MI PSI Practice Exam Question

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Padilla616

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Muskegon, Mi, USA
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!
 
Padilla616 said:
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!
Click to expand...
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.
 
Padilla616 said:
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!
Click to expand...

The question makes no sense.
 
Padilla616 said:
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!
Click to expand...

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.
 
K8MHZ said:
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.
Click to expand...

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.
 
electrofelon said:
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.
Click to expand...

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.
 
K8MHZ said:
I don't understand where the NEC came up with 28 amps.
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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.
 
FLA calculation

FLA calculation

Padilla616 said:
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!
Click to expand...
Mike Holt covers this in a video called Motor Nameplate Full Load Amps. the formula is

(1x746)/(ExEFFxPF)
 
Padilla616 said:
Q: What is the motor nameplate FLA rating ...
Click to expand...

There is no way to mathematically answer this question.
The correct answer can only be found by physically looking at the motor's Nameplate FLA.


The code FLA current is found by looking in the NEC.
The theoretical FLA have already been discussed in post #2.
 
I would guess that they asked for nameplate so you wouldn't use a table in the NEC and perform the calculation in post #2.
 
infinity said:
I would guess that they asked for nameplate so you wouldn't use a table in the NEC and perform the calculation in post #2.
Click to expand...

Mediocre questions get mediocre answers.

The NEC does talk specifically about using the FLA on the nameplate when sizing running overload protection. Nameplate information is not found anywhere but on the motor.
It appears the question is looking for the calculated running amps of the specified motor.
 
conductor size and short circuit and ground fault protection is based on FLC, overload is based on nameplate FLA.
The formula for FLA is (h.p.x746)/(ExEFFxPF). They just want you to know that the FLA is based upon motor ratings and do not truly indicate actual load of motor.
430.6(a)(1)
430.(52)(c)(1)

overload-430.6(a)(2) based on nameplate. FLC=Code, FLA= Actual nameplate.
 
:weeping:
infinity said:
I agree poor question but I think that many here could find the answer they were looking for using Besoeker's method.
Click to expand...


I agree.. Bes nailed it. and we are trying to make it more complicated than it is. Test question are generally not perfect.

Texie the test question was looking for a nameplate amps not the NEC code requirement.
 
K8MHZ said:
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.
Click to expand...
Thank you kindly.
Just arithmetic.
 
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