Art. 310 Ambient temp tables 2011

[wireguy8169]

When would you use Table 310.15(B)(2)(a) versus Table 310.15(B)(2)(b). This came up in class this evening and for the life of me could not find an answer, they did not even cover that in my code change class.

Thanks

 

[Dennis Alwon]

That's a good questions. I have ideas but I really don't know.

 

[wireguy8169]

Yeah that what I said, I noticed it when planning for my class, but could not find any explaination anywhere in either of my code update books, I felt bad cause I did not have an answer and I am not afraid to say I do not know. I knew it was going to be one of the first questions I was asked. So my mission is to find an answer...

thanks

 

[lauraj]

Each table is based off of a different base ambient temperature, 30C for the first one, and 40C for the second one.

 

[Dennis Alwon]

Each table is based off of a different base ambient temperature, 30C for the first one, and 40C for the second one.

yes, so which one is used and when-- that's what the op is asking.

 

[jumper]

It tells you which one to use depending on which ampacity table you are using.

All they did was consolidate the various ones that were at the bottom of each table and add a few more temperatures.

 

[wireguy8169]

Thanks for the responses,

Jumper is what your saying is if your using Table 310.15(B)(16) you would use table 310(15)(B)(2)(a)

of using Table 310.15(B)(17) you would use 310.15(B)(2)(b)?

You posting that and reading it a few more times, seems logical. then if you have more than three current carring conductors you would have to further derate as before using table 310.(15)(B)(3)(a).

Thanks

 

[Dennis Alwon]

Thanks for the responses,

Jumper is what your saying is if your using Table 310.15(B)(16) you would use table 310(15)(B)(2)(a)

of using Table 310.15(B)(17) you would use 310.15(B)(2)(b)?

You posting that and reading it a few more times, seems logical. then if you have more than three current carring conductors you would have to further derate as before using table 310.(15)(B)(3)(a).

Thanks

Close-- Jumper got it- I didn't realize that 310.15(B)(18) was based on 40C. So it is T. 310.15(B)(18) that would use T. 310.15(B)(2)(b) or any other table that is based on 40C. Tables 310.15(B)(18-21)

 

[jumper]

The old ambient temperature tables were also a bit redundant. The correction factor for a CU and a AL conductor of the same size and insulation is the same.