Simple Multiple Choice ?...Please let me know if I'm right, Thanks!

Thread Starter

ElecTechCan

Joined Jun 26, 2010
6
a single phase 1HP motor consumes 9A at supply voltage of 123V at 60Hz at a power factor of 78% while driving a fan. Which of the following statements is true?

a) The motor is overloaded
b) The motor is not overloaded
c) The motor is operating at 50% efficiency
d) The speed of the motor is 3600 rpm

I think the answer is A. I don't think it can be C because the numbers I came out with suggest it's operating above it's 1HP capacity? I don't think it can be D because there's no mention of the # of poles so I don't even know how you would calculate the rpm...

Please let me know if I'm right or help steer me in the right direction, Thanks!
 

t_n_k

Joined Mar 6, 2009
5,455
I'd agree with answer (a) for the following reason ....

1HP=746W

At 123V supply and pf=0.78

Iload(rated)=746/(123*0.78)=7.8A

So at Iload=9A, the rated current is being exceeded which suggests an overload condition.
 
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