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| Subject - 2005 Code book | |
| lctrc789 |
Can any of you who have the new 2005 code book tell me if article 310-15(b) 2a has changed or stayed the same. I had a new foreman on my job who stated that he could put 2 families of three phase circuits per conduit without derating. I told hom NO you can't. The max is 6 current carrying conductors at 80 %. He argued all day I told him to read this article and let me know He said it was in the new code book which I don't care we still follow the application of 2003 code book . What started this was a job we re-done that had two familes in every pipe 8 current carrying conductors with 12 THHN on a 20 amp breaker. I stated that this was either done before the code changed or some one didn't know they should have been on 15 amp breakers. One pipe had 10 current carrying condustors in it as well. Any help would be greatly appreciated on this. I haven't got the new book yet but you can bet I will. Thanks guys |
| iwire | Pat I do not know if there are any changes to that section but I also see no problem with eight 12 AWG current carrying conductors in one raceway with a 20 amp over current device. I will assume the conductors are 90 C. Table 310.16 lists 12 AWG THHN as 30 amps. 30 amps x .8 = 21 amps 21 amp rated conductor on a 20 amp breaker is no problem. You can start the derating process in the 90 C column if you have 90 C wire. This is about the only time that you can use the 90 C column. |
| Ryan_J | There is a change to the section, but it doesn't address what you are discussing. The new text clarifies that ifd there are multiple sets of parrallel conductors in a raceway that each conductor must be counted. This goes along with the change in 310.4 to clarify the same thing. |
| lctrc789 | Bob I understand the derating for wire at 90 degrees, but the rating of breakers is at 75% at 25 amps. Maybe I am wrong here but I always thought that you can use the 90 degree column for wires for derating and the 60 degree column for rating one breaker. If more then one breaker then you derate the terminations at 75 degrees up to 100 amp. At least that is what I was taught in the last three code classes. I can see the two families which is 8 current carrying conductors at a derating of 70 percent. Even then 25 amps X .7 = 17.5 amps and you can go to the next largest size breaker 20amp. But the one pipe has 10 current carrying conductors at which would be 50% derating. 25 amps X.5 = 12.5 amp or 15 amp breaker. I have seen where they will use a ten wire for derating factor and install on 20 amp breaker. This guy is new and I didn't want to cause waves but I know that 10 current carrying conductors we are pushing the limit. I see what you are saying on two families Bob I muffed that one up LOL but ten is pushing it. Do you guys see the code at the rating the same as I do with the derating for terminations on breakers the same as I do. According to The NJATC and Tom Henry that is what I was always told. |
| Pierre Belarge | Ampacity adjustment using THHN conductors can be started using the 90*C column. 12AWG - 30 amps X .5 for ten conductors =15 amps - 240.6 has 15 amps as a standard OCPD size, so we protect that at 15 amps. We do not start ampacity adjustment at the 75*C column for 75*C breakers - we cannot exceed the 75*C column once our calculations are finished. (that is provided the OCPD is rated 75*C)- See 110.14(C) |
| Pierre Belarge | Sorry about the format of my post, it did not line up the way I typed it.
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| David Hyatt | You can only go up in size if it is not part of a multi outlet receptacle circuit. 240.3B1 |
| bobby | Post on 100 amp breaker melting, moved to proper forum. http://www.electricalknowledge.com/forum/topic.asp?TOPIC_ID=945 |
| kbsparky | >>...But the one pipe has 10 current carrying conductors ...<< Are you counting the neutral or grounding wires in this total? If those neutral conductors are only carrying the unbalanced current from multi-wire circuits, then they don't need to included in the total. Nor are the grounding wires to be included. See 310.15(B)(4) and (5) |
| bobby | GFCI post by Bobby, moved to proper forum. http://www.electricalknowledge.com/forum/topic.asp?TOPIC_ID=950 Moderator |