400 amp. service to buss duck

[Anonymous]

I am new to this forum. Is there a code or what code # states that there can only be one set of three phase wires in a pipe or can there be two runs in the same pipe ( if pipe fill allowes ) :?: :?: :?: :?: .but code # is very much needed .

[Wgoodrich]

310.15.B.2.A in the 99 and 2002 states that if you install more than three current carrying conductors in a single raceway or cable then you must start derating that set of conductors.

However this is somewhat true and somewhat misleading. If you install more than 3 current carrying conductors in a raceway indeed you must reduce the ampacity per the calculation of percentage. The misleading part in this is that the calculation would start at the ampacity of that temp rating of your conductors then compared to the maximum temp rating found in 110.14 of the NEC that states in that rule that you must use the ampacity rating found in Table 310.16 in column of 60 degree rating regardless of true temp rating of you insulation for those conductor size 1 awg or smaller. Then that rule goes further to say that you must not exceed 75 degree column if larger than 1 awg conductor.

This means that your ampacity is already lower than what 90 degree wire most commonly used requried to be set in ampacity to the 60 degree column due to 110.14.C.

Then using Table 310.15.B.2.A you could often put up to 9 current carrying conductors and start your deration calculations of a THHN wire in the true temp/amp column of 90 degree. Then once you have derated by that calculation then you must compare back to the 60 degree column for 1 awg or smaller or 75 degree column for 1 awg and larger. The less compared ampacity must be used. Often times the 60 degree column is still lower even after the ampacity deration calculation starting with the higher amp rating of the true temp rate of your insulation then calculated down often with as much as 9 current carrying conductors and still you would be no smaller in ampacity rating in your calculation than the 60 or 75 degree column your are required to compare to per 110.14.C.

Check out the tables mentioned. Also below is a link to a format to calculate ampacity of a conductor found in our homewiringandmore.com web site.

http://www.homewiringandmore.com/homewiringusa/2002/definitions/ampacity/amp.html

If you wish to surf our entire web site then go to the top left corner of this page and click on the moving doityourselfer link to your opening page of your web site. The is two halves one is the 99 and hte latest is the 2002 side. The 2002 side includes pictures in most articles that should help you as your read what we say to understand what is being said by picture example.

Hope this helps

Wg

[Anonymous]

Thank you wgoodrich you answed my question in great detail, I am an electrical contractor in New Port Richey Florida and like most business men I need to know the answer to question as soon as posible, our Chief Electrical Inspector in this county recomended your sight saying that you have good advise, I thank you for taking the time to help all of us that (just cant find were it is in the NEC ).

[Wgoodrich]

Thank you for you kind thoughts and glad that we could help. Also please pass on my thanks to your Chief inspector for his vote of condidence. Many inspectors recommend this site to people needing more indepth info on Code. Seems to serve their citizens best and makes it easier on them trying to explain withoug pictures as examples. Glad our web and forum helps people to learn.

Good Luck

Wg