Thompson Prometric Sample Test Question

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A/A Fuel GTX

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What MINIMUM size copper conductor type THW is required for a feeder circuit that is providing 3 phase, 480V power to a 10 HP and a 5 HP wound rotor, motor load. I figured 14A * 1.25 =17.50A for the 10HP and 7.6A for the 5HP which equals a total load of 25.10A. Used 430.24 for the calcs. Went to 310.16 and looked in the 75C column and chose a #10 conductor. Wrong according to them. How did I miss this?

Choices

1. #8
2. #10
3. #12
4. #14
 

A/A Fuel GTX

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I thought about that Brad but they are saying the correct answer is 4.#14. I have no idea how they arrived at that......
 

A/A Fuel GTX

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bob said:
If you use the 90C col the rating is 25 amps which is incorrect.

If the question called for THW-2, I could see how #14 would be the most correct answer based on the 90C column but the original question specified THW.
 

charlie b

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Re: Thompson Prometric Sample Test Question

hockeyoligist2 said:
Thompson Prometric comes up with a lot of trick questions. . . .
Just how far down the "tricky road" are they willing to go? For example, when I take note of the fact that the word "minimum" is shown in all capital letters, I wonder two things: (1) Was it that way in the question? (2) If so, why the emphasis?

If I wanted to write a question that is likely to fail anyone who takes my test, just to make them pay me to take it again, then I might play with the word "MINIMUM," in the following way. The circumstance that gives the absolutely lowest requirement for the ampacity of a feeder that serves two motors comes from Exception 3 to 430.24. If you interlock the two motors in your question, such that only one can run at a time, then you can get away with a smaller conductor. In fact, you can get away with a #14.

Now that would be extraordinarily unfair, as questions go. But can anyone tell me whether Thompson Prometric is that unfair?
 

A/A Fuel GTX

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Re: Thompson Prometric Sample Test Question

charlie b said:
Just how far down the "tricky road" are they willing to go? For example, when I take note of the fact that the word "minimum" is shown in all capital letters, I wonder two things: (1) Was it that way in the question? (2) If so, why the emphasis?

?

Yes Charlie, the word minimum was in bold letters. Your answer to the question makes sense but how in the world can they expect someone taking one of their tests to go that deep into analyizing a question when they are racing the clock to finish all the questions? I took the Wisconsin Master test last week and there were a couple of kickers but for the most part the questions were straight forward and didn't require a Doctorate in Jurist Prudence to understand.
 

charlie b

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It was just a guess, Tom. I was trying to come up with something, ANYTHING, that might explain their answer of #14. In thinking up a possible explanation, I was not adverse to treating the test's author(s) with unkindness, and crediting them with malicious intent. This is the only explanation I could come up with. I have no idea if it is correct. I hope it is not.

For the record, I agree with your answer.
 

steve66

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Illinois
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Engineer
I think bdarell has it right. They may be using 220.5(B) to erase the fraction of an amp. Either that, or they just printed the wrong answer.

I don't think its really a fair question - design a calculation that comes out to just a fraction of an amp larger than one wire size. You can bet that in the field most people would use the larger wire size. After all, in the real world your 10HP motor may take 15 amps.

Steve
 

bdarnell

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steve66 said:
I think bdarnell has it right

I thought I did until Tom told me the correct answer was #14. That derailed my train.

I don't think its really a fair question

Define "fair" in terms of test preparation. If it's contained in the book, it's "fair". The question is, is it a correct answer ? Most if not all states have a procedure to challenge test results for this very reason. People, test preparers included, can, will, and do make mistakes.

I say it's a wrong answer. If I had missed it by one, I'd challenge it. I don't think Tom missed it by that much (Or that little. Which ever is correct)
 

steve66

Senior Member
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Illinois
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Opps, I should have read closer. I think we are either back to Charlie's idea, or they just made a mistake.

I'd like to think they just made a mistake.
 
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