NEC 110.14

[Rei]

I'm studying for the April exam and would like to ask if anyone can help me clarify the code.

NEC section 110.14©(1) indicated that for circuits rated 100A or less (or marked for 14 AWG through 1 AWG), use the conductor rating rated 60 degree C. My understanding is that when using the table 310.16, we should use the column for 60 degree C versus the 75 degree C despite the question said to use the conductor for 75 degree.

I, however, get confused with this section because I have seen sample question that use the wire size (14 AWG to 1 AWG) from the 60 degree column, and some sample questions still use the 75 degree column. For instance, a question from EC&M's magazine: Two motors (7.5hp and 5hp), single phase, 230V, are connecting together giving that the terminals are rated for 75 degree. What size conductor would you use?

The answer is 4 AWG (40A x 1.25 + 28 = 78A).

I think it should be 3 AWG since AWG 14 to 1 AWG is requred to use the 60 degree column in table 310.16 per 110.14 code, right? I'm confused.

 

[Dark Knight]

I'm studying for the April exam and would like to ask if anyone can help me clarify the code.
NEC section 110.14©(1) indicated that for circuits rated 100A or less (or marked for 14 AWG through 1 AWG), use the conductor rating rated 60 degree C. My understanding is that when using the table 310.16, we should use the column for 60 degree C versus the 75 degree C despite the question said to use the conductor for 75 degree.

I, however, get confused with this section because I have seen sample question that use the wire size (14 AWG to 1 AWG) from the 60 degree column, and some sample questions still use the 75 degree column. For instance, a question from EC&M's magazine: Two motors (7.5hp and 5hp), single phase, 230V, are connecting together giving that the terminals are rated for 75 degree. What size conductor would you use?

The answer is 4 AWG (40A x 1.25 + 28 = 78A).

I think it should be 3 AWG since AWG 14 to 1 AWG is requred to use the 60 degree column in table 310.16 per 110.14 code, right? I'm confused.

Have to take in consideration the type of insulation you are using. (RHH, THHN, etc.) When dealing with motors there are other considerations. I do not have my NEC Code at home but stay tuned, somebody will come with an explanation. I do not remember the exceptions NEC has. Read the small letters under the table. Maybe there is something there that can help you.

 

[Flyer_PE]

I've had this very same discussion recently. You use the temperature rating for your most limiting component. If your connectors are rated for 75 deg. C, you can use the 75 deg. value for the conductor. Typically, your connectors will only be rated for 60 deg. C which then lands you in the 60 degree rating for the cable.

Conversely, if you have 90 degree rated connectors (not very likely in the real world) and you have a cable with a 90 degree rating, you can use the 90 degree rated value for the cable.