Wireways and Auxiliary Gutters

NOTE This standard governs the wireway and the auxiliary gutter as a listed product: the trough and its cover, the fittings that turn, branch, reduce, close, and connect it, the hardware that holds the sections together and keeps the assembly electrically continuous, the supports that carry it, and the field work that classifies, fills, bonds, and tests it. (1.1)

NOTE A wireway is a sheet metal or nonmetallic trough with a hinged or removable cover, in which conductors are laid in place after the trough is installed and reached again at any point along its length, and it is a raceway under NFPA 70 Article 376 or Article 378 with no limit on its length. An auxiliary gutter is the same trough used for a different purpose: it extends the wiring space of switchgear, a switchboard, a panelboard, a meter center, or a motor control center so that conductors can be spliced, tapped, and distributed to the equipment it serves, and it is a supplemental enclosure under NFPA 70 Article 366 rather than a raceway, limited to 30 ft beyond the equipment it supplements. (1.2)

NOTE Which article governs a run is settled by what the run does, not by what it is made of; a trough that carries conductors between two pieces of equipment is a wireway, and the same catalog trough bolted to the top of a switchboard to splice and distribute its feeders is an auxiliary gutter. The two articles set different support intervals, different length limits, and a different rule for when the ampacity adjustment factors apply, so every run is classified before it is filled. (1.3)

NOTE The following are governed elsewhere and are outside this standard: (1.4)

NOTE The classification is written on the shop drawing because it is the one decision every later check depends on: the reviewer who finds a 40 ft auxiliary gutter or a nonmetallic wireway supported at 5 ft intervals finds it on the drawing, before the trough is ordered, rather than at the rough-in inspection. (3.1.2)

NOTE NFPA 70 366.6 requires a sheet metal auxiliary gutter to be listed, and permits one that is not listed only where it is constructed to the sheet thickness, continuity, and cover requirements of NFPA 70 366.100; the listed gutter is the catalog trough every manufacturer ships, and the unlisted gutter is a custom sheet metal box a shop fabricates for a meter center or a switchboard whose wiring space no catalog size fits. The listed product is what nearly every project uses, and the unlisted gutter is accepted where the geometry leaves no listed alternative and the Authority Having Jurisdiction accepts the shop's construction. (4.1.3)

NOTE A fitting from another series bolts to a trough whose flange pattern it was not made for, and the joint it makes is neither the listed joint nor the one the bonding continuity of the assembly was tested with; a project with two series on it also carries two sets of spare covers and two lengths of cover screw for the life of the installation. (4.2.3)

NOTE A wireway is reached again after it is installed, which is the reason to use one, and a run buried in a wall or above an inaccessible ceiling has given that up while keeping the fill limits and support rules written for an accessible trough; the code permits only the pass-through, where the cover on each side of the wall can still be opened. (5.1.7)

NOTE A polyvinyl chloride trough softens as it approaches its listed temperature and becomes brittle below it, grows and shrinks between the two with a coefficient several times that of steel, and chalks and cracks under ultraviolet exposure unless the resin carries an inhibitor; a conductor rated 90 °C running at its rated temperature in a trough listed for 75 °C warms the trough past its listing from the inside. These are the conditions the code names, and each is a question the site answers, which is why the ambient limits are written against the site temperatures rather than a fixed value. (5.2.4)

NOTE Whether a run must be restrained follows from the seismic design category and from the importance factor the code assigns to the loads the run serves, so the field carries the consequence of those inputs rather than a preference; a run feeding a fire pump, egress lighting, or a load a Risk Category IV facility depends on carries the higher importance factor and is restrained in a category where an ordinary run is not, and ASCE 7 Chapter 13 exempts a trapeze-supported run below a weight per foot and a drop length that a small wireway often satisfies. (5.3.2)

NOTE A hinged-cover metal wireway opens along its full length without removing a part, so conductors are laid in from the side and a run next to a switchboard or a motor control center is opened again every time a circuit is added, which is what the lineup wireway in an electrical room is used for; a screw-cover metal wireway carries a lift-off cover held by captive screws, costs less per foot, holds its cover against vibration and against a hand that bumps it, and is the construction the Type 3R, Type 4, and Type 12 troughs are built as, since a gasketed hinge is harder to make than a gasketed flange; a nonmetallic wireway resists the atmosphere that attacks painted or galvanized steel, carries no fault current and so needs an equipment grounding conductor inside it, is limited to 3 ft support intervals unless listed for more, cannot be used in a plenum or where it is subject to physical damage, and grows and shrinks with temperature enough to need expansion fittings; an auxiliary gutter is a metal or nonmetallic trough of any of these constructions used to extend the wiring space of the equipment it is bolted to, limited to 30 ft beyond that equipment, and chosen where feeders are to be spliced, tapped, or redistributed at the equipment rather than carried past it. A project with a lineup wireway in the electrical room and a gutter above a meter center uses two types, and the type of each run is set where the run is scheduled. Neither of the two metal covers is distinctly the norm across projects, so the field asserts no default. (6.1.2)

