Auxiliary Gutter Adjustment Factor

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Royjr717

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Hello folks,

I had a question regarding the verbiage of section 310.15(C)(1) in conjunction with the verbiage of 366.23(A).

310.15(C)(1) states conductors not maintaining spacing for a continuous length longer than 24 inches requires an adjustment factor. Since 366.23(A) references the code section, and not just the table itself, would a gutter box with more than 30 current carrying conductors in a cross-section, need to be for a continuous length of more than 24 inches in the gutter box, in order to require adjustment factors?

I ran into the gutter box below, with more than 30 current carrying conductors in cross section however, it is only for a length of about 16 inches.

4eab2f0e4396ad570e944dbcd5154ebf.jpg



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If you have 30 CCC's or less at a cross section for any length no derating applies. Once you exceed 30 CCC's at a cross section then derating does apply. There is no 24" component to the derating requirement so in this case the 16" dimension is not relevant.

Welcome to the forum. :)
 
Note that in regard to your specific question, it does not change Rob's answer but from the picture it appears you have a metal wireway, Art 376, not an auxiliary gutter, Art 366.

Auxiliary gutters, other than part of a factory assembly, are rare birds.
 
augie47 said:
Note that in regard to your specific question, it does not change Rob's answer but from the picture it appears you have a metal wireway, Art 376, not an auxiliary gutter, Art 366.

Auxiliary gutters, other than part of a factory assembly, are rare birds.
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I thought that too but it's actually an auxiliary gutter too according to the label.

Aux Gutter 001.jpg
 
augie47 said:
Interesting.... looks like it might say"wireway or auxiliary gutter" but it's not real clear. It's not real clear.
The way it is installed it seems to fit the wireway section as it is nippled to the panel.
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It looks like it's either. I would guess that depending on how it's used would determine what code article it falls under.
 
infinity said:
It looks like it's either. I would guess that depending on how it's used would determine what code article it falls under.
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Thank you both for your inputs! I was able to zoom in a little closer to the picture and it appears it reads “WIREWAY OR AUXILIARY GUTTER”. It looks the verbiage is the same in regard to the adjustment factors for either or.

In response to the wireway vs auxiliary gutter point, would a box being identified as either or, depend on how it is installed?


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Also in your picture, you have some conductors bundled, but not all, so derating wouldn't apply. If it did, then we would have some major problems inside a typical distribution panel. When people feel the OCD need to use tie wraps inside a panel to make everything pretty, that is when we have a problem. I know in my area, I haven't seen an inspector bust someone, but I always cut off the tie wraps first thing when enter a panel.
 
This thread might be helpful, especially Post #9 (pictures)

Trough Sizing

Situation: Power Company CT cabinet. I must exit the top of the CT cabinet with the customer side service conductors. My preference is to use a 4” nipple to go up into this trough. The trough will extend past the side of the CT cabinet so that I can drop down in 4” conduit to a trough that will...
forums.mikeholt.com
 
Royjr717 said:
In response to the wireway vs auxiliary gutter point, would a box being identified as either or, depend on how it is installed?
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Yes, it is about their installation.
A wireway is usually connected via a relatively small opening into an enclosure wiring space while an auxiliary gutter opening is usually the entire length or height of the space. An auxiliary gutter is almost never connected by raceways, as their intent is usually to increase the actual wiring space of the parent enclosure.
 
infinity said:
I thought that too but it's actually an auxiliary gutter too according to the label.

View attachment 2577578
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Many are listed as both and the installation determines what it is. Other than a couple of custom made "top hats" for MCC replacement, I don't think I ever saw an actual auxiliary gutter in my 40+ years.
If it connects to the enclosure via nipples, it is not an auxiliary gutter.
 
infinity said:
Once you exceed 30 CCC's at a cross section then derating does apply. There is no 24" component to the derating requirement so in this case the 16" dimension is not relevant.
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2026 NEC Second Draft 310.15(C)(1) starts off "The ampacity of each conductor shall be reduced as shown in Table 310.15(C)(1) where the number of current-carrying conductors in a raceway or cable exceeds three, installed without maintaining spacing for a continuous length longer than 600 mm (24 in.)"

This clarifies that there is a 24" component to the derating requirement. The 2023 NEC was less clear, but the common interpretation that ampacity adjustment is not required within a nipple less than 24" similarly implies a 24" component.

Cheers, Wayne
 
wwhitney said:
This clarifies that there is a 24" component to the derating requirement. The 2023 NEC was less clear, but the common interpretation that ampacity adjustment is not required within a nipple less than 24" similarly implies a 24" component.
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My comment was that the 24" does not apply within the wireway or auxiliary gutter so the 16" (or any other dimension for that matter) mentioned in the OP is irrelevant.
 
infinity said:
My comment was that the 24" does not apply within the wireway or auxiliary gutter so the 16" (or any other dimension for that matter) mentioned in the OP is irrelevant.
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Wireways are raceways, so 310.15(C) says ampacity adjustment applies when the length of the raceway with more than 3 CCCs exceeds 24". 376.22 exempts portions of wireways with 30 or less CCCs from 310.15(C).

So say the bundle in the picture is 32 CCCs that go into the raceway exiting out the back. Say that raceway is a 6" nipple to another enclosure on the opposite side of the wall. Then the length of conductors which don't maintain spacing is 16" + 6" = 22", less than 24", so 310.15(C) does not require ampacity adjustment.

Cheers, Wayne
 
wwhitney said:
Wireways are raceways, so 310.15(C) says ampacity adjustment applies when the length of the raceway with more than 3 CCCs exceeds 24". 376.22 exempts portions of wireways with 30 or less CCCs from 310.15(C).

So say the bundle in the picture is 32 CCCs that go into the raceway exiting out the back. Say that raceway is a 6" nipple to another enclosure on the opposite side of the wall. Then the length of conductors which don't maintain spacing is 16" + 6" = 22", less than 24", so 310.15(C) does not require ampacity adjustment.

Cheers, Wayne
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I never look at the 24" and simply use the exception that Rob cited in post #11. It is very rare that does not result in a length greater than 24".
 
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