Sunday, January 22, 2023
The NEC contains separate articles for Auxiliary Gutters and Metallic Wireways. If you read the articles, especially since a code change in 2020 there is very little different about them at first glance which leads many people to ask...What is the difference between a Gutter and Wireway?
Let's first take a look at the two articles to answer this question. If you have a subscription to NFPA Link, open it now in a separate window, or open your 2023 NEC so you can follow along. Article 366 Auxiliary Gutters and Article 376 Metal Wireways are the two Articles. Article 366.1 Scope informs us this article covers the use, installation, and construction requirements of metal auxiliary gutters and nonmetallic auxiliary gutters and associated fittings. Article 376.1 Scope informs us this article covers the use, installation, and construction specifications for metal wireways and associated fittings.
Based on that information the picture above could be called an auxiliary gutter or a metal wireway....in fact it could be either of them, so that was not helpful in understanding the difference between a metal wireway and an auxiliary gutter. If you are following along in NFPA Link, you have instant access to the answer. If you are using a standard code book, you would need to have the handbook to find the answer to our question. In article 366.1 there is a handbook explanation that is found in the "Enhanced Content" on Link or in the Handbook. The information in the handbook or the enhanced content explains the difference.
Here is how the NEC explains it:
An auxiliary gutter provides additional gutter space for wiring in various types of electrical enclosures and equipment. This additional gutter space may be necessary to provide sufficient room for the number of conductors in an enclosure or to provide adequate wiring bending/deflection space where conductors connect to a terminal. Although the construction of an auxiliary gutter is no different from that of a wireway, the field application of this equipment differentiates an auxiliary gutter from a wireway.
A wireway is a raceway in accordance with the definition of raceway in Article 100. Auxiliary gutters supplement enclosure wiring spaces and are not encompassed by the definition of raceway. Therefore, NEC requirements that apply only to raceways do not apply to auxiliary gutters. An example of such a requirement is 230.7, which prohibits service conductors from being installed in a raceway with conductors that are not service conductors.
This rule applies to wireways installed in accordance with Articles 376 and 378. However, an auxiliary gutter installed to supplement the wiring space of a service equipment enclosure is not a wireway; therefore, service conductors, feeder conductors, and branch-circuit conductors can occupy the same wiring space of an auxiliary gutter. Unlike wireways, which are covered in Articles 376 and 378, auxiliary gutters are permitted to contain bare and insulated copper and aluminum busbars. See 366.23(A) for the ampere rating of bare copper and aluminum busbars installed in auxiliary gutters.
So there we have it. The difference between an auxiliary gutter and a wireway is how it is used. The equipment above could be used in the building as a pull box in a long run of conduit, and then it would be a wireway. Or it could be used above or below a panelboard or switchboard and then it would be an auxiliary gutter.
There are four primary differences in the rules for auxiliary gutters and metal wireways:
1. A gutter is intended to supplement the space for panelboard, switchboard and meter enclosures wire space to permit adequate wiring bending space. A wireway is simply a raceway.
2. A gutter can contain electrical buses and terminations because it is considered a supplemental enclosure. A wireway is a raceway and can not contain buses.
3. A gutter can contain both service conductors and non-service conductors because it is a supplemental enclosure. A wireway can not contain both service and non-service conductors because they are prohibited from being in the same raceway and a wireway is a raceway.
4. A gutter can not extend more than 30 feet beyond the equipment that it supplements. A wireway is just a raceway and therefore there is no prohibition on length.
The wire fill requirements for gutters and wireways used to also be different but a 2020 NEC code change made the wire fill and ampacity derating requirements the same for wireways and gutters.
It is important to remember that a wireway and an auxiliary gutter are the exact same piece of material but depending on how you use them they have different requirements. Be sure to look up these articles and refresh your memory before you order your material and plan your job.
One last point. We tend to call of these pieces of equipment...gutters.... The NEC does not use the term gutters by itself. They are either a wireway or an auxiliary gutter.
I hope this has helped answer the question.
Ted "Smitty" Smith
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