Electric motor calc

[theapprentice72]

Could anyone help me with this motor calc problem i am trying to solve

How many amps is being drawn by (3) 10hp 208v 3 phase motors?

Any help would be greatly appreciated.

 

[ActionDave]

The question can't be answered without knowing what the nameplate on the motors says and how much load is on the motor. The tables at the end of 430 will give you the NEC thoughts on it.

 

[theapprentice72]

I think I was to assume the SF is 1.15. Does that help? This was for a state test and I can't remember all of the question.

 

[augie47]

I would think for a test question, the answer would lie in Table 430.250

 

[theapprentice72]

Yes, I think 430.250 is where I looked.
10hp 208v = 30.8 amps.

Then all I would need to do is multiple 3 by 30.8 amps?

Is it really that simple or am I missing something?

 

[Smart $]

Yes, I think 430.250 is where I looked.
10hp 208v = 30.8 amps.

Then all I would need to do is multiple 3 by 30.8 amps?

Is it really that simple or am I missing something?

Really that simple... if that's all the question stated.

 

[kwired]

Really need to know exactly what the wording of the question is. Most likely for the test they were looking for what minimum ampacity of feeder conductor is needed for those three motors.

As far as a reality of what the three motors would actually draw - it depends on the load being driven. Just because they are 10 HP motors doesn't mean they are loaded to 10HP. They are likely loaded more then 7.5 at least some of the time though otherwise 7.5 HP motors may have been selected for the application.