Colorado Mater Electrician Renewal Exam

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rm1212

Member
i am unsure on these questions...

Q: With a 7.5 horsepower, 3-phase alternating- current motor ate 460 volts, 80% power factor, and a nameplate full-load current rating of 19 amperes, what is the maximum setting for the overload protection?
(a) 19.00 amperes
(b) 21.85 amperes
(c) 22.25 amperes
(d) 23.75 amperes

is the answer (a) 19.oo ??

Q: 4/0 AWG, 75 degree C. aluminum transformer secondary conductors shall be proteced at not more than:
(a)175 amperes
(b)200 amperes
(c) the calculated load connected to transformer
(d) not required for multiphase, delta-wye transformer secondary conductors

is the answer (C)The calculated load connected to transformer?
 
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davizaud

Member
I too am at a loss. Sorry rcarroll but your art. 240.21 didn't not help much other than it pointed back to 450.3 "Transformers". Now 450.3 points back to 240.21 for the conductor which is what we are dealing with.
so you might be on to something. My first thought was with rm1212 and the answer C. But we don't know the voltage, nor the location, nor the type (delta-wye), nor the length and weither or not it's a 2 or 3 wire system.

All we do know it that 4/0 AWG, 75 degree C. aluminum is good for 180 amps. Thus, with your (rcarroll) advise in art. 240.21 (c) which prohibits the use of the next higher breaker; as well as 240 (C) (1) that nullifies the Delta-wye answer, I would be moved to answer B with 175 amps being the next "Lower" breaker as per 240.6.

Help me if I'm wrong.
 
rcarroll

rcarroll

Senior Member
Location
Fort Collins, Colorado
I went with answer A due to the last sentence of 240.21C. I don't have my book but I think it says something like x-former secondarys can't be protected w/ the next size breaker allowed in 240.4.
 
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rm1212

Member
Sorry for not replying sooner. Was out of town. I struggled with this one and appreciate the help through all the replies. I submitted the test and passed. Thanks again and good luck to all.
 
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lbudden

Member
Location
Colorado
My thoughts on question 2 are:
Is answer A or B correct if you are wiring a 30 kva transformer? Since you are not given extra info on size/kva, or whether the 4/0 is for voltage drop, or whether there is a 100 amp panel with main breaker on the end of the secondary, doesn't C seem to fit any ungiven scenarios?
Just curious, I have already submitted mine and passed, but do not know if this answer was correct.
 
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