Noob Questions on Wireway Derating

[don_resqcapt19]

My sheet metal trough does indeed have large openings into the equipment below, without nipples. It also has tubing coming out of the top cover, but I think the key word in the sentence you paraphrased is "the". "If the item in question is connected to the equipment by conduits or nipples". "The" equipment is the equipment below my gutter, whose wiring space the gutter serves to expand. The tubing on the top cover serves as raceways to other stuff, not "the" equipment.

It is still my opinion that it is not expanding the wiring space of the equipment. It is just providing a path way into that equipment.

My comment about nipples into the equipment is just a general comment about the misuse of the term auxiliary gutter.

 

[don_resqcapt19]

where in the code is temperature adjustment required for conductors in a gutter?

Ampacity correction is only based on the ambient of the location where the conductor is installed and has nothing to do with what that conductor may be installed in.

 

[JuliaTruchsess]

It is still my opinion that it is not expanding the wiring space of the equipment. It is just providing a path way into that equipment.

There is no way the bends required for this installation of this equipment could be accommodated without the additional space provided by the gutter. What is your criteria for considering the wiring space "expanded"?

 

[JuliaTruchsess]

Ampacity correction is only based on the ambient of the location where the conductor is installed and has nothing to do with what that conductor may be installed in.

So you're saying that conductors in gutters need to be derated for temperature? That would certainly seem to make sense, as there's no magical conductor-cooling property of gutters that I'm aware of.

 

[kwired]

Ampacity correction is only based on the ambient of the location where the conductor is installed and has nothing to do with what that conductor may be installed in.

I agree. You can even need to make adjustments for open conductors if subject to high ambient temperature. Adjustments can also increase ampacity if ambient temp is low.

So to answer OP's question, I think since the one side of the wireway is subject to 60C one has to consider how that may impact interior temperature of the wireway. If conductors were selected from 310.15(B)(16) they were based on 30C ambient, so anything over that needs adjusted, unless 310.15(A)(2) exception can be applied.

 

[JuliaTruchsess]

I agree. You can even need to make adjustments for open conductors if subject to high ambient temperature. Adjustments can also increase ampacity if ambient temp is low.

So to answer OP's question, I think since the one side of the wireway is subject to 60C one has to consider how that may impact interior temperature of the wireway. If conductors were selected from 310.15(B)(16) they were based on 30C ambient, so anything over that needs adjusted, unless 310.15(A)(2) exception can be applied.

Thanks. With five of the gutter's six sides exposed to ≈30C and one exposed to 60C, I'm pretty sure that the ambient temp around the conductors will be < 50C, and I'm hoping that if that's questioned, an actual measurement of the interior temperature will settle the matter.

 

[don_resqcapt19]

There is no way the bends required for this installation of this equipment could be accommodated without the additional space provided by the gutter. What is your criteria for considering the wiring space "expanded"?

View attachment 22268

That may be an application where I would see it as an auxiliary gutter, but without actually seeing the equipment and reviewing the manufacturer's instructions, there is no way that I can say.
As far as the original derating question, it doesn't make any difference if it is an auxiliary gutter, or a wireway. The ampacity adjustment rule in 366.22, is identical to the one in 376.22. In both cases, ampacity adjustment is only required where there are more than 30 current carrying conductors at any 24" or longer cross section of the gutter or wireway.

 

[JuliaTruchsess]

The ampacity adjustment rule in 366.22, is identical to the one in 376.22. In both cases, ampacity adjustment is only required where there are more than 30 current carrying conductors at any 24" or longer cross section of the gutter or wireway.

366.22 and 366.23 offer exemption from "the adjustment factors in 310.15(B)(3)(a)" if fewer than 31 conductors are present in any cross-section. 310.15(B)(3)(a) specifies derating for number of conductors, it has nothing to do with derating for ambient temperature. Derating for ambient temperature is specified in Article 310.15(B)(2). I don't see anything in Articles 366 or 376 exempting wireways or gutters from compliance with 310.15(B)(2).

 

[ggunn]

366.22 and 366.23 offer exemption from "the adjustment factors in 310.15(B)(3)(a)" if fewer than 31 conductors are present in any cross-section. 310.15(B)(3)(a) specifies derating for number of conductors, it has nothing to do with derating for ambient temperature. Derating for ambient temperature is specified in Article 310.15(B)(2). I don't see anything in Articles 366 or 376 exempting wireways or gutters from compliance with 310.15(B)(2).

No, and there shouldn't be. Conduit fill derate is for heating by current through bundled wires in addition to the derate for ambient temperature.

 

[JuliaTruchsess]

No, and there shouldn't be. Conduit fill derate is for heating by current through bundled wires in addition to the derate for ambient temperature.

:thumbsup:

 

[steve66]

Auxiliary gutters are rare. Most of what people in the field call an auxiliary gutter are really wireways. Auxiliary gutters are intended to expand the wring space of a piece of equipment. To do so they must have large openings between the gutter and the equipment. If the item in question is connected to the equipment by conduits or nipples, it is a wireway and not an auxiliary gutters.

Interesting - I've never heard that before, but it makes sense now. In fact, now that I look in the 2017 NEC Handbook, it pretty much says that in the first two commentary paragraphs.

But it makes one wonder where they came up with the 30' limit. I always assumed that was a length the gutter could extend between two separate pieces of equipment.

Now it seems like its a limit on extending the entire width and height of the enclosure. Did they think someone might actually use an aux gutter that would be more than 30' wide?

 

[ggunn]

Interesting - I've never heard that before, but it makes sense now. In fact, now that I look in the 2017 NEC Handbook, it pretty much says that in the first two commentary paragraphs.

But it makes one wonder where they came up with the 30' limit. I always assumed that was a length the gutter could extend between two separate pieces of equipment.

Now it seems like its a limit on extending the entire width and height of the enclosure. Did they think someone might actually use an aux gutter that would be more than 30' wide?

Do you mean 30" (inches)?

 

[kwired]

Interesting - I've never heard that before, but it makes sense now. In fact, now that I look in the 2017 NEC Handbook, it pretty much says that in the first two commentary paragraphs.

But it makes one wonder where they came up with the 30' limit. I always assumed that was a length the gutter could extend between two separate pieces of equipment.

Now it seems like its a limit on extending the entire width and height of the enclosure. Did they think someone might actually use an aux gutter that would be more than 30' wide?

30 foot limit is the limit on the long dimension, whether it be vertical or horizontal dimension. Not exactly a limit either, just the point where ampacity adjustment rules change if you do exceed that dimension.

 

[steve66]

Do you mean 30" (inches)?

No, 366.12(2) which says 9 meters or 30 feet. That's why I'm confused.​

30 foot limit is the limit on the long dimension, whether it be vertical or horizontal dimension. Not exactly a limit either, just the point where ampacity adjustment rules change if you do exceed that dimension.

Yes, I agree. But we have decided that an aux gutter is not like a wireway that connects 2 pieces of equipment - its something that actually extends the area of the enclosure.

So its more likely to be the same height and depth as the equipment if its on the side of the equipment. If its on the top, its more likely the same width and dept. as the equipment. And there is a 30' limit on extending the enclosure with the gutter. I'm not saying it has to be the same size as the enclosure, but I think we have determined it can't just be a 6"x6" or 12"x12" flanged opening, or anything like that.

With something like that, I just can't imagine where there would ever be a need for a 30' extension.

Maybe in a high bay building where it is a Top Hat on a switchboard? I guess there could be situations where someone would want a top hat tall enough to feed a 2nd or 3rd floor. And that's probably about the limit where having unsupported conductors might start to be an issue.