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Monday, July 24, 2017
Question:
Good Afternoon, Thank you very much for your Code Question of the Day feature. It is a much appreciated service, especially for those new to the trade, like myself. My question is in regard to the use of zip ties in a panel to group "hot" conductors, neutral conductors, and bare equipment grounding conductors (as exemplified in the attached image from a school project: a sample residential service panel). My understanding is that the following three code sections would apply:
Section 110.12 "Electrical equipment shall be installed in a neat and workmanlike manner." (I figure this is why we're using these zip ties in the first place, along with professional pride.)
Section 310.15(B)(3)(a) "...where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(3)(a)." (So, my "hot" conductors in the image are rightly "un-bundled". My neutral conductors may be "bundled" for less than 24 inches, which they are, and my equipment grounding conductors, which shouldn't be carrying a load under normal circumstances, are nevertheless being called "conductors" and fall under the same rule, so less than 24 inches of "bundling" is OK)
Section 334.80 "Where more than two NM cables containing two or more current carrying conductors are installed in contact with thermal insulation without maintaining spacing between the cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a)". (So, here they are talking about "cables" which I understand to mean the group of conductors within the overall sheath, as opposed to bundled individual conductors coming out of multiple different sheaths. Nevertheless, the gist of this section would seem to indicate that if I have conductors in contact with each other's' thermal insulation, the allowable ampacity of each conductor must be adjusted according to the table. There is no mention in this section of the 24 inch limit.)
Barring any other sections of The Code that I'm unaware of that call out this type of "bundling" in an installation I'm inclined to believe that the zip-tying as shown in the picture necessitates an ampacity adjustment according to Table 310.15(B)(3)(a). (Assuming I have no way to prevent the individual circuits from being simultaneously energized as is mentioned in the notes to that table). Is this a correct/reasonable interpretation of The Code or have I missed something?
Thanks very much for your help, Matt
A
Answer:
Hey Matt thanks for your question and the kind words. Yes, if using the ampacity tables more than three current carrying conductors that are installed without maintaining spacing must have their table value ampacities adjusted using Table 310.15(B)(3)(a) as stated in 310.15(B)(3)(a). The note to Table 310.15(B)(3)(a) references 310.15(B)(5) for neutral conductors; grounding and bonding conductors are not counted as stated in 310.15(B)(6).
The percent factors can be applied to the conductor insulation temperature rating (typically 90 degrees C) as stated in the second paragraph of 310.15(B). It is usually not an issue unless the number of current carrying conductors exceeds 9 because of the small conductor overcurrent protection rules in 240.4(D) and terminal temperature limits in 110.14(C). If it is - provide spacing in a neat and workmanlike manner.
Ampacity adjustments are also required for nonmetallic sheathed cables in contact with thermal insulation as stated in that 334.80 but this is the building insulation, not the conductor insulation.