Trough usage

[iwire]

What if the wireway is 12X12X12?

Less than 24" no derating needed or use 310.15(A)(2)

 

[Smart $]

In my opinion, that exception applies anywhere you are required to adjust or correct a conductor's ampacity.

+1 :thumbsup:

 

[Smart $]

...If you were to slide a paper thin razor in a vertical cross section (with power off ) Would it cut through 31 wires or more? Simple as that.

FIFY.

Adjustment only applies to those circuits, not all circuits in the wireway where more exist.

 

[Smart $]

...
It is not explicitly stated, but most analysis I have seen assumes that the cross section is perpendicular to the long dimension of the trough.
Requiring all cross sections (horizontal, vertical, front to back) to meet the 30 conductor limit seems pointless.

Ditto.

 

[infinity]

Less than 24" no derating needed

There have been many attempts to clarify this position but the CMP has rejected them all. Here's one older example:

8-136 Log #2581 NEC-P08 Final Action: Reject
(376.22(B))
________________________________________________________________
Submitter: Paul E. Guidry, Fluor Enterprises, Inc.
Recommendation: Add new text to read as follows:
The adjustment factors in 310.15(B)(3)(A) shall not apply to wireways not
exceeding 0.6m (24 in) in length.
Substantiation: This would be the same conditions and rules currently found
in the Code for conduit nipples. There isn’t any difference between a conduit
nipple and a short length of wireway.
Panel Meeting Action: Reject
Panel Statement: See panel statement on Proposal 8-135.
Number Eligible to Vote: 12
Ballot Results: Affirmative: 12

 

[kwired]

Also remember if you have say a group of motor starters that connect to the aux gutter - if you have control circuits in the gutter those conductors don't have to be counted as current carrying conductors for ampacity adjustment reasons.

 

[romex jockey]

IMO that doesn't apply to wireways.

I always thought it did ,ergo all the ww's out there.....? ~RJ~

 

[romex jockey]

The NEC's take on captive heat is predicated on sizes of enclosures, amounts of conductors ,prevailing environment, etc.

One could install 10 #12's in raceways and/or enclosures large enough to house a buick , and still be held to the same standards as max fill

Objectively speaking, it's like anything but the actual heat is really addressed.....

~RJ~