NOTE This standard covers enclosed metal and nonmetallic troughs used to group, route, and access insulated conductors at and between electrical equipment, comprising both wireways (a raceway) and auxiliary gutters (a supplemental enclosure). (1.1)

NOTE The defining distinction in this standard is between a wireway and an auxiliary gutter, because each is governed by a different NEC article with different fill limits and application restrictions. A wireway is a sheet-metal or nonmetallic trough with a hinged or removable cover used as a raceway to carry conductors from point to point; it is governed by NEC Article 376 (metal) or Article 378 (nonmetallic) and has no length restriction. An auxiliary gutter is a supplemental enclosure that extends from and supplements the wiring space of equipment such as switchboards and distribution centers; it is governed by NEC Article 366 and is not a raceway. (1.2)

NOTE The two assemblies frequently use identical hardware and finishes, so the governing article must be established per segment rather than per product; a single physical trough can change classification along its length. (1.3)

NOTE The edition of NFPA 70 (NEC) that applies shall be the edition adopted by the authority having jurisdiction for the project. (2.3)

NOTE Wireways, auxiliary gutters, and associated fittings shall be products of a single manufacturer to the greatest extent practicable so that fittings, covers, and finishes mate without field modification. (4.1)

NOTE Conductor fill and ampacity derating calculations shall be prepared and stamped by, or under the direction of, the Engineer of Record where required by the AHJ. (4.4)

NOTE UL 870 (9th Edition, 2016, reaffirmed as an ANSI standard in 2023 with no technical changes) is the single product safety standard covering both wireways and auxiliary gutters and their fittings. (4.5)

NOTE Enclosure selection shall match the environment of each installed location, because the NEMA enclosure type controls protection against water, dust, and corrosion and a mismatch is a common field deficiency discovered after rough-in. (5.1)

NOTE NEMA type definitions for wireway and auxiliary gutter selection: Type 1 is general-purpose indoor, suitable for clean dry electrical rooms only (not wet, damp, or outdoor); Type 3R is rain-tight for outdoor use; Type 4 is watertight; Type 4X is watertight with corrosion resistance for washdown and corrosive atmospheres; Type 12 is dust-tight and drip-tight for industrial interiors. (5.2)

NOTE Construction material is the primary durability decision and is driven by the installed environment and by mechanical exposure, not by cost alone. (6.1)

NOTE Steel construction (painted or galvanized) is the standard for indoor and most outdoor work; nonmetallic PVC suits mildly corrosive or nonconductive-requirement areas at smaller sizes; fiberglass suits aggressive corrosive environments where metal would degrade. (6.2)

NOTE Standard wireways and auxiliary gutters are rated 600 V; products listed for 1000 V are available for 1000 V distribution systems and shall be specified where the system voltage exceeds 600 V. (6.7.1)

NOTE The interior cross-section shall be sized so that the conductor fill does not exceed the limit set by the governing NEC article for the segment classification. (6.8.1)

NOTE Specifying a cross-section without also specifying section length and a fittings bill of material leads to quantity RFIs; the schedule shall give width, height, lengths, and fittings together. (6.8.2)

NOTE Cover style governs how conductors are installed and how readily splices and taps can be reached for inspection and future work. (6.9.1)

NOTE Lay-in (hinged) covers allow conductors to be laid into the trough from the side and are preferred for equipment lineups with frequent additions; screw covers and lift-off covers suit fixed runs and locations requiring tamper resistance. (6.9.2)

NOTE Conductor fill and ampacity derating are the two calculations most often misapplied on wireway and gutter work, and they differ by classification; getting the classification right is therefore a precondition to getting the fill right. (7.1)

NOTE At 40 current-carrying conductors in a single cross-section, the Table 310.15(C)(1) adjustment factor is 50%, which halves allowable ampacity; this derating is frequently missed in long equipment lineups carrying many grouped branch and control circuits. (7.6)

NOTE Fittings complete the routing geometry of a wireway or gutter system and shall be listed components of the same product family as the straight sections to ensure dimensional and finish compatibility. (8.1)

NOTE Nonmetallic wireways expand and contract significantly more than steel and require more frequent expansion fittings to prevent buckling or joint failure. (8.5.1)

NOTE Metal wireways and auxiliary gutters serve as part of the equipment grounding path only if the metal-to-metal continuity across every joint is maintained, which paint and plating at section joints can interrupt. (9.1)

NOTE Factory and field testing confirm that the assembly is electrically safe and that the grounding path is continuous before energization. (10.1)

NOTE Support spacing differs by classification and material and is a code requirement, not a convenience; under-supporting a run is a common inspection failure. (11.1)

NOTE Routing, extents, and arrangement of wireway and gutter runs are location-specific and shall be taken from the drawings, not fixed by this standard. (11.9.1)

NOTE Spare covers, fittings, and closure plates allow minor field changes and repairs without a new procurement cycle. (14.1)