I need help studying for my Masters test.

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kefox81

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Hello everyone. I am studying for my Master Electricians Exam. I have having some trouble with it. The test that they are going to let me take is from the 2014 Code. I am using a practice exam. I was hoping that you all could give me some pointers on how to do it better. Here is a question that is really giving me trouble.

When used as service entrance conductors on a residential dwelling, a # 4 THW conductor has an ampacity rating of:
a. 70 amps
b. 85 amps
c. 100 amps
d. 125 amps

I have looked for the correct answer in different sections of the code and still cant find it. What am I doing wrong?
 
kefox81 said:
Hello everyone. I am studying for my Master Electricians Exam. I have having some trouble with it. The test that they are going to let me take is from the 2014 Code. I am using a practice exam. I was hoping that you all could give me some pointers on how to do it better. Here is a question that is really giving me trouble.

When used as service entrance conductors on a residential dwelling, a # 4 THW conductor has an ampacity rating of:
a. 70 amps
b. 85 amps
c. 100 amps
d. 125 amps

I have looked for the correct answer in different sections of the code and still cant find it. What am I doing wrong?
Click to expand...

Look at Table 310.15(B)(16), then look at the conductor types listed in each column.
See if you see the type listed in your test question. Look under/over to the appropriate AWG column and find your answer.
 
In the older code books it was 310.15B. I'm in Virginia and I did a service for my brother in western New York. The inspector pulled out a new code book and they changed it to where you now have to do a calculation, instead of just looking at the chart.

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I really appreciate the help but I'm still not getting it.

I really appreciate the help but I'm still not getting it.

Thanks for all the help. I read the article but I still dont understand it. Can someone walk me through it step by step?
 
Looks like you take 83% of service size SAY 100 AMP multiply by 83% equals 83. I don't have 310.16 in front of me now but I'm willing to bet 83 amps comes #4 on ampacity.

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kefox81 said:
Thanks for all the help. I read the article but I still dont understand it. Can someone walk me through it step by step?
Click to expand...

Do you have a pre-2014 code book? If you look at say the 2011 you will find table 310.15(B)(7). In the 2014 NEC that table was replaced with a calculation. When you do the calculation the conductor sizes (2014 versus 2011) from the table should still be the same.

For example, for the 200 amp service according to the table in the 2011 you would need a minimum of #2/0 copper (175 amps) for that service. Under the 2014 you would use 200 amps * 83% which gives you the minimum conductor ampacity required for a 200 amp service.

200 * 83%=166 amps minimum so #2/0 THHN at 175 amps is good same as the T310.15(B)(7) in the 2011 and earlier code editions. The new method is actually better because it allows for the use of things like parallel conductors which weren't in the old table.
 
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