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Thread: MI PSI Practice Exam Question

  1. #1
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    Jun 2015
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    Muskegon, Mi, USA
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    MI PSI Practice Exam Question

    Hey everyone,

    My apprentice is about to take his Journeyman's test this Thursday through PSI. He got a question wrong on his PSI Practice Test and asked me for input. I'm embarrassed to say I couldn't see how they came up with their answer.

    Q: What is the motor nameplate FLA rating for a 5 HP single-phase motor, 230 volt with an efficiency rating of 95% and a power factor of 90%?

    A: 8 amps
    B: 16amps
    C: 19amps
    D: 25amps

    My apprentice chose the answer D, but the correct answer is C according to the practice test. Can anyone explain the formulas needed to come up with the answer? Any help would be appreciated!

  2. #2
    Join Date
    Sep 2008
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    UK
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    Quote Originally Posted by Padilla616 View Post
    Hey everyone,

    My apprentice is about to take his Journeyman's test this Thursday through PSI. He got a question wrong on his PSI Practice Test and asked me for input. I'm embarrassed to say I couldn't see how they came up with their answer.

    Q: What is the motor nameplate FLA rating for a 5 HP single-phase motor, 230 volt with an efficiency rating of 95% and a power factor of 90%?

    A: 8 amps
    B: 16amps
    C: 19amps
    D: 25amps

    My apprentice chose the answer D, but the correct answer is C according to the practice test. Can anyone explain the formulas needed to come up with the answer? Any help would be appreciated!
    5 HP is 3.73 kW or 3730W. The factor is 0.746.
    Divide that by the pf and efficiency and you get 4363 VA
    Divide that by 230 V to get Amps.
    About 18.97A
    So call it 19A.
    Si hoc legere scis nimium eruditionis habes.

  3. #3
    Join Date
    Jun 2004
    Location
    Cherry Valley NY, Seattle, WA
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    2,833
    Quote Originally Posted by Padilla616 View Post
    Hey everyone,

    My apprentice is about to take his Journeyman's test this Thursday through PSI. He got a question wrong on his PSI Practice Test and asked me for input. I'm embarrassed to say I couldn't see how they came up with their answer.

    Q: What is the motor nameplate FLA rating for a 5 HP single-phase motor, 230 volt with an efficiency rating of 95% and a power factor of 90%?

    A: 8 amps
    B: 16amps
    C: 19amps
    D: 25amps

    My apprentice chose the answer D, but the correct answer is C according to the practice test. Can anyone explain the formulas needed to come up with the answer? Any help would be appreciated!
    The question makes no sense.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  4. #4
    Join Date
    Nov 2010
    Location
    Fort Collins, Colorado
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    2,348
    Quote Originally Posted by Padilla616 View Post
    Hey everyone,

    My apprentice is about to take his Journeyman's test this Thursday through PSI. He got a question wrong on his PSI Practice Test and asked me for input. I'm embarrassed to say I couldn't see how they came up with their answer.

    Q: What is the motor nameplate FLA rating for a 5 HP single-phase motor, 230 volt with an efficiency rating of 95% and a power factor of 90%?

    A: 8 amps
    B: 16amps
    C: 19amps
    D: 25amps

    My apprentice chose the answer D, but the correct answer is C according to the practice test. Can anyone explain the formulas needed to come up with the answer? Any help would be appreciated!
    Are you certain the question and answers are correct? I don't think the correct answer is listed. From a code standpoint the info about the PF and the efficiency is irrelevant and is just part of the question to confuse you. The code would require the use of Table 430.248 which would be 28 amps.

  5. #5
    Join Date
    Mar 2008
    Location
    Michigan. It's a beautiful penninsula, I've looked around.
    Posts
    8,829
    I just Googled a couple 5hp motors and checked the nameplates. One had an FLA of 22, the other 25 at 230 volts.

    Besoeker's math makes total sense to me. I don't understand where the NEC came up with 28 amps.
    Cheers and Stay Safe,

    Marky the Sparky

  6. #6
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    Jun 2004
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    Cherry Valley NY, Seattle, WA
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    Quote Originally Posted by K8MHZ View Post
    I just Googled a couple 5hp motors and checked the nameplates. One had an FLA of 22, the other 25 at 230 volts.

    Besoeker's math makes total sense to me.
    Ok I guess that makes sense: its more of an electrical calculation question not an NEC question. I still think it is a horrible question to put on an electricians test because it would never be calculated that way. IT should have some wording to distinguish it from an NEC question.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  7. #7
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    Mar 2008
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    Michigan. It's a beautiful penninsula, I've looked around.
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    Quote Originally Posted by electrofelon View Post
    Ok I guess that makes sense: its more of an electrical calculation question not an NEC question. I still think it is a horrible question to put on an electricians test because it would never be calculated that way. IT should have some wording to distinguish it from an NEC question.
    I think that 'FLA' should not be part of the question. Instead why not just ask what the current draw of the motor under a full load would be? The only reason I could think would be that somewhere in the course, 'FLA' was defined in a different manner than standard use.
    Cheers and Stay Safe,

    Marky the Sparky

  8. #8
    Join Date
    Jun 2015
    Location
    Muskegon, Mi, USA
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    16
    All together the question did not make much sense to me, but I've never actually had to make that calculation before. Thanks for the quick replies and feedback!

  9. #9
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    Feb 2009
    Location
    Durango, CO, 10 h 20 min without traffic from winged horses.
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    Quote Originally Posted by K8MHZ View Post
    I don't understand where the NEC came up with 28 amps.
    The NEC is generous with amp ratings in the tables in 430 because FLA can vary between motors of the same horsepower and conditions of use vary greatly. If everything but the overload rating gets sized for worst case scenario then a motor can be swapped out with no danger to the premise wiring.
    Once in a while you get shown the light
    In the strangest of places if you look at it right. Robert Hunter

  10. #10
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    Mar 2017
    Location
    Cloverdale,Va.
    Posts
    7

    FLA calculation

    Quote Originally Posted by Padilla616 View Post
    Hey everyone,

    My apprentice is about to take his Journeyman's test this Thursday through PSI. He got a question wrong on his PSI Practice Test and asked me for input. I'm embarrassed to say I couldn't see how they came up with their answer.

    Q: What is the motor nameplate FLA rating for a 5 HP single-phase motor, 230 volt with an efficiency rating of 95% and a power factor of 90%?

    A: 8 amps
    B: 16amps
    C: 19amps
    D: 25amps

    My apprentice chose the answer D, but the correct answer is C according to the practice test. Can anyone explain the formulas needed to come up with the answer? Any help would be appreciated!
    Mike Holt covers this in a video called Motor Nameplate Full Load Amps. the formula is

    (1x746)/(ExEFFxPF)

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