Wireway Fill

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krthomp33

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New guy here, so I apologize if this has been covered already. I searched, and didn't find any thing about it.

I have installed a 12 X 12 wire way, 66 inches long. The inspector has told me that I cant run any more than 30 current carrying conductors through this before I have to de rate. The wire way is above 2 panels, with 2- 2 1/2 X 24 nipples running into the panels. This is so all my MC is landed in the wireway, and not the top of the panels. I contend that I have not exceeded
the 20% fill, but he is insisting that the max is 30, regardless of the size of the wireway.


any info would be appreciated!
 
Re: Wireway Fill

376.22 Number of Conductors. The sum of the crosssectional 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.
 
Re: Wireway Fill

Originally posted by pierre:
376.22 Number of Conductors. The sum of the crosssectional 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.
Click to expand...
I understand the code aspect, but in essence this is telling me that if I have a 18X18 wireway that is 10 feet long, I can only put 30 #14 current carrying conductors in this wireway......doesn't seem to make sense
 
Re: Wireway Fill

So assume that you were on the Code Making Panel when that rule was written. How would you write it? If you have a better idea, please visit the "Proposals for the 2008 NEC" forum and plan on making a proposal. We will help you put it together so the panel will have to take a good look at it and maybe change the rule.

The NEC belong to and is written by all of us, not just the ones on the Code Making Panels. Without proposals, the Code doesn't change. :D
 
Re: Wireway Fill

376.22 does not limit you to 30 current carrying conductors. You can install more than 30, up to 20% fill. Once you exceed 30 current carrying conductors, you are required to apply ampacity adjustment. I am not so sure why you are making such a big deal out of this?
 
Re: Wireway Fill

Sounds like your application may be for Auxiliary Gutter per Art.366 instead of wireway.
However you may find that it will not make any difference as far as your questions go.
 
Re: Wireway Fill

I would assume the derating factors would only apply for more than 30 conductors in the same cross-sectional of the wireway. Does every one agree to that? Now that I read the article, it really isn't worded that way.

And, I still feel a divider in one wireway makes two wireways (if the fill of each half is less than 20%). You might ask your AHJ if he will go for that.

Steve
 
Re: Wireway Fill

krthomp33,

The inspector is correct, also pierre's post is correct.

Here is another angle applied and approved many times:
The derating factors in 310.15 B.2.a apply where conductors are stacked or bundled longer than 24 inches. This means that the 30 conductor rule only applies to the conductors bundled longer than that.
It sounds like you are using the wireway as a collector box and the branch circuits enter the top and run either straight down through to the panel, or offset slightly to enter a conduit into one of the panels. If done as cleanly as possible you should be able to limit your exposure to the 30 conductor derating rule. To do this any MC entering the top should be within 18 - 19 inches of the conduits at the bottom that the conductors are using to get into the panelboards. Also as allowed in the exceptions, keep your nipple length to 24 inches or less to avoid the derating requirement.

[ March 21, 2005, 02:53 PM: Message edited by: marketman ]
 
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