(C) Adjustment Factors
Where conductors of different systems, as provided in 300.3, are installed in a common raceway or cable, the adjustment factors shown in Table 310.15(C)(1) shall apply only to the number of power and lighting conductors (Articles 210, 215, 220, and 230).
Informational Note No. 1: See Annex B for adjustment factors for more than three current-carrying conductors in a raceway or cable with load diversity.
Informational Note No. 2: See 366.23 for adjustment factors for conductors and ampacity for bare copper and aluminum bars in auxiliary gutters and 376.22(B) for adjustment factors for conductors in metal wireways.
(a) Where conductors are installed in cable trays, the provisions of 392.80 shall apply.
(b) Adjustment factors shall not apply to conductors in raceways having a length not exceeding 600 mm (24 in.).
(c) Adjustment factors shall not apply to underground conductors entering or leaving an outdoor trench if those conductors have physical protection in the form of rigid metal conduit, intermediate metal conduit, rigid polyvinyl chloride conduit (PVC), or reinforced thermosetting resin conduit (RTRC) having a length not exceeding 3.05 m (10 ft), and if the number of conductors does not exceed four.
(d) Adjustment factors shall not apply to Type AC cable or to Type MC cable under the following conditions:
- The cables do not have an overall outer jacket.
- Each cable has not more than three current-carrying conductors.
- The conductors are 12 AWG copper.
- Not more than 20 current-carrying conductors are installed without maintaining spacing, are stacked, or are supported on "bridle rings."
Exception to (4): If cables meeting the requirements in 310.15(C)(1)(d)(1) through (C)(1)(d)(3) with more than 20 current-carrying conductors are installed longer than 600 mm (24 in.) without maintaining spacing, are stacked, or are supported on bridle rings, a 60 percent adjustment factor shall be applied,
Table 310.15(C)(1) Adjustment Factors for More Than Three Current-Carrying Conductors
|Number of Conductors*||Percent of Values in Table 310.16 Through Table 310.19 as Adjusted for Ambient Temperature if Necessary|
|41 and above||35|
|*Number of conductors is the total number of conductors in the raceway or cable, including spare conductors. The count shall be adjusted in accordance with 310.15(E) and (F). The count shall not include conductors that are connected to electrical components that cannot be simultaneously energized.|