Are any of you attending the NEC ROC meetings in Redondo Beach, CA this week? If so look me up as i would love to see ya.
I will be reporting on five committees during my 12 day visit. So, any of you California HI’s out in that area…stop by.
Some proposed changes for the 2014 NEC :
Section 310.15(B)(7) - will have a significant change in terms of how the ampacity corrections are done in the 2014 NEC with regards to 120/240V Single Phase , single phase “cheat” table we have all become familar with since the early 1960’s or earlier ; I am no code historian nor does it interest me. However, the change is significant because the CMP [Code-Making Panel] explained that for years many people considered the “mini” table as not requiring additional corrections or adjustments (we used to call it derating…FYI) with regards to elevated temperatures and the like. It was made clear that the use of Section 310.15(B)(7) always meant to require additional adjustments or corrections where deemed needed and the change in the 2014 NEC will clarify this.
Well, as usual I did not answer the real question at hand. What is taking the place of the table in 310.15(B)(7) and will we still get a reduction in conductor size for conditions specified in that section. Well the short answer is yes but you know I can’t provide a short answer. The CMP determined that a correction factor of .83 or 83% would be applied to service entrance conductors and feeders based on 83% of the main service rating as the determining factor and then corrections are to be applied. So how does that work…well I knew you would ask.
A 200A rated service disconnect(just so happens to be the OCPD as well) within a 200A rated enclosure. If you take 200A x .83 you get 166A. Now, at that point you would go to 310.15(B)(16) and find a conductor in the 75 degree column that would have an ampacity of at least 166A. Let’s choose 4/0 AL which has an ampacity (before any adjustments or corrections) of 180A. If you remember the “mini” table allowed 4/0 AL for a 200A service anyway…so I think you see that there is no real change except to make it clear that other adjustments do apply if temperature or more than 3 CCC’s apply but I think you can do the math from there.
Oh…One final note; The term “Main Power Feeder” is no longer being used in this section because it now becomes a moot point. Since the size of the feeder would have to be based on the size of the Main Service Disconnect ratings it would not benefit any electrician to try and use this table other than for what used to be known as a Main Power Feeder anyway…Hope I cleared that up for everyone and personally I think it is a good change as it helps to express fully the intent of the section.