NOTE The 30 ft limit is what separates a gutter from a raceway: within it, the trough is treated as part of the equipment it is bolted to, with the equipment's wiring space rules for bending and the gutter's own rules for support and fill; beyond it, the trough is carrying conductors between points and the raceway article applies. The gutter article never permitted a device inside the trough because a device needs the working space, the dead front, and the barriers that the equipment enclosure furnishes and the trough does not. (6.2.5)

NOTE A UL 870 trough is listed at 600 V, which covers every system through 600 V, and that is the rating on nearly every project; a trough listed at 1000 V is built with the same sheet metal and a different spacing at the joints and is furnished where the conductors are the 1000 V direct-current circuits of a photovoltaic or energy storage system, since a 600 V trough cannot enclose them. (6.3.2)

NOTE Steel is the material every indoor trough and most outdoor troughs are made of, in a painted or galvanized sheet, and it serves every enclosure type in a non-corrosive atmosphere, which is why it is the default; Type 304 stainless steel holds up where the atmosphere carries moisture and mild chemicals and where the trough is washed down, and Type 316 holds up where chlorides are present, at a cost several times that of painted steel; aluminum weighs about a third of steel for the same section, resists the atmosphere that rusts bare steel, and is attacked by the alkali in wet concrete and by chlorides, so it is chosen for a long outdoor run on a light structure and not for a coastal site; rigid polyvinyl chloride and fiberglass-reinforced polyester carry no fault current, hold up where the corrodent attacks stainless steel, and are the materials a nonmetallic wireway is made of, with fiberglass holding its shape at a higher temperature and over a longer unsupported span than polyvinyl chloride. (7.1.2)

NOTE A dry electrical room or equipment space is where a trough sits on most projects, which is why Type 1 is the default; Type 3R sheds rain and is built with a drip shield at the cover and drain openings at the bottom, and it is the type a trough between two outdoor enclosures or along an exterior wall carries; Type 4 is gasketed against hose-directed water and is the type a trough in a wash-down area carries; Type 4X is Type 4 in a material that resists corrosion, and it is the type a trough in a corrosive atmosphere carries; Type 12 is gasketed against dust, lint, and dripping oil and is the type a trough on a plant floor, in a machine shop, or in a textile or woodworking area carries. The gasketed types are built as screw-cover troughs, so a Type 4, 4X, or 12 selection and a hinged cover are not both available from every series. (7.2.2)

NOTE An opening cut in the field in a Type 3R, 4, 4X, or 12 trough other than at a location and by a method the listing permits removes the environmental rating, and the rework is charged to the party that made the cut. (7.2.10)

NOTE ANSI 61 gray is the finish the switchboards, panelboards, and motor control centers on a project are painted, and a trough that adjoins them is usually painted to match, which is why it is the default; ANSI 49 is the darker gray some Owners standardize on; a trough hot-dip galvanized after fabrication carries zinc over every cut edge and weld and is the finish of a steel trough installed outdoors or in a damp industrial space where a scratch through paint would rust; unpainted galvanized sheet is what a Type 1 trough in a ceiling space nobody sees is often ordered as, and it costs least; a mill finish is what a stainless steel or an aluminum trough is furnished with, since neither needs a coating; a custom color is chosen where the run is exposed in a finished space or where the Owner color-codes the system it serves. (7.3.2)

NOTE A trough with no knockouts is entered where the conduits land, by a punch that cuts a round opening the hub or connector fits, and it keeps the enclosure type since no knockout ring is left loose; a trough with factory knockouts is entered faster at the sizes and spacings the factory chose, and where a knockout is not where a conduit lands the opening is field-cut anyway. Factory knockouts are furnished only in a Type 1 or a Type 3R trough, since a knockout in a gasketed trough breaks the type, and whether an Owner wants them in a Type 1 run depends on how many conduits enter and whether the run will be entered again later. Neither is distinctly the norm, so the field asserts no default. (7.5.2)

