Need help with test question

[Artical430]

When an AC general - use snap switch is used as a controller for a single - phase, 2 hp, 240 - volt, AC motor, the switch is required to have a rating of at least _____
A. 10 amperes
B. 15 amperes
C. 20 amperes
D. 30 amperes

 

[GoldDigger]

We do not directly answer test or homework questions. You might tell us what you think is the correct answer and why, or where you might look in the NEC for the answer and we can probably help you from there.
Hint: What does the code take as the default full load current for a 2HP 240V motor? Where would you look to find out?

 

[Artical430]

My forum name is artical 430..because this is one of my favorite articals....table 430.248 located in artical 430 is where I got the 12 amperes from..

 

[Dennis Alwon]

430.109(C) has the answer

(C) Stationary Motors of 2 Horsepower or Less. For stationary
motors rated at 2 hp or less and 300 volts or less, the disconnecting
means shall be permitted to be one of the devices
specified in (1), (2), or (3):
(1) A general-use switch having an ampere rating not less
than twice the full-load current rating of the motor
(2) On ac circuits, a general-use snap switch suitable only for
use on ac (not general-use ac–dc snap switches) where
the motor full-load current rating is not more than
80 percent of the ampere rating of the switch
(3) A listed manual motor controller having a horsepower
rating not less than the rating of the motor and marked
“Suitable as Motor Disconnect”

 

[Hv&Lv]

So give us your answer and the reasoning. Thinking through and getting It wrong, then having the answer explained is better than to just be handed the answer.
thinking through and getting it right can be bad also if the guess is lucky, that’s why I like to hear the reasoning...
it sticks with you forever this way...

 

[Artical430]

I agree with you totally Hv & Lv...I am new to this forum and I did not know the protocol...
I was thinking like you stated...take my 12 amperes and multiple the 12 amperes by 80% which gives me 9.6 amperes...so the correct answer would be 10 amperes....or I could take my 12 amperes and divide by a 125% and get the answer of 9.6 amperes ...which would give me the answer of 10 amperes....but the book is informing me about national electrical code article 430.22...this is where my confusion is located...

 

[Dennis Alwon]

I agree with you totally Hv & Lv...I am new to this forum and I did not know the protocol...
I was thinking like you stated...take my 12 amperes and multiple the 12 amperes by 80% which gives me 9.6 amperes...so the correct answer would be 10 amperes....or I could take my 12 amperes and divide by a 125% and get the answer of 9.6 amperes ...which would give me the answer of 10 amperes....but the book is informing me about national electrical code article 430.22...this is where my confusion is located...

No, you don't take 80% of the 12 amps. You multiply the 12 amps by 125%. The switch itself must be rated large enough to handle the load and then some. A 20 amp switch at 80% is 16 amps. That would work but 80% of a 15 amp switch is 12 amps. So....

 

[Artical430]

To Dennis Alwon...the question is....
When an AC general - use snap switch is used as a controller for a single - phase, 2 hp, 240 - volt, AC motor, the switch is required to have a rating of at least _____
A. 10 amperes
B. 15 amperes
C. 20 amperes
D. 30 amperes


So we all took a look at national electrical code article 430.109 (C)(2)...

 

[Artical430]

Ok...I get your point Dennis Alwon...you are stating to just increase the ampere rating of my switch by 25%...but increase the ampere of the switch by the full load current of the motor. this makes sense because the full load current of my motor will not change....ok I got it...and thank you so much for helping me understand....I am taking a 100 question master electrical prep exam that you have to finish with in 5 hours...and that was one of the question I missed....I only missed 8 question and finished the test at about 4 hour and 42 minutes...so I have gotten a lot faster and much more accurate...ok I will keep trying for that 100%...

 

[Dennis Alwon]

If you have a 20 amp breaker and take 80% you get 16 amps. If you have a load of 16 amps and multiply by 125% you get 20 amps. Multiplying by 125% is the same as dividing by 80%

So take your 12 amp load and divide by 80% and you get 15 amps.

 

[Dennis Alwon]

Btw, if you only got 8 wrong that is pretty good. I am sure you will do fine. Congrats on the hard work

 

[Artical430]

Ok...artical 430.109 (C)(2)..where the motor full -load current rating is not more than 80% of the ampere rating of the switch....(Heance)....12 × 1.25%...the full load current of the motor is not more than 80 % of the ampere rating of the switch..got it...