Understanding SE and Art. 110.14

[Geraldselectric]

I had a test question which stated, "When sizing SE conductor for a min 100a one family dwelling, a #3 thwn copper should be used or if applying 310.15b6, a #4 copper thwn should be used. I understand how to get the #4 from the table. But looking at 310.16, I can only get a #3 looking at 75 degree column. I am confused with art. 100.14 because I thought if there is 100a or less, you must look at the 60 degree column with the exception of motors. Is there an exception I am missing for SE conductors that allows me to go straight to the 75 degree column? Thank You

 

[celtic]

I am confused with art. 100.14 because I thought if there is 100a or less, you must look at the 60 degree column with the exception of motors. Is there an exception I am missing for SE conductors that allows me to go straight to the 75 degree column? Thank You

You're missing something:
110.14(C)(1)

Equipment Provisions.
The determination of termination provisions of equipment shall be based on 110.14(C)(1)(a) or (C)(1)(b). Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination provisions shall be based on Table 310.16 as appropriately modified by 310.15(B)(6).

 

[Geraldselectric]

Thank you for your reply. But, using the above test question and no other information, how am I allowed to go straight to the 75 degree column and look up 100A to get a #3? I guess I am asking why if it is 100A or less, am I not to look in the 60 degree column? I understand if it was 101 or more amps.

 

[George Stolz]

I think it's just a matter of knowing that circuit breakers are manufactured with 75 degree terminations.

I agree that this is a lousy test question, I've never felt comfortable with that one. I think the key is, get the others right too.

 

[celtic]

I'm guessing here .... It is "assumed" that you will know "most" equipment is marked as 75?...but you may run into existing equipment that may have no markings.

 

[Geraldselectric]

Ok, then the test question is probably assuming 75 degree termination, but they should let the test taker know that. I was playing it safe and selecting from the 60 degree column. Thanks for your help.

 

[infinity]

Ok, then the test question is probably assuming 75 degree termination, but they should let the test taker know that. I was playing it safe and selecting from the 60 degree column. Thanks for your help.

I agree the question is a poor one. Questions regarding ampacity, IMO should always mention the assumed temperature rating.

 

[QES]

so when one must assumed, 60c will be the answer?

 

[George Stolz]

QES: Got me, I don't write the tests!

 

[QES]

I just recalled that this was a similar part to a practice problem for a P.E. exam. If the problem does not tell you the temp rating and it is uder 100amp, then you must used 60c. but this problem tell you the type of conductors, so from the table you can use 75c.
look at 110.14(1)(a)(3)