# Re: breaker switch

#13125
Spir Georges GHALI
Participant

@guest said:
how much ampere should i use for my 15hp, 220v, 3 phase motor?

Dear;

refer to your information about the motor, and to decide the nominal current should be used, we should calculate the nominal current for this motor as follow :

You mentioned to the Motor’s power in ” HP : 15 “, the supply voltage ” 220V “, and it’s ” 3 Phases Motor “, to be able to calculate the nominal current, I assumed that the Voltage is between 2 phases, and the Power Factor for this Motor is ” Cos φ = 0.80 “, so :

I = P / 1.732 x U x Cos φ

I = 15 x 745 / 1.732 x 220 x 0.805

I = 36.6 A

In this case, if you will use a Switch, his nominal current should be at least ” 40A “, bur be careful by using only Switch  there’s no any protection for your motor, but if you want to use ” Contactor + Thermal Relay ” you can use : 40A Contactor, and  Thermal Relay can be adjusted at ” 36 A “.

By the way, if the Voltage value between 2 phases is different, the calculation should be redone to have the relevant value of Nominal Current, and the same for ” Cos  φ “