wireway derating per 376.20(B)

[SparkyRules]

As I read this is states any "cross section" of a wire way, containing MORE than 30 CCC shall be subject to the derating of 310.15(B)(3) a . In my discussion with another they interpret this not as "any" cross section ( like if you cut across the area in question) but more like "if" the wires cross with in that section of wireway OR at a Cross ( like a Tee or a X intersection. I would be glad to be wrong here, but me thinks this is not what they meant?

 

[infinity]

Your interpretation, the first part in parentheses is correct.

 

[SparkyRules]

Thank you, It does seem pretty well sated as such!

 

[SparkyRules]

This is an arugument by "another" against how I understand this, any comments? Here is their view.

Cross section is any intersecting point in the wireway or 20% total area fill of wireway
If there were 30 current carrying conductors bundled up in a cross section it would violate but in this install the conductors are never bundled to create heat dissipation problems. If the intent was to never have more than 30 conductors in any given gutter or wireway there would be countless violations in motor control centers, etc. That code section intent is to limit excessive bundling mostly caused from undersized hot troughs

 

[SparkyRules]

This is a example of what this means as a question by the same folks. Here is their question. (I would say yes it must be de-rated by this example given, but only the greater of the 2 de-ratings would apply.) so if I have 4 conduits each containing 8 current carrying conductors (assume adjustment and correction have been applied to those) and I enter a wireway on one end and exit the opposite end and the conductors are passing straight through and the conduits are in line with one another on entry and exit is this a code violation? If I were to cross the wireway at any given cross section as you are explaining I would have 32 ccc. Let’s also say for the examples sake the wireway has been sized properly.

 

[kwired]

This is an arugument by "another" against how I understand this, any comments? Here is their view.

Cross section is any intersecting point in the wireway or 20% total area fill of wireway
If there were 30 current carrying conductors bundled up in a cross section it would violate but in this install the conductors are never bundled to create heat dissipation problems. If the intent was to never have more than 30 conductors in any given gutter or wireway there would be countless violations in motor control centers, etc. That code section intent is to limit excessive bundling mostly caused from undersized hot troughs

It might possibly be overlooked often, but the 30 conductor rule applies in MCC wireways. Also note that the control conductors in such application are not considered current carrying conductors for the sake of introducing heating effects to the wireway. So you can have conductors from 10 different three phase three wire motors in a wireway section in MCC and not need to consider adjustments. Not too often you probably have more than ten controllers in a single vertical section and if you do they are likely for small motors and if you only have a couple amps on a 14 or 12 AWG you still have lots of room for ampacity adjustment. A horizontal wireway say at top of the MCC might be where there is more potential for issues here.

 

[infinity]

This is a example of what this means as a question by the same folks. Here is their question. (I would say yes it must be de-rated by this example given, but only the greater of the 2 de-ratings would apply.) so if I have 4 conduits each containing 8 current carrying conductors (assume adjustment and correction have been applied to those) and I enter a wireway on one end and exit the opposite end and the conductors are passing straight through and the conduits are in line with one another on entry and exit is this a code violation? If I were to cross the wireway at any given cross section as you are explaining I would have 32 ccc. Let’s also say for the examples sake the wireway has been sized properly.

Yes in your example you have 32 CCC (4*8=32) in the wireway at any cross section.