Table 310.16. Conductor Ampacity Question

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prs1025

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Table 310.16 gives ampacities for not more than 3 current-carrying conductors [C.C.C.] in raceway, cable, or earth.
My company uses Panduit Wiring Duct in our industrial control cabinets. Should this be considered raceway so that table 310.15(B)(2)(a) would need to be used to adjust the ampacities in 310.16 for more than 3 C.C.C.?
I have heard both, that it is raceway and that it isn't since it permits the flow of air through wiring slots. Can someone who knows more than me help clear this up? Thank you.
 
If you look at 310.15(B)(2) it says that an adjustment is made when conductors in a raceway or cable are stacked or bubdled for more that 24 inches. I would think that in the wiring duct the conductors would be stacked. How many do you have?
 
If these are control wires, I would say use engineering because only a limited amount of those wires will be carrying current at any given time and the the total current will be limited by the size of fuses off control xfmr. If these are power wires, you may have to do some derating.
If you are using more than 2' of Wiring Duct, IMO the wires would be bundled and subject to derating per the NEC see 310.15 B2.
 
Thank you gentlemen for your responses.
I didn't see where it says this adjustment applies to wires bundled for more than 24". Could you point this section out to me?
These are in fact power wires. They wire to motor protectors (with thermal overload protection, trip class 10) and contactors, which have been sized for the given FLA of each motor. The wires are not really bundled. They are loose in the Panduit but I guess you could consider them to be stacked. There can be as many as 30 conductors live at any given time. Our standard wire is 105 Deg C but I'm not sure how this is taken into account when using 310.16 to size conductors.
 
Read 310.15(B)(2) .

Our standard wire is 105 Deg C but I'm not sure how this is taken into account when using 310.16 to size conductors.
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You use the 90C rating to make the adjustment. However the result must not exceed the 75C rating for the same wire size.
 
If you are building panels that will be labeld by an NRTL like UL then the NEC does not apply internal to your panel. Follow the standards of your testing agency such as UL508A. If your panel will not be labeld then follow NFPA79 which includes all applicable sections of the NEC.
 
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