Table 310.15(B)(6)

[bphgravity]

What is the history and substantiation for Table 310.15(B)(6)?

The current carrying capacity is significantly increased per this table for dwelling units only. If I have a 200A service and plan to use type TW conductors, the table permits me to use 2/0 where 310.16 would require at least 250-kcmil. If I load that service to close to 200A, wouldn't the temperature exceed 60 degrees C?

Can it be inferred that dwellings typically don't load services to their maximum rating where as a non-dwelling is more likely to? This seems to be a hazardous assumption.

 

[peter d]

Re: Table 310.15(B)(6)

Can it be inferred that dwellings typically don't load services to their maximum rating where as a non-dwelling is more likely to?

Without knowing any of the history behind the code section, I would say the answer is "yes."

This seems to be a hazardous assumption.

I disagree, only based on the thousands upon thousands of applications of that table, one of which is in my own house.

 

[charlie]

Re: Table 310.15(B)(6)

Bryan, you will be hard pressed to find a conductor larger than #1 Cu. that is rated for 60?C.

If memory serves me correctly, the chart was originally developed by EEI and based on their load profiles of dwellings across the country. Homes just do not have a peak load for a long enough time to cause conductors to heat up and cause a problem with the application of this chart. To answer your question though, yes you can overload the service entrance conductors if you can maintain the load for a significant amount of time. History has shown that that?type of loading is almost impossible to be done in a residence.