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#16376 - 11/10/02 06:13 PM Derating
Wirenuttt Offline

Registered: 11/10/02
Posts: 267
Loc: Massachusetts
I noticed in a foundry that their electric conduits in the ceiling to feed various equipment looked like spegheti. The company would like to run major conduit runs through 2 or 3 large J.B.a spread out all overhead around different areas where you can just pipe up and attach electric equipment hard wired, spliced, and ran through a larger conduit back to the panelboard. There could be a possbility of 10-20 ckts. Does the derating factors of 310-16 apply here, and if so, does this installation warrant???

[This message has been edited by Wirenuttt (edited 11-10-2002).]

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#16377 - 11/11/02 03:25 AM Re: Derating
sparky Offline

Registered: 10/18/00
Posts: 5545
welcome Wirenuttt

IMO, derating would apply, T310.15(B)(2)(a) would dictate 50% off of 310.16 ( 10-20 conductors), however note the math starts at the 90degC collum there.

some consideration for the cieling 'ambient' temp may also apply

The interesting thing is the JB vs. a trough, and the magic '29' conductor limit here;

376.22 Number of Conductors.
The sum of the cross-sectional areas of all contained conductors at any cross section of a wireway shall not exceed 20 percent of the interior cross-sectional area of the wireway. The derating factors in 310.15(B)(2)(a) shall be applied only where the number of current-carrying conductors, including neutral conductors classified as current-carrying under the provisions of 310.15(B)(4), exceeds 30. Conductors for signaling circuits or controller conductors between a motor and its starter and used only for starting duty shall not be considered as current-carrying conductors.


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