# 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 )

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

• For efficiency is not compulsory if we don’t have the value.,we can ignore the value :D

• Steve says:

Can you tell me what amperage draw would be for a 1.1 hp motor running on 24 volts

• hasan says:

If it’s single phase then
p=vi.pf.
1.1×746=24ix1
i=34.2amp
If its three phase then
p=1.732vixpf here pf=.8
i=24.67amp.

• EMMANUEL says:

What is the current draw for a 3phase 415V 60HP electric motor?

• What is the 3 Phase AC Current draw for an 80A DC Motor running at 440VDC?
Thank you
Robert Karkafi
Engineered Drive Systems
Los Angeles, Ca

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?

• Yes Steve..it true.You can include with efficiency value if you know but if not you can skip it.

• manno says:

What is 1..732

• Square root 3 = 1.732

• M.NARESH says:

√3 = 1.732

3. amir says:

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.

• Hi,Normally i just put PF to 1 but it’s ok to put PF 0.8

5. Akash rajhuns says:

hiii

you can also use

KW = √3 × V× I × cos¢

cos¢ = 0.8

• Yes Akash,Thanks for sharing the formula

6. aashish tripathi says:

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

• M.NARESH says:

KW/KVA

7. dheeraj says:

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

8. jacob says:

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

11. chinna says:

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.

• tukaram haldankar goa says:

60 multiply by 0.746 as converting ratio you will get watts per hour and multiple for 12 hour is 44.760 kilowatts per hour multiple for 12 hour is 537.12 for 12 hour, calculate this kw multiple ain unit charges by electricity per unit you will get your bill……

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

• bac +84919261294 says:

yes

14. john says:

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

15. john says:

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. Tushar says:

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

• rupesh says:

kw/kva

21. anil says:

Is motor rpm is necessary to calcultae full load current?

• binod jaipuria says:

Short trick kw to full load ampere

• John Lemau says:

Not necessary. Full RPM = Full load ampere

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.

• sushil says:

i phase 230 volt motor

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. Viren says:

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

26. Starting current of 10 HP induction Motor is_________ times full load current
A)5
B)8
C)10
D)20

• John Lemau says:

It depend what motor starter that you use..

DOL –> 5- 6 X FLA
AUTO TRANS –> 3-4 X FLA
STAR DELTA –> 3-4 X FLA

The best is VFD – Variable Frequency Drive

27. Vikash says:

We have motor rating in KW, it means KW power take in how much time

• Time in sec. Or hour

28. karthi says:

what is the current rating of 200hp motor?

• John Lemau says:

Full load amp for 200hp approximate = 275 AMP

29. Jitendra Lohar says:

1. How to calculate stating current of single phase and three phase motor ?
2. How to decide or calculate start capacitor or running capacitor for single phase motor ?

30. inayat Hussain says:

A motor follows the operation as
20kW 120 sec
10kW 120 sec
Stopped 280 sec

What will be the continuous rating of motor for above operation.

31. Ashish Patidar says:

I have 2 same motor (equal power, rating and brand) 3 Phase, running on same type of job on two different machines, one of them is drawing 45 amps where as other is drawing 50 amps of current. They run 24*7 in plant so i want know is how much unit each one consuming ??

32. NIRMAL says:

WHAT IS FULL LOAD CURRENT FOR 30 HP 3 PHSAE MOTOR?

33. art says:

Good way of explaining, and pleasant post to take facts regarding my presentation subject matter,
which i am going to convey in college.