# current drawn by motor

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

1. ### shahnawaz Thread Starter Active Member

Dec 30, 2008
37
0
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.

2. ### BillB3857 Senior Member

Feb 28, 2009
2,399
348
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 Distinguished Member

Jun 22, 2012
4,779
707
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 Expert

Mar 14, 2008
12,522
3,064
That would be only for one particular mains voltage. The current per HP varies with the voltage.

5. ### GetDeviceInfo Senior Member

Jun 7, 2009
1,571
230
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?