Multiconductor cable 4/0 larger in cable tray

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jsmith05

Member
Location
Dallas, TX
Does the NEC allow mulitconductor cable 4/0 in larger in ventiliated cable tray without having to space the cable one cable diameter or greater, that is assume the multiconductor cables are installed in a single layer side by side with no spacing and do not exceed the tray widith? If so is the ampacity table 310.16 and no derating is required? Does the grounding conductor required to be single layer or can it be on top of the cables?
 

erickench

Senior Member
Location
Brooklyn, NY
NEC 392.11(A)(3) applies to uncovered trays only. If the tray is covered I would assume that you can install them in a single layer with no spacing and no temperature correction. The ampacity in this case would not exceed 95% of the allowable ampacities of NEC Tables 310.16 and 310.18.
 
If you are using a tray rated cable you may want to look at 392.11(B)(4). Since your cables are triplexed. With the proper spacing, 2.15 x diameter you could use Table 310.20 without any derating. To use Table 310.20 you must be careful that you can make your termination within 10% of the overal length of the cable tray run into your termination cabinet per 310.15 (A)(2) exception.
 
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