Definition 376.22

Can someone please give me the definition of cross section fill?

I have a gutter 8x8 and the inspector called me on crossfill, if I remember route the emt so the wires go straight thru does that eliminate the crossfill issue?
 

jumper

Senior Member
It is a percentage. For you it would be 8"*8"=64 sq in, 64 x.20=12.8 sq in.

So at no point can the wireway cross section be filled more than 12.8 sq. in.

Imagine if you took a knife and sliced the wireway across the width at any point, like a loaf of bread, your cross section would be like a slice of bread.

View attachment 14552
 
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al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
. . . route the emt so the wires go straight thru does that eliminate the crossfill issue?
Welcome to the Forum.

"Crossfill" is an interesting contraction of the Code term of "cross-section fill". I haven't heard it before.

I'm guessing, having not seen the gutter your inspector gigged, but I'll bet that there is a place in your 8" X 8" gutter where the wires are the most packed. . . that is, the wires are the densest. And I'll bet that the wires in the packed spot are running the long way of the gutter.

This is a pain to do long hand, but, it's like math, that gives you shortcuts after you learn the long way of doing it.

Go to Chapter 9 Table 5, and write down the square inch number for each of the guage and type of conductor you have passing through the most packed part of the 8" X 8" gutter.

Now, count each of the conductors in the gutter, by size and type (unless they are all THHN). Multiply the number of, say, #12 times the square inches from Table 5, Chapter 9, and write that down. Do the same thing for all the other sizes and types. Add all the square inch numbers together and you have the "total size" of the wires in that cross-section area. . . . . The question to you is, is this "total size" equal to or smaller than the percentage of the over all cross-section area (64 square inches) that you are allowed by Code?

Who knows, your calculation might show the inspector that your installation is OK. Try it.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
You would need more than 30 CCC's (I think that Bob meant 30;)) before derating is required not 30 conductors. Also Bob stated you look OK.
 

Carultch

Senior Member
Location
Massachusetts
So basically I can't have more then 30 wires cross each other at any givin point in the gutter

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Unless the length in question is so little, that you comply with the 10% / 10 ft length exception, also known as the "stub rule". This means that for each current-carrying conductor that has a concern, the remaining length has to be at least 10 times as long as the length in question, and the length in question has to be under 10 ft.

Otherwise, once you have a 31st wire in the gutter, you have to apply the 31% ampacity adjustment factor.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
So basically I can't have more then 30 wires cross each other at any givin point in the gutter
My first response mis-understood your question.

Think of the gutter as like a loaf of bread. Consider one slice of "bread" from that Gutter (thanks to Infinity for the image.) No more than 30 conductors can PASS THROUGH the slice of "bread".

I suspect that the way you use "cross" is little different the "cross section".
 

Carultch

Senior Member
Location
Massachusetts
Gutter is 8x8x8

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Right, but if the overall conductor length is only about 8 ft, that doesn't count for this exception. The remaining length outside of the region in question, has to be at least 10 times as long as the length of the region in question.
 
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