kW & HP ) to ampere ( I )?

1) Kilo watt (kW) to ampere ( I )

For 3 phase power supply ; kW = I x V x 1.732 x pf

For 1 phase power supply ; kW = I x V  x pf

Example : 1 unit compressor size rated 37 kw,415 VAC,3 phase and 80% pf,calculate the full load ampere?

Calculation :

kW = I x V x 1.732 x pf

I = kW / (V x 1.732 x pf )

I = 37 / (415 x 1.732 x 0.8 )

I = (37 / 575) x 1000

I = 64.4 ampere ( full load ampere)

 

2) Horse power ( hp ) to ampere ( I )

First we must convert from hp to kW using this formula :

1 Hp = 0.746 kW

After that use the formula kW to ampere :

For 3 phase power supply ; kW = I x V x 1.732 x pf

For 1 phase power supply ; kW = I x V x pf

 

Example :-

1 unit induction motor power rated 25 hp,200 VAC,3 phase,90 % power factor,calculated the full load ampere.

Calculation :-

kW = 25 hp x 0.746

kW = 18.65

kW = I x V x 1.732 x pf

I = kW / V x 1.732 x pf

I = 18.65 / ( 200 x 1.732 x 0.9 )

I = (18.65 / 311.76) x 1000

I = 59.8 ampere ( full load ampere )

Comments

  1. Should we take into consideration the efficiency of the motor?.

  2. Steve Sedgwick says:

    In your formula Efficiency factor is not accounted – is there some reason for this. I thought the formula was kW = I x V x 1.732 x pf x Efficiency?

  3. Hi. May I help you to calculate the electrical load list of power plan.
    amir.masror@gmail.com

  4. Ronald says:

    Hi! Is the power factor required also? or If I didn’t know the p.f. can I use 0.8? Our motor specs are 18.5KW, 460V, 3PH.

  5. Akash rajhuns says:

    hiii

    you can also use

    KW = √3 × V× I × cos¢

    cos¢ = 0.8

  6. aashish tripathi says:

    how could we calculate if we don’t know pf…?

  7. dheeraj says:

    a motors rating 10kw !!!!! what its means this motor will consume 10 kw per sec ??? or 10 kw per hr?????

  8. how did you come about the 1000?please assist

  9. HARI KRISHNA SINGH says:

    how can i found 3 ph motor efficiency

  10. Joshy.G.S says:

    You should say P = √3VIcos¢
    Watt is the unit of power, to convert Watt to kilo watt divide by 1000
    Then no confusion about 1000

  11. a 48v dc motor with nominal power 11kw. how can i calculate pf

  12. NIRMAL MEHTA says:

    WHAT IS THE FORMULA AS UNDER:
    440 V, 60 H.P., 55 AMPS, PF .95 & 12 HOURS
    NOW WE WANT HOW MUCH UNITS WILL CONSUMPTION AS ABOVE POINTS.

  13. M.NARESH says:

    1 HP = .746 KW
    GIVEN DATA IS 20 HP AND WE NEED TO FIND THE AMPS RATING

    20 HP = 20 * 0.746
    = 14.92 KW
    HERE 14.92 KW , IT IS 3-PHASE ( ABOVE 4 KW WE CONSIDER 3-PHASE AS PER NEC )

    P = √3 V I cos¢
    P = 14.92 KW
    V = 415 V
    cos¢ = 0.8
    √3 = 1.732
    I = ????

    P = √3 V I cos¢
    I = ( P / √3 V cos¢ )
    I = (( 14.92*1000 ) / ( 1.732 * 415 * 0.8 ))
    I = 25.94 A
    I = 26 A

  14. I made a blower. The fan is OD 33.5″
    6″thickness and 55 kg Wight
    Which power motor required (HP)

  15. I made a blower. The fan is OD 33.5″
    6″thickness and 55 kg Wight
    Which power motor required (HP)
    2800 rpm

  16. tushar says:

    hiee, for 3 phase 1kw ac motor how much the maximum current rating is acceptable?

  17. Littu chirayil says:

    How to calculate amper when horsepower is given for 3 phase ?

  18. himanshu says:

    A 20 H.P, 3 Phase supply ,50Hz , 440 Volt in induction motor .find out full load current?

  19. we are having 3-phase BLDC hub motor (800W ,48V).
    we have to run this motor for 2 hours with Lithium-ion battery.
    Then how to decide the battery capacity?

  20. Narsing says:

    how to find pf

  21. Is motor rpm is necessary to calcultae full load current?

  22. MEshari says:

    how to Calculate the actual running current of a motor such as: moter name plate:
    P=75KW
    V=440
    Pf=.89
    phase=3
    incoming V=480V using softstarter

  23. sushil says:

    which type (watt) inverter require for run 1 hp electric motor.
    pls given best answer .

  24. Hi Gents
    I have a pump with Diesel engine 1450 RPM, 160 KW, Soi wants to change the diesel engine by Electrical Motor 1450 RPM, 160 KW, 3 Ph, 380 Volts, 50 Hz, so I need to know how many Amp. I need for each one phase ( they write in the motor 280 Amp is this total for all 3 ph or 280 Amp for each one phase ) Cheers….

  25. Hi, if I’m having 15 kW motor , 3phase, pf .8 star-delta starter. How can I find How much current will flow in star condition & how much in Delta?! Pls answer. Thank you

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