Noob Questions on Wireway Derating

[JuliaTruchsess]

1. How is "ambient temperature" defined with regard to a wireway? My wireway may have one face exposed to a warmer temperature than its other faces. Would the internal temperature of the wireway be considered an adequate measurement of the effective ambient? Can I slap some insulating material on the face exposed to higher temp in order to reduce the "ambient" for derating purposes?
2. For cross-sectional fill calculation purposes, is the OD of the wire with insulation used, or the cross-sectional conductor area?

Thanks.

 

[petersonra]

1. How is "ambient temperature" defined with regard to a wireway? My wireway may have one face exposed to a warmer temperature than its other faces. Would the internal temperature of the wireway be considered an adequate measurement of the effective ambient? Can I slap some insulating material on the face exposed to higher temp in order to reduce the "ambient" for derating purposes?
2. For cross-sectional fill calculation purposes, is the OD of the wire with insulation used, or the cross-sectional conductor area?

Thanks.

I think the ambient temperature being referred to is the temperature outside of the wireway. Note there is some provision somewhere for short runs of wireway through warmer ambients that does not require "de-rating".

A heat shield with a small air space between the heat shield and the wireway might well be enough to keep the ambient temperature down enough that you don't have to make temperature adjustments.

I don't recall any provision in the code for insulation as a means of changing temperature adjustments.

The OD of the wire with insulation is used.

 

[JuliaTruchsess]

I think the ambient temperature being referred to is the temperature outside of the wireway. Note there is some provision somewhere for short runs of wireway through warmer ambients that does not require "de-rating".

The wireway is in the same ambient for its entire 6-foot run. The top and front are in 25C, the bottom is on top of cabinets that should be around 35C or less, and the rear faces 60C.

The OD of the wire with insulation is used.

Thanks

 

[petersonra]

The wireway is in the same ambient for its entire 6-foot run. The top and front are in 25C, the bottom is on top of cabinets that should be around 35C or less, and the rear faces 60C.

is this a conduit or a trough of some sort?

is there some way you can claim it is a gutter or enclosure instead of a raceway?

 

[JuliaTruchsess]

It's a metal wireway ("trough") as described in Article 376, which is a type of raceway per the NEC. Not clear on the distinction between wireway and gutter, but I think it's not too significant in my application. It houses large conductors going between three pieces of equipment (cabinets) on top of which it sits and to which it is fastened, so maybe some kind of "enclosure" definition could apply, I don't know.

 

[petersonra]

It's a metal wireway ("trough") as described in Article 376, which is a type of raceway per the NEC. Not clear on the distinction between wireway and gutter, but I think it's not too significant in my application. It houses large conductors going between three pieces of equipment (cabinets) on top of which it sits and to which it is fastened, so maybe some kind of "enclosure" definition could apply, I don't know.

gutters and enclosures are not raceways so the temperature adjustments for conductors in a raceway do not apply.

it sounds like what you have is really a gutter.

 

[JuliaTruchsess]

gutters and enclosures are not raceways so the temperature adjustments for conductors in a raceway do not apply.

it sounds like what you have is really a gutter.

So this sheet metal construction on top of the cabinets could be considered a gutter?

 

[drktmplr12]

So this sheet metal construction on top of the cabinets could be considered a gutter?

View attachment 22257

gutter or wireway i would say. not a raceway imo.

you just have to be sure the gutter is sized correctly for bend radius, if needed. i don't know what conductors you are running, or if you are doing an angle pull.. but that height looks precariously short for any large diameter conductor to bend.

 

[petersonra]

366.2 Definitions.
Metal Auxiliary Gutter. A sheet metal enclosure used to
supplement wiring spaces at meter centers, distribution
centers, switchgear, switchboards, and similar points of wiring
systems. The enclosure has hinged or removable covers for
housing and protecting electrical wires, cable, and busbars.
The enclosure is designed for conductors to be laid or set in
place after the enclosures have been installed as a complete
system.

Incidentally, the code does not say you cannot use a piece of wireway as a gutter.

personally, though, I would use something that does not claim to be a raceway so i would not have to argue with the inspector about it.

 

[JuliaTruchsess]

The cabinet openings are wide parallel to the long axis of the gutter, so bend radius shouldn't be an issue, but we'll model it to be sure, thanks.

I can't find any exemption for temperature derating in gutters in the NEC, though. I see the exemption from fill derating under 310.15(B)(3)(a), but not from temperature derating.

 

[JuliaTruchsess]

Incidentally, the code does not say you cannot use a piece of wireway as a gutter.

personally, though, I would use something that does not claim to be a raceway so i would not have to argue with the inspector about it.

Ah, I thought gutters were a type of raceway, but I think now that I was mistaken, although one has to squint hard at the Code to see it. Thanks.

 

[petersonra]

I can't find any exemption for temperature derating in gutters in the NEC, though. I see the exemption from fill derating under 310.15(B)(3)(a), but not from temperature derating.

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

 

[JuliaTruchsess]

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

I thought gutters were raceways, but apparently that's not the prevailing interpretation.

 

[drktmplr12]

consider the engineering supervision criteria under 310.15 (C) if you really want to get exact. you might be able to squeeze more through the cables than the tables suggest.

 

[romex jockey]

The cabinet openings are wide parallel to the long axis of the gutter, so bend radius shouldn't be an issue, but we'll model it to be sure, thanks.

I can't find any exemption for temperature derating in gutters in the NEC, though. I see the exemption from fill derating under 310.15(B)(3)(a), but not from temperature derating.

depending on the definition (367.22 being your first) , the ex here is a consideration>

310.15 A(2) Selection of Ampacity. Where more than one ampacity
applies for a given circuit length, the lowest value shall be used.
Exception: Where different ampacities apply to portions of a circuit, the
higher ampacity shall be permitted to be used if the total portion(s) of
the circuit with lower ampacity does not exceed the lesser of 3.0 m
(10 ft) or 10 percent of the total circuit.

~RJ~

 

[steve66]

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

310.15 B 2?

 

[steve66]

I thought gutters were raceways, but apparently that's not the prevailing interpretation.

Aux. gutters cannot go more than 30' beyond the equipment that it supplements (366.12). I usually use that as a guide.

So if its a limited run like you have, the aux. gutter section is probably going to be easier to comply with.

If its a longer run, then its more likely to be a wireway, and if it goes out past beyond 30', then it would have to be a wireway.

And I'm not sure that an aux gutter is not a raceway. But aux. gutters do have their own requirements for derating and fill that replace the typical requirements for a raceway or a wireway.

But obviously, on top of complying with the code, you are going to want to engineer it so the heat is not a problem.

 

[petersonra]

I see your point. I think the exemptions in the gutter article apply to adjustments due to number of CCC and not temperature adjustments.

 

[don_resqcapt19]

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.

 

[JuliaTruchsess]

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.

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.