Code book question

[yaoyaodes]

I am confused about the table Table 310.15(B)(2)(a) Ambient Temperature Correction Factors Based on 30°C (86°F) , and Table 310.15(B)(2)(b) Ambient Temperature Correction Factors Based on 40ºC (104ºF). Can someone explain to me.

 

[Zach Stone P.E.]

I am confused about the table Table 310.15(B)(2)(a) Ambient Temperature Correction Factors Based on 30°C (86°F) , and Table 310.15(B)(2)(b) Ambient Temperature Correction Factors Based on 40ºC (104ºF). Can someone explain to me.

30ºC Ambient Conductors:

The conductor ampacity Tables 310.15(B)(16) through (16) are based on 30ºC Ambient (look at the title of the table).

To temperature correct these conductors for a different ambient temperature, use table 310.15(B)(2)(a) Ambient Temperature Correction Factors Based on 30°C Ambient (86°F).


40ºC Ambient Conductors:

The conductor ampacity Tables 310.15(B)(18) through (20) are based on 40ºC Ambient (look at the title of the table).

To temperature correct these conductors for a different ambient temperature, use table 310.15(B)(2)(b) Ambient Temperature Correction Factors Based on 40ºC Ambient (104ºF).

 

[yaoyaodes]

30ºC Ambient Conductors:

The conductor ampacity Tables 310.15(B)(16) through (16) are based on 30ºC Ambient (look at the title of the table).

To temperature correct these conductors for a different ambient temperature, use table 310.15(B)(2)(a) Ambient Temperature Correction Factors Based on 30°C Ambient (86°F).


40ºC Ambient Conductors:

The conductor ampacity Tables 310.15(B)(18) through (20) are based on 40ºC Ambient (look at the title of the table).

To temperature correct these conductors for a different ambient temperature, use table 310.15(B)(2)(b) Ambient Temperature Correction Factors Based on 40ºC Ambient (104ºF).

Thanks for the quick reply. Sorry I did not describe my question clearly. I am confused about the table Table 310.15(B)(2)(a) already includes the 40-degree ambient temperature, why there is another table about 40 degree? The title says Ambient Temperature Correction Factors Based on 30°C (86°F). is the 30 degree conductor rating?

 

[Zach Stone P.E.]

Thanks for the quick reply. Sorry I did not describe my question clearly. I am confused about the table Table 310.15(B)(2)(a) already includes the 40-degree ambient temperature, why there is another table about 40 degree? The title says Ambient Temperature Correction Factors Based on 30°C (86°F). is the 30 degree conductor rating?

The conductor allowable ampacity ratings given in Tables 310.15(B)(16) through (20) are based on an ambient temperature of either 30ºC or 40ºC.

If the ambient temperature where the conductor is installed is hotter than this amount, then the conductor will not be able to handle as much current, so a derating factor is applied from either table 310.15(B)(2)(a) or (b) to calculate the new lower allowable ampacity for a hotter ambient temperature.

Ambient temperature is the temperature of the immediate surroundings where the conductor is installed.

We teach this is much greater depth in our live class at www.electricalpereview.com if you are looking for additional help.

 

[yaoyaodes]

How do I know which table to use?

 

[Zach Stone P.E.]

How do I know which table to use?

Which ambient temperature correction table? Use the correction table for 30ºC conductors if the allowable ampacity comes from a 30ºC table, and use the correction table for 40ºC conductors if the allowable ampacity comes from a 40ºC table (see my first response in this thread).

 

[yaoyaodes]

Which ambient temperature correction table? Use the correction table for 30ºC conductors if the allowable ampacity comes from a 30ºC table, and use the correction table for 40ºC conductors if the allowable ampacity comes from a 40ºC table (see my first response in this thread).

I see what you mean now. Thanks for your patient. Now I get it.

 

[Zach Stone P.E.]

I see what you mean now. Thanks for your patient. Now I get it.

Happy to help