NOTE The cross-section is a project quantity: it is set by the conductors the fill calculation puts in the fullest section of the run, by the bending space the conductors need where they deflect, by the wiring space of the equipment the run adjoins, and by the clearance available where the run passes under ductwork, piping, and cable tray at a shared elevation, so it is scheduled on the drawings for each run rather than selected once for the project. (7.6.2)

NOTE The 20% limit of the code is what nearly every project specifies, and a run filled to it still has four fifths of its area open, which is the margin the lay-in construction trades on; a lower design fill is written where the Owner expects to add circuits to the run through the life of the installation and wants the trough sized for them at the start, at the cost of a larger trough on day one. (8.1.2)

NOTE A metal trough radiates the heat its conductors generate and the code treats it as open air up to 30 current-carrying conductors, which is the count at which the bundle in the trough begins to behave as a bundle in a raceway; a nonmetallic trough holds its heat, so the gutter article applies the raceway rule from the first conductor. A lineup wireway carrying every branch circuit from a panelboard passes 30 conductors sooner than it looks, and the conductor that was sized without the adjustment is the one that runs hot. (8.2.3)

NOTE A power distribution block is a listed block with a line terminal and several load terminals, mounted in the trough, that lets one feeder be split into several without a splice on the conductor, and it is what an auxiliary gutter above a meter center or a switchboard is built around; a splice or tap connector joins conductors directly and is insulated after it is made, which costs less than a block, takes more room, and is what a wireway carrying a few circuits is tapped with; a run with no splices or taps is a pull-through, chosen where the Owner wants every connection inside a device enclosure where it can be found, inspected, and labeled with the equipment. Which of these a project wants depends on whether the run is a gutter distributing feeders or a wireway carrying circuits, and on the Owner's maintenance practice, so the field asserts no default. (8.3.2)

NOTE A polyvinyl chloride trough grows about 3 1/2 in. per 100 ft over a 100 °F change, a fiberglass trough about a fifth of that, and a steel trough about two thirds of an inch; the code writes the rule for the nonmetallic trough because a straight run of it that is pinned at both ends buckles between its supports in summer and pulls its joints open in winter, while a steel run of the same length carries the stress into its joints without showing it until the bonding connection at a joint has worked loose. (9.3.4)

NOTE A painted trough joined with plain bolts through painted flanges is mechanically continuous and electrically a chain of paint films, and the fault current the trough is meant to return finds its way through whatever else touches it; the listing is what tests the joint hardware for the bonding path, which is why the hardware the listing furnishes is the hardware the joint is made with. (10.6)

NOTE The inspection against the fill calculation is made before the cover closes for the last time because the conductor that was added after the calculation, to pick up a circuit that was not on the schedule, is invisible once the cover is on and is the conductor that puts the run over 30 at the fullest section. (12.4)

NOTE NFPA 70 376.30 supports a metal wireway at each end and at intervals not exceeding 5 ft, and permits an interval up to 10 ft only where the wireway is listed for it; NFPA 70 378.30 supports a nonmetallic wireway at 3 ft unless listed for more, and never more than 10 ft; NFPA 70 366.30 supports a sheet metal auxiliary gutter at 5 ft and a nonmetallic one at 3 ft. The 5 ft interval is what nearly every metal run is supported at, which is why it is the default, and the field exists for the engineer who wants a closer interval than the code or the listing allows, for a run that carries a heavy fill, a run that will be opened and loaded often, or a run on a structure that moves. (13.2.2)

NOTE The equipment standard furnishes the opening and the wiring space on the equipment side and hands the trough to this standard; the connector between the two is the trough manufacturer's, and the flange pattern, the opening size, and the location are coordinated between the two manufacturers before either is released, because an opening cut in the field in a listed enclosure is what the equipment standards charge back. (13.3.3)

NOTE One year is the manufacturer's standard term for a trough, which has no moving part but a hinge and no component that wears, and it is the term nearly every project accepts; a longer term is bought where the Owner holds every product on the project to one warranty length or where a finish in a corrosive atmosphere is the concern, and the manufacturer prices the added years into the trough. (15.2)

NOTE Warranty commencement at shipment is the manufacturer's usual term, and it consumes the warranty while the sections sit in storage and the run is assembled; commencement at energization or substantial completion moves the coverage to the period the Owner is operating the run, and the manufacturer prices the added months into the trough. (15.4)

NOTE The spares under this standard are the parts that let a run be opened, extended, or closed again without waiting on the manufacturer's lead time: the end plate that closes a run after a section is removed, the hardware for a joint remade, and the paint for a scratch that would otherwise rust. (16.3)