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

Discussion in 'Homework Help' started by ElecTechCan, Jul 4, 2010.

  1. ElecTechCan

    Thread Starter New Member

    Jun 26, 2010
    6
    0
    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!
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    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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