a. a decrease

b. an increase

c. no change

I can't find anything on this in my book... I don't know enough to even guess what the answer is. If anyone knows, I was wondering how you came up with the answer, what is the logic behind it? I just have no idea, this one has stumped me

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Any who, here are the three questions I am struggling with.

***2014 NEC***

I believe I am correct on this question, and the answer key is wrong:

QUESTION 1.The ampacity of a No. 12 THHN conductor in a raceway with an ambient temperature of 28*C is ____ A.

My answer: 30A

Answer key: 31.2A

Other two answers: 15A and 20A

The answer I selected is 30A. The answer key says it is 31.2A. I'm assuming the question meant copper conductor, and based on 310.15(B)(16), the ampacity would be 30A. Using table 310.15(B)(2)(a), the correction factor for 28*C is 1.00 (26-30*C). According to the answer key answer of 31.2A, the correction factor would need to be 1.04 which would be in the 21-25*C range. I believe 30A would be the correct answer.

QUESTION 2. A 4/0 THHN copper conductor installed in free air on a 480V circuit at a temperature of 30*C will have an allowable ampacity of ____ A.

My answer: 260A

Answer key: 405A

Other two answers: 205A and 405A.

From what I read in the chapter, there were no examples of ampacity being affected by voltage under 2000v, or being in free air.

QUESTION 3. A TC cable with No. 6 THHN wire in a cable tray and with a spacing of one cable width between the multi-conductor cables will have an allowable ampacity of ____ A.

My answer: 75A

Answer key: 105A

Other two answers: 85A and 110A

This is I was just completely unsure of. Would love to have some guidance on figuring this one out. ]]>

As background, we are part of a team of MBA students at the University of Minnesota taking an experiential consulting course.

As an element of this course, we are performing a VFD market assessment. Our goal is to understand the strengths and weaknesses of VFD technology and to gain insights into the the consumer perspective for purchasing and utilizing VFD within industrial applications. This information will be incorporated into our final presentation and will help us formulate recommendations.

We appreciate your time! Thank you!

Survey Link: https://umn.qualtrics.com/jfe1/form/SV_bwQC58PFdSEq43b ]]>

The circuit looks like this:

I was given impedance of each component and information about AC source (voltage 66 V, angle 1.09 rad, sinus characteristic).

My solution:

Few components' impedance is 0

1) Calculating impedance of whole circuit from the source. (Paralel combination of i3 (red) and i7 (orange) part + i1 (green) part in a series)

2) Calculating I (I=U/Z), which is the same value as I1?

3) Calculating I7 from a loop (II. Kirchhoff's law)

4) Calculating I3 from point C (I. Kirchoff's law)

I entered the values into a school system and all of them are wrong. I guess I can't calculate I1 the way I did?

I'm trying to upload my solution but it keeps failing. It's gonna be in section below.

Thanks for helping me.

Okay, my solution is here -> https://s18.postimg.org/8lnx1q3bt/20161125_172949.jpg

If so can you tell me how you were able to get the waiver? ]]>