Minnesota MN Masters Exam Test

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westernexplorer

westernexplorer

Senior Member
Jim Shorts said:
Sign circuit is not required in every feeder. Only required for the building. No way to tell by the question if this feeder is supplying the sign circuit.
Click to expand...

NEC 220.40 requires that the FEEDER or SERVICE shall not be less than the sum of the loads on the branch circuits supplied.......

The Sign Circuit is REQUIRED to calculated into the FEEDER OR SERVICE conductors for the building......

I will guess there is more missing from the OP problem...... The exam question would be very specific....
 
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boku0003

Member
I am taking the Minnesota Master exam either November or December 2009. I have 2 other guys now that I am studying with. If anyone else would like to join it would be great. Even if it is only via internet. We have all the questions we can remember from the exam (we have already taken it) in a Word document that is around 10 pages long. So please let me know if you are interested. The more the merrier.

boku0003@umn.edu
 
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boku0003

Member
310.16 Question

310.16 Question

Ok, here's one that's been bugging me and I remember having a problem
with it on the exam that I struggled with. Don't remember exactly how
it was worded, but this question should simulate my question:

95A non-continuous load using THHN at 87 degrees F. What size wire is
needed?


1. If you ignore the 87 degrees F part for now and size according to
the terminal rule found in 110.14(C), you go to the 60C column
(because the load is under 100A) and pick the 2 AWG wire that's rated
95A at 60C.
2. However it's at 87F, so we have to "derate" according to the table
at the bottom of 310.16. So we go over to the 90C column and at 87F,
it is derated at 0.96. So take 95A and divide be 0.96 and you get 99
Amps. So in the 90C column, that is 3 AWG wire which is rated at
110A.


Problem, that is smaller than 2AWG wire. So we didn't really "derate"
the wire. We went smaller because of the temp increase, which doesn't
make sense.


Ok, now add the following: Continuous load, 4 conductors in a raceway
that's 1 inch above the roof on a rooftop. How about if after
applying the 1.25 continuous, or derating, you go from 95 to over 100
A. Do you move over to the 75C column for the terminals? Now it gets
even more confusing.


Anyone know how to straighten this out? It would be greatly
appreciated. Do I just pick the larger of the wires? If so, which
derating factors do I combine (more than 3 conductors, temp rise, etc)?
 
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boku0003

Member
Question

Question

Finding Feeder Neutral. Given and 800 ampere 480/277 service with a load of 70,000 VA and a non-linear load of 30,000 VA. What is the feeder neutral?
 
dwmacpherson

dwmacpherson

Member
Location
Indianapolis
Dont know if Minnesota uses the same testing agency that they do in Indy, if it is the Thomson Prometric, I would highly recommend simply learning the code book and how to use it efficiently. I could be way off base for an answer here, but I took the Master's Exam and passed the first time with an 84. Little disappointed it wasn't a little harder. It was very little calcs and general knowledge and a lot of knowing were to find answers in the code. I did take a Mike Holt exam prep course too. Reasonably priced and very informative.
 
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boku0003

Member
Nope. I remembered the question pretty well. I wrote it down as soon as I got home from the exam. So what I wrote is pretty much all that was on the exam. There was no mention of a sign circuit. Whether or not you need to include it, it was not in the question.
 
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M

Minnesotaelectric

Member
Find ampacity in 310.16 based on wire without taking into consideration 110.14.
Then do all your derating for ambient temp., location on rooftop, current carrying conductors in conduit.
After you have this ampacity then if it is greater than what is allowed in 110.14, you have to use the 60 degree column instead.
 
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